blob: 4b70ec29a4e971e3beb6a7a8092366799c7aec30 [file] [log] [blame]
Georg Brandl116aa622007-08-15 14:28:22 +00001.. highlightlang:: c
2
3
4.. _initialization:
5
6*****************************************
7Initialization, Finalization, and Threads
8*****************************************
9
10
Antoine Pitrou8b50b832011-01-15 11:57:42 +000011Initializing and finalizing the interpreter
12===========================================
13
14
Georg Brandl60203b42010-10-06 10:11:56 +000015.. c:function:: void Py_Initialize()
Georg Brandl116aa622007-08-15 14:28:22 +000016
17 .. index::
18 single: Py_SetProgramName()
19 single: PyEval_InitThreads()
Georg Brandl116aa622007-08-15 14:28:22 +000020 single: modules (in module sys)
21 single: path (in module sys)
Georg Brandl1a3284e2007-12-02 09:40:06 +000022 module: builtins
Georg Brandl116aa622007-08-15 14:28:22 +000023 module: __main__
24 module: sys
25 triple: module; search; path
26 single: PySys_SetArgv()
Antoine Pitrouf978fac2010-05-21 17:25:34 +000027 single: PySys_SetArgvEx()
Georg Brandl116aa622007-08-15 14:28:22 +000028 single: Py_Finalize()
29
30 Initialize the Python interpreter. In an application embedding Python, this
31 should be called before using any other Python/C API functions; with the
Antoine Pitrou9bd3bbc2011-03-13 23:28:28 +010032 exception of :c:func:`Py_SetProgramName` and :c:func:`Py_SetPath`. This initializes
Georg Brandl116aa622007-08-15 14:28:22 +000033 the table of loaded modules (``sys.modules``), and creates the fundamental
Georg Brandl1a3284e2007-12-02 09:40:06 +000034 modules :mod:`builtins`, :mod:`__main__` and :mod:`sys`. It also initializes
Georg Brandl116aa622007-08-15 14:28:22 +000035 the module search path (``sys.path``). It does not set ``sys.argv``; use
Georg Brandl60203b42010-10-06 10:11:56 +000036 :c:func:`PySys_SetArgvEx` for that. This is a no-op when called for a second time
37 (without calling :c:func:`Py_Finalize` first). There is no return value; it is a
Georg Brandl116aa622007-08-15 14:28:22 +000038 fatal error if the initialization fails.
39
40
Georg Brandl60203b42010-10-06 10:11:56 +000041.. c:function:: void Py_InitializeEx(int initsigs)
Georg Brandl116aa622007-08-15 14:28:22 +000042
Georg Brandl60203b42010-10-06 10:11:56 +000043 This function works like :c:func:`Py_Initialize` if *initsigs* is 1. If
Georg Brandl116aa622007-08-15 14:28:22 +000044 *initsigs* is 0, it skips initialization registration of signal handlers, which
45 might be useful when Python is embedded.
46
Georg Brandl116aa622007-08-15 14:28:22 +000047
Georg Brandl60203b42010-10-06 10:11:56 +000048.. c:function:: int Py_IsInitialized()
Georg Brandl116aa622007-08-15 14:28:22 +000049
50 Return true (nonzero) when the Python interpreter has been initialized, false
Georg Brandl60203b42010-10-06 10:11:56 +000051 (zero) if not. After :c:func:`Py_Finalize` is called, this returns false until
52 :c:func:`Py_Initialize` is called again.
Georg Brandl116aa622007-08-15 14:28:22 +000053
54
Georg Brandl60203b42010-10-06 10:11:56 +000055.. c:function:: void Py_Finalize()
Georg Brandl116aa622007-08-15 14:28:22 +000056
Georg Brandl60203b42010-10-06 10:11:56 +000057 Undo all initializations made by :c:func:`Py_Initialize` and subsequent use of
Georg Brandl116aa622007-08-15 14:28:22 +000058 Python/C API functions, and destroy all sub-interpreters (see
Georg Brandl60203b42010-10-06 10:11:56 +000059 :c:func:`Py_NewInterpreter` below) that were created and not yet destroyed since
60 the last call to :c:func:`Py_Initialize`. Ideally, this frees all memory
Georg Brandl116aa622007-08-15 14:28:22 +000061 allocated by the Python interpreter. This is a no-op when called for a second
Georg Brandl60203b42010-10-06 10:11:56 +000062 time (without calling :c:func:`Py_Initialize` again first). There is no return
Georg Brandl116aa622007-08-15 14:28:22 +000063 value; errors during finalization are ignored.
64
65 This function is provided for a number of reasons. An embedding application
66 might want to restart Python without having to restart the application itself.
67 An application that has loaded the Python interpreter from a dynamically
68 loadable library (or DLL) might want to free all memory allocated by Python
69 before unloading the DLL. During a hunt for memory leaks in an application a
70 developer might want to free all memory allocated by Python before exiting from
71 the application.
72
73 **Bugs and caveats:** The destruction of modules and objects in modules is done
74 in random order; this may cause destructors (:meth:`__del__` methods) to fail
75 when they depend on other objects (even functions) or modules. Dynamically
76 loaded extension modules loaded by Python are not unloaded. Small amounts of
77 memory allocated by the Python interpreter may not be freed (if you find a leak,
78 please report it). Memory tied up in circular references between objects is not
79 freed. Some memory allocated by extension modules may not be freed. Some
80 extensions may not work properly if their initialization routine is called more
Georg Brandl60203b42010-10-06 10:11:56 +000081 than once; this can happen if an application calls :c:func:`Py_Initialize` and
82 :c:func:`Py_Finalize` more than once.
Georg Brandl116aa622007-08-15 14:28:22 +000083
84
Antoine Pitrou8b50b832011-01-15 11:57:42 +000085Process-wide parameters
86=======================
Georg Brandl116aa622007-08-15 14:28:22 +000087
88
Georg Brandl60203b42010-10-06 10:11:56 +000089.. c:function:: void Py_SetProgramName(wchar_t *name)
Georg Brandl116aa622007-08-15 14:28:22 +000090
91 .. index::
92 single: Py_Initialize()
93 single: main()
94 single: Py_GetPath()
95
Georg Brandl60203b42010-10-06 10:11:56 +000096 This function should be called before :c:func:`Py_Initialize` is called for
Georg Brandl116aa622007-08-15 14:28:22 +000097 the first time, if it is called at all. It tells the interpreter the value
Georg Brandl60203b42010-10-06 10:11:56 +000098 of the ``argv[0]`` argument to the :c:func:`main` function of the program
Martin v. Löwis790465f2008-04-05 20:41:37 +000099 (converted to wide characters).
Georg Brandl60203b42010-10-06 10:11:56 +0000100 This is used by :c:func:`Py_GetPath` and some other functions below to find
Georg Brandl116aa622007-08-15 14:28:22 +0000101 the Python run-time libraries relative to the interpreter executable. The
102 default value is ``'python'``. The argument should point to a
Martin v. Löwis790465f2008-04-05 20:41:37 +0000103 zero-terminated wide character string in static storage whose contents will not
Georg Brandl116aa622007-08-15 14:28:22 +0000104 change for the duration of the program's execution. No code in the Python
105 interpreter will change the contents of this storage.
106
107
Georg Brandl60203b42010-10-06 10:11:56 +0000108.. c:function:: wchar* Py_GetProgramName()
Georg Brandl116aa622007-08-15 14:28:22 +0000109
110 .. index:: single: Py_SetProgramName()
111
Georg Brandl60203b42010-10-06 10:11:56 +0000112 Return the program name set with :c:func:`Py_SetProgramName`, or the default.
Georg Brandl116aa622007-08-15 14:28:22 +0000113 The returned string points into static storage; the caller should not modify its
114 value.
115
116
Georg Brandl60203b42010-10-06 10:11:56 +0000117.. c:function:: wchar_t* Py_GetPrefix()
Georg Brandl116aa622007-08-15 14:28:22 +0000118
119 Return the *prefix* for installed platform-independent files. This is derived
120 through a number of complicated rules from the program name set with
Georg Brandl60203b42010-10-06 10:11:56 +0000121 :c:func:`Py_SetProgramName` and some environment variables; for example, if the
Georg Brandl116aa622007-08-15 14:28:22 +0000122 program name is ``'/usr/local/bin/python'``, the prefix is ``'/usr/local'``. The
123 returned string points into static storage; the caller should not modify its
124 value. This corresponds to the :makevar:`prefix` variable in the top-level
125 :file:`Makefile` and the :option:`--prefix` argument to the :program:`configure`
126 script at build time. The value is available to Python code as ``sys.prefix``.
127 It is only useful on Unix. See also the next function.
128
129
Georg Brandl60203b42010-10-06 10:11:56 +0000130.. c:function:: wchar_t* Py_GetExecPrefix()
Georg Brandl116aa622007-08-15 14:28:22 +0000131
132 Return the *exec-prefix* for installed platform-*dependent* files. This is
133 derived through a number of complicated rules from the program name set with
Georg Brandl60203b42010-10-06 10:11:56 +0000134 :c:func:`Py_SetProgramName` and some environment variables; for example, if the
Georg Brandl116aa622007-08-15 14:28:22 +0000135 program name is ``'/usr/local/bin/python'``, the exec-prefix is
136 ``'/usr/local'``. The returned string points into static storage; the caller
137 should not modify its value. This corresponds to the :makevar:`exec_prefix`
138 variable in the top-level :file:`Makefile` and the :option:`--exec-prefix`
139 argument to the :program:`configure` script at build time. The value is
140 available to Python code as ``sys.exec_prefix``. It is only useful on Unix.
141
142 Background: The exec-prefix differs from the prefix when platform dependent
143 files (such as executables and shared libraries) are installed in a different
144 directory tree. In a typical installation, platform dependent files may be
145 installed in the :file:`/usr/local/plat` subtree while platform independent may
146 be installed in :file:`/usr/local`.
147
148 Generally speaking, a platform is a combination of hardware and software
149 families, e.g. Sparc machines running the Solaris 2.x operating system are
150 considered the same platform, but Intel machines running Solaris 2.x are another
151 platform, and Intel machines running Linux are yet another platform. Different
152 major revisions of the same operating system generally also form different
153 platforms. Non-Unix operating systems are a different story; the installation
154 strategies on those systems are so different that the prefix and exec-prefix are
155 meaningless, and set to the empty string. Note that compiled Python bytecode
156 files are platform independent (but not independent from the Python version by
157 which they were compiled!).
158
159 System administrators will know how to configure the :program:`mount` or
160 :program:`automount` programs to share :file:`/usr/local` between platforms
161 while having :file:`/usr/local/plat` be a different filesystem for each
162 platform.
163
164
Georg Brandl60203b42010-10-06 10:11:56 +0000165.. c:function:: wchar_t* Py_GetProgramFullPath()
Georg Brandl116aa622007-08-15 14:28:22 +0000166
167 .. index::
168 single: Py_SetProgramName()
169 single: executable (in module sys)
170
171 Return the full program name of the Python executable; this is computed as a
172 side-effect of deriving the default module search path from the program name
Georg Brandl60203b42010-10-06 10:11:56 +0000173 (set by :c:func:`Py_SetProgramName` above). The returned string points into
Georg Brandl116aa622007-08-15 14:28:22 +0000174 static storage; the caller should not modify its value. The value is available
175 to Python code as ``sys.executable``.
176
177
Georg Brandl60203b42010-10-06 10:11:56 +0000178.. c:function:: wchar_t* Py_GetPath()
Georg Brandl116aa622007-08-15 14:28:22 +0000179
180 .. index::
181 triple: module; search; path
182 single: path (in module sys)
Kristján Valur Jónsson3b69db22010-09-27 05:32:54 +0000183 single: Py_SetPath()
Georg Brandl116aa622007-08-15 14:28:22 +0000184
Benjamin Peterson46a99002010-01-09 18:45:30 +0000185 Return the default module search path; this is computed from the program name
Georg Brandl60203b42010-10-06 10:11:56 +0000186 (set by :c:func:`Py_SetProgramName` above) and some environment variables.
Benjamin Peterson46a99002010-01-09 18:45:30 +0000187 The returned string consists of a series of directory names separated by a
188 platform dependent delimiter character. The delimiter character is ``':'``
189 on Unix and Mac OS X, ``';'`` on Windows. The returned string points into
190 static storage; the caller should not modify its value. The list
191 :data:`sys.path` is initialized with this value on interpreter startup; it
192 can be (and usually is) modified later to change the search path for loading
193 modules.
Georg Brandl116aa622007-08-15 14:28:22 +0000194
Christian Heimes5b5e81c2007-12-31 16:14:33 +0000195 .. XXX should give the exact rules
Georg Brandl116aa622007-08-15 14:28:22 +0000196
197
Georg Brandl60203b42010-10-06 10:11:56 +0000198.. c:function:: void Py_SetPath(const wchar_t *)
Kristján Valur Jónsson3b69db22010-09-27 05:32:54 +0000199
200 .. index::
201 triple: module; search; path
202 single: path (in module sys)
203 single: Py_GetPath()
204
205 Set the default module search path. If this function is called before
Georg Brandlfa4f7f92010-10-06 10:14:08 +0000206 :c:func:`Py_Initialize`, then :c:func:`Py_GetPath` won't attempt to compute a
207 default search path but uses the one provided instead. This is useful if
208 Python is embedded by an application that has full knowledge of the location
209 of all modules. The path components should be separated by semicolons.
Kristján Valur Jónsson3b69db22010-09-27 05:32:54 +0000210
Georg Brandlfa4f7f92010-10-06 10:14:08 +0000211 This also causes :data:`sys.executable` to be set only to the raw program
212 name (see :c:func:`Py_SetProgramName`) and for :data:`sys.prefix` and
213 :data:`sys.exec_prefix` to be empty. It is up to the caller to modify these
214 if required after calling :c:func:`Py_Initialize`.
215
Kristján Valur Jónsson3b69db22010-09-27 05:32:54 +0000216
Georg Brandl60203b42010-10-06 10:11:56 +0000217.. c:function:: const char* Py_GetVersion()
Georg Brandl116aa622007-08-15 14:28:22 +0000218
219 Return the version of this Python interpreter. This is a string that looks
220 something like ::
221
Georg Brandle6bcc912008-05-12 18:05:20 +0000222 "3.0a5+ (py3k:63103M, May 12 2008, 00:53:55) \n[GCC 4.2.3]"
Georg Brandl116aa622007-08-15 14:28:22 +0000223
224 .. index:: single: version (in module sys)
225
226 The first word (up to the first space character) is the current Python version;
227 the first three characters are the major and minor version separated by a
228 period. The returned string points into static storage; the caller should not
Georg Brandle6bcc912008-05-12 18:05:20 +0000229 modify its value. The value is available to Python code as :data:`sys.version`.
Georg Brandl116aa622007-08-15 14:28:22 +0000230
231
Georg Brandl60203b42010-10-06 10:11:56 +0000232.. c:function:: const char* Py_GetPlatform()
Georg Brandl116aa622007-08-15 14:28:22 +0000233
234 .. index:: single: platform (in module sys)
235
236 Return the platform identifier for the current platform. On Unix, this is
237 formed from the "official" name of the operating system, converted to lower
238 case, followed by the major revision number; e.g., for Solaris 2.x, which is
239 also known as SunOS 5.x, the value is ``'sunos5'``. On Mac OS X, it is
240 ``'darwin'``. On Windows, it is ``'win'``. The returned string points into
241 static storage; the caller should not modify its value. The value is available
242 to Python code as ``sys.platform``.
243
244
Georg Brandl60203b42010-10-06 10:11:56 +0000245.. c:function:: const char* Py_GetCopyright()
Georg Brandl116aa622007-08-15 14:28:22 +0000246
247 Return the official copyright string for the current Python version, for example
248
249 ``'Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam'``
250
251 .. index:: single: copyright (in module sys)
252
253 The returned string points into static storage; the caller should not modify its
254 value. The value is available to Python code as ``sys.copyright``.
255
256
Georg Brandl60203b42010-10-06 10:11:56 +0000257.. c:function:: const char* Py_GetCompiler()
Georg Brandl116aa622007-08-15 14:28:22 +0000258
259 Return an indication of the compiler used to build the current Python version,
260 in square brackets, for example::
261
262 "[GCC 2.7.2.2]"
263
264 .. index:: single: version (in module sys)
265
266 The returned string points into static storage; the caller should not modify its
267 value. The value is available to Python code as part of the variable
268 ``sys.version``.
269
270
Georg Brandl60203b42010-10-06 10:11:56 +0000271.. c:function:: const char* Py_GetBuildInfo()
Georg Brandl116aa622007-08-15 14:28:22 +0000272
273 Return information about the sequence number and build date and time of the
274 current Python interpreter instance, for example ::
275
276 "#67, Aug 1 1997, 22:34:28"
277
278 .. index:: single: version (in module sys)
279
280 The returned string points into static storage; the caller should not modify its
281 value. The value is available to Python code as part of the variable
282 ``sys.version``.
283
284
Georg Brandl60203b42010-10-06 10:11:56 +0000285.. c:function:: void PySys_SetArgvEx(int argc, wchar_t **argv, int updatepath)
Georg Brandl116aa622007-08-15 14:28:22 +0000286
287 .. index::
288 single: main()
289 single: Py_FatalError()
290 single: argv (in module sys)
291
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000292 Set :data:`sys.argv` based on *argc* and *argv*. These parameters are
Georg Brandl60203b42010-10-06 10:11:56 +0000293 similar to those passed to the program's :c:func:`main` function with the
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000294 difference that the first entry should refer to the script file to be
295 executed rather than the executable hosting the Python interpreter. If there
296 isn't a script that will be run, the first entry in *argv* can be an empty
297 string. If this function fails to initialize :data:`sys.argv`, a fatal
Georg Brandl60203b42010-10-06 10:11:56 +0000298 condition is signalled using :c:func:`Py_FatalError`.
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000299
Antoine Pitrouf978fac2010-05-21 17:25:34 +0000300 If *updatepath* is zero, this is all the function does. If *updatepath*
301 is non-zero, the function also modifies :data:`sys.path` according to the
302 following algorithm:
303
304 - If the name of an existing script is passed in ``argv[0]``, the absolute
305 path of the directory where the script is located is prepended to
306 :data:`sys.path`.
307 - Otherwise (that is, if *argc* is 0 or ``argv[0]`` doesn't point
308 to an existing file name), an empty string is prepended to
309 :data:`sys.path`, which is the same as prepending the current working
310 directory (``"."``).
311
312 .. note::
313 It is recommended that applications embedding the Python interpreter
314 for purposes other than executing a single script pass 0 as *updatepath*,
315 and update :data:`sys.path` themselves if desired.
316 See `CVE-2008-5983 <http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-5983>`_.
317
318 On versions before 3.1.3, you can achieve the same effect by manually
319 popping the first :data:`sys.path` element after having called
Georg Brandl60203b42010-10-06 10:11:56 +0000320 :c:func:`PySys_SetArgv`, for example using::
Antoine Pitrouf978fac2010-05-21 17:25:34 +0000321
322 PyRun_SimpleString("import sys; sys.path.pop(0)\n");
323
324 .. versionadded:: 3.1.3
Georg Brandl116aa622007-08-15 14:28:22 +0000325
Christian Heimes5b5e81c2007-12-31 16:14:33 +0000326 .. XXX impl. doesn't seem consistent in allowing 0/NULL for the params;
327 check w/ Guido.
Georg Brandl116aa622007-08-15 14:28:22 +0000328
Georg Brandl116aa622007-08-15 14:28:22 +0000329
Georg Brandl60203b42010-10-06 10:11:56 +0000330.. c:function:: void PySys_SetArgv(int argc, wchar_t **argv)
Antoine Pitrouf978fac2010-05-21 17:25:34 +0000331
Georg Brandl60203b42010-10-06 10:11:56 +0000332 This function works like :c:func:`PySys_SetArgvEx` with *updatepath* set to 1.
Antoine Pitrouf978fac2010-05-21 17:25:34 +0000333
334
Georg Brandl60203b42010-10-06 10:11:56 +0000335.. c:function:: void Py_SetPythonHome(wchar_t *home)
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000336
337 Set the default "home" directory, that is, the location of the standard
Georg Brandlde0ab5e2010-12-02 18:02:01 +0000338 Python libraries. See :envvar:`PYTHONHOME` for the meaning of the
339 argument string.
340
Benjamin Peterson4ac9ce42009-10-04 14:49:41 +0000341 The argument should point to a zero-terminated character string in static
342 storage whose contents will not change for the duration of the program's
343 execution. No code in the Python interpreter will change the contents of
344 this storage.
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000345
346
Georg Brandl60203b42010-10-06 10:11:56 +0000347.. c:function:: w_char* Py_GetPythonHome()
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000348
349 Return the default "home", that is, the value set by a previous call to
Georg Brandl60203b42010-10-06 10:11:56 +0000350 :c:func:`Py_SetPythonHome`, or the value of the :envvar:`PYTHONHOME`
Benjamin Peterson5c6d7872009-02-06 02:40:07 +0000351 environment variable if it is set.
352
353
Georg Brandl116aa622007-08-15 14:28:22 +0000354.. _threads:
355
356Thread State and the Global Interpreter Lock
357============================================
358
359.. index::
360 single: global interpreter lock
361 single: interpreter lock
362 single: lock, interpreter
363
Georg Brandlf285bcc2010-10-19 21:07:16 +0000364The Python interpreter is not fully thread-safe. In order to support
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000365multi-threaded Python programs, there's a global lock, called the :term:`global
366interpreter lock` or :term:`GIL`, that must be held by the current thread before
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000367it can safely access Python objects. Without the lock, even the simplest
368operations could cause problems in a multi-threaded program: for example, when
369two threads simultaneously increment the reference count of the same object, the
370reference count could end up being incremented only once instead of twice.
Georg Brandl116aa622007-08-15 14:28:22 +0000371
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000372.. index:: single: setswitchinterval() (in module sys)
Georg Brandl116aa622007-08-15 14:28:22 +0000373
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000374Therefore, the rule exists that only the thread that has acquired the
375:term:`GIL` may operate on Python objects or call Python/C API functions.
376In order to emulate concurrency of execution, the interpreter regularly
377tries to switch threads (see :func:`sys.setswitchinterval`). The lock is also
378released around potentially blocking I/O operations like reading or writing
379a file, so that other Python threads can run in the meantime.
Georg Brandl116aa622007-08-15 14:28:22 +0000380
381.. index::
382 single: PyThreadState
383 single: PyThreadState
384
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000385The Python interpreter keeps some thread-specific bookkeeping information
386inside a data structure called :c:type:`PyThreadState`. There's also one
387global variable pointing to the current :c:type:`PyThreadState`: it can
388be retrieved using :c:func:`PyThreadState_Get`.
Georg Brandl116aa622007-08-15 14:28:22 +0000389
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000390Releasing the GIL from extension code
391-------------------------------------
392
393Most extension code manipulating the :term:`GIL` has the following simple
394structure::
Georg Brandl116aa622007-08-15 14:28:22 +0000395
396 Save the thread state in a local variable.
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000397 Release the global interpreter lock.
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000398 ... Do some blocking I/O operation ...
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000399 Reacquire the global interpreter lock.
Georg Brandl116aa622007-08-15 14:28:22 +0000400 Restore the thread state from the local variable.
401
402This is so common that a pair of macros exists to simplify it::
403
404 Py_BEGIN_ALLOW_THREADS
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000405 ... Do some blocking I/O operation ...
Georg Brandl116aa622007-08-15 14:28:22 +0000406 Py_END_ALLOW_THREADS
407
408.. index::
409 single: Py_BEGIN_ALLOW_THREADS
410 single: Py_END_ALLOW_THREADS
411
Georg Brandl60203b42010-10-06 10:11:56 +0000412The :c:macro:`Py_BEGIN_ALLOW_THREADS` macro opens a new block and declares a
413hidden local variable; the :c:macro:`Py_END_ALLOW_THREADS` macro closes the
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000414block. These two macros are still available when Python is compiled without
415thread support (they simply have an empty expansion).
Georg Brandl116aa622007-08-15 14:28:22 +0000416
417When thread support is enabled, the block above expands to the following code::
418
419 PyThreadState *_save;
420
421 _save = PyEval_SaveThread();
422 ...Do some blocking I/O operation...
423 PyEval_RestoreThread(_save);
424
Georg Brandl116aa622007-08-15 14:28:22 +0000425.. index::
426 single: PyEval_RestoreThread()
Georg Brandl116aa622007-08-15 14:28:22 +0000427 single: PyEval_SaveThread()
Georg Brandl116aa622007-08-15 14:28:22 +0000428
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000429Here is how these functions work: the global interpreter lock is used to protect the pointer to the
430current thread state. When releasing the lock and saving the thread state,
431the current thread state pointer must be retrieved before the lock is released
432(since another thread could immediately acquire the lock and store its own thread
433state in the global variable). Conversely, when acquiring the lock and restoring
434the thread state, the lock must be acquired before storing the thread state
435pointer.
Georg Brandl116aa622007-08-15 14:28:22 +0000436
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000437.. note::
438 Calling system I/O functions is the most common use case for releasing
439 the GIL, but it can also be useful before calling long-running computations
440 which don't need access to Python objects, such as compression or
441 cryptographic functions operating over memory buffers. For example, the
442 standard :mod:`zlib` and :mod:`hashlib` modules release the GIL when
443 compressing or hashing data.
Georg Brandl116aa622007-08-15 14:28:22 +0000444
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000445Non-Python created threads
446--------------------------
Georg Brandl116aa622007-08-15 14:28:22 +0000447
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000448When threads are created using the dedicated Python APIs (such as the
449:mod:`threading` module), a thread state is automatically associated to them
450and the code showed above is therefore correct. However, when threads are
451created from C (for example by a third-party library with its own thread
452management), they don't hold the GIL, nor is there a thread state structure
453for them.
454
455If you need to call Python code from these threads (often this will be part
456of a callback API provided by the aforementioned third-party library),
457you must first register these threads with the interpreter by
458creating a thread state data structure, then acquiring the GIL, and finally
459storing their thread state pointer, before you can start using the Python/C
460API. When you are done, you should reset the thread state pointer, release
461the GIL, and finally free the thread state data structure.
462
463The :c:func:`PyGILState_Ensure` and :c:func:`PyGILState_Release` functions do
464all of the above automatically. The typical idiom for calling into Python
465from a C thread is::
Georg Brandl116aa622007-08-15 14:28:22 +0000466
467 PyGILState_STATE gstate;
468 gstate = PyGILState_Ensure();
469
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000470 /* Perform Python actions here. */
Georg Brandl116aa622007-08-15 14:28:22 +0000471 result = CallSomeFunction();
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000472 /* evaluate result or handle exception */
Georg Brandl116aa622007-08-15 14:28:22 +0000473
474 /* Release the thread. No Python API allowed beyond this point. */
475 PyGILState_Release(gstate);
476
Georg Brandl60203b42010-10-06 10:11:56 +0000477Note that the :c:func:`PyGILState_\*` functions assume there is only one global
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000478interpreter (created automatically by :c:func:`Py_Initialize`). Python
Georg Brandl116aa622007-08-15 14:28:22 +0000479supports the creation of additional interpreters (using
Georg Brandl60203b42010-10-06 10:11:56 +0000480:c:func:`Py_NewInterpreter`), but mixing multiple interpreters and the
481:c:func:`PyGILState_\*` API is unsupported.
Georg Brandl116aa622007-08-15 14:28:22 +0000482
Benjamin Peterson0df35a92009-10-04 20:32:25 +0000483Another important thing to note about threads is their behaviour in the face
Georg Brandl60203b42010-10-06 10:11:56 +0000484of the C :c:func:`fork` call. On most systems with :c:func:`fork`, after a
Benjamin Peterson0df35a92009-10-04 20:32:25 +0000485process forks only the thread that issued the fork will exist. That also
486means any locks held by other threads will never be released. Python solves
487this for :func:`os.fork` by acquiring the locks it uses internally before
488the fork, and releasing them afterwards. In addition, it resets any
489:ref:`lock-objects` in the child. When extending or embedding Python, there
490is no way to inform Python of additional (non-Python) locks that need to be
491acquired before or reset after a fork. OS facilities such as
Ezio Melotti861d27f2011-04-20 21:32:40 +0300492:c:func:`pthread_atfork` would need to be used to accomplish the same thing.
Georg Brandl60203b42010-10-06 10:11:56 +0000493Additionally, when extending or embedding Python, calling :c:func:`fork`
Benjamin Peterson0df35a92009-10-04 20:32:25 +0000494directly rather than through :func:`os.fork` (and returning to or calling
495into Python) may result in a deadlock by one of Python's internal locks
496being held by a thread that is defunct after the fork.
Georg Brandl60203b42010-10-06 10:11:56 +0000497:c:func:`PyOS_AfterFork` tries to reset the necessary locks, but is not
Benjamin Peterson0df35a92009-10-04 20:32:25 +0000498always able to.
Georg Brandl116aa622007-08-15 14:28:22 +0000499
Antoine Pitrou8b50b832011-01-15 11:57:42 +0000500
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000501High-level API
502--------------
503
504These are the most commonly used types and functions when writing C extension
505code, or when embedding the Python interpreter:
506
Georg Brandl60203b42010-10-06 10:11:56 +0000507.. c:type:: PyInterpreterState
Georg Brandl116aa622007-08-15 14:28:22 +0000508
509 This data structure represents the state shared by a number of cooperating
510 threads. Threads belonging to the same interpreter share their module
511 administration and a few other internal items. There are no public members in
512 this structure.
513
514 Threads belonging to different interpreters initially share nothing, except
515 process state like available memory, open file descriptors and such. The global
516 interpreter lock is also shared by all threads, regardless of to which
517 interpreter they belong.
518
519
Georg Brandl60203b42010-10-06 10:11:56 +0000520.. c:type:: PyThreadState
Georg Brandl116aa622007-08-15 14:28:22 +0000521
522 This data structure represents the state of a single thread. The only public
Georg Brandl60203b42010-10-06 10:11:56 +0000523 data member is :c:type:`PyInterpreterState \*`:attr:`interp`, which points to
Georg Brandl116aa622007-08-15 14:28:22 +0000524 this thread's interpreter state.
525
526
Georg Brandl60203b42010-10-06 10:11:56 +0000527.. c:function:: void PyEval_InitThreads()
Georg Brandl116aa622007-08-15 14:28:22 +0000528
529 .. index::
Antoine Pitrouf5cf4352011-01-15 14:31:49 +0000530 single: PyEval_AcquireThread()
Georg Brandl116aa622007-08-15 14:28:22 +0000531 single: PyEval_ReleaseThread()
532 single: PyEval_SaveThread()
533 single: PyEval_RestoreThread()
534
535 Initialize and acquire the global interpreter lock. It should be called in the
536 main thread before creating a second thread or engaging in any other thread
Antoine Pitrouf5cf4352011-01-15 14:31:49 +0000537 operations such as ``PyEval_ReleaseThread(tstate)``. It is not needed before
538 calling :c:func:`PyEval_SaveThread` or :c:func:`PyEval_RestoreThread`.
Georg Brandl116aa622007-08-15 14:28:22 +0000539
Antoine Pitrou9bd3bbc2011-03-13 23:28:28 +0100540 This is a no-op when called for a second time.
Georg Brandl116aa622007-08-15 14:28:22 +0000541
Antoine Pitrou9bb98772011-03-15 20:22:50 +0100542 .. versionchanged:: 3.2
543 This function cannot be called before :c:func:`Py_Initialize()` anymore.
544
Georg Brandl2067bfd2008-05-25 13:05:15 +0000545 .. index:: module: _thread
Georg Brandl116aa622007-08-15 14:28:22 +0000546
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000547 .. note::
548 When only the main thread exists, no GIL operations are needed. This is a
549 common situation (most Python programs do not use threads), and the lock
550 operations slow the interpreter down a bit. Therefore, the lock is not
551 created initially. This situation is equivalent to having acquired the lock:
552 when there is only a single thread, all object accesses are safe. Therefore,
553 when this function initializes the global interpreter lock, it also acquires
554 it. Before the Python :mod:`_thread` module creates a new thread, knowing
555 that either it has the lock or the lock hasn't been created yet, it calls
556 :c:func:`PyEval_InitThreads`. When this call returns, it is guaranteed that
557 the lock has been created and that the calling thread has acquired it.
Georg Brandl116aa622007-08-15 14:28:22 +0000558
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000559 It is **not** safe to call this function when it is unknown which thread (if
560 any) currently has the global interpreter lock.
Georg Brandl116aa622007-08-15 14:28:22 +0000561
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000562 This function is not available when thread support is disabled at compile time.
Georg Brandl116aa622007-08-15 14:28:22 +0000563
564
Georg Brandl60203b42010-10-06 10:11:56 +0000565.. c:function:: int PyEval_ThreadsInitialized()
Georg Brandl116aa622007-08-15 14:28:22 +0000566
Georg Brandl60203b42010-10-06 10:11:56 +0000567 Returns a non-zero value if :c:func:`PyEval_InitThreads` has been called. This
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000568 function can be called without holding the GIL, and therefore can be used to
Georg Brandl116aa622007-08-15 14:28:22 +0000569 avoid calls to the locking API when running single-threaded. This function is
570 not available when thread support is disabled at compile time.
571
Georg Brandl116aa622007-08-15 14:28:22 +0000572
Georg Brandl60203b42010-10-06 10:11:56 +0000573.. c:function:: PyThreadState* PyEval_SaveThread()
Georg Brandl116aa622007-08-15 14:28:22 +0000574
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000575 Release the global interpreter lock (if it has been created and thread
576 support is enabled) and reset the thread state to *NULL*, returning the
577 previous thread state (which is not *NULL*). If the lock has been created,
578 the current thread must have acquired it. (This function is available even
579 when thread support is disabled at compile time.)
Georg Brandl116aa622007-08-15 14:28:22 +0000580
581
Georg Brandl60203b42010-10-06 10:11:56 +0000582.. c:function:: void PyEval_RestoreThread(PyThreadState *tstate)
Georg Brandl116aa622007-08-15 14:28:22 +0000583
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000584 Acquire the global interpreter lock (if it has been created and thread
585 support is enabled) and set the thread state to *tstate*, which must not be
586 *NULL*. If the lock has been created, the current thread must not have
587 acquired it, otherwise deadlock ensues. (This function is available even
588 when thread support is disabled at compile time.)
Georg Brandl116aa622007-08-15 14:28:22 +0000589
Christian Heimesd8654cf2007-12-02 15:22:16 +0000590
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000591.. c:function:: PyThreadState* PyThreadState_Get()
592
593 Return the current thread state. The global interpreter lock must be held.
594 When the current thread state is *NULL*, this issues a fatal error (so that
595 the caller needn't check for *NULL*).
596
597
598.. c:function:: PyThreadState* PyThreadState_Swap(PyThreadState *tstate)
599
600 Swap the current thread state with the thread state given by the argument
601 *tstate*, which may be *NULL*. The global interpreter lock must be held
602 and is not released.
603
604
Georg Brandl60203b42010-10-06 10:11:56 +0000605.. c:function:: void PyEval_ReInitThreads()
Christian Heimesd8654cf2007-12-02 15:22:16 +0000606
Georg Brandl60203b42010-10-06 10:11:56 +0000607 This function is called from :c:func:`PyOS_AfterFork` to ensure that newly
Christian Heimesd8654cf2007-12-02 15:22:16 +0000608 created child processes don't hold locks referring to threads which
609 are not running in the child process.
610
611
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000612The following functions use thread-local storage, and are not compatible
613with sub-interpreters:
614
615.. c:function:: PyGILState_STATE PyGILState_Ensure()
616
617 Ensure that the current thread is ready to call the Python C API regardless
618 of the current state of Python, or of the global interpreter lock. This may
619 be called as many times as desired by a thread as long as each call is
620 matched with a call to :c:func:`PyGILState_Release`. In general, other
621 thread-related APIs may be used between :c:func:`PyGILState_Ensure` and
622 :c:func:`PyGILState_Release` calls as long as the thread state is restored to
623 its previous state before the Release(). For example, normal usage of the
624 :c:macro:`Py_BEGIN_ALLOW_THREADS` and :c:macro:`Py_END_ALLOW_THREADS` macros is
625 acceptable.
626
627 The return value is an opaque "handle" to the thread state when
628 :c:func:`PyGILState_Ensure` was called, and must be passed to
629 :c:func:`PyGILState_Release` to ensure Python is left in the same state. Even
630 though recursive calls are allowed, these handles *cannot* be shared - each
631 unique call to :c:func:`PyGILState_Ensure` must save the handle for its call
632 to :c:func:`PyGILState_Release`.
633
634 When the function returns, the current thread will hold the GIL and be able
635 to call arbitrary Python code. Failure is a fatal error.
636
637
638.. c:function:: void PyGILState_Release(PyGILState_STATE)
639
640 Release any resources previously acquired. After this call, Python's state will
641 be the same as it was prior to the corresponding :c:func:`PyGILState_Ensure` call
642 (but generally this state will be unknown to the caller, hence the use of the
643 GILState API).
644
645 Every call to :c:func:`PyGILState_Ensure` must be matched by a call to
646 :c:func:`PyGILState_Release` on the same thread.
647
648
Sandro Tosi61baee02011-08-08 00:16:54 +0200649.. c:function:: PyThreadState PyGILState_GetThisThreadState()
650
651 Get the current thread state for this thread. May return ``NULL`` if no
652 GILState API has been used on the current thread. Note that the main thread
653 always has such a thread-state, even if no auto-thread-state call has been
654 made on the main thread. This is mainly a helper/diagnostic function.
655
656
Georg Brandl116aa622007-08-15 14:28:22 +0000657The following macros are normally used without a trailing semicolon; look for
658example usage in the Python source distribution.
659
660
Georg Brandl60203b42010-10-06 10:11:56 +0000661.. c:macro:: Py_BEGIN_ALLOW_THREADS
Georg Brandl116aa622007-08-15 14:28:22 +0000662
663 This macro expands to ``{ PyThreadState *_save; _save = PyEval_SaveThread();``.
664 Note that it contains an opening brace; it must be matched with a following
Georg Brandl60203b42010-10-06 10:11:56 +0000665 :c:macro:`Py_END_ALLOW_THREADS` macro. See above for further discussion of this
Georg Brandl116aa622007-08-15 14:28:22 +0000666 macro. It is a no-op when thread support is disabled at compile time.
667
668
Georg Brandl60203b42010-10-06 10:11:56 +0000669.. c:macro:: Py_END_ALLOW_THREADS
Georg Brandl116aa622007-08-15 14:28:22 +0000670
671 This macro expands to ``PyEval_RestoreThread(_save); }``. Note that it contains
672 a closing brace; it must be matched with an earlier
Georg Brandl60203b42010-10-06 10:11:56 +0000673 :c:macro:`Py_BEGIN_ALLOW_THREADS` macro. See above for further discussion of
Georg Brandl116aa622007-08-15 14:28:22 +0000674 this macro. It is a no-op when thread support is disabled at compile time.
675
676
Georg Brandl60203b42010-10-06 10:11:56 +0000677.. c:macro:: Py_BLOCK_THREADS
Georg Brandl116aa622007-08-15 14:28:22 +0000678
679 This macro expands to ``PyEval_RestoreThread(_save);``: it is equivalent to
Georg Brandl60203b42010-10-06 10:11:56 +0000680 :c:macro:`Py_END_ALLOW_THREADS` without the closing brace. It is a no-op when
Georg Brandl116aa622007-08-15 14:28:22 +0000681 thread support is disabled at compile time.
682
683
Georg Brandl60203b42010-10-06 10:11:56 +0000684.. c:macro:: Py_UNBLOCK_THREADS
Georg Brandl116aa622007-08-15 14:28:22 +0000685
686 This macro expands to ``_save = PyEval_SaveThread();``: it is equivalent to
Georg Brandl60203b42010-10-06 10:11:56 +0000687 :c:macro:`Py_BEGIN_ALLOW_THREADS` without the opening brace and variable
Georg Brandl116aa622007-08-15 14:28:22 +0000688 declaration. It is a no-op when thread support is disabled at compile time.
689
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000690
691Low-level API
692-------------
693
Georg Brandl116aa622007-08-15 14:28:22 +0000694All of the following functions are only available when thread support is enabled
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000695at compile time, and must be called only when the global interpreter lock has
696been created.
Georg Brandl116aa622007-08-15 14:28:22 +0000697
698
Georg Brandl60203b42010-10-06 10:11:56 +0000699.. c:function:: PyInterpreterState* PyInterpreterState_New()
Georg Brandl116aa622007-08-15 14:28:22 +0000700
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000701 Create a new interpreter state object. The global interpreter lock need not
702 be held, but may be held if it is necessary to serialize calls to this
703 function.
Georg Brandl116aa622007-08-15 14:28:22 +0000704
705
Georg Brandl60203b42010-10-06 10:11:56 +0000706.. c:function:: void PyInterpreterState_Clear(PyInterpreterState *interp)
Georg Brandl116aa622007-08-15 14:28:22 +0000707
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000708 Reset all information in an interpreter state object. The global interpreter
709 lock must be held.
Georg Brandl116aa622007-08-15 14:28:22 +0000710
711
Georg Brandl60203b42010-10-06 10:11:56 +0000712.. c:function:: void PyInterpreterState_Delete(PyInterpreterState *interp)
Georg Brandl116aa622007-08-15 14:28:22 +0000713
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000714 Destroy an interpreter state object. The global interpreter lock need not be
715 held. The interpreter state must have been reset with a previous call to
Georg Brandl60203b42010-10-06 10:11:56 +0000716 :c:func:`PyInterpreterState_Clear`.
Georg Brandl116aa622007-08-15 14:28:22 +0000717
718
Georg Brandl60203b42010-10-06 10:11:56 +0000719.. c:function:: PyThreadState* PyThreadState_New(PyInterpreterState *interp)
Georg Brandl116aa622007-08-15 14:28:22 +0000720
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000721 Create a new thread state object belonging to the given interpreter object.
722 The global interpreter lock need not be held, but may be held if it is
723 necessary to serialize calls to this function.
Georg Brandl116aa622007-08-15 14:28:22 +0000724
725
Georg Brandl60203b42010-10-06 10:11:56 +0000726.. c:function:: void PyThreadState_Clear(PyThreadState *tstate)
Georg Brandl116aa622007-08-15 14:28:22 +0000727
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000728 Reset all information in a thread state object. The global interpreter lock
729 must be held.
Georg Brandl116aa622007-08-15 14:28:22 +0000730
731
Georg Brandl60203b42010-10-06 10:11:56 +0000732.. c:function:: void PyThreadState_Delete(PyThreadState *tstate)
Georg Brandl116aa622007-08-15 14:28:22 +0000733
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000734 Destroy a thread state object. The global interpreter lock need not be held.
735 The thread state must have been reset with a previous call to
Georg Brandl60203b42010-10-06 10:11:56 +0000736 :c:func:`PyThreadState_Clear`.
Georg Brandl116aa622007-08-15 14:28:22 +0000737
738
Georg Brandl60203b42010-10-06 10:11:56 +0000739.. c:function:: PyObject* PyThreadState_GetDict()
Georg Brandl116aa622007-08-15 14:28:22 +0000740
741 Return a dictionary in which extensions can store thread-specific state
742 information. Each extension should use a unique key to use to store state in
743 the dictionary. It is okay to call this function when no current thread state
744 is available. If this function returns *NULL*, no exception has been raised and
745 the caller should assume no current thread state is available.
746
Georg Brandl116aa622007-08-15 14:28:22 +0000747
Georg Brandl60203b42010-10-06 10:11:56 +0000748.. c:function:: int PyThreadState_SetAsyncExc(long id, PyObject *exc)
Georg Brandl116aa622007-08-15 14:28:22 +0000749
750 Asynchronously raise an exception in a thread. The *id* argument is the thread
751 id of the target thread; *exc* is the exception object to be raised. This
752 function does not steal any references to *exc*. To prevent naive misuse, you
753 must write your own C extension to call this. Must be called with the GIL held.
754 Returns the number of thread states modified; this is normally one, but will be
755 zero if the thread id isn't found. If *exc* is :const:`NULL`, the pending
756 exception (if any) for the thread is cleared. This raises no exceptions.
757
Georg Brandl116aa622007-08-15 14:28:22 +0000758
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000759.. c:function:: void PyEval_AcquireThread(PyThreadState *tstate)
Georg Brandl116aa622007-08-15 14:28:22 +0000760
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000761 Acquire the global interpreter lock and set the current thread state to
762 *tstate*, which should not be *NULL*. The lock must have been created earlier.
763 If this thread already has the lock, deadlock ensues.
Georg Brandl116aa622007-08-15 14:28:22 +0000764
Antoine Pitrou5ace8e92011-01-15 13:11:48 +0000765 :c:func:`PyEval_RestoreThread` is a higher-level function which is always
766 available (even when thread support isn't enabled or when threads have
767 not been initialized).
768
Georg Brandl116aa622007-08-15 14:28:22 +0000769
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000770.. c:function:: void PyEval_ReleaseThread(PyThreadState *tstate)
Georg Brandl116aa622007-08-15 14:28:22 +0000771
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000772 Reset the current thread state to *NULL* and release the global interpreter
773 lock. The lock must have been created earlier and must be held by the current
774 thread. The *tstate* argument, which must not be *NULL*, is only used to check
775 that it represents the current thread state --- if it isn't, a fatal error is
776 reported.
Georg Brandl116aa622007-08-15 14:28:22 +0000777
Antoine Pitrou5ace8e92011-01-15 13:11:48 +0000778 :c:func:`PyEval_SaveThread` is a higher-level function which is always
779 available (even when thread support isn't enabled or when threads have
780 not been initialized).
781
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000782
783.. c:function:: void PyEval_AcquireLock()
784
785 Acquire the global interpreter lock. The lock must have been created earlier.
786 If this thread already has the lock, a deadlock ensues.
787
Antoine Pitrou5ace8e92011-01-15 13:11:48 +0000788 .. deprecated:: 3.2
Antoine Pitrouf5cf4352011-01-15 14:31:49 +0000789 This function does not update the current thread state. Please use
Antoine Pitrou5ace8e92011-01-15 13:11:48 +0000790 :c:func:`PyEval_RestoreThread` or :c:func:`PyEval_AcquireThread`
791 instead.
792
Antoine Pitroubedd2c22011-01-15 12:54:19 +0000793
794.. c:function:: void PyEval_ReleaseLock()
795
796 Release the global interpreter lock. The lock must have been created earlier.
Georg Brandl116aa622007-08-15 14:28:22 +0000797
Antoine Pitrou5ace8e92011-01-15 13:11:48 +0000798 .. deprecated:: 3.2
Antoine Pitrouf5cf4352011-01-15 14:31:49 +0000799 This function does not update the current thread state. Please use
Antoine Pitrou5ace8e92011-01-15 13:11:48 +0000800 :c:func:`PyEval_SaveThread` or :c:func:`PyEval_ReleaseThread`
801 instead.
802
Georg Brandl116aa622007-08-15 14:28:22 +0000803
Antoine Pitrou8b50b832011-01-15 11:57:42 +0000804Sub-interpreter support
805=======================
806
807While in most uses, you will only embed a single Python interpreter, there
808are cases where you need to create several independent interpreters in the
809same process and perhaps even in the same thread. Sub-interpreters allow
Antoine Pitrou9bf8d1c2011-01-15 12:21:53 +0000810you to do that. You can switch between sub-interpreters using the
811:c:func:`PyThreadState_Swap` function. You can create and destroy them
812using the following functions:
Antoine Pitrou8b50b832011-01-15 11:57:42 +0000813
814
815.. c:function:: PyThreadState* Py_NewInterpreter()
816
817 .. index::
818 module: builtins
819 module: __main__
820 module: sys
821 single: stdout (in module sys)
822 single: stderr (in module sys)
823 single: stdin (in module sys)
824
825 Create a new sub-interpreter. This is an (almost) totally separate environment
826 for the execution of Python code. In particular, the new interpreter has
827 separate, independent versions of all imported modules, including the
828 fundamental modules :mod:`builtins`, :mod:`__main__` and :mod:`sys`. The
829 table of loaded modules (``sys.modules``) and the module search path
830 (``sys.path``) are also separate. The new environment has no ``sys.argv``
831 variable. It has new standard I/O stream file objects ``sys.stdin``,
832 ``sys.stdout`` and ``sys.stderr`` (however these refer to the same underlying
833 file descriptors).
834
835 The return value points to the first thread state created in the new
836 sub-interpreter. This thread state is made in the current thread state.
837 Note that no actual thread is created; see the discussion of thread states
838 below. If creation of the new interpreter is unsuccessful, *NULL* is
839 returned; no exception is set since the exception state is stored in the
840 current thread state and there may not be a current thread state. (Like all
841 other Python/C API functions, the global interpreter lock must be held before
842 calling this function and is still held when it returns; however, unlike most
843 other Python/C API functions, there needn't be a current thread state on
844 entry.)
845
846 .. index::
847 single: Py_Finalize()
848 single: Py_Initialize()
849
850 Extension modules are shared between (sub-)interpreters as follows: the first
851 time a particular extension is imported, it is initialized normally, and a
852 (shallow) copy of its module's dictionary is squirreled away. When the same
853 extension is imported by another (sub-)interpreter, a new module is initialized
854 and filled with the contents of this copy; the extension's ``init`` function is
855 not called. Note that this is different from what happens when an extension is
856 imported after the interpreter has been completely re-initialized by calling
857 :c:func:`Py_Finalize` and :c:func:`Py_Initialize`; in that case, the extension's
858 ``initmodule`` function *is* called again.
859
860 .. index:: single: close() (in module os)
861
862
863.. c:function:: void Py_EndInterpreter(PyThreadState *tstate)
864
865 .. index:: single: Py_Finalize()
866
867 Destroy the (sub-)interpreter represented by the given thread state. The given
868 thread state must be the current thread state. See the discussion of thread
869 states below. When the call returns, the current thread state is *NULL*. All
870 thread states associated with this interpreter are destroyed. (The global
871 interpreter lock must be held before calling this function and is still held
872 when it returns.) :c:func:`Py_Finalize` will destroy all sub-interpreters that
873 haven't been explicitly destroyed at that point.
874
875
876Bugs and caveats
877----------------
878
879Because sub-interpreters (and the main interpreter) are part of the same
880process, the insulation between them isn't perfect --- for example, using
881low-level file operations like :func:`os.close` they can
882(accidentally or maliciously) affect each other's open files. Because of the
883way extensions are shared between (sub-)interpreters, some extensions may not
884work properly; this is especially likely when the extension makes use of
885(static) global variables, or when the extension manipulates its module's
886dictionary after its initialization. It is possible to insert objects created
887in one sub-interpreter into a namespace of another sub-interpreter; this should
888be done with great care to avoid sharing user-defined functions, methods,
889instances or classes between sub-interpreters, since import operations executed
890by such objects may affect the wrong (sub-)interpreter's dictionary of loaded
Antoine Pitrouf1dfe732011-01-15 12:10:48 +0000891modules.
Antoine Pitrou8b50b832011-01-15 11:57:42 +0000892
Antoine Pitrouf1dfe732011-01-15 12:10:48 +0000893Also note that combining this functionality with :c:func:`PyGILState_\*` APIs
Ezio Melottid92ab082011-05-05 14:19:48 +0300894is delicate, because these APIs assume a bijection between Python thread states
Antoine Pitrouf1dfe732011-01-15 12:10:48 +0000895and OS-level threads, an assumption broken by the presence of sub-interpreters.
896It is highly recommended that you don't switch sub-interpreters between a pair
897of matching :c:func:`PyGILState_Ensure` and :c:func:`PyGILState_Release` calls.
898Furthermore, extensions (such as :mod:`ctypes`) using these APIs to allow calling
899of Python code from non-Python created threads will probably be broken when using
900sub-interpreters.
Antoine Pitrou8b50b832011-01-15 11:57:42 +0000901
Benjamin Petersona54c9092009-01-13 02:11:23 +0000902
903Asynchronous Notifications
904==========================
905
Benjamin Petersond23f8222009-04-05 19:13:16 +0000906A mechanism is provided to make asynchronous notifications to the main
Benjamin Petersona54c9092009-01-13 02:11:23 +0000907interpreter thread. These notifications take the form of a function
908pointer and a void argument.
909
910.. index:: single: setcheckinterval() (in module sys)
911
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000912Every check interval, when the global interpreter lock is released and
Ezio Melotti0639d5a2009-12-19 23:26:38 +0000913reacquired, Python will also call any such provided functions. This can be used
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000914for example by asynchronous IO handlers. The notification can be scheduled from
915a worker thread and the actual call than made at the earliest convenience by the
916main thread where it has possession of the global interpreter lock and can
917perform any Python API calls.
Benjamin Petersona54c9092009-01-13 02:11:23 +0000918
Ezio Melottia782cca2011-04-28 00:53:14 +0300919.. c:function:: int Py_AddPendingCall(int (*func)(void *), void *arg)
Benjamin Petersona54c9092009-01-13 02:11:23 +0000920
921 .. index:: single: Py_AddPendingCall()
922
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000923 Post a notification to the Python main thread. If successful, *func* will be
924 called with the argument *arg* at the earliest convenience. *func* will be
925 called having the global interpreter lock held and can thus use the full
926 Python API and can take any action such as setting object attributes to
927 signal IO completion. It must return 0 on success, or -1 signalling an
928 exception. The notification function won't be interrupted to perform another
929 asynchronous notification recursively, but it can still be interrupted to
930 switch threads if the global interpreter lock is released, for example, if it
Ezio Melotti0639d5a2009-12-19 23:26:38 +0000931 calls back into Python code.
Benjamin Petersona54c9092009-01-13 02:11:23 +0000932
933 This function returns 0 on success in which case the notification has been
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000934 scheduled. Otherwise, for example if the notification buffer is full, it
935 returns -1 without setting any exception.
Benjamin Petersona54c9092009-01-13 02:11:23 +0000936
Benjamin Petersonef3e4c22009-04-11 19:48:14 +0000937 This function can be called on any thread, be it a Python thread or some
938 other system thread. If it is a Python thread, it doesn't matter if it holds
939 the global interpreter lock or not.
Benjamin Petersona54c9092009-01-13 02:11:23 +0000940
Georg Brandl705d9d52009-05-05 09:29:50 +0000941 .. versionadded:: 3.1
Benjamin Petersona54c9092009-01-13 02:11:23 +0000942
943
Georg Brandl116aa622007-08-15 14:28:22 +0000944.. _profiling:
945
946Profiling and Tracing
947=====================
948
949.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
950
951
952The Python interpreter provides some low-level support for attaching profiling
953and execution tracing facilities. These are used for profiling, debugging, and
954coverage analysis tools.
955
Georg Brandle6bcc912008-05-12 18:05:20 +0000956This C interface allows the profiling or tracing code to avoid the overhead of
957calling through Python-level callable objects, making a direct C function call
958instead. The essential attributes of the facility have not changed; the
959interface allows trace functions to be installed per-thread, and the basic
960events reported to the trace function are the same as had been reported to the
961Python-level trace functions in previous versions.
Georg Brandl116aa622007-08-15 14:28:22 +0000962
963
Georg Brandl60203b42010-10-06 10:11:56 +0000964.. c:type:: int (*Py_tracefunc)(PyObject *obj, PyFrameObject *frame, int what, PyObject *arg)
Georg Brandl116aa622007-08-15 14:28:22 +0000965
Georg Brandl60203b42010-10-06 10:11:56 +0000966 The type of the trace function registered using :c:func:`PyEval_SetProfile` and
967 :c:func:`PyEval_SetTrace`. The first parameter is the object passed to the
Georg Brandl116aa622007-08-15 14:28:22 +0000968 registration function as *obj*, *frame* is the frame object to which the event
969 pertains, *what* is one of the constants :const:`PyTrace_CALL`,
970 :const:`PyTrace_EXCEPTION`, :const:`PyTrace_LINE`, :const:`PyTrace_RETURN`,
971 :const:`PyTrace_C_CALL`, :const:`PyTrace_C_EXCEPTION`, or
972 :const:`PyTrace_C_RETURN`, and *arg* depends on the value of *what*:
973
974 +------------------------------+--------------------------------------+
975 | Value of *what* | Meaning of *arg* |
976 +==============================+======================================+
977 | :const:`PyTrace_CALL` | Always *NULL*. |
978 +------------------------------+--------------------------------------+
979 | :const:`PyTrace_EXCEPTION` | Exception information as returned by |
980 | | :func:`sys.exc_info`. |
981 +------------------------------+--------------------------------------+
982 | :const:`PyTrace_LINE` | Always *NULL*. |
983 +------------------------------+--------------------------------------+
Georg Brandld0b0e1d2010-10-15 16:42:37 +0000984 | :const:`PyTrace_RETURN` | Value being returned to the caller, |
985 | | or *NULL* if caused by an exception. |
Georg Brandl116aa622007-08-15 14:28:22 +0000986 +------------------------------+--------------------------------------+
Georg Brandld0b0e1d2010-10-15 16:42:37 +0000987 | :const:`PyTrace_C_CALL` | Function object being called. |
Georg Brandl116aa622007-08-15 14:28:22 +0000988 +------------------------------+--------------------------------------+
Georg Brandld0b0e1d2010-10-15 16:42:37 +0000989 | :const:`PyTrace_C_EXCEPTION` | Function object being called. |
Georg Brandl116aa622007-08-15 14:28:22 +0000990 +------------------------------+--------------------------------------+
Georg Brandld0b0e1d2010-10-15 16:42:37 +0000991 | :const:`PyTrace_C_RETURN` | Function object being called. |
Georg Brandl116aa622007-08-15 14:28:22 +0000992 +------------------------------+--------------------------------------+
993
994
Georg Brandl60203b42010-10-06 10:11:56 +0000995.. c:var:: int PyTrace_CALL
Georg Brandl116aa622007-08-15 14:28:22 +0000996
Georg Brandl60203b42010-10-06 10:11:56 +0000997 The value of the *what* parameter to a :c:type:`Py_tracefunc` function when a new
Georg Brandl116aa622007-08-15 14:28:22 +0000998 call to a function or method is being reported, or a new entry into a generator.
999 Note that the creation of the iterator for a generator function is not reported
1000 as there is no control transfer to the Python bytecode in the corresponding
1001 frame.
1002
1003
Georg Brandl60203b42010-10-06 10:11:56 +00001004.. c:var:: int PyTrace_EXCEPTION
Georg Brandl116aa622007-08-15 14:28:22 +00001005
Georg Brandl60203b42010-10-06 10:11:56 +00001006 The value of the *what* parameter to a :c:type:`Py_tracefunc` function when an
Georg Brandl116aa622007-08-15 14:28:22 +00001007 exception has been raised. The callback function is called with this value for
1008 *what* when after any bytecode is processed after which the exception becomes
1009 set within the frame being executed. The effect of this is that as exception
1010 propagation causes the Python stack to unwind, the callback is called upon
1011 return to each frame as the exception propagates. Only trace functions receives
1012 these events; they are not needed by the profiler.
1013
1014
Georg Brandl60203b42010-10-06 10:11:56 +00001015.. c:var:: int PyTrace_LINE
Georg Brandl116aa622007-08-15 14:28:22 +00001016
1017 The value passed as the *what* parameter to a trace function (but not a
1018 profiling function) when a line-number event is being reported.
1019
1020
Georg Brandl60203b42010-10-06 10:11:56 +00001021.. c:var:: int PyTrace_RETURN
Georg Brandl116aa622007-08-15 14:28:22 +00001022
Georg Brandl60203b42010-10-06 10:11:56 +00001023 The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a
Georg Brandl116aa622007-08-15 14:28:22 +00001024 call is returning without propagating an exception.
1025
1026
Georg Brandl60203b42010-10-06 10:11:56 +00001027.. c:var:: int PyTrace_C_CALL
Georg Brandl116aa622007-08-15 14:28:22 +00001028
Georg Brandl60203b42010-10-06 10:11:56 +00001029 The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a C
Georg Brandl116aa622007-08-15 14:28:22 +00001030 function is about to be called.
1031
1032
Georg Brandl60203b42010-10-06 10:11:56 +00001033.. c:var:: int PyTrace_C_EXCEPTION
Georg Brandl116aa622007-08-15 14:28:22 +00001034
Georg Brandl60203b42010-10-06 10:11:56 +00001035 The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a C
Georg Brandl7cb13192010-08-03 12:06:29 +00001036 function has raised an exception.
Georg Brandl116aa622007-08-15 14:28:22 +00001037
1038
Georg Brandl60203b42010-10-06 10:11:56 +00001039.. c:var:: int PyTrace_C_RETURN
Georg Brandl116aa622007-08-15 14:28:22 +00001040
Georg Brandl60203b42010-10-06 10:11:56 +00001041 The value for the *what* parameter to :c:type:`Py_tracefunc` functions when a C
Georg Brandl116aa622007-08-15 14:28:22 +00001042 function has returned.
1043
1044
Georg Brandl60203b42010-10-06 10:11:56 +00001045.. c:function:: void PyEval_SetProfile(Py_tracefunc func, PyObject *obj)
Georg Brandl116aa622007-08-15 14:28:22 +00001046
1047 Set the profiler function to *func*. The *obj* parameter is passed to the
1048 function as its first parameter, and may be any Python object, or *NULL*. If
1049 the profile function needs to maintain state, using a different value for *obj*
1050 for each thread provides a convenient and thread-safe place to store it. The
1051 profile function is called for all monitored events except the line-number
1052 events.
1053
1054
Georg Brandl60203b42010-10-06 10:11:56 +00001055.. c:function:: void PyEval_SetTrace(Py_tracefunc func, PyObject *obj)
Georg Brandl116aa622007-08-15 14:28:22 +00001056
1057 Set the tracing function to *func*. This is similar to
Georg Brandl60203b42010-10-06 10:11:56 +00001058 :c:func:`PyEval_SetProfile`, except the tracing function does receive line-number
Georg Brandl116aa622007-08-15 14:28:22 +00001059 events.
1060
Georg Brandl60203b42010-10-06 10:11:56 +00001061.. c:function:: PyObject* PyEval_GetCallStats(PyObject *self)
Christian Heimesd8654cf2007-12-02 15:22:16 +00001062
1063 Return a tuple of function call counts. There are constants defined for the
1064 positions within the tuple:
Georg Brandl48310cd2009-01-03 21:18:54 +00001065
Christian Heimesd8654cf2007-12-02 15:22:16 +00001066 +-------------------------------+-------+
1067 | Name | Value |
1068 +===============================+=======+
1069 | :const:`PCALL_ALL` | 0 |
1070 +-------------------------------+-------+
1071 | :const:`PCALL_FUNCTION` | 1 |
1072 +-------------------------------+-------+
1073 | :const:`PCALL_FAST_FUNCTION` | 2 |
1074 +-------------------------------+-------+
1075 | :const:`PCALL_FASTER_FUNCTION`| 3 |
1076 +-------------------------------+-------+
1077 | :const:`PCALL_METHOD` | 4 |
1078 +-------------------------------+-------+
1079 | :const:`PCALL_BOUND_METHOD` | 5 |
1080 +-------------------------------+-------+
1081 | :const:`PCALL_CFUNCTION` | 6 |
1082 +-------------------------------+-------+
1083 | :const:`PCALL_TYPE` | 7 |
1084 +-------------------------------+-------+
1085 | :const:`PCALL_GENERATOR` | 8 |
1086 +-------------------------------+-------+
1087 | :const:`PCALL_OTHER` | 9 |
1088 +-------------------------------+-------+
1089 | :const:`PCALL_POP` | 10 |
1090 +-------------------------------+-------+
Georg Brandl48310cd2009-01-03 21:18:54 +00001091
Christian Heimesd8654cf2007-12-02 15:22:16 +00001092 :const:`PCALL_FAST_FUNCTION` means no argument tuple needs to be created.
1093 :const:`PCALL_FASTER_FUNCTION` means that the fast-path frame setup code is used.
1094
1095 If there is a method call where the call can be optimized by changing
1096 the argument tuple and calling the function directly, it gets recorded
1097 twice.
1098
1099 This function is only present if Python is compiled with :const:`CALL_PROFILE`
1100 defined.
Georg Brandl116aa622007-08-15 14:28:22 +00001101
1102.. _advanced-debugging:
1103
1104Advanced Debugger Support
1105=========================
1106
1107.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
1108
1109
1110These functions are only intended to be used by advanced debugging tools.
1111
1112
Georg Brandl60203b42010-10-06 10:11:56 +00001113.. c:function:: PyInterpreterState* PyInterpreterState_Head()
Georg Brandl116aa622007-08-15 14:28:22 +00001114
1115 Return the interpreter state object at the head of the list of all such objects.
1116
Georg Brandl116aa622007-08-15 14:28:22 +00001117
Georg Brandl60203b42010-10-06 10:11:56 +00001118.. c:function:: PyInterpreterState* PyInterpreterState_Next(PyInterpreterState *interp)
Georg Brandl116aa622007-08-15 14:28:22 +00001119
1120 Return the next interpreter state object after *interp* from the list of all
1121 such objects.
1122
Georg Brandl116aa622007-08-15 14:28:22 +00001123
Georg Brandl60203b42010-10-06 10:11:56 +00001124.. c:function:: PyThreadState * PyInterpreterState_ThreadHead(PyInterpreterState *interp)
Georg Brandl116aa622007-08-15 14:28:22 +00001125
Georg Brandl60203b42010-10-06 10:11:56 +00001126 Return the a pointer to the first :c:type:`PyThreadState` object in the list of
Georg Brandl116aa622007-08-15 14:28:22 +00001127 threads associated with the interpreter *interp*.
1128
Georg Brandl116aa622007-08-15 14:28:22 +00001129
Georg Brandl60203b42010-10-06 10:11:56 +00001130.. c:function:: PyThreadState* PyThreadState_Next(PyThreadState *tstate)
Georg Brandl116aa622007-08-15 14:28:22 +00001131
1132 Return the next thread state object after *tstate* from the list of all such
Georg Brandl60203b42010-10-06 10:11:56 +00001133 objects belonging to the same :c:type:`PyInterpreterState` object.
Georg Brandl116aa622007-08-15 14:28:22 +00001134