| This file describes some special Python build types enabled via |
| compile-time preprocessor defines. |
| |
| --------------------------------------------------------------------------- |
| Py_REF_DEBUG introduced in 1.4 |
| named REF_DEBUG before 1.4 |
| |
| Turn on aggregate reference counting. This arranges that extern |
| _Py_RefTotal hold a count of all references, the sum of ob_refcnt across |
| all objects. In a debug-mode build, this is where the "8288" comes from |
| in |
| |
| >>> 23 |
| 23 |
| [8288 refs] |
| >>> |
| |
| Note that if this count increases when you're not storing away new objects, |
| there's probably a leak. Remember, though, that in interactive mode the |
| special name "_" holds a reference to the last result displayed! |
| |
| Py_REF_DEBUG also checks after every decref to verify that the refcount |
| hasn't gone negative, and causes an immediate fatal error if it has. |
| |
| Special gimmicks: |
| |
| sys.gettotalrefcount() |
| Return current total of all refcounts. |
| Available under Py_REF_DEBUG in Python 2.3. |
| Before 2.3, Py_TRACE_REFS was required to enable this function. |
| --------------------------------------------------------------------------- |
| Py_TRACE_REFS introduced in 1.4 |
| named TRACE_REFS before 1.4 |
| |
| Turn on heavy reference debugging. This is major surgery. Every PyObject |
| grows two more pointers, to maintain a doubly-linked list of all live |
| heap-allocated objects (note that, e.g., most builtin type objects are not |
| in this list, as they're statically allocated). Note that because the |
| fundamental PyObject layout changes, Python modules compiled with |
| Py_TRACE_REFS are incompatible with modules compiled without it. |
| |
| Py_TRACE_REFS implies Py_REF_DEBUG. |
| |
| Special gimmicks: |
| |
| sys.getobjects(max[, type]) |
| Return list of the (no more than) max most-recently allocated objects, |
| most recently allocated first in the list, least-recently allocated |
| last in the list. max=0 means no limit on list length. |
| If an optional type object is passed, the list is also restricted to |
| objects of that type. |
| The return list itself, and some temp objects created just to call |
| sys.getobjects(), are excluded from the return list. Note that the |
| list returned is just another object, though, so may appear in the |
| return list the next time you call getobjects(); note that every |
| object in the list is kept alive too, simply by virtue of being in |
| the list. |
| |
| envar PYTHONDUMPREFS |
| If this envar exists, Py_Finalize() arranges to print a list of |
| all still-live heap objects. |
| --------------------------------------------------------------------------- |
| PYMALLOC_DEBUG introduced in 2.3 |
| |
| When pymalloc is enabled (WITH_PYMALLOC is defined), calls to the PyObject_ |
| memory routines are handled by Python's own small-object allocator, while |
| calls to the PyMem_ memory routines are directed to the system malloc/ |
| realloc/free. If PYMALLOC_DEBUG is also defined, calls to both PyObject_ |
| and PyMem_ memory routines are directed to a special debugging mode of |
| Python's small-object allocator. |
| |
| This mode fills dynamically allocated memory blocks with special, |
| recognizable bit patterns, and adds debugging info on each end of |
| dynamically allocated memory blocks. The special bit patterns are: |
| |
| #define CLEANBYTE 0xCB /* clean (newly allocated) memory */ |
| #define DEADBYTE 0xDB /* dead (newly freed) memory */ |
| #define FORBIDDENBYTE 0xFB /* fordidden -- untouchable bytes */ |
| |
| Strings of these bytes are unlikely to be valid addresses, floats, or 7-bit |
| ASCII strings. |
| |
| 8 bytes are added at each end of each block of N bytes requested. The |
| memory layout is like so, where p represents the address returned by a |
| malloc-like or realloc-like function (p[i:j] means the slice of bytes |
| from *(p+i) inclusive up to *(p+j) exclusive; note that the treatment |
| of negative indices differs from a Python slice): |
| |
| p[-8:-4] |
| Number of bytes originally asked for. 4-byte unsigned integer, |
| big-endian (easier to read in a memory dump). |
| p[-4:0] |
| Copies of FORBIDDENBYTE. Used to catch under- writes and reads. |
| p[0:N] |
| The requested memory, filled with copies of CLEANBYTE, used to catch |
| reference to uninitialized memory. |
| When a realloc-like function is called requesting a larger memory |
| block, the new excess bytes are also filled with CLEANBYTE. |
| When a free-like function is called, these are overwritten with |
| DEADBYTE, to catch reference to freed memory. When a realloc- |
| like function is called requesting a smaller memory block, the excess |
| old bytes are also filled with DEADBYTE. |
| p[N:N+4] |
| Copies of FORBIDDENBYTE. Used to catch over- writes and reads. |
| p[N+4:N+8] |
| A serial number, incremented by 1 on each call to a malloc-like or |
| realloc-like function. |
| 4-byte unsigned integer, big-endian. |
| If "bad memory" is detected later, the serial number gives an |
| excellent way to set a breakpoint on the next run, to capture the |
| instant at which this block was passed out. The static function |
| bumpserialno() in obmalloc.c is the only place the serial number |
| is incremented, and exists so you can set such a breakpoint easily. |
| |
| A realloc-like or free-like function first checks that the FORBIDDENBYTEs |
| at each end are intact. If they've been altered, diagnostic output is |
| written to stderr, and the program is aborted via Py_FatalError(). The |
| other main failure mode is provoking a memory error when a program |
| reads up one of the special bit patterns and tries to use it as an address. |
| If you get in a debugger then and look at the object, you're likely |
| to see that it's entirely filled with 0xDB (meaning freed memory is |
| getting used) or 0xCB (meaning uninitialized memory is getting used). |
| |
| Note that PYMALLOC_DEBUG requires WITH_PYMALLOC. |
| |
| Special gimmicks: |
| |
| envar PYTHONMALLOCSTATS |
| If this envar exists, a report of pymalloc summary statistics is |
| printed to stderr whenever a new arena is allocated, and also |
| by Py_Finalize(). |
| --------------------------------------------------------------------------- |
| Py_DEBUG introduced in 1.5 |
| named DEBUG before 1.5 |
| |
| This is what is generally meant by "a debug build" of Python. |
| |
| Py_DEBUG implies LLTRACE, Py_REF_DEBUG, Py_TRACE_REFS, and |
| PYMALLOC_DEBUG (if WITH_PYMALLOC is enabled). In addition, C |
| assert()s are enabled (via the C way: by not defining NDEBUG), and |
| some routines do additional sanity checks inside "#ifdef Py_DEBUG" |
| blocks. |
| --------------------------------------------------------------------------- |
| COUNT_ALLOCS introduced in 0.9.9 |
| partly broken in 2.2 and 2.2.1 |
| |
| Each type object grows three new members: |
| |
| /* Number of times an object of this type was allocated. */ |
| int tp_allocs; |
| |
| /* Number of times an object of this type was deallocated. */ |
| int tp_frees; |
| |
| /* Highwater mark: the maximum value of tp_allocs - tp_frees so |
| * far; or, IOW, the largest number of objects of this type alive at |
| * the same time. |
| */ |
| int tp_maxalloc; |
| |
| Allocation and deallocation code keeps these counts up to date. |
| Py_Finalize() displays a summary of the info returned by sys.getcounts() |
| (see below), along with assorted other special allocation counts (like |
| the number of tuple allocations satisfied by a tuple free-list, the number |
| of 1-character strings allocated, etc). |
| |
| Before Python 2.2, type objects were immortal, and the COUNT_ALLOCS |
| implementation relies on that. As of Python 2.2, heap-allocated type/ |
| class objects can go away. COUNT_ALLOCS can blow up in 2.2 and 2.2.1 |
| because of this; this was fixed in 2.2.2. Use of COUNT_ALLOCS makes |
| all heap-allocated type objects immortal, except for those for which no |
| object of that type is ever allocated. |
| |
| Special gimmicks: |
| |
| sys.getcounts() |
| Return a list of 4-tuples, one entry for each type object for which |
| at least one object of that type was allocated. Each tuple is of |
| the form: |
| |
| (tp_name, tp_allocs, tp_frees, tp_maxalloc) |
| |
| Each distinct type object gets a distinct entry in this list, even |
| if two or more type objects have the same tp_name (in which case |
| there's no way to distinguish them by looking at this list). The |
| list is ordered by time of first object allocation: the type object |
| for which the first allocation of an object of that type occurred |
| most recently is at the front of the list. |
| --------------------------------------------------------------------------- |
| LLTRACE introduced well before 1.0 |
| |
| Compile in support of Low Level TRACE-ing of the main interpreter loop. |
| |
| When this preprocessor symbol is defined, before eval_frame |
| (eval_code2 before 2.2) executes a frame's code it checks the frame's |
| global namespace for a variable "__lltrace__". If such a variable is |
| found, mounds of information about what the interpreter is doing are |
| sprayed to stdout, such as every opcode and opcode argument and values |
| pushed onto and popped off the value stack. |
| |
| Not useful very often, but very useful when needed. |