bpo-30832: Remove own implementation for thread-local storage (#2537)
* bpo-30832: Remove own implementation for thread-local storage
CPython has provided the own implementation for thread-local storage
(TLS) on Python/thread.c, it's used in the case which a platform has
not supplied native TLS. However, currently all supported platforms
(NT and pthreads) have provided native TLS and defined the
Py_HAVE_NATIVE_TLS macro with unconditional in any case.
* bpo-30832: replace NT with Windows
* bpo-30832: change to directive chain
* bpo-30832: remove comemnt which making no sense
diff --git a/Misc/NEWS.d/next/C API/2017-07-03-17-25-40.bpo-30832.PcTAEP.rst b/Misc/NEWS.d/next/C API/2017-07-03-17-25-40.bpo-30832.PcTAEP.rst
new file mode 100644
index 0000000..1cdacf3
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2017-07-03-17-25-40.bpo-30832.PcTAEP.rst
@@ -0,0 +1,7 @@
+Remove own implementation for thread-local storage.
+
+CPython has provided the own implementation for thread-local storage (TLS)
+on Python/thread.c, it's used in the case which a platform has not supplied
+native TLS. However, currently all supported platforms (Windows and pthreads)
+have provided native TLS and defined the Py_HAVE_NATIVE_TLS macro with
+unconditional in any case.
diff --git a/Python/thread.c b/Python/thread.c
index ed697ac..4d2f2c3 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -81,14 +81,14 @@
or the size specified by the THREAD_STACK_SIZE macro. */
static size_t _pythread_stacksize = 0;
-#ifdef _POSIX_THREADS
-#define PYTHREAD_NAME "pthread"
-#include "thread_pthread.h"
-#endif
-
-#ifdef NT_THREADS
-#define PYTHREAD_NAME "nt"
-#include "thread_nt.h"
+#if defined(_POSIX_THREADS)
+# define PYTHREAD_NAME "pthread"
+# include "thread_pthread.h"
+#elif defined(NT_THREADS)
+# define PYTHREAD_NAME "nt"
+# include "thread_nt.h"
+#else
+# error "Require native thread feature. See https://bugs.python.org/issue30832"
#endif
@@ -114,13 +114,7 @@
#endif
}
-#ifndef Py_HAVE_NATIVE_TLS
-/* If the platform has not supplied a platform specific
- TLS implementation, provide our own.
- This code stolen from "thread_sgi.h", where it was the only
- implementation of an existing Python TLS API.
-*/
/* ------------------------------------------------------------------------
Per-thread data ("key") support.
@@ -157,205 +151,6 @@
that calls to PyThread_create_key() are serialized externally.
------------------------------------------------------------------------ */
-/* A singly-linked list of struct key objects remembers all the key->value
- * associations. File static keyhead heads the list. keymutex is used
- * to enforce exclusion internally.
- */
-struct key {
- /* Next record in the list, or NULL if this is the last record. */
- struct key *next;
-
- /* The thread id, according to PyThread_get_thread_ident(). */
- unsigned long id;
-
- /* The key and its associated value. */
- int key;
- void *value;
-};
-
-static struct key *keyhead = NULL;
-static PyThread_type_lock keymutex = NULL;
-static int nkeys = 0; /* PyThread_create_key() hands out nkeys+1 next */
-
-/* Internal helper.
- * If the current thread has a mapping for key, the appropriate struct key*
- * is returned. NB: value is ignored in this case!
- * If there is no mapping for key in the current thread, then:
- * If value is NULL, NULL is returned.
- * Else a mapping of key to value is created for the current thread,
- * and a pointer to a new struct key* is returned; except that if
- * malloc() can't find room for a new struct key*, NULL is returned.
- * So when value==NULL, this acts like a pure lookup routine, and when
- * value!=NULL, this acts like dict.setdefault(), returning an existing
- * mapping if one exists, else creating a new mapping.
- *
- * Caution: this used to be too clever, trying to hold keymutex only
- * around the "p->next = keyhead; keyhead = p" pair. That allowed
- * another thread to mutate the list, via key deletion, concurrent with
- * find_key() crawling over the list. Hilarity ensued. For example, when
- * the for-loop here does "p = p->next", p could end up pointing at a
- * record that PyThread_delete_key_value() was concurrently free()'ing.
- * That could lead to anything, from failing to find a key that exists, to
- * segfaults. Now we lock the whole routine.
- */
-static struct key *
-find_key(int set_value, int key, void *value)
-{
- struct key *p, *prev_p;
- unsigned long id = PyThread_get_thread_ident();
-
- if (!keymutex)
- return NULL;
- PyThread_acquire_lock(keymutex, 1);
- prev_p = NULL;
- for (p = keyhead; p != NULL; p = p->next) {
- if (p->id == id && p->key == key) {
- if (set_value)
- p->value = value;
- goto Done;
- }
- /* Sanity check. These states should never happen but if
- * they do we must abort. Otherwise we'll end up spinning
- * in a tight loop with the lock held. A similar check is done
- * in pystate.c tstate_delete_common(). */
- if (p == prev_p)
- Py_FatalError("tls find_key: small circular list(!)");
- prev_p = p;
- if (p->next == keyhead)
- Py_FatalError("tls find_key: circular list(!)");
- }
- if (!set_value && value == NULL) {
- assert(p == NULL);
- goto Done;
- }
- p = (struct key *)PyMem_RawMalloc(sizeof(struct key));
- if (p != NULL) {
- p->id = id;
- p->key = key;
- p->value = value;
- p->next = keyhead;
- keyhead = p;
- }
- Done:
- PyThread_release_lock(keymutex);
- return p;
-}
-
-/* Return a new key. This must be called before any other functions in
- * this family, and callers must arrange to serialize calls to this
- * function. No violations are detected.
- */
-int
-PyThread_create_key(void)
-{
- /* All parts of this function are wrong if it's called by multiple
- * threads simultaneously.
- */
- if (keymutex == NULL)
- keymutex = PyThread_allocate_lock();
- return ++nkeys;
-}
-
-/* Forget the associations for key across *all* threads. */
-void
-PyThread_delete_key(int key)
-{
- struct key *p, **q;
-
- PyThread_acquire_lock(keymutex, 1);
- q = &keyhead;
- while ((p = *q) != NULL) {
- if (p->key == key) {
- *q = p->next;
- PyMem_RawFree((void *)p);
- /* NB This does *not* free p->value! */
- }
- else
- q = &p->next;
- }
- PyThread_release_lock(keymutex);
-}
-
-int
-PyThread_set_key_value(int key, void *value)
-{
- struct key *p;
-
- p = find_key(1, key, value);
- if (p == NULL)
- return -1;
- else
- return 0;
-}
-
-/* Retrieve the value associated with key in the current thread, or NULL
- * if the current thread doesn't have an association for key.
- */
-void *
-PyThread_get_key_value(int key)
-{
- struct key *p = find_key(0, key, NULL);
-
- if (p == NULL)
- return NULL;
- else
- return p->value;
-}
-
-/* Forget the current thread's association for key, if any. */
-void
-PyThread_delete_key_value(int key)
-{
- unsigned long id = PyThread_get_thread_ident();
- struct key *p, **q;
-
- PyThread_acquire_lock(keymutex, 1);
- q = &keyhead;
- while ((p = *q) != NULL) {
- if (p->key == key && p->id == id) {
- *q = p->next;
- PyMem_RawFree((void *)p);
- /* NB This does *not* free p->value! */
- break;
- }
- else
- q = &p->next;
- }
- PyThread_release_lock(keymutex);
-}
-
-/* Forget everything not associated with the current thread id.
- * This function is called from PyOS_AfterFork_Child(). It is necessary
- * because other thread ids which were in use at the time of the fork
- * may be reused for new threads created in the forked process.
- */
-void
-PyThread_ReInitTLS(void)
-{
- unsigned long id = PyThread_get_thread_ident();
- struct key *p, **q;
-
- if (!keymutex)
- return;
-
- /* As with interpreter_lock in PyEval_ReInitThreads()
- we just create a new lock without freeing the old one */
- keymutex = PyThread_allocate_lock();
-
- /* Delete all keys which do not match the current thread id */
- q = &keyhead;
- while ((p = *q) != NULL) {
- if (p->id != id) {
- *q = p->next;
- PyMem_RawFree((void *)p);
- /* NB This does *not* free p->value! */
- }
- else
- q = &p->next;
- }
-}
-
-#endif /* Py_HAVE_NATIVE_TLS */
PyDoc_STRVAR(threadinfo__doc__,
"sys.thread_info\n\
diff --git a/Python/thread_nt.h b/Python/thread_nt.h
index 8158ff8..47eb4b6 100644
--- a/Python/thread_nt.h
+++ b/Python/thread_nt.h
@@ -348,10 +348,6 @@
#define THREAD_SET_STACKSIZE(x) _pythread_nt_set_stacksize(x)
-/* use native Windows TLS functions */
-#define Py_HAVE_NATIVE_TLS
-
-#ifdef Py_HAVE_NATIVE_TLS
int
PyThread_create_key(void)
{
@@ -408,5 +404,3 @@
void
PyThread_ReInitTLS(void)
{}
-
-#endif
diff --git a/Python/thread_pthread.h b/Python/thread_pthread.h
index 399d28c..268dec4 100644
--- a/Python/thread_pthread.h
+++ b/Python/thread_pthread.h
@@ -608,7 +608,6 @@
#define THREAD_SET_STACKSIZE(x) _pythread_pthread_set_stacksize(x)
-#define Py_HAVE_NATIVE_TLS
int
PyThread_create_key(void)