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https://github.com/python/cpython
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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
This commit is contained in:
Masayuki Yamamoto
Victor Stinner
parent
5e87592fd1
commit
aa0aa0492c
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@ -0,0 +1,7 @@
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Remove own implementation for thread-local storage.
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CPython has provided the own implementation for thread-local storage (TLS)
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on Python/thread.c, it's used in the case which a platform has not supplied
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native TLS. However, currently all supported platforms (Windows and pthreads)
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have provided native TLS and defined the Py_HAVE_NATIVE_TLS macro with
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unconditional in any case.
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221
Python/thread.c
221
Python/thread.c
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@ -81,14 +81,14 @@ PyThread_init_thread(void)
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or the size specified by the THREAD_STACK_SIZE macro. */
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static size_t _pythread_stacksize = 0;
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#ifdef _POSIX_THREADS
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#define PYTHREAD_NAME "pthread"
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#include "thread_pthread.h"
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#endif
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#ifdef NT_THREADS
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#define PYTHREAD_NAME "nt"
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#include "thread_nt.h"
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#if defined(_POSIX_THREADS)
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# define PYTHREAD_NAME "pthread"
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# include "thread_pthread.h"
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#elif defined(NT_THREADS)
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# define PYTHREAD_NAME "nt"
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# include "thread_nt.h"
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#else
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# error "Require native thread feature. See https://bugs.python.org/issue30832"
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#endif
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@ -114,13 +114,7 @@ PyThread_set_stacksize(size_t size)
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#endif
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}
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#ifndef Py_HAVE_NATIVE_TLS
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/* If the platform has not supplied a platform specific
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TLS implementation, provide our own.
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This code stolen from "thread_sgi.h", where it was the only
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implementation of an existing Python TLS API.
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*/
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/* ------------------------------------------------------------------------
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Per-thread data ("key") support.
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@ -157,205 +151,6 @@ any of the other functions are called. There's also a hidden assumption
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that calls to PyThread_create_key() are serialized externally.
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------------------------------------------------------------------------ */
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/* A singly-linked list of struct key objects remembers all the key->value
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* associations. File static keyhead heads the list. keymutex is used
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* to enforce exclusion internally.
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*/
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struct key {
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/* Next record in the list, or NULL if this is the last record. */
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struct key *next;
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/* The thread id, according to PyThread_get_thread_ident(). */
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unsigned long id;
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/* The key and its associated value. */
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int key;
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void *value;
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};
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static struct key *keyhead = NULL;
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static PyThread_type_lock keymutex = NULL;
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static int nkeys = 0; /* PyThread_create_key() hands out nkeys+1 next */
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/* Internal helper.
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* If the current thread has a mapping for key, the appropriate struct key*
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* is returned. NB: value is ignored in this case!
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* If there is no mapping for key in the current thread, then:
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* If value is NULL, NULL is returned.
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* Else a mapping of key to value is created for the current thread,
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* and a pointer to a new struct key* is returned; except that if
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* malloc() can't find room for a new struct key*, NULL is returned.
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* So when value==NULL, this acts like a pure lookup routine, and when
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* value!=NULL, this acts like dict.setdefault(), returning an existing
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* mapping if one exists, else creating a new mapping.
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*
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* Caution: this used to be too clever, trying to hold keymutex only
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* around the "p->next = keyhead; keyhead = p" pair. That allowed
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* another thread to mutate the list, via key deletion, concurrent with
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* find_key() crawling over the list. Hilarity ensued. For example, when
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* the for-loop here does "p = p->next", p could end up pointing at a
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* record that PyThread_delete_key_value() was concurrently free()'ing.
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* That could lead to anything, from failing to find a key that exists, to
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* segfaults. Now we lock the whole routine.
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*/
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static struct key *
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find_key(int set_value, int key, void *value)
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{
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struct key *p, *prev_p;
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unsigned long id = PyThread_get_thread_ident();
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if (!keymutex)
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return NULL;
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PyThread_acquire_lock(keymutex, 1);
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prev_p = NULL;
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for (p = keyhead; p != NULL; p = p->next) {
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if (p->id == id && p->key == key) {
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if (set_value)
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p->value = value;
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goto Done;
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}
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/* Sanity check. These states should never happen but if
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* they do we must abort. Otherwise we'll end up spinning
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* in a tight loop with the lock held. A similar check is done
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* in pystate.c tstate_delete_common(). */
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if (p == prev_p)
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Py_FatalError("tls find_key: small circular list(!)");
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prev_p = p;
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if (p->next == keyhead)
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Py_FatalError("tls find_key: circular list(!)");
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}
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if (!set_value && value == NULL) {
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assert(p == NULL);
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goto Done;
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}
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p = (struct key *)PyMem_RawMalloc(sizeof(struct key));
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if (p != NULL) {
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p->id = id;
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p->key = key;
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p->value = value;
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p->next = keyhead;
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keyhead = p;
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}
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Done:
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PyThread_release_lock(keymutex);
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return p;
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}
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/* Return a new key. This must be called before any other functions in
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* this family, and callers must arrange to serialize calls to this
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* function. No violations are detected.
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*/
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int
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PyThread_create_key(void)
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{
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/* All parts of this function are wrong if it's called by multiple
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* threads simultaneously.
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*/
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if (keymutex == NULL)
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keymutex = PyThread_allocate_lock();
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return ++nkeys;
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}
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/* Forget the associations for key across *all* threads. */
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void
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PyThread_delete_key(int key)
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{
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struct key *p, **q;
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PyThread_acquire_lock(keymutex, 1);
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q = &keyhead;
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while ((p = *q) != NULL) {
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if (p->key == key) {
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*q = p->next;
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PyMem_RawFree((void *)p);
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/* NB This does *not* free p->value! */
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}
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else
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q = &p->next;
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}
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PyThread_release_lock(keymutex);
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}
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int
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PyThread_set_key_value(int key, void *value)
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{
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struct key *p;
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p = find_key(1, key, value);
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if (p == NULL)
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return -1;
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else
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return 0;
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}
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/* Retrieve the value associated with key in the current thread, or NULL
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* if the current thread doesn't have an association for key.
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*/
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void *
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PyThread_get_key_value(int key)
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{
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struct key *p = find_key(0, key, NULL);
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if (p == NULL)
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return NULL;
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else
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return p->value;
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}
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/* Forget the current thread's association for key, if any. */
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void
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PyThread_delete_key_value(int key)
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{
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unsigned long id = PyThread_get_thread_ident();
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struct key *p, **q;
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PyThread_acquire_lock(keymutex, 1);
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q = &keyhead;
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while ((p = *q) != NULL) {
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if (p->key == key && p->id == id) {
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*q = p->next;
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PyMem_RawFree((void *)p);
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/* NB This does *not* free p->value! */
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break;
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}
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else
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q = &p->next;
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}
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PyThread_release_lock(keymutex);
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}
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/* Forget everything not associated with the current thread id.
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* This function is called from PyOS_AfterFork_Child(). It is necessary
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* because other thread ids which were in use at the time of the fork
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* may be reused for new threads created in the forked process.
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*/
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void
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PyThread_ReInitTLS(void)
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{
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unsigned long id = PyThread_get_thread_ident();
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struct key *p, **q;
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if (!keymutex)
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return;
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/* As with interpreter_lock in PyEval_ReInitThreads()
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we just create a new lock without freeing the old one */
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keymutex = PyThread_allocate_lock();
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/* Delete all keys which do not match the current thread id */
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q = &keyhead;
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while ((p = *q) != NULL) {
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if (p->id != id) {
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*q = p->next;
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PyMem_RawFree((void *)p);
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/* NB This does *not* free p->value! */
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}
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else
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q = &p->next;
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}
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}
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#endif /* Py_HAVE_NATIVE_TLS */
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PyDoc_STRVAR(threadinfo__doc__,
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"sys.thread_info\n\
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@ -348,10 +348,6 @@ _pythread_nt_set_stacksize(size_t size)
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#define THREAD_SET_STACKSIZE(x) _pythread_nt_set_stacksize(x)
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/* use native Windows TLS functions */
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#define Py_HAVE_NATIVE_TLS
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#ifdef Py_HAVE_NATIVE_TLS
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int
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PyThread_create_key(void)
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{
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@ -408,5 +404,3 @@ PyThread_delete_key_value(int key)
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void
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PyThread_ReInitTLS(void)
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{}
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#endif
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@ -608,7 +608,6 @@ _pythread_pthread_set_stacksize(size_t size)
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#define THREAD_SET_STACKSIZE(x) _pythread_pthread_set_stacksize(x)
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#define Py_HAVE_NATIVE_TLS
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int
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PyThread_create_key(void)
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