[Python-checkins] python/dist/src/Python pystate.c, 2.29,
2.29.6.1 thread.c, 2.46.10.1, 2.46.10.2
arigo at users.sourceforge.net
arigo at users.sourceforge.net
Tue Nov 9 16:35:26 CET 2004
Update of /cvsroot/python/python/dist/src/Python
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv26605/Python
Modified Files:
Tag: release23-maint
pystate.c thread.c
Log Message:
Backported thread fixes from 2.4 (by mostly copying pystate.c over from 2.4):
* using malloc() and free() directly, as explained in the new comment
* coding style in the PyGILState_*() functions
* the recent destroy-tstate-without-holding-the-GIL bug
* lock fixes and many more comments in thread.c
Index: pystate.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Python/pystate.c,v
retrieving revision 2.29
retrieving revision 2.29.6.1
diff -u -d -r2.29 -r2.29.6.1
--- pystate.c 13 Jul 2003 10:41:53 -0000 2.29
+++ pystate.c 9 Nov 2004 15:35:23 -0000 2.29.6.1
@@ -3,6 +3,16 @@
#include "Python.h"
+/* --------------------------------------------------------------------------
+CAUTION
+
+Always use malloc() and free() directly in this file. A number of these
+functions are advertised as safe to call when the GIL isn't held, and in
+a debug build Python redirects (e.g.) PyMem_NEW (etc) to Python's debugging
+obmalloc functions. Those aren't thread-safe (they rely on the GIL to avoid
+the expense of doing their own locking).
+-------------------------------------------------------------------------- */
+
#ifdef HAVE_DLOPEN
#ifdef HAVE_DLFCN_H
#include <dlfcn.h>
@@ -41,7 +51,8 @@
PyInterpreterState *
PyInterpreterState_New(void)
{
- PyInterpreterState *interp = PyMem_NEW(PyInterpreterState, 1);
+ PyInterpreterState *interp = (PyInterpreterState *)
+ malloc(sizeof(PyInterpreterState));
if (interp != NULL) {
HEAD_INIT();
@@ -116,7 +127,7 @@
Py_FatalError("PyInterpreterState_Delete: remaining threads");
*p = interp->next;
HEAD_UNLOCK();
- PyMem_DEL(interp);
+ free(interp);
}
@@ -130,7 +141,8 @@
PyThreadState *
PyThreadState_New(PyInterpreterState *interp)
{
- PyThreadState *tstate = PyMem_NEW(PyThreadState, 1);
+ PyThreadState *tstate = (PyThreadState *)malloc(sizeof(PyThreadState));
+
if (_PyThreadState_GetFrame == NULL)
_PyThreadState_GetFrame = threadstate_getframe;
@@ -223,7 +235,7 @@
}
*p = tstate->next;
HEAD_UNLOCK();
- PyMem_DEL(tstate);
+ free(tstate);
}
@@ -268,7 +280,7 @@
_PyThreadState_Current = new;
/* It should not be possible for more than one thread state
- to be used for a thread. Check this the best we can in debug
+ to be used for a thread. Check this the best we can in debug
builds.
*/
#if defined(Py_DEBUG) && defined(WITH_THREAD)
@@ -313,7 +325,7 @@
int
PyThreadState_SetAsyncExc(long id, PyObject *exc) {
- PyThreadState *tstate = PyThreadState_Get();
+ PyThreadState *tstate = PyThreadState_GET();
PyInterpreterState *interp = tstate->interp;
PyThreadState *p;
int count = 0;
@@ -382,21 +394,25 @@
static PyInterpreterState *autoInterpreterState = NULL;
static int autoTLSkey = 0;
-/* Internal initialization/finalization functions called by
- Py_Initialize/Py_Finalize
+/* Internal initialization/finalization functions called by
+ Py_Initialize/Py_Finalize
*/
-void _PyGILState_Init(PyInterpreterState *i, PyThreadState *t)
+void
+_PyGILState_Init(PyInterpreterState *i, PyThreadState *t)
{
- assert(i && t); /* must init with a valid states */
+ assert(i && t); /* must init with valid states */
autoTLSkey = PyThread_create_key();
autoInterpreterState = i;
/* Now stash the thread state for this thread in TLS */
- PyThread_set_key_value(autoTLSkey, (void *)t);
- assert(t->gilstate_counter==0); /* must be a new thread state */
+ assert(PyThread_get_key_value(autoTLSkey) == NULL);
+ if (PyThread_set_key_value(autoTLSkey, (void *)t) < 0)
+ Py_FatalError("Couldn't create autoTLSkey mapping");
+ assert(t->gilstate_counter == 0); /* must be a new thread state */
t->gilstate_counter = 1;
}
-void _PyGILState_Fini(void)
+void
+_PyGILState_Fini(void)
{
PyThread_delete_key(autoTLSkey);
autoTLSkey = 0;
@@ -404,80 +420,84 @@
}
/* The public functions */
-PyThreadState *PyGILState_GetThisThreadState(void)
+PyThreadState *
+PyGILState_GetThisThreadState(void)
{
- if (autoInterpreterState==NULL || autoTLSkey==0)
+ if (autoInterpreterState == NULL || autoTLSkey == 0)
return NULL;
- return (PyThreadState *) PyThread_get_key_value(autoTLSkey);
+ return (PyThreadState *)PyThread_get_key_value(autoTLSkey);
}
-PyGILState_STATE PyGILState_Ensure(void)
+PyGILState_STATE
+PyGILState_Ensure(void)
{
int current;
PyThreadState *tcur;
- /* Note that we do not auto-init Python here - apart from
- potential races with 2 threads auto-initializing, pep-311
+ /* Note that we do not auto-init Python here - apart from
+ potential races with 2 threads auto-initializing, pep-311
spells out other issues. Embedders are expected to have
called Py_Initialize() and usually PyEval_InitThreads().
*/
assert(autoInterpreterState); /* Py_Initialize() hasn't been called! */
tcur = PyThread_get_key_value(autoTLSkey);
- if (tcur==NULL) {
+ if (tcur == NULL) {
/* Create a new thread state for this thread */
tcur = PyThreadState_New(autoInterpreterState);
- if (tcur==NULL)
+ if (tcur == NULL)
Py_FatalError("Couldn't create thread-state for new thread");
- PyThread_set_key_value(autoTLSkey, (void *)tcur);
+ if (PyThread_set_key_value(autoTLSkey, (void *)tcur) < 0)
+ Py_FatalError("Couldn't create autoTLSkey mapping");
current = 0; /* new thread state is never current */
- } else
+ }
+ else
current = PyThreadState_IsCurrent(tcur);
- if (!current)
+ if (current == 0)
PyEval_RestoreThread(tcur);
/* Update our counter in the thread-state - no need for locks:
- tcur will remain valid as we hold the GIL.
- - the counter is safe as we are the only thread "allowed"
+ - the counter is safe as we are the only thread "allowed"
to modify this value
*/
- tcur->gilstate_counter++;
+ ++tcur->gilstate_counter;
return current ? PyGILState_LOCKED : PyGILState_UNLOCKED;
}
-void PyGILState_Release(PyGILState_STATE oldstate)
+void
+PyGILState_Release(PyGILState_STATE oldstate)
{
PyThreadState *tcur = PyThread_get_key_value(autoTLSkey);
- if (tcur==NULL)
+ if (tcur == NULL)
Py_FatalError("auto-releasing thread-state, "
"but no thread-state for this thread");
/* We must hold the GIL and have our thread state current */
/* XXX - remove the check - the assert should be fine,
- but while this is very new (April 2003), the extra check
+ but while this is very new (April 2003), the extra check
by release-only users can't hurt.
*/
- if (!PyThreadState_IsCurrent(tcur))
+ if (! PyThreadState_IsCurrent(tcur))
Py_FatalError("This thread state must be current when releasing");
- assert (PyThreadState_IsCurrent(tcur));
- tcur->gilstate_counter -= 1;
- assert (tcur->gilstate_counter >= 0); /* illegal counter value */
+ assert(PyThreadState_IsCurrent(tcur));
+ --tcur->gilstate_counter;
+ assert(tcur->gilstate_counter >= 0); /* illegal counter value */
- /* If we are about to destroy this thread-state, we must
- clear it while the lock is held, as destructors may run
- */
- if (tcur->gilstate_counter==0) {
+ /* If we're going to destroy this thread-state, we must
+ * clear it while the GIL is held, as destructors may run.
+ */
+ if (tcur->gilstate_counter == 0) {
/* can't have been locked when we created it */
- assert(oldstate==PyGILState_UNLOCKED);
+ assert(oldstate == PyGILState_UNLOCKED);
PyThreadState_Clear(tcur);
+ /* Delete the thread-state. Note this releases the GIL too!
+ * It's vital that the GIL be held here, to avoid shutdown
+ * races; see bugs 225673 and 1061968 (that nasty bug has a
+ * habit of coming back).
+ */
+ PyThreadState_DeleteCurrent();
+ /* Delete this thread from our TLS. */
+ PyThread_delete_key_value(autoTLSkey);
}
-
/* Release the lock if necessary */
- if (oldstate==PyGILState_UNLOCKED)
+ else if (oldstate == PyGILState_UNLOCKED)
PyEval_ReleaseThread(tcur);
-
- /* Now complete destruction of the thread if necessary */
- if (tcur->gilstate_counter==0) {
- /* Delete this thread from our TLS */
- PyThread_delete_key_value(autoTLSkey);
- /* Delete the thread-state */
- PyThreadState_Delete(tcur);
- }
}
#endif /* WITH_THREAD */
Index: thread.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Python/thread.c,v
retrieving revision 2.46.10.1
retrieving revision 2.46.10.2
diff -u -d -r2.46.10.1 -r2.46.10.2
--- thread.c 20 Sep 2003 11:13:18 -0000 2.46.10.1
+++ thread.c 9 Nov 2004 15:35:23 -0000 2.46.10.2
@@ -146,54 +146,132 @@
This code stolen from "thread_sgi.h", where it was the only
implementation of an existing Python TLS API.
*/
-/*
- * Per-thread data ("key") support.
- */
+/* ------------------------------------------------------------------------
+Per-thread data ("key") support.
+
+Use PyThread_create_key() to create a new key. This is typically shared
+across threads.
+
+Use PyThread_set_key_value(thekey, value) to associate void* value with
+thekey in the current thread. Each thread has a distinct mapping of thekey
+to a void* value. Caution: if the current thread already has a mapping
+for thekey, value is ignored.
+
+Use PyThread_get_key_value(thekey) to retrieve the void* value associated
+with thekey in the current thread. This returns NULL if no value is
+associated with thekey in the current thread.
+
+Use PyThread_delete_key_value(thekey) to forget the current thread's associated
+value for thekey. PyThread_delete_key(thekey) forgets the values associated
+with thekey across *all* threads.
+
+While some of these functions have error-return values, none set any
+Python exception.
+
+None of the functions does memory management on behalf of the void* values.
+You need to allocate and deallocate them yourself. If the void* values
+happen to be PyObject*, these functions don't do refcount operations on
+them either.
+
+The GIL does not need to be held when calling these functions; they supply
+their own locking. This isn't true of PyThread_create_key(), though (see
+next paragraph).
+
+There's a hidden assumption that PyThread_create_key() will be called before
+any of the other functions are called. There's also a hidden assumption
+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(). */
long id;
+
+ /* The key and its associated value. */
int key;
void *value;
};
static struct key *keyhead = NULL;
-static int nkeys = 0;
static PyThread_type_lock keymutex = NULL;
+static int nkeys = 0; /* PyThread_create_key() hands out nkeys+1 next */
-static struct key *find_key(int key, void *value)
+/* 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 key, void *value)
{
struct key *p;
long id = PyThread_get_thread_ident();
+
+ PyThread_acquire_lock(keymutex, 1);
for (p = keyhead; p != NULL; p = p->next) {
if (p->id == id && p->key == key)
- return p;
+ goto Done;
+ }
+ if (value == NULL) {
+ assert(p == NULL);
+ goto Done;
}
- if (value == NULL)
- return NULL;
p = (struct key *)malloc(sizeof(struct key));
if (p != NULL) {
p->id = id;
p->key = key;
p->value = value;
- PyThread_acquire_lock(keymutex, 1);
p->next = keyhead;
keyhead = p;
- PyThread_release_lock(keymutex);
}
+ Done:
+ PyThread_release_lock(keymutex);
return p;
}
-int PyThread_create_key(void)
+/* 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;
}
-void PyThread_delete_key(int key)
+/* 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) {
@@ -208,28 +286,46 @@
PyThread_release_lock(keymutex);
}
-int PyThread_set_key_value(int key, void *value)
+/* Confusing: If the current thread has an association for key,
+ * value is ignored, and 0 is returned. Else an attempt is made to create
+ * an association of key to value for the current thread. 0 is returned
+ * if that succeeds, but -1 is returned if there's not enough memory
+ * to create the association. value must not be NULL.
+ */
+int
+PyThread_set_key_value(int key, void *value)
{
- struct key *p = find_key(key, value);
+ struct key *p;
+
+ assert(value != NULL);
+ p = find_key(key, value);
if (p == NULL)
return -1;
else
return 0;
}
-void *PyThread_get_key_value(int key)
+/* 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(key, NULL);
+
if (p == NULL)
return NULL;
else
return p->value;
}
-void PyThread_delete_key_value(int key)
+/* Forget the current thread's association for key, if any. */
+void
+PyThread_delete_key_value(int key)
{
long id = PyThread_get_thread_ident();
struct key *p, **q;
+
PyThread_acquire_lock(keymutex, 1);
q = &keyhead;
while ((p = *q) != NULL) {
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