Source

cpython-withatomic / Python / thread.c

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/* Thread package.
   This is intended to be usable independently from Python.
   The implementation for system foobar is in a file thread_foobar.h
   which is included by this file dependent on config settings.
   Stuff shared by all thread_*.h files is collected here. */

#include "Python.h"

#ifndef DONT_HAVE_STDIO_H
#include <stdio.h>
#endif

#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#else
#ifdef Py_DEBUG
extern char *getenv(const char *);
#endif
#endif

#ifdef __DGUX
#define _USING_POSIX4A_DRAFT6
#endif

#ifdef __sgi
#ifndef HAVE_PTHREAD_H /* XXX Need to check in configure.in */
#undef _POSIX_THREADS
#endif
#endif

#include "pythread.h"

#ifndef _POSIX_THREADS

#ifdef __sgi
#define SGI_THREADS
#endif

#ifdef HAVE_THREAD_H
#define SOLARIS_THREADS
#endif

#if defined(sun) && !defined(SOLARIS_THREADS)
#define SUN_LWP
#endif

#if defined(__MWERKS__) && !defined(__BEOS__)
#define _POSIX_THREADS
#endif

#endif /* _POSIX_THREADS */


#ifdef Py_DEBUG
static int thread_debug = 0;
#define dprintf(args)	(void)((thread_debug & 1) && printf args)
#define d2printf(args)	((thread_debug & 8) && printf args)
#else
#define dprintf(args)
#define d2printf(args)
#endif

static int initialized;

static void PyThread__init_thread(void); /* Forward */

void PyThread_init_thread(void)
{
#ifdef Py_DEBUG
	char *p = getenv("THREADDEBUG");

	if (p) {
		if (*p)
			thread_debug = atoi(p);
		else
			thread_debug = 1;
	}
#endif /* Py_DEBUG */
	if (initialized)
		return;
	initialized = 1;
	dprintf(("PyThread_init_thread called\n"));
	PyThread__init_thread();
}

#ifdef SGI_THREADS
#include "thread_sgi.h"
#endif

#ifdef SOLARIS_THREADS
#include "thread_solaris.h"
#endif

#ifdef SUN_LWP
#include "thread_lwp.h"
#endif

#ifdef HAVE_PTH
#include "thread_pth.h"
#undef _POSIX_THREADS
#endif

#ifdef _POSIX_THREADS
#include "thread_pthread.h"
#endif

#ifdef C_THREADS
#include "thread_cthread.h"
#endif

#ifdef NT_THREADS
#include "thread_nt.h"
#endif

#ifdef OS2_THREADS
#include "thread_os2.h"
#endif

#ifdef BEOS_THREADS
#include "thread_beos.h"
#endif

#ifdef WINCE_THREADS
#include "thread_wince.h"
#endif

#ifdef PLAN9_THREADS
#include "thread_plan9.h"
#endif

#ifdef ATHEOS_THREADS
#include "thread_atheos.h"
#endif

/*
#ifdef FOOBAR_THREADS
#include "thread_foobar.h"
#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.

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 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 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)
			goto Done;
	}
	if (value == NULL) {
		assert(p == NULL);
		goto Done;
	}
	p = (struct key *)malloc(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;
			free((void *)p);
			/* NB This does *not* free p->value! */
		}
		else
			q = &p->next;
	}
	PyThread_release_lock(keymutex);
}

/* 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;

	assert(value != NULL);
	p = find_key(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(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)
{
	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;
			free((void *)p);
			/* NB This does *not* free p->value! */
			break;
		}
		else
			q = &p->next;
	}
	PyThread_release_lock(keymutex);
}

#endif /* Py_HAVE_NATIVE_TLS */