Python/thread_pthread.h

/***********************************************************
Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam,
The Netherlands.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
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Centrum or CWI or Corporation for National Research Initiatives or
CNRI not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior
permission.

While CWI is the initial source for this software, a modified version
is made available by the Corporation for National Research Initiatives
(CNRI) at the Internet address ftp://ftp.python.org.

STICHTING MATHEMATISCH CENTRUM AND CNRI DISCLAIM ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH
CENTRUM OR CNRI BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
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******************************************************************/

/* Posix threads interface */

#include <stdlib.h>
#include <pthread.h>

#ifdef _AIX

#ifndef SCHED_BG_NP
/* SCHED_BG_NP is defined if using AIX DCE pthreads
 * but it is unsupported by AIX 4 pthreads. Default
 * attributes for AIX 4 pthreads equal to NULL. For
 * AIX DCE pthreads they should be left unchanged.
 */
#define pthread_attr_default NULL
#define pthread_mutexattr_default NULL
#define pthread_condattr_default NULL
#endif

#else
#define pthread_attr_default ((pthread_attr_t *)0)
#define pthread_mutexattr_default ((pthread_mutexattr_t *)0)
#define pthread_condattr_default ((pthread_condattr_t *)0)
#endif

/* A pthread mutex isn't sufficient to model the Python lock type
 * because, according to Draft 5 of the docs (P1003.4a/D5), both of the
 * following are undefined:
 *  -> a thread tries to lock a mutex it already has locked
 *  -> a thread tries to unlock a mutex locked by a different thread
 * pthread mutexes are designed for serializing threads over short pieces
 * of code anyway, so wouldn't be an appropriate implementation of
 * Python's locks regardless.
 *
 * The pthread_lock struct implements a Python lock as a "locked?" bit
 * and a <condition, mutex> pair.  In general, if the bit can be acquired
 * instantly, it is, else the pair is used to block the thread until the
 * bit is cleared.     9 May 1994 tim@ksr.com
 */

typedef struct {
	char             locked; /* 0=unlocked, 1=locked */
	/* a <cond, mutex> pair to handle an acquire of a locked lock */
	pthread_cond_t   lock_released;
	pthread_mutex_t  mut;
} pthread_lock;

#define CHECK_STATUS(name)  if (status < 0) { perror(name); error=1; }

/*
 * Initialization.
 */
static void _init_thread _P0()
{
}

/*
 * Thread support.
 */


int start_new_thread _P2(func, void (*func) _P((void *)), arg, void *arg)
{
	pthread_t th;
	int success;
	dprintf(("start_new_thread called\n"));
	if (!initialized)
		init_thread();
	success = pthread_create(&th, pthread_attr_default,
				 (void* (*) _P((void *)))func, arg);
	return success < 0 ? 0 : 1;
}

long get_thread_ident _P0()
{
	pthread_t threadid;
	if (!initialized)
		init_thread();
	/* Jump through some hoops for Alpha OSF/1 */
	threadid = pthread_self();
	return (long) *(long *) &threadid;
}

static void do_exit_thread _P1(no_cleanup, int no_cleanup)
{
	dprintf(("exit_thread called\n"));
	if (!initialized)
		if (no_cleanup)
			_exit(0);
		else
			exit(0);
}

void exit_thread _P0()
{
	do_exit_thread(0);
}

void _exit_thread _P0()
{
	do_exit_thread(1);
}

#ifndef NO_EXIT_PROG
static void do_exit_prog _P2(status, int status, no_cleanup, int no_cleanup)
{
	dprintf(("exit_prog(%d) called\n", status));
	if (!initialized)
		if (no_cleanup)
			_exit(status);
		else
			exit(status);
}

void exit_prog _P1(status, int status)
{
	do_exit_prog(status, 0);
}

void _exit_prog _P1(status, int status)
{
	do_exit_prog(status, 1);
}
#endif /* NO_EXIT_PROG */

/*
 * Lock support.
 */
type_lock allocate_lock _P0()
{
	pthread_lock *lock;
	int status, error = 0;

	dprintf(("allocate_lock called\n"));
	if (!initialized)
		init_thread();

	lock = (pthread_lock *) malloc(sizeof(pthread_lock));
	if (lock) {
		lock->locked = 0;

		status = pthread_mutex_init(&lock->mut,
					    pthread_mutexattr_default);
		CHECK_STATUS("pthread_mutex_init");

		status = pthread_cond_init(&lock->lock_released,
					   pthread_condattr_default);
		CHECK_STATUS("pthread_cond_init");

		if (error) {
			free((void *)lock);
			lock = 0;
		}
	}

	dprintf(("allocate_lock() -> %lx\n", (long)lock));
	return (type_lock) lock;
}

void free_lock _P1(lock, type_lock lock)
{
	pthread_lock *thelock = (pthread_lock *)lock;
	int status, error = 0;

	dprintf(("free_lock(%lx) called\n", (long)lock));

	status = pthread_mutex_destroy( &thelock->mut );
	CHECK_STATUS("pthread_mutex_destroy");

	status = pthread_cond_destroy( &thelock->lock_released );
	CHECK_STATUS("pthread_cond_destroy");

	free((void *)thelock);
}

int acquire_lock _P2(lock, type_lock lock, waitflag, int waitflag)
{
	int success;
	pthread_lock *thelock = (pthread_lock *)lock;
	int status, error = 0;

	dprintf(("acquire_lock(%lx, %d) called\n", (long)lock, waitflag));

	status = pthread_mutex_lock( &thelock->mut );
	CHECK_STATUS("pthread_mutex_lock[1]");
	success = thelock->locked == 0;
	if (success) thelock->locked = 1;
	status = pthread_mutex_unlock( &thelock->mut );
	CHECK_STATUS("pthread_mutex_unlock[1]");

	if ( !success && waitflag ) {
		/* continue trying until we get the lock */

		/* mut must be locked by me -- part of the condition
		 * protocol */
		status = pthread_mutex_lock( &thelock->mut );
		CHECK_STATUS("pthread_mutex_lock[2]");
		while ( thelock->locked ) {
			status = pthread_cond_wait(&thelock->lock_released,
						   &thelock->mut);
			CHECK_STATUS("pthread_cond_wait");
		}
		thelock->locked = 1;
		status = pthread_mutex_unlock( &thelock->mut );
		CHECK_STATUS("pthread_mutex_unlock[2]");
		success = 1;
	}
	if (error) success = 0;
	dprintf(("acquire_lock(%lx, %d) -> %d\n", (long)lock, waitflag, success));
	return success;
}

void release_lock _P1(lock, type_lock lock)
{
	pthread_lock *thelock = (pthread_lock *)lock;
	int status, error = 0;

	dprintf(("release_lock(%lx) called\n", (long)lock));

	status = pthread_mutex_lock( &thelock->mut );
	CHECK_STATUS("pthread_mutex_lock[3]");

	thelock->locked = 0;

	status = pthread_mutex_unlock( &thelock->mut );
	CHECK_STATUS("pthread_mutex_unlock[3]");

	/* wake up someone (anyone, if any) waiting on the lock */
	status = pthread_cond_signal( &thelock->lock_released );
	CHECK_STATUS("pthread_cond_signal");
}

/*
 * Semaphore support.
 */

struct semaphore {
	pthread_mutex_t mutex;
	pthread_cond_t cond;
	int value;
};

type_sema allocate_sema _P1(value, int value)
{
	struct semaphore *sema;
	int status, error = 0;

	dprintf(("allocate_sema called\n"));
	if (!initialized)
		init_thread();

	sema = (struct semaphore *) malloc(sizeof(struct semaphore));
	if (sema != NULL) {
		sema->value = value;
		status = pthread_mutex_init(&sema->mutex,
					    pthread_mutexattr_default);
		CHECK_STATUS("pthread_mutex_init");
		status = pthread_cond_init(&sema->cond,
					   pthread_condattr_default);
		CHECK_STATUS("pthread_cond_init");
		if (error) {
			free((void *) sema);
			sema = NULL;
		}
	}
	dprintf(("allocate_sema() -> %lx\n", (long) sema));
	return (type_sema) sema;
}

void free_sema _P1(sema, type_sema sema)
{
	int status, error = 0;
	struct semaphore *thesema = (struct semaphore *) sema;

	dprintf(("free_sema(%lx) called\n", (long) sema));
	status = pthread_cond_destroy(&thesema->cond);
	CHECK_STATUS("pthread_cond_destroy");
	status = pthread_mutex_destroy(&thesema->mutex);
	CHECK_STATUS("pthread_mutex_destroy");
	free((void *) thesema);
}

int down_sema _P2(sema, type_sema sema, waitflag, int waitflag)
{
	int status, error = 0, success;
	struct semaphore *thesema = (struct semaphore *) sema;

	dprintf(("down_sema(%lx, %d) called\n", (long) sema, waitflag));
	status = pthread_mutex_lock(&thesema->mutex);
	CHECK_STATUS("pthread_mutex_lock");
	if (waitflag) {
		while (!error && thesema->value <= 0) {
			status = pthread_cond_wait(&thesema->cond,
						   &thesema->mutex);
			CHECK_STATUS("pthread_cond_wait");
		}
	}
	if (error)
		success = 0;
	else if (thesema->value > 0) {
		thesema->value--;
		success = 1;
	}
	else
		success = 0;
	status = pthread_mutex_unlock(&thesema->mutex);
	CHECK_STATUS("pthread_mutex_unlock");
	dprintf(("down_sema(%lx) return\n", (long) sema));
	return success;
}

void up_sema _P1(sema, type_sema sema)
{
	int status, error = 0;
	struct semaphore *thesema = (struct semaphore *) sema;

	dprintf(("up_sema(%lx)\n", (long) sema));
	status = pthread_mutex_lock(&thesema->mutex);
	CHECK_STATUS("pthread_mutex_lock");
	thesema->value++;
	status = pthread_cond_signal(&thesema->cond);
	CHECK_STATUS("pthread_cond_signal");
	status = pthread_mutex_unlock(&thesema->mutex);
	CHECK_STATUS("pthread_mutex_unlock");
}