lock.c

开源备份软件源码 AMANDA, the Advanced Maryland Automatic Network Disk Archiver, is a backup system that a

/* Locking in multithreaded situations.
   Copyright (C) 2005-2006 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

/* Written by Bruno Haible <[e-mail]>, 2005.
   Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-solaris.h,
   gthr-win32.h.  */

#include <config.h>

#include "lock.h"

/* ========================================================================= */

#if USE_POSIX_THREADS

/* Use the POSIX threads library.  */

# if PTHREAD_IN_USE_DETECTION_HARD

/* The function to be executed by a dummy thread.  */
static void *
dummy_thread_func (void *arg)
{
  return arg;
}

int
glthread_in_use (void)
{
  static int tested;
  static int result; /* 1: linked with -lpthread, 0: only with libc */

  if (!tested)
    {
      pthread_t thread;

      if (pthread_create (&thread, NULL, dummy_thread_func, NULL) != 0)
	/* Thread creation failed.  */
	result = 0;
      else
	{
	  /* Thread creation works.  */
	  void *retval;
	  if (pthread_join (thread, &retval) != 0)
	    abort ();
	  result = 1;
	}
      tested = 1;
    }
  return result;
}

# endif

/* -------------------------- gl_lock_t datatype -------------------------- */

/* ------------------------- gl_rwlock_t datatype ------------------------- */

# if HAVE_PTHREAD_RWLOCK

#  if !defined PTHREAD_RWLOCK_INITIALIZER

void
glthread_rwlock_init (gl_rwlock_t *lock)
{
  if (pthread_rwlock_init (&lock->rwlock, NULL) != 0)
    abort ();
  lock->initialized = 1;
}

void
glthread_rwlock_rdlock (gl_rwlock_t *lock)
{
  if (!lock->initialized)
    {
      if (pthread_mutex_lock (&lock->guard) != 0)
	abort ();
      if (!lock->initialized)
	glthread_rwlock_init (lock);
      if (pthread_mutex_unlock (&lock->guard) != 0)
	abort ();
    }
  if (pthread_rwlock_rdlock (&lock->rwlock) != 0)
    abort ();
}

void
glthread_rwlock_wrlock (gl_rwlock_t *lock)
{
  if (!lock->initialized)
    {
      if (pthread_mutex_lock (&lock->guard) != 0)
	abort ();
      if (!lock->initialized)
	glthread_rwlock_init (lock);
      if (pthread_mutex_unlock (&lock->guard) != 0)
	abort ();
    }
  if (pthread_rwlock_wrlock (&lock->rwlock) != 0)
    abort ();
}

void
glthread_rwlock_unlock (gl_rwlock_t *lock)
{
  if (!lock->initialized)
    abort ();
  if (pthread_rwlock_unlock (&lock->rwlock) != 0)
    abort ();
}

void
glthread_rwlock_destroy (gl_rwlock_t *lock)
{
  if (!lock->initialized)
    abort ();
  if (pthread_rwlock_destroy (&lock->rwlock) != 0)
    abort ();
  lock->initialized = 0;
}

#  endif

# else

void
glthread_rwlock_init (gl_rwlock_t *lock)
{
  if (pthread_mutex_init (&lock->lock, NULL) != 0)
    abort ();
  if (pthread_cond_init (&lock->waiting_readers, NULL) != 0)
    abort ();
  if (pthread_cond_init (&lock->waiting_writers, NULL) != 0)
    abort ();
  lock->waiting_writers_count = 0;
  lock->runcount = 0;
}

void
glthread_rwlock_rdlock (gl_rwlock_t *lock)
{
  if (pthread_mutex_lock (&lock->lock) != 0)
    abort ();
  /* Test whether only readers are currently running, and whether the runcount
     field will not overflow.  */
  /* POSIX says: "It is implementation-defined whether the calling thread
     acquires the lock when a writer does not hold the lock and there are
     writers blocked on the lock."  Let's say, no: give the writers a higher
     priority.  */
  while (!(lock->runcount + 1 > 0 && lock->waiting_writers_count == 0))
    {
      /* This thread has to wait for a while.  Enqueue it among the
	 waiting_readers.  */
      if (pthread_cond_wait (&lock->waiting_readers, &lock->lock) != 0)
	abort ();
    }
  lock->runcount++;
  if (pthread_mutex_unlock (&lock->lock) != 0)
    abort ();
}

void
glthread_rwlock_wrlock (gl_rwlock_t *lock)
{
  if (pthread_mutex_lock (&lock->lock) != 0)
    abort ();
  /* Test whether no readers or writers are currently running.  */
  while (!(lock->runcount == 0))
    {
      /* This thread has to wait for a while.  Enqueue it among the
	 waiting_writers.  */
      lock->waiting_writers_count++;
      if (pthread_cond_wait (&lock->waiting_writers, &lock->lock) != 0)
	abort ();
      lock->waiting_writers_count--;
    }
  lock->runcount--; /* runcount becomes -1 */
  if (pthread_mutex_unlock (&lock->lock) != 0)
    abort ();
}

void
glthread_rwlock_unlock (gl_rwlock_t *lock)
{
  if (pthread_mutex_lock (&lock->lock) != 0)
    abort ();
  if (lock->runcount < 0)
    {
      /* Drop a writer lock.  */
      if (!(lock->runcount == -1))
	abort ();
      lock->runcount = 0;
    }
  else
    {
      /* Drop a reader lock.  */
      if (!(lock->runcount > 0))
	abort ();
      lock->runcount--;
    }
  if (lock->runcount == 0)
    {
      /* POSIX recommends that "write locks shall take precedence over read
	 locks", to avoid "writer starvation".  */
      if (lock->waiting_writers_count > 0)
	{
	  /* Wake up one of the waiting writers.  */
	  if (pthread_cond_signal (&lock->waiting_writers) != 0)
	    abort ();
	}
      else
	{
	  /* Wake up all waiting readers.  */
	  if (pthread_cond_broadcast (&lock->waiting_readers) != 0)
	    abort ();
	}
    }
  if (pthread_mutex_unlock (&lock->lock) != 0)
    abort ();
}

void
glthread_rwlock_destroy (gl_rwlock_t *lock)
{
  if (pthread_mutex_destroy (&lock->lock) != 0)
    abort ();
  if (pthread_cond_destroy (&lock->waiting_readers) != 0)
    abort ();
  if (pthread_cond_destroy (&lock->waiting_writers) != 0)
    abort ();
}

# endif

/* --------------------- gl_recursive_lock_t datatype --------------------- */

# if HAVE_PTHREAD_MUTEX_RECURSIVE

#  if !(defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER || defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP)

void
glthread_recursive_lock_init (gl_recursive_lock_t *lock)
{
  pthread_mutexattr_t attributes;

  if (pthread_mutexattr_init (&attributes) != 0)
    abort ();
  if (pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE) != 0)
    abort ();
  if (pthread_mutex_init (&lock->recmutex, &attributes) != 0)
    abort ();
  if (pthread_mutexattr_destroy (&attributes) != 0)
    abort ();
  lock->initialized = 1;
}

void
glthread_recursive_lock_lock (gl_recursive_lock_t *lock)
{
  if (!lock->initialized)
    {
      if (pthread_mutex_lock (&lock->guard) != 0)
	abort ();
      if (!lock->initialized)
	glthread_recursive_lock_init (lock);
      if (pthread_mutex_unlock (&lock->guard) != 0)
	abort ();
    }
  if (pthread_mutex_lock (&lock->recmutex) != 0)
    abort ();
}

void
glthread_recursive_lock_unlock (gl_recursive_lock_t *lock)
{
  if (!lock->initialized)
    abort ();
  if (pthread_mutex_unlock (&lock->recmutex) != 0)
    abort ();
}

void
glthread_recursive_lock_destroy (gl_recursive_lock_t *lock)
{
  if (!lock->initialized)
    abort ();
  if (pthread_mutex_destroy (&lock->recmutex) != 0)
    abort ();
  lock->initialized = 0;
}

#  endif

# else

void
glthread_recursive_lock_init (gl_recursive_lock_t *lock)
{
  if (pthread_mutex_init (&lock->mutex, NULL) != 0)
    abort ();
  lock->owner = (pthread_t) 0;
  lock->depth = 0;
}

void
glthread_recursive_lock_lock (gl_recursive_lock_t *lock)
{
  pthread_t self = pthread_self ();
  if (lock->owner != self)
    {
      if (pthread_mutex_lock (&lock->mutex) != 0)
	abort ();
      lock->owner = self;
    }
  if (++(lock->depth) == 0) /* wraparound? */
    abort ();
}

void
glthread_recursive_lock_unlock (gl_recursive_lock_t *lock)
{
  if (lock->owner != pthread_self ())
    abort ();
  if (lock->depth == 0)
    abort ();
  if (--(lock->depth) == 0)
    {
      lock->owner = (pthread_t) 0;
      if (pthread_mutex_unlock (&lock->mutex) != 0)
	abort ();
    }
}

void
glthread_recursive_lock_destroy (gl_recursive_lock_t *lock)
{
  if (lock->owner != (pthread_t) 0)
    abort ();
  if (pthread_mutex_destroy (&lock->mutex) != 0)
    abort ();
}

# endif

/* -------------------------- gl_once_t datatype -------------------------- */

static const pthread_once_t fresh_once = PTHREAD_ONCE_INIT;

int
glthread_once_singlethreaded (pthread_once_t *once_control)
{
  /* We don't know whether pthread_once_t is an integer type, a floating-point
     type, a pointer type, or a structure type.  */
  char *firstbyte = (char *)once_control;
  if (*firstbyte == *(const char *)&fresh_once)
    {
      /* First time use of once_control.  Invert the first byte.  */
      *firstbyte = ~ *(const char *)&fresh_once;
      return 1;
    }
  else
    return 0;
}

#endif

/* ========================================================================= */

#if USE_PTH_THREADS

/* Use the GNU Pth threads library.  */

/* -------------------------- gl_lock_t datatype -------------------------- */

/* ------------------------- gl_rwlock_t datatype ------------------------- */

/* --------------------- gl_recursive_lock_t datatype --------------------- */

/* -------------------------- gl_once_t datatype -------------------------- */

void
glthread_once_call (void *arg)
{
  void (**gl_once_temp_addr) (void) = (void (**) (void)) arg;
  void (*initfunction) (void) = *gl_once_temp_addr;
  initfunction ();
}

int
glthread_once_singlethreaded (pth_once_t *once_control)
{
  /* We know that pth_once_t is an integer type.  */
  if (*once_control == PTH_ONCE_INIT)
    {
      /* First time use of once_control.  Invert the marker.  */
      *once_control = ~ PTH_ONCE_INIT;
      return 1;
    }
  else
    return 0;
}

#endif

/* ========================================================================= */

#if USE_SOLARIS_THREADS

/* Use the old Solaris threads library.  */

/* -------------------------- gl_lock_t datatype -------------------------- */

/* ------------------------- gl_rwlock_t datatype ------------------------- */

/* --------------------- gl_recursive_lock_t datatype --------------------- */

void
glthread_recursive_lock_init (gl_recursive_lock_t *lock)
{
  if (mutex_init (&lock->mutex, USYNC_THREAD, NULL) != 0)
    abort ();
  lock->owner = (thread_t) 0;
  lock->depth = 0;
}

void
glthread_recursive_lock_lock (gl_recursive_lock_t *lock)
{
  thread_t self = thr_self ();
  if (lock->owner != self)
    {
      if (mutex_lock (&lock->mutex) != 0)
	abort ();
      lock->owner = self;
    }
  if (++(lock->depth) == 0) /* wraparound? */
    abort ();
}

void
glthread_recursive_lock_unlock (gl_recursive_lock_t *lock)
{
  if (lock->owner != thr_self ())
    abort ();
  if (lock->depth == 0)
    abort ();
  if (--(lock->depth) == 0)