sync_posix.h

/**************************************************************************/
/*                                                                        */
/*                                 OCaml                                  */
/*                                                                        */
/*          Xavier Leroy and Damien Doligez, INRIA Rocquencourt           */
/*                                                                        */
/*   Copyright 1996 Institut National de Recherche en Informatique et     */
/*     en Automatique.                                                    */
/*                                                                        */
/*   All rights reserved.  This file is distributed under the terms of    */
/*   the GNU Lesser General Public License version 2.1, with the          */
/*   special exception on linking described in the file LICENSE.          */
/*                                                                        */
/**************************************************************************/

/* POSIX thread implementation of the user facing Mutex and Condition */
/* To be included in runtime/sync.c */

#ifndef CAML_SYNC_POSIX_H
#define CAML_SYNC_POSIX_H

#include <errno.h>
#include <pthread.h>
#include <string.h>

#include "caml/sync.h"

#ifdef __linux__
#include <features.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/futex.h>
#include <limits.h>
#endif

typedef int sync_retcode;

/* Mutexes */

Caml_inline int sync_mutex_create(sync_mutex * res)
{
  int rc;
  pthread_mutexattr_t attr;
  sync_mutex m;

  rc = pthread_mutexattr_init(&attr);
  if (rc != 0) goto error1;
  rc = pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK);
  if (rc != 0) goto error2;
  m = caml_stat_alloc_noexc(sizeof(pthread_mutex_t));
  if (m == NULL) { rc = ENOMEM; goto error2; }
  rc = pthread_mutex_init(m, &attr);
  if (rc != 0) goto error3;
  pthread_mutexattr_destroy(&attr);
  *res = m;
  return 0;
error3:
  caml_stat_free(m);
error2:
  pthread_mutexattr_destroy(&attr);
error1:
  return rc;
}

Caml_inline int sync_mutex_destroy(sync_mutex m)
{
  int rc;
  rc = pthread_mutex_destroy(m);
  caml_stat_free(m);
  return rc;
}

Caml_inline int sync_mutex_lock(sync_mutex m)
{
  return pthread_mutex_lock(m);
}

#define MUTEX_PREVIOUSLY_UNLOCKED 0
#define MUTEX_ALREADY_LOCKED EBUSY

Caml_inline int sync_mutex_trylock(sync_mutex m)
{
  return pthread_mutex_trylock(m);
}

Caml_inline int sync_mutex_unlock(sync_mutex m)
{
  return pthread_mutex_unlock(m);
}

/* If we're using glibc, use a custom condition variable implementation to
   avoid this bug: https://sourceware.org/bugzilla/show_bug.cgi?id=25847

   For now we only have this on linux because it directly uses the linux futex
   syscalls. */
#if defined(__linux__) && defined(__GNU_LIBRARY__) && defined(__GLIBC__) && defined(__GLIBC_MINOR__)
static int custom_condvar_init(custom_condvar * cv)
{
  cv->counter = 0;
  return 0;
}

static int custom_condvar_destroy(custom_condvar * cv)
{
  return 0;
}

static int custom_condvar_wait(custom_condvar * cv, pthread_mutex_t * mutex)
{
  unsigned old_count = cv->counter;
  pthread_mutex_unlock(mutex);
  syscall(SYS_futex, &cv->counter, FUTEX_WAIT_PRIVATE, old_count, NULL, NULL, 0);
  pthread_mutex_lock(mutex);
  return 0;
}

static int custom_condvar_signal(custom_condvar * cv)
{
  __sync_add_and_fetch(&cv->counter, 1);
  syscall(SYS_futex, &cv->counter, FUTEX_WAKE_PRIVATE, 1, NULL, NULL, 0);
  return 0;
}

static int custom_condvar_broadcast(custom_condvar * cv)
{
  __sync_add_and_fetch(&cv->counter, 1);
  syscall(SYS_futex, &cv->counter, FUTEX_WAKE_PRIVATE, INT_MAX, NULL, NULL, 0);
  return 0;
}
#else
static int custom_condvar_init(custom_condvar * cv)
{
  pthread_condattr_t attr;
  pthread_condattr_init(&attr);
#if defined(_POSIX_TIMERS) &&                   \
  defined(_POSIX_MONOTONIC_CLOCK) &&            \
  _POSIX_MONOTONIC_CLOCK != (-1)
  pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
#endif
  return pthread_cond_init(cv, &attr);
}

static int custom_condvar_destroy(custom_condvar * cv)
{
  return pthread_cond_destroy(cv);
}

static int custom_condvar_wait(custom_condvar * cv, pthread_mutex_t * mutex)
{
  return pthread_cond_wait(cv, mutex);
}

static int custom_condvar_signal(custom_condvar * cv)
{
  return pthread_cond_signal(cv);
}

static int custom_condvar_broadcast(custom_condvar * cv)
{
  return pthread_cond_broadcast(cv);
}
#endif


/* Condition variables */

Caml_inline int sync_condvar_create(sync_condvar * res)
{
  int rc;
  sync_condvar c = caml_stat_alloc_noexc(sizeof(custom_condvar));
  if (c == NULL) return ENOMEM;
  rc = custom_condvar_init(c);
  if (rc != 0) { caml_stat_free(c); return rc; }
  *res = c;
  return 0;
}

Caml_inline int sync_condvar_destroy(sync_condvar c)
{
  int rc;
  rc = custom_condvar_destroy(c);
  caml_stat_free(c);
  return rc;
}

Caml_inline int sync_condvar_signal(sync_condvar c)
{
  return custom_condvar_signal(c);
}

Caml_inline int sync_condvar_broadcast(sync_condvar c)
{
  return custom_condvar_broadcast(c);
}

Caml_inline int sync_condvar_wait(sync_condvar c, sync_mutex m)
{
  return custom_condvar_wait(c, m);
}

/* Reporting errors */

Caml_inline void sync_check_error(int retcode, char * msg)
{
  char * err;
  char buf[1024];
  int errlen, msglen;
  value str;

  if (retcode == 0) return;
  if (retcode == ENOMEM) caml_raise_out_of_memory();
  err = caml_strerror(retcode, buf, sizeof(buf));
  msglen = strlen(msg);
  errlen = strlen(err);
  str = caml_alloc_string(msglen + 2 + errlen);
  memcpy (&Byte(str, 0), msg, msglen);
  memcpy (&Byte(str, msglen), ": ", 2);
  memcpy (&Byte(str, msglen + 2), err, errlen);
  caml_raise_sys_error(str);
}

#endif /* CAML_SYNC_POSIX_H */