locks.c

/* nbdkit
 * Copyright (C) 2013-2020 Red Hat Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * * Neither the name of Red Hat nor the names of its contributors may be
 * used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>

#include "internal.h"

/* Note that the plugin's thread model cannot change after being
 * loaded, so caching it here is safe.
 */
unsigned thread_model = -1;

static pthread_mutex_t connection_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_mutex_t all_requests_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_rwlock_t unload_prevention_lock = PTHREAD_RWLOCK_INITIALIZER;

/* Map thread model to string; use only from single-threaded context */
const char *
name_of_thread_model (int model)
{
  static char buf[] = "-2147483648 # unknown thread model!";

  switch (model) {
  case NBDKIT_THREAD_MODEL_SERIALIZE_CONNECTIONS:
    return "serialize_connections";
  case NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS:
    return "serialize_all_requests";
  case NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS:
    return "serialize_requests";
  case NBDKIT_THREAD_MODEL_PARALLEL:
    return "parallel";
  }
  snprintf (buf, sizeof buf, "%d # unknown thread model!", model);
  return buf;
}

void
lock_init_thread_model (void)
{
  thread_model = top->thread_model (top);
  debug ("using thread model: %s", name_of_thread_model (thread_model));
  assert (thread_model <= NBDKIT_THREAD_MODEL_PARALLEL);
}

void
lock_connection (void)
{
  if (thread_model <= NBDKIT_THREAD_MODEL_SERIALIZE_CONNECTIONS &&
      pthread_mutex_lock (&connection_lock))
    abort ();
}

void
unlock_connection (void)
{
  if (thread_model <= NBDKIT_THREAD_MODEL_SERIALIZE_CONNECTIONS &&
      pthread_mutex_unlock (&connection_lock))
    abort ();
}

void
lock_request (void)
{
  struct connection *conn = threadlocal_get_conn ();

  if (thread_model <= NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS &&
      pthread_mutex_lock (&all_requests_lock))
    abort ();

  if (conn && thread_model <= NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS &&
      pthread_mutex_lock (&conn->request_lock))
    abort ();

  if (pthread_rwlock_rdlock (&unload_prevention_lock))
    abort ();
}

void
unlock_request ()
{
  struct connection *conn = threadlocal_get_conn ();

  if (pthread_rwlock_unlock (&unload_prevention_lock))
    abort ();

  if (conn && thread_model <= NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS &&
      pthread_mutex_unlock (&conn->request_lock))
    abort ();

  if (thread_model <= NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS &&
      pthread_mutex_unlock (&all_requests_lock))
    abort ();
}

void
lock_unload (void)
{
  if (pthread_rwlock_wrlock (&unload_prevention_lock))
    abort ();
}

void
unlock_unload (void)
{
  if (pthread_rwlock_unlock (&unload_prevention_lock))
    abort ();
}