func_lock.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007, Tilghman Lesher
 *
 * Tilghman Lesher <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief Dialplan mutexes
 *
 * \author Tilghman Lesher <[email protected]>
 *
 * \ingroup functions
 *
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <signal.h>

#include "asterisk/lock.h"
#include "asterisk/file.h"
#include "asterisk/channel.h"
#include "asterisk/pbx.h"
#include "asterisk/module.h"
#include "asterisk/linkedlists.h"
#include "asterisk/astobj2.h"
#include "asterisk/utils.h"
#include "asterisk/cli.h"

/*** DOCUMENTATION
   <function name="LOCK" language="en_US">
      <synopsis>
         Attempt to obtain a named mutex.
      </synopsis>
      <syntax>
         <parameter name="lockname" required="true" />
      </syntax>
      <description>
         <para>Attempts to grab a named lock exclusively, and prevents other channels from
         obtaining the same lock.  LOCK will wait for the lock to become available.
         Returns <literal>1</literal> if the lock was obtained or <literal>0</literal> on error.</para>
         <note><para>To avoid the possibility of a deadlock, LOCK will only attempt to
         obtain the lock for 3 seconds if the channel already has another lock.</para></note>
         <note>
            <para>If <literal>live_dangerously</literal> in <literal>asterisk.conf</literal>
            is set to <literal>no</literal>, this function can only be executed from the
            dialplan, and not directly from external protocols.</para>
         </note>
      </description>
   </function>
   <function name="TRYLOCK" language="en_US">
      <synopsis>
         Attempt to obtain a named mutex.
      </synopsis>
      <syntax>
         <parameter name="lockname" required="true" />
      </syntax>
      <description>
         <para>Attempts to grab a named lock exclusively, and prevents other channels
         from obtaining the same lock.  Returns <literal>1</literal> if the lock was
         available or <literal>0</literal> otherwise.</para>
         <note>
            <para>If <literal>live_dangerously</literal> in <literal>asterisk.conf</literal>
            is set to <literal>no</literal>, this function can only be executed from the
            dialplan, and not directly from external protocols.</para>
         </note>
      </description>
   </function>
   <function name="UNLOCK" language="en_US">
      <synopsis>
         Unlocks a named mutex.
      </synopsis>
      <syntax>
         <parameter name="lockname" required="true" />
      </syntax>
      <description>
         <para>Unlocks a previously locked mutex. Returns <literal>1</literal> if the channel
         had a lock or <literal>0</literal> otherwise.</para>
         <note><para>It is generally unnecessary to unlock in a hangup routine, as any locks
         held are automatically freed when the channel is destroyed.</para></note>
         <note>
            <para>If <literal>live_dangerously</literal> in <literal>asterisk.conf</literal>
            is set to <literal>no</literal>, this function can only be executed from the
            dialplan, and not directly from external protocols.</para>
         </note>
      </description>
   </function>
 ***/



static AST_LIST_HEAD_STATIC(locklist, lock_frame);

static void lock_free(void *data);
static void lock_fixup(void *data, struct ast_channel *oldchan, struct ast_channel *newchan);
static int unloading = 0;

static const struct ast_datastore_info lock_info = {
   .type = "MUTEX",
   .destroy = lock_free,
   .chan_fixup = lock_fixup,
};

struct lock_frame {
   AST_LIST_ENTRY(lock_frame) entries;
   ast_mutex_t mutex;
   ast_cond_t cond;
   /*! count is needed so if a recursive mutex exits early, we know how many times to unlock it. */
   unsigned int count;
   /*! Count of waiting of requesters for the named lock */
   unsigned int requesters;
   /*! who owns us */
   struct ast_channel *owner;
   /*! name of the lock */
   char name[0];
};

struct channel_lock_frame {
   AST_LIST_ENTRY(channel_lock_frame) list;
   /*! Need to save channel pointer here, because during destruction, we won't have it. */
   struct ast_channel *channel;
   struct lock_frame *lock_frame;
};

static void lock_free(void *data)
{
   AST_LIST_HEAD(, channel_lock_frame) *oldlist = data;
   struct channel_lock_frame *clframe;
   AST_LIST_LOCK(oldlist);
   while ((clframe = AST_LIST_REMOVE_HEAD(oldlist, list))) {
      /* Only unlock if we own the lock */
      if (clframe->channel == clframe->lock_frame->owner) {
         ast_mutex_lock(&clframe->lock_frame->mutex);
         clframe->lock_frame->count = 0;
         clframe->lock_frame->owner = NULL;
         ast_cond_signal(&clframe->lock_frame->cond);
         ast_mutex_unlock(&clframe->lock_frame->mutex);
      }
      ast_free(clframe);
   }
   AST_LIST_UNLOCK(oldlist);
   AST_LIST_HEAD_DESTROY(oldlist);
   ast_free(oldlist);

   ast_module_unref(ast_module_info->self);
}

static void lock_fixup(void *data, struct ast_channel *oldchan, struct ast_channel *newchan)
{
   struct ast_datastore *lock_store = ast_channel_datastore_find(oldchan, &lock_info, NULL);
   AST_LIST_HEAD(, channel_lock_frame) *list;
   struct channel_lock_frame *clframe = NULL;

   if (!lock_store) {
      return;
   }
   list = lock_store->data;

   AST_LIST_LOCK(list);
   AST_LIST_TRAVERSE(list, clframe, list) {
      if (clframe->lock_frame->owner == oldchan) {
         clframe->lock_frame->owner = newchan;
      }
      clframe->channel = newchan;
   }
   AST_LIST_UNLOCK(list);
}

static int get_lock(struct ast_channel *chan, char *lockname, int trylock)
{
   struct ast_datastore *lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
   struct lock_frame *current;
   struct channel_lock_frame *clframe = NULL;
   AST_LIST_HEAD(, channel_lock_frame) *list;
   int res = 0;
   struct timespec timeout = { 0, };
   struct timeval now;

   if (!lock_store) {
      if (unloading) {
         ast_log(LOG_ERROR, "%sLOCK has no datastore and func_lock is unloading, failing.\n",
               trylock ? "TRY" : "");
         return -1;
      }

      lock_store = ast_datastore_alloc(&lock_info, NULL);
      if (!lock_store) {
         ast_log(LOG_ERROR, "Unable to allocate new datastore.  No locks will be obtained.\n");
         return -1;
      }

      list = ast_calloc(1, sizeof(*list));
      if (!list) {
         ast_log(LOG_ERROR,
            "Unable to allocate datastore list head.  %sLOCK will fail.\n",
            trylock ? "TRY" : "");
         ast_datastore_free(lock_store);
         return -1;
      }

      lock_store->data = list;
      AST_LIST_HEAD_INIT(list);
      ast_channel_datastore_add(chan, lock_store);

      /* We cannot unload until this channel has released the lock_store */
      ast_module_ref(ast_module_info->self);
   } else
      list = lock_store->data;

   /* Lock already exists? */
   AST_LIST_LOCK(&locklist);
   AST_LIST_TRAVERSE(&locklist, current, entries) {
      if (strcmp(current->name, lockname) == 0) {
         break;
      }
   }

   if (!current) {
      if (unloading) {
         ast_log(LOG_ERROR,
            "Lock doesn't exist whilst unloading.  %sLOCK will fail.\n",
            trylock ? "TRY" : "");
         /* Don't bother */
         AST_LIST_UNLOCK(&locklist);
         return -1;
      }

      /* Create new lock entry */
      current = ast_calloc(1, sizeof(*current) + strlen(lockname) + 1);
      if (!current) {
         AST_LIST_UNLOCK(&locklist);
         return -1;
      }

      strcpy(current->name, lockname); /* SAFE */
      if ((res = ast_mutex_init(&current->mutex))) {
         ast_log(LOG_ERROR, "Unable to initialize mutex: %s\n", strerror(res));
         ast_free(current);
         AST_LIST_UNLOCK(&locklist);
         return -1;
      }
      if ((res = ast_cond_init(&current->cond, NULL))) {
         ast_log(LOG_ERROR, "Unable to initialize condition variable: %s\n", strerror(res));
         ast_mutex_destroy(&current->mutex);
         ast_free(current);
         AST_LIST_UNLOCK(&locklist);
         return -1;
      }
      AST_LIST_INSERT_TAIL(&locklist, current, entries);
   }
   /* Add to requester list */
   ast_mutex_lock(&current->mutex);
   current->requesters++;
   ast_mutex_unlock(&current->mutex);
   AST_LIST_UNLOCK(&locklist);

   /* Found lock or created one - now find or create the corresponding link in the channel */
   AST_LIST_LOCK(list);
   AST_LIST_TRAVERSE(list, clframe, list) {
      if (clframe->lock_frame == current) {
         break;
      }
   }

   if (!clframe) {
      if (unloading) {
         ast_log(LOG_ERROR,
            "Busy unloading.  %sLOCK will fail.\n",
            trylock ? "TRY" : "");
         /* Don't bother */
         ast_mutex_lock(&current->mutex);
         current->requesters--;
         ast_mutex_unlock(&current->mutex);
         AST_LIST_UNLOCK(list);
         return -1;
      }

      if (!(clframe = ast_calloc(1, sizeof(*clframe)))) {
         ast_log(LOG_ERROR,
            "Unable to allocate channel lock frame.  %sLOCK will fail.\n",
            trylock ? "TRY" : "");
         ast_mutex_lock(&current->mutex);
         current->requesters--;
         ast_mutex_unlock(&current->mutex);
         AST_LIST_UNLOCK(list);
         return -1;
      }

      clframe->lock_frame = current;
      clframe->channel = chan;
      AST_LIST_INSERT_TAIL(list, clframe, list);
   }
   AST_LIST_UNLOCK(list);

   /* If we already own the lock, then we're being called recursively.
    * Keep track of how many times that is, because we need to unlock
    * the same amount, before we'll release this one.
    */
   if (current->owner == chan) {
      /* We're not a requester, we already have it */
      ast_mutex_lock(&current->mutex);
      current->requesters--;
      ast_mutex_unlock(&current->mutex);
      current->count++;
      return 0;
   }

   /* Wait up to three seconds from now for LOCK. */
   now = ast_tvnow();
   timeout.tv_sec = now.tv_sec + 3;
   timeout.tv_nsec = now.tv_usec * 1000;

   ast_mutex_lock(&current->mutex);

   res = 0;
   while (!trylock && !res && current->owner) {
      res = ast_cond_timedwait(&current->cond, &current->mutex, &timeout);
   }
   if (current->owner) {
      /* timeout;
       * trylock; or
       * cond_timedwait failed.
       *
       * either way, we fail to obtain the lock.
       */
      res = -1;
   } else {
      current->owner = chan;
      current->count++;
      res = 0;
   }
   /* Remove from requester list */
   current->requesters--;
   if (res && unloading)
      ast_cond_signal(&current->cond);
   ast_mutex_unlock(&current->mutex);

   return res;
}

static int unlock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
{
   struct ast_datastore *lock_store;
   struct channel_lock_frame *clframe;
   AST_LIST_HEAD(, channel_lock_frame) *list;

   if (!chan) {
      return -1;
   }

   lock_store = ast_channel_datastore_find(chan, &lock_info, NULL);
   if (!lock_store) {
      ast_log(LOG_WARNING, "No datastore for dialplan locks.  Nothing was ever locked!\n");
      ast_copy_string(buf, "0", len);
      return 0;
   }

   if (!(list = lock_store->data)) {
      ast_debug(1, "This should NEVER happen\n");
      ast_copy_string(buf, "0", len);
      return 0;
   }

   /* Find item in the channel list */
   AST_LIST_LOCK(list);
   AST_LIST_TRAVERSE(list, clframe, list) {
      if (clframe->lock_frame && clframe->lock_frame->owner == chan && strcmp(clframe->lock_frame->name, data) == 0) {
         break;
      }
   }
   /* We never destroy anything until channel destruction, which will never
    * happen while this routine is executing, so we don't need to hold the
    * lock beyond this point. */
   AST_LIST_UNLOCK(list);

   if (!clframe) {
      /* We didn't have this lock in the first place */
      ast_copy_string(buf, "0", len);
      return 0;
   }

   if (--clframe->lock_frame->count == 0) {
      ast_mutex_lock(&clframe->lock_frame->mutex);
      clframe->lock_frame->owner = NULL;
      ast_cond_signal(&clframe->lock_frame->cond);
      ast_mutex_unlock(&clframe->lock_frame->mutex);
   }

   ast_copy_string(buf, "1", len);
   return 0;
}

static int lock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
{
   if (!chan) {
      return -1;
   }
   ast_autoservice_start(chan);
   ast_copy_string(buf, get_lock(chan, data, 0) ? "0" : "1", len);
   ast_autoservice_stop(chan);

   return 0;
}

static int trylock_read(struct ast_channel *chan, const char *cmd, char *data, char *buf, size_t len)
{
   if (!chan) {
      return -1;
   }
   ast_autoservice_start(chan);
   ast_copy_string(buf, get_lock(chan, data, 1) ? "0" : "1", len);
   ast_autoservice_stop(chan);

   return 0;
}

static char *handle_cli_locks_show(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   int c = 0;
   struct lock_frame* current;
   switch (cmd) {
   case CLI_INIT:
      e->command = "dialplan locks show";
      e->usage =
         "Usage: dialplan locks show\n"
         "       List all locks known to func_lock, along with their current status.\n";
      return NULL;
   case CLI_GENERATE:
      return NULL;
   }

   ast_cli(a->fd, "func_lock locks:\n");
   ast_cli(a->fd, "%-40s Requesters Owner\n", "Name");
   AST_LIST_LOCK(&locklist);
   AST_LIST_TRAVERSE(&locklist, current, entries) {
      ast_mutex_lock(&current->mutex);
      ast_cli(a->fd, "%-40s %-10d %s\n", current->name, current->requesters,
            current->owner ? ast_channel_name(current->owner) : "(unlocked)");
      ast_mutex_unlock(&current->mutex);
      c++;
   }
   AST_LIST_UNLOCK(&locklist);
   ast_cli(a->fd, "%d total locks listed.\n", c);

   return 0;
}

static struct ast_custom_function lock_function = {
   .name = "LOCK",
   .read = lock_read,
   .read_max = 2,
};

static struct ast_custom_function trylock_function = {
   .name = "TRYLOCK",
   .read = trylock_read,
   .read_max = 2,
};

static struct ast_custom_function unlock_function = {
   .name = "UNLOCK",
   .read = unlock_read,
   .read_max = 2,
};

static struct ast_cli_entry cli_locks_show = AST_CLI_DEFINE(handle_cli_locks_show, "List func_lock locks.");

static int unload_module(void)
{
   struct lock_frame *current;

   /* Module flag */
   unloading = 1;

   /* Make it impossible for new requesters to be added
    * NOTE:  channels could already be in get_lock() */
   ast_custom_function_unregister(&lock_function);
   ast_custom_function_unregister(&trylock_function);

   ast_cli_unregister(&cli_locks_show);

   AST_LIST_LOCK(&locklist);
   while ((current = AST_LIST_REMOVE_HEAD(&locklist, entries))) {
      int warned = 0;
      ast_mutex_lock(&current->mutex);
      while (current->owner || current->requesters) {
         if (!warned) {
            ast_log(LOG_WARNING, "Waiting for %d requesters for %s lock %s.\n",
                  current->requesters, current->owner ? "locked" : "unlocked",
                  current->name);
            warned = 1;
         }
         /* either the mutex is locked, or other parties are currently in get_lock,
          * we need to wait for all of those to clear first */
         ast_cond_wait(&current->cond, &current->mutex);
      }
      ast_mutex_unlock(&current->mutex);
      /* At this point we know:
       * 1. the lock has been released,
       * 2. there are no requesters (nor should any be able to sneak in).
       */
      ast_mutex_destroy(&current->mutex);
      ast_cond_destroy(&current->cond);
      ast_free(current);
   }
   AST_LIST_UNLOCK(&locklist);
   AST_LIST_HEAD_DESTROY(&locklist);

   /* At this point we can safely stop access to UNLOCK */
   ast_custom_function_unregister(&unlock_function);

   return 0;
}

static int load_module(void)
{
   int res = ast_custom_function_register_escalating(&lock_function, AST_CFE_READ);
   res |= ast_custom_function_register_escalating(&trylock_function, AST_CFE_READ);
   res |= ast_custom_function_register_escalating(&unlock_function, AST_CFE_READ);
   res |= ast_cli_register(&cli_locks_show);

   return res;
}

AST_MODULE_INFO_STANDARD(ASTERISK_GPL_KEY, "Dialplan mutexes");