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");