func_lock.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2007, Tilghman Lesher
 *
 * Tilghman Lesher <func_lock_2007@the-tilghman.com>
 *
 * 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 <func_lock_2007@the-tilghman.com>
 *
 * \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>
        <see-also>
            <ref type="function">TRYLOCK</ref>
            <ref type="function">UNLOCK</ref>
        </see-also>
    </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>
        <see-also>
            <ref type="function">LOCK</ref>
            <ref type="function">UNLOCK</ref>
        </see-also>
    </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>
        <see-also>
            <ref type="function">LOCK</ref>
            <ref type="function">TRYLOCK</ref>
        </see-also>
    </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");