taskpool.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2025, Sangoma Technologies Corporation
 *
 * Joshua Colp <jcolp@sangoma.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.
 */
 
 
#include "asterisk.h"
 
#include "asterisk/_private.h"
#include "asterisk/taskpool.h"
#include "asterisk/taskprocessor.h"
#include "asterisk/astobj2.h"
#include "asterisk/serializer_shutdown_group.h"
#include "asterisk/utils.h"
#include "asterisk/time.h"
#include "asterisk/sched.h"
 
/*!
 * \brief A taskpool taskprocessor
 */
struct taskpool_taskprocessor {
    /*! The underlying taskprocessor */
    struct ast_taskprocessor *taskprocessor;
    /*! The last time a task was pushed to this taskprocessor */
    struct timeval last_pushed;
};
 
/*!
 * \brief A container of taskprocessors
 */
struct taskpool_taskprocessors {
    /*! A vector of taskprocessors */
    AST_VECTOR(, struct taskpool_taskprocessor *) taskprocessors;
    /*! The next taskprocessor to use for pushing */
    unsigned int taskprocessor_num;
};
 
typedef void (*taskpool_selector)(struct ast_taskpool *pool, struct taskpool_taskprocessors *taskprocessors,
    struct taskpool_taskprocessor **taskprocessor, unsigned int *growth_threshold_reached);
 
/*!
 * \brief An opaque taskpool structure
 *
 * A taskpool is a collection of taskprocessors that
 * execute tasks, each from their own queue. A selector
 * determines which taskprocessor to queue to at push
 * time.
 */
struct ast_taskpool {
    /*! The static taskprocessors, those which will always exist */
    struct taskpool_taskprocessors static_taskprocessors;
    /*! The dynamic taskprocessors, those which will be created as needed */
    struct taskpool_taskprocessors dynamic_taskprocessors;
    /*! True if the taskpool is in the process of shutting down */
    int shutting_down;
    /*! Taskpool-specific options */
    struct ast_taskpool_options options;
    /*! Dynamic pool shrinking scheduled item */
    int shrink_sched_id;
    /*! The taskprocessor selector to use */
    taskpool_selector selector;
    /*! The name of the taskpool */
    char name[0];
};
 
/*! \brief The threshold for a taskprocessor at which we consider the pool needing to grow (50% of high water threshold) */
#define TASKPOOL_GROW_THRESHOLD (AST_TASKPROCESSOR_HIGH_WATER_LEVEL * 5) / 10
 
/*! \brief Scheduler used for dynamic pool shrinking */
static struct ast_sched_context *sched;
 
/*! \brief Thread storage for the current taskpool */
AST_THREADSTORAGE_RAW(current_taskpool_pool);
 
/*!
 * \internal
 * \brief Get the current taskpool associated with this thread.
 */
static struct ast_taskpool *ast_taskpool_get_current(void)
{
    return ast_threadstorage_get_ptr(&current_taskpool_pool);
}
 
/*!
 * \internal
 * \brief Shutdown task for taskpool taskprocessor
 */
 static int taskpool_taskprocessor_stop(void *data)
 {
    struct ast_taskpool *pool = ast_taskpool_get_current();
 
    /* If a thread stop callback is set on the options, call it */
    if (pool->options.thread_end) {
        pool->options.thread_end();
    }
 
    ao2_cleanup(pool);
 
     return 0;
 }
 
/*! \internal */
static void taskpool_taskprocessor_dtor(void *obj)
{
    struct taskpool_taskprocessor *taskprocessor = obj;
 
    if (taskprocessor->taskprocessor && ast_taskprocessor_push(taskprocessor->taskprocessor, taskpool_taskprocessor_stop, NULL)) {
        /* We can't actually do anything if this fails, so just accept reality */
    }
 
    ast_taskprocessor_unreference(taskprocessor->taskprocessor);
}
 
/*!
 * \internal
 * \brief Startup task for taskpool taskprocessor
 */
static int taskpool_taskprocessor_start(void *data)
{
    struct ast_taskpool *pool = data;
 
    /* Set the pool on the thread for this taskprocessor, inheriting the
     * reference passed to the task itself.
     */
    ast_threadstorage_set_ptr(&current_taskpool_pool, pool);
 
    /* If a thread start callback is set on the options, call it */
    if (pool->options.thread_start) {
        pool->options.thread_start();
    }
 
    return 0;
}
 
/*!
 * \internal
 * \brief Allocate a taskpool specific taskprocessor
 */
static struct taskpool_taskprocessor *taskpool_taskprocessor_alloc(struct ast_taskpool *pool, char type)
{
    struct taskpool_taskprocessor *taskprocessor;
    char tps_name[AST_TASKPROCESSOR_MAX_NAME + 1];
 
    /* We don't actually need locking for each pool taskprocessor, as the only thing
     * mutable is the underlying taskprocessor which has its own internal locking.
     */
    taskprocessor = ao2_alloc_options(sizeof(*taskprocessor), taskpool_taskprocessor_dtor, AO2_ALLOC_OPT_LOCK_NOLOCK);
    if (!taskprocessor) {
        return NULL;
    }
 
    /* Create name with seq number appended. */
    ast_taskprocessor_build_name(tps_name, sizeof(tps_name), "taskpool/%c:%s", type, pool->name);
 
    taskprocessor->taskprocessor = ast_taskprocessor_get(tps_name, TPS_REF_DEFAULT);
    if (!taskprocessor->taskprocessor) {
        ao2_ref(taskprocessor, -1);
        return NULL;
    }
 
    taskprocessor->last_pushed = ast_tvnow();
 
    if (ast_taskprocessor_push(taskprocessor->taskprocessor, taskpool_taskprocessor_start, ao2_bump(pool))) {
        ao2_ref(pool, -1);
        /* Prevent the taskprocessor from queueing the stop task by explicitly unreferencing and setting it to
         * NULL here.
         */
        ast_taskprocessor_unreference(taskprocessor->taskprocessor);
        taskprocessor->taskprocessor = NULL;
        return NULL;
    }
 
    return taskprocessor;
}
 
/*!
 * \internal
 * \brief Initialize the taskpool taskprocessors structure
 */
static int taskpool_taskprocessors_init(struct taskpool_taskprocessors *taskprocessors, unsigned int size)
{
    if (AST_VECTOR_INIT(&taskprocessors->taskprocessors, size)) {
        return -1;
    }
 
    return 0;
}
 
/*!
 * \internal
 * \brief Clean up the taskpool taskprocessors structure
 */
static void taskpool_taskprocessors_cleanup(struct taskpool_taskprocessors *taskprocessors)
{
    /* Access/manipulation of taskprocessors is done with the lock held, and
     * with a check of the shutdown flag done. This means that outside of holding
     * the lock we can safely muck with it. Pushing to the taskprocessor is done
     * outside of the lock, but with a reference to the taskprocessor held.
     */
    AST_VECTOR_CALLBACK_VOID(&taskprocessors->taskprocessors, ao2_cleanup);
    AST_VECTOR_FREE(&taskprocessors->taskprocessors);
}
 
/*!
 * \internal
 * \brief Determine if a taskpool taskprocessor is idle
 */
#define TASKPROCESSOR_IS_IDLE(tps, timeout) (ast_tvdiff_ms(ast_tvnow(), tps->last_pushed) > (timeout))
 
/*! \internal
 * \brief Taskpool dynamic pool shrink function
 */
static int taskpool_dynamic_pool_shrink(const void *data)
{
    struct ast_taskpool *pool = (struct ast_taskpool *)data;
    int num_removed;
 
    ao2_lock(pool);
 
    /* If the pool is shutting down, do nothing and don't reschedule */
    if (pool->shutting_down) {
        ao2_unlock(pool);
        ao2_ref(pool, -1);
        return 0;
    }
 
    /* Go through the dynamic taskprocessors and find any which have been idle long enough and remove them */
    num_removed = AST_VECTOR_REMOVE_ALL_CMP_UNORDERED(&pool->dynamic_taskprocessors.taskprocessors, pool->options.idle_timeout * 1000,
        TASKPROCESSOR_IS_IDLE, ao2_cleanup);
    if (num_removed) {
        /* If we've removed any taskprocessors the taskprocessor_num may no longer be valid, so update it */
        if (pool->dynamic_taskprocessors.taskprocessor_num >= AST_VECTOR_SIZE(&pool->dynamic_taskprocessors.taskprocessors)) {
            pool->dynamic_taskprocessors.taskprocessor_num = 0;
        }
    }
 
    ao2_unlock(pool);
 
    /* It is possible for the pool to have been shut down between unlocking and returning, this is
     * inherently a race condition we can't eliminate so we will catch it on the next iteration.
     */
    return pool->options.idle_timeout * 1000;
}
 
/*!
 * \internal
 * \brief Sequential taskprocessor selector
 */
 static void taskpool_sequential_selector(struct ast_taskpool *pool, struct taskpool_taskprocessors *taskprocessors,
    struct taskpool_taskprocessor **taskprocessor, unsigned int *growth_threshold_reached)
{
    unsigned int taskprocessor_num = taskprocessors->taskprocessor_num;
 
    if (!AST_VECTOR_SIZE(&taskprocessors->taskprocessors)) {
        *growth_threshold_reached = 1;
        return;
    }
 
    taskprocessors->taskprocessor_num++;
    if (taskprocessors->taskprocessor_num == AST_VECTOR_SIZE(&taskprocessors->taskprocessors)) {
        taskprocessors->taskprocessor_num = 0;
    }
 
    *taskprocessor = AST_VECTOR_GET(&taskprocessors->taskprocessors, taskprocessor_num);
 
    /* Check to see if this has reached the growth threshold */
    *growth_threshold_reached = (ast_taskprocessor_size((*taskprocessor)->taskprocessor) >= pool->options.growth_threshold) ? 1 : 0;
}
 
/*!
 * \interal
 * \brief Least full taskprocessor selector
 */
static void taskpool_least_full_selector(struct ast_taskpool *pool, struct taskpool_taskprocessors *taskprocessors,
    struct taskpool_taskprocessor **taskprocessor, unsigned int *growth_threshold_reached)
{
    struct taskpool_taskprocessor *least_full = NULL;
    unsigned int i;
 
    if (!AST_VECTOR_SIZE(&taskprocessors->taskprocessors)) {
        *growth_threshold_reached = 1;
        return;
    }
 
    /* We assume that the growth threshold has not yet been reached, until proven otherwise */
    *growth_threshold_reached = 0;
 
    for (i = 0; i < AST_VECTOR_SIZE(&taskprocessors->taskprocessors); i++) {
        struct taskpool_taskprocessor *tp = AST_VECTOR_GET(&taskprocessors->taskprocessors, i);
 
        /* If this taskprocessor has no outstanding tasks, it is the best choice */
        if (!ast_taskprocessor_size(tp->taskprocessor)) {
            *taskprocessor = tp;
            return;
        }
 
        /* If any of the taskprocessors have reached the growth threshold then we should grow the pool */
        if (ast_taskprocessor_size(tp->taskprocessor) >= pool->options.growth_threshold) {
            *growth_threshold_reached = 1;
        }
 
        /* The taskprocessor with the fewest tasks should be used */
        if (!least_full || ast_taskprocessor_size(tp->taskprocessor) < ast_taskprocessor_size(least_full->taskprocessor)) {
            least_full = tp;
        }
    }
 
    *taskprocessor = least_full;
}
 
struct ast_taskpool *ast_taskpool_create(const char *name,
        const struct ast_taskpool_options *options)
{
    struct ast_taskpool *pool;
 
    /* Enforce versioning on the passed-in options */
    if (options->version != AST_TASKPOOL_OPTIONS_VERSION) {
        return NULL;
    }
 
    pool = ao2_alloc(sizeof(*pool) + strlen(name) + 1, NULL);
    if (!pool) {
        return NULL;
    }
 
    strcpy(pool->name, name); /* Safe */
    memcpy(&pool->options, options, sizeof(pool->options));
    pool->shrink_sched_id = -1;
 
    /* Verify the passed-in options are valid, and adjust if needed */
    if (options->initial_size < options->minimum_size) {
        pool->options.initial_size = options->minimum_size;
        ast_log(LOG_WARNING, "Taskpool '%s' has an initial size of %d, which is less than the minimum size of %d. Adjusting to %d.\n",
            name, options->initial_size, options->minimum_size, options->minimum_size);
    }
 
    if (options->max_size && pool->options.initial_size > options->max_size) {
        pool->options.max_size = pool->options.initial_size;
        ast_log(LOG_WARNING, "Taskpool '%s' has a max size of %d, which is less than the initial size of %d. Adjusting to %d.\n",
            name, options->max_size, pool->options.initial_size, pool->options.initial_size);
    }
 
    if (!options->auto_increment) {
        if (!pool->options.minimum_size) {
            pool->options.minimum_size = 1;
            ast_log(LOG_WARNING, "Taskpool '%s' has a minimum size of 0, which is not valid without auto increment. Adjusting to 1.\n", name);
        }
        if (!pool->options.max_size) {
            pool->options.max_size = pool->options.minimum_size;
            ast_log(LOG_WARNING, "Taskpool '%s' has a max size of 0, which is not valid without auto increment. Adjusting to %d.\n", name, pool->options.minimum_size);
        }
        if (pool->options.minimum_size != pool->options.max_size) {
            pool->options.minimum_size = pool->options.max_size;
            pool->options.initial_size = pool->options.max_size;
            ast_log(LOG_WARNING, "Taskpool '%s' has a minimum size of %d, while max size is %d. Adjusting all sizes to %d due to lack of auto increment.\n",
                name, options->minimum_size, pool->options.max_size, pool->options.max_size);
        }
    } else if (!options->growth_threshold) {
        pool->options.growth_threshold = TASKPOOL_GROW_THRESHOLD;
    }
 
    if (options->selector == AST_TASKPOOL_SELECTOR_DEFAULT || options->selector == AST_TASKPOOL_SELECTOR_LEAST_FULL) {
        pool->selector = taskpool_least_full_selector;
    } else if (options->selector == AST_TASKPOOL_SELECTOR_SEQUENTIAL) {
        pool->selector = taskpool_sequential_selector;
    } else {
        ast_log(LOG_WARNING, "Taskpool '%s' has an invalid selector of %d. Adjusting to default selector.\n",
            name, options->selector);
        pool->selector = taskpool_least_full_selector;
    }
 
    if (taskpool_taskprocessors_init(&pool->static_taskprocessors, pool->options.minimum_size)) {
        ao2_ref(pool, -1);
        return NULL;
    }
 
    /* Create the static taskprocessors based on the passed-in options */
    for (int i = 0; i < pool->options.minimum_size; i++) {
        struct taskpool_taskprocessor *taskprocessor;
 
        taskprocessor = taskpool_taskprocessor_alloc(pool, 's');
        if (!taskprocessor) {
            /* The reference to pool is passed to ast_taskpool_shutdown */
            ast_taskpool_shutdown(pool);
            return NULL;
        }
 
        if (AST_VECTOR_APPEND(&pool->static_taskprocessors.taskprocessors, taskprocessor)) {
            ao2_ref(taskprocessor, -1);
            /* The reference to pool is passed to ast_taskpool_shutdown */
            ast_taskpool_shutdown(pool);
            return NULL;
        }
    }
 
    if (taskpool_taskprocessors_init(&pool->dynamic_taskprocessors,
        pool->options.initial_size - pool->options.minimum_size)) {
        ast_taskpool_shutdown(pool);
        return NULL;
    }
 
    /* Create the dynamic taskprocessor based on the passed-in options */
    for (int i = 0; i < (pool->options.initial_size - pool->options.minimum_size); i++) {
        struct taskpool_taskprocessor *taskprocessor;
 
        taskprocessor = taskpool_taskprocessor_alloc(pool, 'd');
        if (!taskprocessor) {
            /* The reference to pool is passed to ast_taskpool_shutdown */
            ast_taskpool_shutdown(pool);
            return NULL;
        }
 
        if (AST_VECTOR_APPEND(&pool->dynamic_taskprocessors.taskprocessors, taskprocessor)) {
            ao2_ref(taskprocessor, -1);
            /* The reference to pool is passed to ast_taskpool_shutdown */
            ast_taskpool_shutdown(pool);
            return NULL;
        }
    }
 
    /* If idle timeout support is enabled kick off a scheduled task to shrink the dynamic pool periodically, we do
     * this no matter if there are dynamic taskprocessor present to reduce the work needed within the push function
     * and to reduce complexity.
     */
    if (options->idle_timeout && options->auto_increment) {
        pool->shrink_sched_id = ast_sched_add(sched, options->idle_timeout * 1000, taskpool_dynamic_pool_shrink, ao2_bump(pool));
        if (pool->shrink_sched_id < 0) {
            ao2_ref(pool, -1);
            /* The second reference to pool is passed to ast_taskpool_shutdown */
            ast_taskpool_shutdown(pool);
            return NULL;
        }
    }
 
    return pool;
}
 
size_t ast_taskpool_taskprocessors_count(struct ast_taskpool *pool)
{
    size_t count;
 
    ao2_lock(pool);
    count = AST_VECTOR_SIZE(&pool->static_taskprocessors.taskprocessors) + AST_VECTOR_SIZE(&pool->dynamic_taskprocessors.taskprocessors);
    ao2_unlock(pool);
 
    return count;
}
 
#define TASKPOOL_QUEUE_SIZE_ADD(tps, size) (size += ast_taskprocessor_size(tps->taskprocessor))
 
long ast_taskpool_queue_size(struct ast_taskpool *pool)
{
    long queue_size = 0;
 
    ao2_lock(pool);
    AST_VECTOR_CALLBACK_VOID(&pool->static_taskprocessors.taskprocessors, TASKPOOL_QUEUE_SIZE_ADD, queue_size);
    AST_VECTOR_CALLBACK_VOID(&pool->dynamic_taskprocessors.taskprocessors, TASKPOOL_QUEUE_SIZE_ADD, queue_size);
    ao2_unlock(pool);
 
    return queue_size;
}
 
/*! \internal
 * \brief Taskpool dynamic pool grow function
 */
static void taskpool_dynamic_pool_grow(struct ast_taskpool *pool, struct taskpool_taskprocessor **taskprocessor)
{
    unsigned int num_to_add = pool->options.auto_increment;
    int i;
 
    if (!num_to_add) {
        return;
    }
 
    /* If a maximum size is enforced, then determine if we have to limit how many taskprocessors we add */
    if (pool->options.max_size) {
        unsigned int current_size = AST_VECTOR_SIZE(&pool->dynamic_taskprocessors.taskprocessors) + AST_VECTOR_SIZE(&pool->static_taskprocessors.taskprocessors);
 
        if (current_size + num_to_add > pool->options.max_size) {
            num_to_add = pool->options.max_size - current_size;
        }
    }
 
    for (i = 0; i < num_to_add; i++) {
        struct taskpool_taskprocessor *new_taskprocessor;
 
        new_taskprocessor = taskpool_taskprocessor_alloc(pool, 'd');
        if (!new_taskprocessor) {
            return;
        }
 
        if (AST_VECTOR_APPEND(&pool->dynamic_taskprocessors.taskprocessors, new_taskprocessor)) {
            ao2_ref(new_taskprocessor, -1);
            return;
        }
 
        if (i == 0) {
            /* On the first iteration we return the taskprocessor we just added */
            *taskprocessor = new_taskprocessor;
            /* We assume we will be going back to the first taskprocessor, since we are at the end of the vector */
            pool->dynamic_taskprocessors.taskprocessor_num = 0;
        } else if (i == 1) {
            /* On the second iteration we update the next taskprocessor to use to be this one */
            pool->dynamic_taskprocessors.taskprocessor_num = AST_VECTOR_SIZE(&pool->dynamic_taskprocessors.taskprocessors) - 1;
        }
    }
}
 
int ast_taskpool_push(struct ast_taskpool *pool, int (*task)(void *data), void *data)
{
    RAII_VAR(struct taskpool_taskprocessor *, taskprocessor, NULL, ao2_cleanup);
 
    /* Select the taskprocessor in the pool to use for pushing this task */
    ao2_lock(pool);
    if (!pool->shutting_down) {
        unsigned int growth_threshold_reached = 0;
 
        /* A selector doesn't set taskprocessor to NULL, it will only change the value if a better
         * taskprocessor is found. This means that even if the selector for a dynamic taskprocessor
         * fails for some reason, it will still fall back to the initially found static one if
         * it is present.
         */
        pool->selector(pool, &pool->static_taskprocessors, &taskprocessor, &growth_threshold_reached);
        if (pool->options.auto_increment && growth_threshold_reached) {
            /* If we need to grow then try dynamic taskprocessors */
            pool->selector(pool, &pool->dynamic_taskprocessors, &taskprocessor, &growth_threshold_reached);
            if (growth_threshold_reached) {
                /* If we STILL need to grow then grow the dynamic taskprocessor pool if allowed */
                taskpool_dynamic_pool_grow(pool, &taskprocessor);
            }
 
            /* If a dynamic taskprocessor was used update its last push time */
            if (taskprocessor) {
                taskprocessor->last_pushed = ast_tvnow();
            }
        }
        ao2_bump(taskprocessor);
    }
    ao2_unlock(pool);
 
    if (!taskprocessor) {
        return -1;
    }
 
    if (ast_taskprocessor_push(taskprocessor->taskprocessor, task, data)) {
        return -1;
    }
 
    return 0;
}
 
/*!
 * \internal Structure used for synchronous task
 */
struct taskpool_sync_task {
    ast_mutex_t lock;
    ast_cond_t cond;
    int complete;
    int fail;
    int (*task)(void *);
    void *task_data;
};
 
/*!
 * \internal Initialization function for synchronous task
 */
static int taskpool_sync_task_init(struct taskpool_sync_task *sync_task, int (*task)(void *), void *data)
{
    ast_mutex_init(&sync_task->lock);
    ast_cond_init(&sync_task->cond, NULL);
    sync_task->complete = 0;
    sync_task->fail = 0;
    sync_task->task = task;
    sync_task->task_data = data;
    return 0;
}
 
/*!
 * \internal Cleanup function for synchronous task
 */
static void taskpool_sync_task_cleanup(struct taskpool_sync_task *sync_task)
{
    ast_mutex_destroy(&sync_task->lock);
    ast_cond_destroy(&sync_task->cond);
}
 
/*!
 * \internal Function for executing a sychronous task
 */
static int taskpool_sync_task(void *data)
{
    struct taskpool_sync_task *sync_task = data;
    int ret;
 
    sync_task->fail = sync_task->task(sync_task->task_data);
 
    /*
     * Once we unlock sync_task->lock after signaling, we cannot access
     * sync_task again.  The thread waiting within ast_taskpool_push_wait()
     * is free to continue and release its local variable (sync_task).
     */
    ast_mutex_lock(&sync_task->lock);
    sync_task->complete = 1;
    ast_cond_signal(&sync_task->cond);
    ret = sync_task->fail;
    ast_mutex_unlock(&sync_task->lock);
    return ret;
}
 
int ast_taskpool_push_wait(struct ast_taskpool *pool, int (*task)(void *data), void *data)
{
    struct taskpool_sync_task sync_task;
 
    /* If we are already executing within a taskpool taskprocessor then
     * don't bother pushing a new task, just directly execute the task.
     */
    if (ast_taskpool_get_current()) {
        return task(data);
    }
 
    if (taskpool_sync_task_init(&sync_task, task, data)) {
        return -1;
    }
 
    if (ast_taskpool_push(pool, taskpool_sync_task, &sync_task)) {
        taskpool_sync_task_cleanup(&sync_task);
        return -1;
    }
 
    ast_mutex_lock(&sync_task.lock);
    while (!sync_task.complete) {
        ast_cond_wait(&sync_task.cond, &sync_task.lock);
    }
    ast_mutex_unlock(&sync_task.lock);
 
    taskpool_sync_task_cleanup(&sync_task);
    return sync_task.fail;
}
 
void ast_taskpool_shutdown(struct ast_taskpool *pool)
{
    if (!pool) {
        return;
    }
 
    /* Mark this pool as shutting down so nothing new is pushed */
    ao2_lock(pool);
    pool->shutting_down = 1;
    ao2_unlock(pool);
 
    /* Stop the shrink scheduled item if present */
    AST_SCHED_DEL_UNREF(sched, pool->shrink_sched_id, ao2_ref(pool, -1));
 
    /* Clean up all the taskprocessors */
    taskpool_taskprocessors_cleanup(&pool->static_taskprocessors);
    taskpool_taskprocessors_cleanup(&pool->dynamic_taskprocessors);
 
    ao2_ref(pool, -1);
}
 
struct serializer {
    /*! Taskpool the serializer will use to process the jobs. */
    struct ast_taskpool *pool;
    /*! Which group will wait for this serializer to shutdown. */
    struct ast_serializer_shutdown_group *shutdown_group;
};
 
static void serializer_dtor(void *obj)
{
    struct serializer *ser = obj;
 
    ao2_cleanup(ser->pool);
    ser->pool = NULL;
    ao2_cleanup(ser->shutdown_group);
    ser->shutdown_group = NULL;
}
 
static struct serializer *serializer_create(struct ast_taskpool *pool,
    struct ast_serializer_shutdown_group *shutdown_group)
{
    struct serializer *ser;
 
    /* This object has a lock so it can be used to ensure exclusive access
     * to the execution of tasks within the serializer.
     */
    ser = ao2_alloc(sizeof(*ser), serializer_dtor);
    if (!ser) {
        return NULL;
    }
    ser->pool = ao2_bump(pool);
    ser->shutdown_group = ao2_bump(shutdown_group);
    return ser;
}
 
AST_THREADSTORAGE_RAW(current_taskpool_serializer);
 
static int execute_tasks(void *data)
{
    struct ast_taskpool *pool = ast_taskpool_get_current();
    struct ast_taskprocessor *tps = data;
    struct ast_taskprocessor_listener *listener = ast_taskprocessor_listener(tps);
    struct serializer *ser = ast_taskprocessor_listener_get_user_data(listener);
    size_t remaining, requeue = 0;
 
    /* In a normal scenario this lock will not be in contention with
     * anything else. It is only if a synchronous task is pushed to
     * the serializer that it may be blocked on the synchronous
     * task thread. This is done to ensure that only one thread is executing
     * tasks from the serializer at a given time, and not out of order
     * either.
     */
    ao2_lock(ser);
 
    ast_threadstorage_set_ptr(&current_taskpool_serializer, tps);
    for (remaining = ast_taskprocessor_size(tps); remaining > 0; remaining--) {
        requeue = ast_taskprocessor_execute(tps);
    }
    ast_threadstorage_set_ptr(&current_taskpool_serializer, NULL);
 
    ao2_unlock(ser);
 
    /* If there are remaining tasks we requeue, this way the serializer
     * does not hold exclusivity of the taskpool taskprocessor
     */
    if (requeue) {
        /* Ownership passes to the new task */
        if (ast_taskpool_push(pool, execute_tasks, tps)) {
            ast_taskprocessor_unreference(tps);
        }
    } else {
        ast_taskprocessor_unreference(tps);
    }
 
    return 0;
}
 
static void serializer_task_pushed(struct ast_taskprocessor_listener *listener, int was_empty)
{
    if (was_empty) {
        struct serializer *ser = ast_taskprocessor_listener_get_user_data(listener);
        struct ast_taskprocessor *tps = ast_taskprocessor_listener_get_tps(listener);
 
        if (ast_taskpool_push(ser->pool, execute_tasks, tps)) {
            ast_taskprocessor_unreference(tps);
        }
    }
}
 
static int serializer_start(struct ast_taskprocessor_listener *listener)
{
    /* No-op */
    return 0;
}
 
static void serializer_shutdown(struct ast_taskprocessor_listener *listener)
{
    struct serializer *ser = ast_taskprocessor_listener_get_user_data(listener);
 
    if (ser->shutdown_group) {
        ast_serializer_shutdown_group_dec(ser->shutdown_group);
    }
    ao2_cleanup(ser);
}
 
static struct ast_taskprocessor_listener_callbacks serializer_tps_listener_callbacks = {
    .task_pushed = serializer_task_pushed,
    .start = serializer_start,
    .shutdown = serializer_shutdown,
};
 
struct ast_taskprocessor *ast_taskpool_serializer_get_current(void)
{
    return ast_threadstorage_get_ptr(&current_taskpool_serializer);
}
 
struct ast_taskprocessor *ast_taskpool_serializer_group(const char *name,
    struct ast_taskpool *pool, struct ast_serializer_shutdown_group *shutdown_group)
{
    struct serializer *ser;
    struct ast_taskprocessor_listener *listener;
    struct ast_taskprocessor *tps;
 
    ser = serializer_create(pool, shutdown_group);
    if (!ser) {
        return NULL;
    }
 
    listener = ast_taskprocessor_listener_alloc(&serializer_tps_listener_callbacks, ser);
    if (!listener) {
        ao2_ref(ser, -1);
        return NULL;
    }
 
    tps = ast_taskprocessor_create_with_listener(name, listener);
    if (!tps) {
        /* ser ref transferred to listener but not cleaned without tps */
        ao2_ref(ser, -1);
    } else if (shutdown_group) {
        ast_serializer_shutdown_group_inc(shutdown_group);
    }
 
    ao2_ref(listener, -1);
    return tps;
}
 
struct ast_taskprocessor *ast_taskpool_serializer(const char *name, struct ast_taskpool *pool)
{
    return ast_taskpool_serializer_group(name, pool, NULL);
}
 
/*!
 * \internal An empty task callback, used to ensure the serializer does not
 * go empty. */
static int taskpool_serializer_empty_task(void *data)
{
    return 0;
}
 
int ast_taskpool_serializer_push_wait(struct ast_taskprocessor *serializer, int (*task)(void *data), void *data)
{
    struct ast_taskprocessor_listener *listener = ast_taskprocessor_listener(serializer);
    struct serializer *ser = ast_taskprocessor_listener_get_user_data(listener);
    struct ast_taskprocessor *prior_serializer;
    struct taskpool_sync_task sync_task;
 
    /* If not in a taskpool taskprocessor we can just queue the task like normal and
     * wait. */
    if (!ast_taskpool_get_current()) {
        if (taskpool_sync_task_init(&sync_task, task, data)) {
            return -1;
        }
 
        if (ast_taskprocessor_push(serializer, taskpool_sync_task, &sync_task)) {
            taskpool_sync_task_cleanup(&sync_task);
            return -1;
        }
 
        ast_mutex_lock(&sync_task.lock);
        while (!sync_task.complete) {
            ast_cond_wait(&sync_task.cond, &sync_task.lock);
        }
        ast_mutex_unlock(&sync_task.lock);
 
        taskpool_sync_task_cleanup(&sync_task);
        return sync_task.fail;
    }
 
    /* It is possible that we are already executing within a serializer, so stash the existing
     * away so we can restore it.
     */
    prior_serializer = ast_taskpool_serializer_get_current();
 
    ao2_lock(ser);
 
    /* There are two cases where we can or have to directly execute this task:
     * 1. There are no other tasks in the serializer
     * 2. We are already in the serializer
     * In the second case if we don't execute the task now, we will deadlock waiting
     * on it as it will never occur.
     */
    if (!ast_taskprocessor_size(serializer) || prior_serializer == serializer) {
        ast_threadstorage_set_ptr(&current_taskpool_serializer, serializer);
        sync_task.fail = task(data);
        ao2_unlock(ser);
        ast_threadstorage_set_ptr(&current_taskpool_serializer, prior_serializer);
        return sync_task.fail;
    }
 
    if (taskpool_sync_task_init(&sync_task, task, data)) {
        ao2_unlock(ser);
        return -1;
    }
 
    /* First we queue the serialized task */
    if (ast_taskprocessor_push(serializer, taskpool_sync_task, &sync_task)) {
        taskpool_sync_task_cleanup(&sync_task);
        ao2_unlock(ser);
        return -1;
    }
 
    /* Next we queue the empty task to ensure the serializer doesn't reach empty, this
     * stops two tasks from being queued for the same serializer at the same time.
     */
    if (ast_taskprocessor_push(serializer, taskpool_serializer_empty_task, NULL)) {
        taskpool_sync_task_cleanup(&sync_task);
        ao2_unlock(ser);
        return -1;
    }
 
    /* Now we execute the tasks on the serializer until our sync task is complete */
    ast_threadstorage_set_ptr(&current_taskpool_serializer, serializer);
    while (!sync_task.complete) {
        /* The sync task is guaranteed to be executed, so doing a while loop on the complete
         * flag is safe.
         */
        ast_taskprocessor_execute(serializer);
    }
    taskpool_sync_task_cleanup(&sync_task);
    ao2_unlock(ser);
 
    ast_threadstorage_set_ptr(&current_taskpool_serializer, prior_serializer);
 
    return sync_task.fail;
}
 
/*!
 * \internal
 * \brief Clean up resources on Asterisk shutdown
 */
static void taskpool_shutdown(void)
{
    if (sched) {
        ast_sched_context_destroy(sched);
        sched = NULL;
    }
}
 
int ast_taskpool_init(void)
{
    sched = ast_sched_context_create();
    if (!sched) {
        return -1;
    }
 
    if (ast_sched_start_thread(sched)) {
        return -1;
    }
 
    ast_register_cleanup(taskpool_shutdown);
 
    return 0;
}