src/util/u_queue.c - third_party/mesa - Git at Google

 /*
  * Copyright © 2016 Advanced Micro Devices, Inc.
  * All Rights Reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
  * "Software"), to deal in the Software without restriction, including
  * without limitation the rights to use, copy, modify, merge, publish,
  * distribute, sub license, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to
  * the following conditions:
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  * NON-INFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS, AUTHORS
  * AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
  * USE OR OTHER DEALINGS IN THE SOFTWARE.
  *
  * The above copyright notice and this permission notice (including the
  * next paragraph) shall be included in all copies or substantial portions
  * of the Software.
  */

 #include "u_queue.h"
 #include "util/u_string.h"

 static void util_queue_killall_and_wait(struct util_queue *queue);

 /****************************************************************************
  * Wait for all queues to assert idle when exit() is called.
  *
  * Otherwise, C++ static variable destructors can be called while threads
  * are using the static variables.
  */

 static once_flag atexit_once_flag = ONCE_FLAG_INIT;
 static struct list_head queue_list;
 static mtx_t exit_mutex = _MTX_INITIALIZER_NP;

 static void
 atexit_handler(void)
 {
    struct util_queue *iter;

    mtx_lock(&exit_mutex);
    /* Wait for all queues to assert idle. */
    LIST_FOR_EACH_ENTRY(iter, &queue_list, head) {
       util_queue_killall_and_wait(iter);
    }
    mtx_unlock(&exit_mutex);
 }

 static void
 global_init(void)
 {
    LIST_INITHEAD(&queue_list);
    atexit(atexit_handler);
 }

 static void
 add_to_atexit_list(struct util_queue *queue)
 {
    call_once(&atexit_once_flag, global_init);

    mtx_lock(&exit_mutex);
    LIST_ADD(&queue->head, &queue_list);
    mtx_unlock(&exit_mutex);
 }

 static void
 remove_from_atexit_list(struct util_queue *queue)
 {
    struct util_queue *iter, *tmp;

    mtx_lock(&exit_mutex);
    LIST_FOR_EACH_ENTRY_SAFE(iter, tmp, &queue_list, head) {
       if (iter == queue) {
          LIST_DEL(&iter->head);
          break;
       }
    }
    mtx_unlock(&exit_mutex);
 }

 /****************************************************************************
  * util_queue_fence
  */

 static void
 util_queue_fence_signal(struct util_queue_fence *fence)
 {
    mtx_lock(&fence->mutex);
    fence->signalled = true;
    cnd_broadcast(&fence->cond);
    mtx_unlock(&fence->mutex);
 }

 void
 util_queue_fence_wait(struct util_queue_fence *fence)
 {
    mtx_lock(&fence->mutex);
    while (!fence->signalled)
       cnd_wait(&fence->cond, &fence->mutex);
    mtx_unlock(&fence->mutex);
 }

 void
 util_queue_fence_init(struct util_queue_fence *fence)
 {
    memset(fence, 0, sizeof(*fence));
    (void) mtx_init(&fence->mutex, mtx_plain);
    cnd_init(&fence->cond);
    fence->signalled = true;
 }

 void
 util_queue_fence_destroy(struct util_queue_fence *fence)
 {
    assert(fence->signalled);

    /* Ensure that another thread is not in the middle of
     * util_queue_fence_signal (having set the fence to signalled but still
     * holding the fence mutex).
     *
     * A common contract between threads is that as soon as a fence is signalled
     * by thread A, thread B is allowed to destroy it. Since
     * util_queue_fence_is_signalled does not lock the fence mutex (for
     * performance reasons), we must do so here.
     */
    mtx_lock(&fence->mutex);
    mtx_unlock(&fence->mutex);

    cnd_destroy(&fence->cond);
    mtx_destroy(&fence->mutex);
 }

 /****************************************************************************
  * util_queue implementation
  */

 struct thread_input {
    struct util_queue *queue;
    int thread_index;
 };

 static int
 util_queue_thread_func(void *input)
 {
    struct util_queue *queue = ((struct thread_input*)input)->queue;
    int thread_index = ((struct thread_input*)input)->thread_index;

    free(input);

    if (queue->name) {
       char name[16];
       util_snprintf(name, sizeof(name), "%s:%i", queue->name, thread_index);
       u_thread_setname(name);
    }

    while (1) {
       struct util_queue_job job;

       mtx_lock(&queue->lock);
       assert(queue->num_queued >= 0 && queue->num_queued <= queue->max_jobs);

       /* wait if the queue is empty */
       while (!queue->kill_threads && queue->num_queued == 0)
          cnd_wait(&queue->has_queued_cond, &queue->lock);

       if (queue->kill_threads) {
          mtx_unlock(&queue->lock);
          break;
       }

       job = queue->jobs[queue->read_idx];
       memset(&queue->jobs[queue->read_idx], 0, sizeof(struct util_queue_job));
       queue->read_idx = (queue->read_idx + 1) % queue->max_jobs;

       queue->num_queued--;
       cnd_signal(&queue->has_space_cond);
       mtx_unlock(&queue->lock);

       if (job.job) {
          job.execute(job.job, thread_index);
          util_queue_fence_signal(job.fence);
          if (job.cleanup)
             job.cleanup(job.job, thread_index);
       }
    }

    /* signal remaining jobs before terminating */
    mtx_lock(&queue->lock);
    for (unsigned i = queue->read_idx; i != queue->write_idx;
         i = (i + 1) % queue->max_jobs) {
       if (queue->jobs[i].job) {
          util_queue_fence_signal(queue->jobs[i].fence);
          queue->jobs[i].job = NULL;
       }
    }
    queue->read_idx = queue->write_idx;
    queue->num_queued = 0;
    mtx_unlock(&queue->lock);
    return 0;
 }

 bool
 util_queue_init(struct util_queue *queue,
                 const char *name,
                 unsigned max_jobs,
                 unsigned num_threads,
                 unsigned flags)
 {
    unsigned i;

    memset(queue, 0, sizeof(*queue));
    queue->name = name;
    queue->flags = flags;
    queue->num_threads = num_threads;
    queue->max_jobs = max_jobs;

    queue->jobs = (struct util_queue_job*)
                  calloc(max_jobs, sizeof(struct util_queue_job));
    if (!queue->jobs)
       goto fail;

    (void) mtx_init(&queue->lock, mtx_plain);

    queue->num_queued = 0;
    cnd_init(&queue->has_queued_cond);
    cnd_init(&queue->has_space_cond);

    queue->threads = (thrd_t*) calloc(num_threads, sizeof(thrd_t));
    if (!queue->threads)
       goto fail;

    /* start threads */
    for (i = 0; i < num_threads; i++) {
       struct thread_input *input =
          (struct thread_input *) malloc(sizeof(struct thread_input));
       input->queue = queue;
       input->thread_index = i;

       queue->threads[i] = u_thread_create(util_queue_thread_func, input);

       if (!queue->threads[i]) {
          free(input);

          if (i == 0) {
             /* no threads created, fail */
             goto fail;
          } else {
             /* at least one thread created, so use it */
             queue->num_threads = i;
             break;
          }
       }

       if (flags & UTIL_QUEUE_INIT_USE_MINIMUM_PRIORITY) {
    #if defined(__linux__) && defined(SCHED_IDLE)
          struct sched_param sched_param = {0};

          /* The nice() function can only set a maximum of 19.
           * SCHED_IDLE is the same as nice = 20.
           *
           * Note that Linux only allows decreasing the priority. The original
           * priority can't be restored.
           */
          pthread_setschedparam(queue->threads[i], SCHED_IDLE, &sched_param);
    #endif
       }
    }

    add_to_atexit_list(queue);
    return true;

 fail:
    free(queue->threads);

    if (queue->jobs) {
       cnd_destroy(&queue->has_space_cond);
       cnd_destroy(&queue->has_queued_cond);
       mtx_destroy(&queue->lock);
       free(queue->jobs);
    }
    /* also util_queue_is_initialized can be used to check for success */
    memset(queue, 0, sizeof(*queue));
    return false;
 }

 static void
 util_queue_killall_and_wait(struct util_queue *queue)
 {
    unsigned i;

    /* Signal all threads to terminate. */
    mtx_lock(&queue->lock);
    queue->kill_threads = 1;
    cnd_broadcast(&queue->has_queued_cond);
    mtx_unlock(&queue->lock);

    for (i = 0; i < queue->num_threads; i++)
       thrd_join(queue->threads[i], NULL);
    queue->num_threads = 0;
 }

 void
 util_queue_destroy(struct util_queue *queue)
 {
    util_queue_killall_and_wait(queue);
    remove_from_atexit_list(queue);

    cnd_destroy(&queue->has_space_cond);
    cnd_destroy(&queue->has_queued_cond);
    mtx_destroy(&queue->lock);
    free(queue->jobs);
    free(queue->threads);
 }

 void
 util_queue_add_job(struct util_queue *queue,
                    void *job,
                    struct util_queue_fence *fence,
                    util_queue_execute_func execute,
                    util_queue_execute_func cleanup)
 {
    struct util_queue_job *ptr;

    assert(fence->signalled);

    mtx_lock(&queue->lock);
    if (queue->kill_threads) {
       mtx_unlock(&queue->lock);
       /* well no good option here, but any leaks will be
        * short-lived as things are shutting down..
        */
       return;
    }

    fence->signalled = false;

    assert(queue->num_queued >= 0 && queue->num_queued <= queue->max_jobs);

    if (queue->num_queued == queue->max_jobs) {
       if (queue->flags & UTIL_QUEUE_INIT_RESIZE_IF_FULL) {
          /* If the queue is full, make it larger to avoid waiting for a free
           * slot.
           */
          unsigned new_max_jobs = queue->max_jobs + 8;
          struct util_queue_job *jobs =
             (struct util_queue_job*)calloc(new_max_jobs,
                                            sizeof(struct util_queue_job));
          assert(jobs);

          /* Copy all queued jobs into the new list. */
          unsigned num_jobs = 0;
          unsigned i = queue->read_idx;

          do {
             jobs[num_jobs++] = queue->jobs[i];
             i = (i + 1) % queue->max_jobs;
          } while (i != queue->write_idx);

          assert(num_jobs == queue->num_queued);

          free(queue->jobs);
          queue->jobs = jobs;
          queue->read_idx = 0;
          queue->write_idx = num_jobs;
          queue->max_jobs = new_max_jobs;
       } else {
          /* Wait until there is a free slot. */
          while (queue->num_queued == queue->max_jobs)
             cnd_wait(&queue->has_space_cond, &queue->lock);
       }
    }

    ptr = &queue->jobs[queue->write_idx];
    assert(ptr->job == NULL);
    ptr->job = job;
    ptr->fence = fence;
    ptr->execute = execute;
    ptr->cleanup = cleanup;
    queue->write_idx = (queue->write_idx + 1) % queue->max_jobs;

    queue->num_queued++;
    cnd_signal(&queue->has_queued_cond);
    mtx_unlock(&queue->lock);
 }

 /**
  * Remove a queued job. If the job hasn't started execution, it's removed from
  * the queue. If the job has started execution, the function waits for it to
  * complete.
  *
  * In all cases, the fence is signalled when the function returns.
  *
  * The function can be used when destroying an object associated with the job
  * when you don't care about the job completion state.
  */
 void
 util_queue_drop_job(struct util_queue *queue, struct util_queue_fence *fence)
 {
    bool removed = false;

    if (util_queue_fence_is_signalled(fence))
       return;

    mtx_lock(&queue->lock);
    for (unsigned i = queue->read_idx; i != queue->write_idx;
         i = (i + 1) % queue->max_jobs) {
       if (queue->jobs[i].fence == fence) {
          if (queue->jobs[i].cleanup)
             queue->jobs[i].cleanup(queue->jobs[i].job, -1);

          /* Just clear it. The threads will treat as a no-op job. */
          memset(&queue->jobs[i], 0, sizeof(queue->jobs[i]));
          removed = true;
          break;
       }
    }
    mtx_unlock(&queue->lock);

    if (removed)
       util_queue_fence_signal(fence);
    else
       util_queue_fence_wait(fence);
 }

 int64_t
 util_queue_get_thread_time_nano(struct util_queue *queue, unsigned thread_index)
 {
    /* Allow some flexibility by not raising an error. */
    if (thread_index >= queue->num_threads)
       return 0;

    return u_thread_get_time_nano(queue->threads[thread_index]);
 }
	/*
	* Copyright © 2016 Advanced Micro Devices, Inc.
	* All Rights Reserved.
	*
	* Permission is hereby granted, free of charge, to any person obtaining
	* a copy of this software and associated documentation files (the
	* "Software"), to deal in the Software without restriction, including
	* without limitation the rights to use, copy, modify, merge, publish,
	* distribute, sub license, and/or sell copies of the Software, and to
	* permit persons to whom the Software is furnished to do so, subject to
	* the following conditions:
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
	* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	* NON-INFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS, AUTHORS
	* AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
	* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
	* USE OR OTHER DEALINGS IN THE SOFTWARE.
	*
	* The above copyright notice and this permission notice (including the
	* next paragraph) shall be included in all copies or substantial portions
	* of the Software.
	*/

	#include "u_queue.h"
	#include "util/u_string.h"

	static void util_queue_killall_and_wait(struct util_queue *queue);

	/****************************************************************************
	* Wait for all queues to assert idle when exit() is called.
	*
	* Otherwise, C++ static variable destructors can be called while threads
	* are using the static variables.
	*/

	static once_flag atexit_once_flag = ONCE_FLAG_INIT;
	static struct list_head queue_list;
	static mtx_t exit_mutex = _MTX_INITIALIZER_NP;

	static void
	atexit_handler(void)
	{
	struct util_queue *iter;

	mtx_lock(&exit_mutex);
	/* Wait for all queues to assert idle. */
	LIST_FOR_EACH_ENTRY(iter, &queue_list, head) {
	util_queue_killall_and_wait(iter);
	}
	mtx_unlock(&exit_mutex);
	}

	static void
	global_init(void)
	{
	LIST_INITHEAD(&queue_list);
	atexit(atexit_handler);
	}

	static void
	add_to_atexit_list(struct util_queue *queue)
	{
	call_once(&atexit_once_flag, global_init);

	mtx_lock(&exit_mutex);
	LIST_ADD(&queue->head, &queue_list);
	mtx_unlock(&exit_mutex);
	}

	static void
	remove_from_atexit_list(struct util_queue *queue)
	{
	struct util_queue iter, tmp;

	mtx_lock(&exit_mutex);
	LIST_FOR_EACH_ENTRY_SAFE(iter, tmp, &queue_list, head) {
	if (iter == queue) {
	LIST_DEL(&iter->head);
	break;
	}
	}
	mtx_unlock(&exit_mutex);
	}

	/****************************************************************************
	* util_queue_fence
	*/

	static void
	util_queue_fence_signal(struct util_queue_fence *fence)
	{
	mtx_lock(&fence->mutex);
	fence->signalled = true;
	cnd_broadcast(&fence->cond);
	mtx_unlock(&fence->mutex);
	}

	void
	util_queue_fence_wait(struct util_queue_fence *fence)
	{
	mtx_lock(&fence->mutex);
	while (!fence->signalled)
	cnd_wait(&fence->cond, &fence->mutex);
	mtx_unlock(&fence->mutex);
	}

	void
	util_queue_fence_init(struct util_queue_fence *fence)
	{
	memset(fence, 0, sizeof(*fence));
	(void) mtx_init(&fence->mutex, mtx_plain);
	cnd_init(&fence->cond);
	fence->signalled = true;
	}

	void
	util_queue_fence_destroy(struct util_queue_fence *fence)
	{
	assert(fence->signalled);

	/* Ensure that another thread is not in the middle of
	* util_queue_fence_signal (having set the fence to signalled but still
	* holding the fence mutex).
	*
	* A common contract between threads is that as soon as a fence is signalled
	* by thread A, thread B is allowed to destroy it. Since
	* util_queue_fence_is_signalled does not lock the fence mutex (for
	* performance reasons), we must do so here.
	*/
	mtx_lock(&fence->mutex);
	mtx_unlock(&fence->mutex);

	cnd_destroy(&fence->cond);
	mtx_destroy(&fence->mutex);
	}

	/****************************************************************************
	* util_queue implementation
	*/

	struct thread_input {
	struct util_queue *queue;
	int thread_index;
	};

	static int
	util_queue_thread_func(void *input)
	{
	struct util_queue queue = ((struct thread_input)input)->queue;
	int thread_index = ((struct thread_input*)input)->thread_index;

	free(input);

	if (queue->name) {
	char name[16];
	util_snprintf(name, sizeof(name), "%s:%i", queue->name, thread_index);
	u_thread_setname(name);
	}

	while (1) {
	struct util_queue_job job;

	mtx_lock(&queue->lock);
	assert(queue->num_queued >= 0 && queue->num_queued <= queue->max_jobs);

	/* wait if the queue is empty */
	while (!queue->kill_threads && queue->num_queued == 0)
	cnd_wait(&queue->has_queued_cond, &queue->lock);

	if (queue->kill_threads) {
	mtx_unlock(&queue->lock);
	break;
	}

	job = queue->jobs[queue->read_idx];
	memset(&queue->jobs[queue->read_idx], 0, sizeof(struct util_queue_job));
	queue->read_idx = (queue->read_idx + 1) % queue->max_jobs;

	queue->num_queued--;
	cnd_signal(&queue->has_space_cond);
	mtx_unlock(&queue->lock);

	if (job.job) {
	job.execute(job.job, thread_index);
	util_queue_fence_signal(job.fence);
	if (job.cleanup)
	job.cleanup(job.job, thread_index);
	}
	}

	/* signal remaining jobs before terminating */
	mtx_lock(&queue->lock);
	for (unsigned i = queue->read_idx; i != queue->write_idx;
	i = (i + 1) % queue->max_jobs) {
	if (queue->jobs[i].job) {
	util_queue_fence_signal(queue->jobs[i].fence);
	queue->jobs[i].job = NULL;
	}
	}
	queue->read_idx = queue->write_idx;
	queue->num_queued = 0;
	mtx_unlock(&queue->lock);
	return 0;
	}

	bool
	util_queue_init(struct util_queue *queue,
	const char *name,
	unsigned max_jobs,
	unsigned num_threads,
	unsigned flags)
	{
	unsigned i;

	memset(queue, 0, sizeof(*queue));
	queue->name = name;
	queue->flags = flags;
	queue->num_threads = num_threads;
	queue->max_jobs = max_jobs;

	queue->jobs = (struct util_queue_job*)
	calloc(max_jobs, sizeof(struct util_queue_job));
	if (!queue->jobs)
	goto fail;

	(void) mtx_init(&queue->lock, mtx_plain);

	queue->num_queued = 0;
	cnd_init(&queue->has_queued_cond);
	cnd_init(&queue->has_space_cond);

	queue->threads = (thrd_t*) calloc(num_threads, sizeof(thrd_t));
	if (!queue->threads)
	goto fail;

	/* start threads */
	for (i = 0; i < num_threads; i++) {
	struct thread_input *input =
	(struct thread_input *) malloc(sizeof(struct thread_input));
	input->queue = queue;
	input->thread_index = i;

	queue->threads[i] = u_thread_create(util_queue_thread_func, input);

	if (!queue->threads[i]) {
	free(input);

	if (i == 0) {
	/* no threads created, fail */
	goto fail;
	} else {
	/* at least one thread created, so use it */
	queue->num_threads = i;
	break;
	}
	}

	if (flags & UTIL_QUEUE_INIT_USE_MINIMUM_PRIORITY) {
	#if defined(__linux__) && defined(SCHED_IDLE)
	struct sched_param sched_param = {0};

	/* The nice() function can only set a maximum of 19.
	* SCHED_IDLE is the same as nice = 20.
	*
	* Note that Linux only allows decreasing the priority. The original
	* priority can't be restored.
	*/
	pthread_setschedparam(queue->threads[i], SCHED_IDLE, &sched_param);
	#endif
	}
	}

	add_to_atexit_list(queue);
	return true;

	fail:
	free(queue->threads);

	if (queue->jobs) {
	cnd_destroy(&queue->has_space_cond);
	cnd_destroy(&queue->has_queued_cond);
	mtx_destroy(&queue->lock);
	free(queue->jobs);
	}
	/* also util_queue_is_initialized can be used to check for success */
	memset(queue, 0, sizeof(*queue));
	return false;
	}

	static void
	util_queue_killall_and_wait(struct util_queue *queue)
	{
	unsigned i;

	/* Signal all threads to terminate. */
	mtx_lock(&queue->lock);
	queue->kill_threads = 1;
	cnd_broadcast(&queue->has_queued_cond);
	mtx_unlock(&queue->lock);

	for (i = 0; i < queue->num_threads; i++)
	thrd_join(queue->threads[i], NULL);
	queue->num_threads = 0;
	}

	void
	util_queue_destroy(struct util_queue *queue)
	{
	util_queue_killall_and_wait(queue);
	remove_from_atexit_list(queue);

	cnd_destroy(&queue->has_space_cond);
	cnd_destroy(&queue->has_queued_cond);
	mtx_destroy(&queue->lock);
	free(queue->jobs);
	free(queue->threads);
	}

	void
	util_queue_add_job(struct util_queue *queue,
	void *job,
	struct util_queue_fence *fence,
	util_queue_execute_func execute,
	util_queue_execute_func cleanup)
	{
	struct util_queue_job *ptr;

	assert(fence->signalled);

	mtx_lock(&queue->lock);
	if (queue->kill_threads) {
	mtx_unlock(&queue->lock);
	/* well no good option here, but any leaks will be
	* short-lived as things are shutting down..
	*/
	return;
	}

	fence->signalled = false;

	assert(queue->num_queued >= 0 && queue->num_queued <= queue->max_jobs);

	if (queue->num_queued == queue->max_jobs) {
	if (queue->flags & UTIL_QUEUE_INIT_RESIZE_IF_FULL) {
	/* If the queue is full, make it larger to avoid waiting for a free
	* slot.
	*/
	unsigned new_max_jobs = queue->max_jobs + 8;
	struct util_queue_job *jobs =
	(struct util_queue_job*)calloc(new_max_jobs,
	sizeof(struct util_queue_job));
	assert(jobs);

	/* Copy all queued jobs into the new list. */
	unsigned num_jobs = 0;
	unsigned i = queue->read_idx;

	do {
	jobs[num_jobs++] = queue->jobs[i];
	i = (i + 1) % queue->max_jobs;
	} while (i != queue->write_idx);

	assert(num_jobs == queue->num_queued);

	free(queue->jobs);
	queue->jobs = jobs;
	queue->read_idx = 0;
	queue->write_idx = num_jobs;
	queue->max_jobs = new_max_jobs;
	} else {
	/* Wait until there is a free slot. */
	while (queue->num_queued == queue->max_jobs)
	cnd_wait(&queue->has_space_cond, &queue->lock);
	}
	}

	ptr = &queue->jobs[queue->write_idx];
	assert(ptr->job == NULL);
	ptr->job = job;
	ptr->fence = fence;
	ptr->execute = execute;
	ptr->cleanup = cleanup;
	queue->write_idx = (queue->write_idx + 1) % queue->max_jobs;

	queue->num_queued++;
	cnd_signal(&queue->has_queued_cond);
	mtx_unlock(&queue->lock);
	}

	/**
	* Remove a queued job. If the job hasn't started execution, it's removed from
	* the queue. If the job has started execution, the function waits for it to
	* complete.
	*
	* In all cases, the fence is signalled when the function returns.
	*
	* The function can be used when destroying an object associated with the job
	* when you don't care about the job completion state.
	*/
	void
	util_queue_drop_job(struct util_queue queue, struct util_queue_fence fence)
	{
	bool removed = false;

	if (util_queue_fence_is_signalled(fence))
	return;

	mtx_lock(&queue->lock);
	for (unsigned i = queue->read_idx; i != queue->write_idx;
	i = (i + 1) % queue->max_jobs) {
	if (queue->jobs[i].fence == fence) {
	if (queue->jobs[i].cleanup)
	queue->jobs[i].cleanup(queue->jobs[i].job, -1);

	/* Just clear it. The threads will treat as a no-op job. */
	memset(&queue->jobs[i], 0, sizeof(queue->jobs[i]));
	removed = true;
	break;
	}
	}
	mtx_unlock(&queue->lock);

	if (removed)
	util_queue_fence_signal(fence);
	else
	util_queue_fence_wait(fence);
	}

	int64_t
	util_queue_get_thread_time_nano(struct util_queue *queue, unsigned thread_index)
	{
	/* Allow some flexibility by not raising an error. */
	if (thread_index >= queue->num_threads)
	return 0;

	return u_thread_get_time_nano(queue->threads[thread_index]);
	}