[Mesa-dev] [PATCH 4/7] util/queue: add ability to kill a subset of threads

[Marek Olšák]

From: Marek Olšák <marek.olsak at amd.com>

for ARB_parallel_shader_compile
---
 src/util/u_queue.c | 52 ++++++++++++++++++++++++++++++----------------
 src/util/u_queue.h |  5 ++---
 2 files changed, 36 insertions(+), 21 deletions(-)

diff --git a/src/util/u_queue.c b/src/util/u_queue.c
index 48c5c79552d..cfd2a08e3c8 100644
--- a/src/util/u_queue.c
+++ b/src/util/u_queue.c
@@ -26,42 +26,43 @@
 
 #include "u_queue.h"
 
 #include <time.h>
 
 #include "util/os_time.h"
 #include "util/u_string.h"
 #include "util/u_thread.h"
 #include "u_process.h"
 
-static void util_queue_killall_and_wait(struct util_queue *queue);
+static void
+util_queue_kill_threads(struct util_queue *queue, unsigned keep_num_threads);
 
 /****************************************************************************
  * 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);
+      util_queue_kill_threads(iter, 0);
    }
    mtx_unlock(&exit_mutex);
 }
 
 static void
 global_init(void)
 {
    LIST_INITHEAD(&queue_list);
    atexit(atexit_handler);
 }
@@ -259,55 +260,58 @@ util_queue_thread_func(void *input)
       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)
+      while (thread_index < queue->num_threads && queue->num_queued == 0)
          cnd_wait(&queue->has_queued_cond, &queue->lock);
 
-      if (queue->kill_threads) {
+      /* only kill threads that are above "num_threads" */
+      if (thread_index >= queue->num_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 */
+   /* signal remaining jobs if all threads are being terminated */
    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;
+   if (queue->num_threads == 0) {
+      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;
    }
-   queue->read_idx = queue->write_idx;
-   queue->num_queued = 0;
    mtx_unlock(&queue->lock);
    return 0;
 }
 
 static bool
 util_queue_create_thread(struct util_queue *queue, unsigned index)
 {
    struct thread_input *input =
       (struct thread_input *) malloc(sizeof(struct thread_input));
    input->queue = queue;
@@ -418,60 +422,72 @@ fail:
       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)
+util_queue_kill_threads(struct util_queue *queue, unsigned keep_num_threads)
 {
    unsigned i;
 
    /* Signal all threads to terminate. */
+   mtx_lock(&queue->finish_lock);
+
+   if (keep_num_threads >= queue->num_threads) {
+      mtx_unlock(&queue->finish_lock);
+      return;
+   }
+
    mtx_lock(&queue->lock);
-   queue->kill_threads = 1;
+   unsigned old_num_threads = queue->num_threads;
+   /* Setting num_threads is what causes the threads to terminate.
+    * Then cnd_broadcast wakes them up and they will exit their function.
+    */
+   queue->num_threads = keep_num_threads;
    cnd_broadcast(&queue->has_queued_cond);
    mtx_unlock(&queue->lock);
 
-   for (i = 0; i < queue->num_threads; i++)
+   for (i = keep_num_threads; i < old_num_threads; i++)
       thrd_join(queue->threads[i], NULL);
-   queue->num_threads = 0;
+
+   mtx_unlock(&queue->finish_lock);
 }
 
 void
 util_queue_destroy(struct util_queue *queue)
 {
-   util_queue_killall_and_wait(queue);
+   util_queue_kill_threads(queue, 0);
    remove_from_atexit_list(queue);
 
    cnd_destroy(&queue->has_space_cond);
    cnd_destroy(&queue->has_queued_cond);
    mtx_destroy(&queue->finish_lock);
    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;
 
    mtx_lock(&queue->lock);
-   if (queue->kill_threads) {
+   if (queue->num_threads == 0) {
       mtx_unlock(&queue->lock);
       /* well no good option here, but any leaks will be
        * short-lived as things are shutting down..
        */
       return;
    }
 
    util_queue_fence_reset(fence);
 
    assert(queue->num_queued >= 0 && queue->num_queued <= queue->max_jobs);
diff --git a/src/util/u_queue.h b/src/util/u_queue.h
index 4e63a76aab2..756fa53e1bf 100644
--- a/src/util/u_queue.h
+++ b/src/util/u_queue.h
@@ -194,29 +194,28 @@ typedef void (*util_queue_execute_func)(void *job, int thread_index);
 struct util_queue_job {
    void *job;
    struct util_queue_fence *fence;
    util_queue_execute_func execute;
    util_queue_execute_func cleanup;
 };
 
 /* Put this into your context. */
 struct util_queue {
    char name[14]; /* 13 characters = the thread name without the index */
-   mtx_t finish_lock; /* only for util_queue_finish */
+   mtx_t finish_lock; /* for util_queue_finish and protects threads/num_threads */
    mtx_t lock;
    cnd_t has_queued_cond;
    cnd_t has_space_cond;
    thrd_t *threads;
    unsigned flags;
    int num_queued;
-   unsigned num_threads;
-   int kill_threads;
+   unsigned num_threads; /* decreasing this number will terminate threads */
    int max_jobs;
    int write_idx, read_idx; /* ring buffer pointers */
    struct util_queue_job *jobs;
 
    /* for cleanup at exit(), protected by exit_mutex */
    struct list_head head;
 };
 
 bool util_queue_init(struct util_queue *queue,
                      const char *name,
-- 
2.17.1