Due to the nature of multithreading, using a "ready check" mechanism may
introduce a deadlock. For example:
Suppose all tasks have been submitted to the executor, and the last thread
checks the entire list and finds
no ready tasks. It then goes to sleep, waiting for a new task. However, for
some multithreading-related reason,
a task becomes ready after the check. Since no other thread is aware of this
and no new tasks are being added to
the executor, a deadlock occurs.
In VVC, this function is unnecessary because we use a scoreboard. All tasks
submitted to the executor are ready tasks.
---
libavcodec/vvc/thread.c | 8 --------
libavutil/executor.c | 6 ++----
libavutil/executor.h | 3 ---
3 files changed, 2 insertions(+), 15 deletions(-)
diff --git a/libavcodec/vvc/thread.c b/libavcodec/vvc/thread.c
index 86a7753c6a..6208cc1811 100644
--- a/libavcodec/vvc/thread.c
+++ b/libavcodec/vvc/thread.c
@@ -372,13 +372,6 @@ static int task_is_stage_ready(VVCTask *t, int add)
return task_has_target_score(t, stage, score);
}
-static int task_ready(const AVTask *_t, void *user_data)
-{
- VVCTask *t = (VVCTask*)_t;
-
- return task_is_stage_ready(t, 0);
-}
-
#define CHECK(a, b) \
do { \
if ((a) != (b)) \
@@ -689,7 +682,6 @@ AVExecutor* ff_vvc_executor_alloc(VVCContext *s, const int
thread_count)
s,
sizeof(VVCLocalContext),
task_priority_higher,
- task_ready,
task_run,
};
return av_executor_alloc(&callbacks, thread_count);
diff --git a/libavutil/executor.c b/libavutil/executor.c
index bfce2ac444..64e6cc0775 100644
--- a/libavutil/executor.c
+++ b/libavutil/executor.c
@@ -79,10 +79,8 @@ static void add_task(AVTask **prev, AVTask *t)
static int run_one_task(AVExecutor *e, void *lc)
{
AVTaskCallbacks *cb = &e->cb;
- AVTask **prev;
+ AVTask **prev = &e->tasks;
- for (prev = &e->tasks; *prev && !cb->ready(*prev, cb->user_data); prev =
&(*prev)->next)
- /* nothing */;
if (*prev) {
AVTask *t = remove_task(prev, *prev);
if (e->thread_count > 0)
@@ -143,7 +141,7 @@ AVExecutor* av_executor_alloc(const AVTaskCallbacks *cb,
int thread_count)
{
AVExecutor *e;
int has_lock = 0, has_cond = 0;
- if (!cb || !cb->user_data || !cb->ready || !cb->run ||
!cb->priority_higher)
+ if (!cb || !cb->user_data || !cb->run || !cb->priority_higher)
return NULL;
e = av_mallocz(sizeof(*e));
diff --git a/libavutil/executor.h b/libavutil/executor.h
index 0eb21c10c8..7af53c92ce 100644
--- a/libavutil/executor.h
+++ b/libavutil/executor.h
@@ -36,9 +36,6 @@ typedef struct AVTaskCallbacks {
// return 1 if a's priority > b's priority
int (*priority_higher)(const AVTask *a, const AVTask *b);
- // task is ready for run
- int (*ready)(const AVTask *t, void *user_data);
-
// run the task
int (*run)(AVTask *t, void *local_context, void *user_data);
} AVTaskCallbacks;
--
2.34.1
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