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.
We still need several refactors to improve the current VVC decoder's performance,
which will frequently break the API/ABI. To mitigate this, we've copied the executor from
avutil to avcodec. Once the API/ABI is stable, we will move this class back to avutil
Before the patch, disable threads support at configure/build time
was the only method to force zero thread in executor. However,
it's common practice for libavcodec to run on caller's thread when
user specify thread number to one. And for WASM environment, whether
threads are supported needs to be detected at runtime. So executor
should support zero thread at runtime.
A single thread executor can be useful, e.g., to handle network
protocol. So we can't take thread_count one as zero thread, which
disabled a valid usercase.
Other libraries take -threads 0 to mean auto. Executor as a low
level utils doesn't do cpu detect. So take thread_count zero as
zero thread, literally.
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
Nuo Mi
Zhao Zhili