Weston Pace created ARROW-16498:
-----------------------------------
Summary: [C++] Fix potential deadlock in
arrow::compute::TaskScheduler
Key: ARROW-16498
URL: https://issues.apache.org/jira/browse/ARROW-16498
Project: Apache Arrow
Issue Type: Bug
Components: C++
Reporter: Weston Pace
An extremely simplified version of the task scheduler's ScheduleMore method it
looks something like:
{noformat}
void ScheduleMore(int num_to_schedule) {
tasks_that_need_running_.fetch_add(num_to_schedule);
if (!weak_lock.lock()) {
// If someone else is scheduling then return early
return;
}
auto tasks = PickTasks();
weak_lock.unlock();
}
{noformat}
It is possible for one thread to have the lock, and find 0 tasks. But then,
before it gives up the lock, another thread adds tasks and fails to acquire the
lock. Neither thread will schedule anything even though there are tasks to
run. This can lead to deadlock.
The proposed PR changes the logic to (still extremely simplified):
{noformat}
void ScheduleMore(int num_to_schedule) {
tasks_that_need_running_.fetch_add(num_to_schedule);
tasks_added_recently.store(true);
if (!weak_lock.lock()) {
// If someone else is scheduling then return early
return;
}
auto tasks = PickTasks();
if (tasks_added_recently.compare_exchange_strong(true, false)) {
if (tasks.empty()) {
ScheduleMore();
}
}
weak_lock.unlock();
}
{noformat}
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