westonpace commented on PR #13091:
URL: https://github.com/apache/arrow/pull/13091#issuecomment-1120093156
CC @michalursa
`TaskScheduler, StressTwo` should reproduce this but it can still be a bit
of a pain on a fast system. Added a print statement between:
```
const auto& tasks = PickTasks(num_new_tasks);
```
and
```
if (static_cast<int>(tasks.size()) < num_new_tasks) {
```
adds enough of a delay to trigger this fairly reliably (you will also have
to comment out the fix).
This fix should be a pretty light-touch but it does add one compare_and_swap
in the `ScheduleMore` method. Another potential fix would be to turn the
following lock into a full on spinlock:
```
for (;;) {
int expected = num_tasks_to_schedule_.value.load();
if (num_tasks_to_schedule_.value.compare_exchange_strong(expected, 0)) {
num_new_tasks += expected;
break;
}
}
```
changing it to:
```
for (;;) {
int expected = num_tasks_to_schedule_.value.load();
if (expected == 0) {
continue;
}
if (num_tasks_to_schedule_.value.compare_exchange_strong(expected, 0)) {
num_new_tasks += expected;
break;
}
}
```
Let me know if you want to try anything different.
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