Fix UB in cancelled tasks again #579
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As reported in #577, #578 didn't fix the UB in cancelled tasks. There were two bugs in that "fix": 1. we were writing the coroutine handle to resume *after* synchronizing between the two racing operation states, leading to a data race when the deferred stop source completed second; and 2. it's wrong to call `continuation_.done()` to store the coroutine handle to be resumed later because `done()` completes the operation with `set_done()` as a side effect. This diff fixes both issues. Instead of storing a coroutine handle to be resumed, we store an enum value that describes which coroutine handle to resume (so we don't eagerly invoke `done()`), and we do the store before synchronizing to eliminate the data race. I've added a unit test that fails with a TSAN-detected data race without the fix, and the fix silences the TSAN error. I also clang-formatted `task.hpp` and the modified test file.
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@glebov-andrey, do you want to patch this in and see if it fixes your issue? |
janondrusek
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Oct 27, 2023
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Looks good, thanks! |
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As reported in #577, #578 didn't fix the UB in cancelled tasks. There were two bugs in that "fix":
continuation_.done()to store the coroutine handle to be resumed later becausedone()completes the operation withset_done()as a side effect.This diff fixes both issues. Instead of storing a coroutine handle to be resumed, we store an enum value that describes which coroutine handle to resume (so we don't eagerly invoke
done()), and we do the store before synchronizing to eliminate the data race.I've added a unit test that fails with a TSAN-detected data race without the fix, and the fix silences the TSAN error.
I also clang-formatted
task.hppand the modified test file.