On Jul 17 12:51, Jon Turney wrote: > On 14/07/2023 14:04, Jon Turney wrote: > > On 13/07/2023 19:53, Corinna Vinschen wrote: > > > > > > normally after 10 seconds. (See the commentary in pthread::cancel() > > > > > > in > > > > > > thread.cc, where it checks if the target thread is inside the > > > > > > kernel, > > > > > > and silently converts the cancellation into a deferred one) > > > > > > > > > > Nevertheless, I think this is ok to do. The description of > > > > > pthread_cancel > > > > > contains this: > > > > > > > > > > Asynchronous cancelability means that the thread can be canceled at > > > > > any time (usually immediately, but the system does not > > > > > guarantee this). > > > > > > > > > > And > > > > > > > > > > The above steps happen asynchronously with respect to the > > > > > pthread_cancel() call; the return status of pthread_cancel() merely > > > > > informs the caller whether the cancellation request was > > > > > successfully > > > > > queued. > > > > > > > > > > So any assumption *when* the cancallation takes place is may be wrong. > > > > Yeah. > > > > I think the flakiness is when we happen to try to async cancel while in > > the Windows kernel, which implicitly converts to a deferred > > cancellation, but there are no cancellation points in the the thread, so > > it arrives at pthread_exit() and returns a exit code other than > > PTHREAD_CANCELED. > > > > I did consider making the test non-flaky by adding a final call to > > pthread_testcancel(), to notice any failed async cancellation which has > > been converted to a deferred one. > > > > But then that is just the same as the deferred cancellation tests, and > > confirms the cancellation happens, but not that it's async, which is > > part of the point of the test. > > > > I guess this could also check that not all of the threads ran for all 10 > > seconds, which would indicate that at least some of them were cancelled > > asynchronously. > > I wrote this, attached, which does indeed make this test more reliable. > > You point is well made that this is making assumptions about how quickly > async cancellation works that are not required by the standard > > (It would be a valid, if strange implementation, if async cancellation > always took 10 seconds to take effect, which this test assumes isn't the > case) > > Perhaps there is a better way to write a test that async cancellation works > in the absence of cancellation points, but it eludes me...
Same here, so just go ahead. Thanks, Corinna
