#8684: hWaitForInput cannot be interrupted by async exceptions on unix -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: 13497, 13525 | Blocking: Related Tickets: #12912, #13525 | Differential Rev(s): Phab:D42 Wiki Page: | -------------------------------------+------------------------------------- Comment (by nh2): Some more trouble on Windows (also for `-threaded`): If the FD is a [https://github.com/ghc/ghc/blob/ghc-8.2.1-release/libraries/base/cbits/input... FILE_TYPE_CHAR], then the implementation of `ccall interruptible` ([https://downloads.haskell.org/~ghc/8.2.1/docs/html/users_guide/ffi- chap.html#interruptible-foreign-calls see here]) via `CancelSynchronousIo` doesn't seem to kill the [https://github.com/nh2/ghc/blob/bug-8684 -interruptible-hWaitForInput/libraries/base/cbits/inputReady.c#L306 WaitForSingleObject()] invocation. Unfortunately, the call to [https://github.com/ghc/ghc/blob/ghc-8.2.1-release/rts/win32/OSThreads.c#L569 CancelSynchronousIo(), here named pCSIO()], does not actually check the return value of [https://msdn.microsoft.com/en- us/library/windows/desktop/aa363794(v=vs.85).aspx the function], which returns a `BOOL success`.
If this function cannot find a request to cancel, the return value is 0 (zero), and `GetLastError` returns `ERROR_NOT_FOUND`.
In my case, when logging it, I see it returns error code 1168, which is `ERROR_NOT_FOUND`, so apparently nothing was cancelled. As a result, my example program from the issue description runs for 5 seconds instead of one. With a bit more instrumentation, I get this: {{{ fdReady called with msecs = 5000 calling WaitForSingleObject calling pCSIO pCSIO ret 0 pCSIO error: 1168 WaitForSingleObject rc 258 (WAIT_TIMEOUT) }}} After 1 second, as expected, it's `calling pCSIO`, but it doesn't cancel anything due to the error, so after 5 seconds `WaitForSingleObject rc 258 (WAIT_TIMEOUT)` happens. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8684#comment:25 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler