Hi, On 2020-06-23 21:50:26 -0400, Chapman Flack wrote: > On 06/23/20 21:44, Andres Freund wrote: > > > I think that's way harder than what you make it sound here. The locking > > for shm_mq doesn't really work inside a process. In contrast to the > > single threaded case something like a volatile write to > > ParallelMessagePending doesn't guarantee much, because there's no > > guaranteed memory ordering between threads. And more. > > It occurred to me after I sent the message this morning that my suggestion > (2) could subsume (1). And requires nothing more than a single volatile > write of a boolean, and getting called back at a convenient time on the > single main thread.
A single volatile write wouldn't guarantee you much in the presence of multiple threads. You could very well end up with a concurrent CHECK_FOR_INTERRUPTS() in the main thread unsetting InterruptPending, but not yet seeing / processing ParallelMessagePending. Nor would it wake up the main process if it's currently waiting on a latch. Greetings, Andres Freund
