Date: Fri, 27 Apr 2012 18:40:16 -0700 From: Matt Birkholz <m...@birkholz.chandler.az.us>
... and let's get concrete with the existing thread-event mechanism. Please don't. It's extremely hard to engineer anything reliably with it. Any discussion of SIGNAL-THREAD-EVENT that doesn't involve blocking and unblocking thread events, race conditions, atomicity and data structure invariants, &c., is a recipe for disaster. We need to get rid of it except, at most, as a debugging operation and as an internal mechanism for implementing more principled abstractions. One example of a more principled abstraction is Scheme-CML, based on Concurrent ML: http://mumble.net/~campbell/darcs/scheme-cml/ We also need a better story about interruption, perhaps like Racket's breaks, but not as the basic mechanism for thread communication. > [...] Imagine if you couldn't safely do debug prints from a worker thread! I can only imagine doing it safely if the debug-print procedure grabs the port/mutex for the duration of the message output (write-line?) process. It doesn't help for the debug-printing routine to grab a mutex if nobody else is cooperating with it. And if you're desperately chasing down a thread synchronization problem with debug-prints, there's a good chance someone has forgotten to cooperate. A write-line made up of tiny atomic write-chars is no more "safe" except for the precious buffer pointers. I would call them a costly set of suspenders IF they kept the pants from falling down. Thread-safe and child-proof are marketing terms. Interleaving output is one thing. Crashing because of corrupted internal data structures is quite another. > MIT Scheme has some particularly bad failure modes when you rub its > sockets the wrong way from multiple threads, i.e. producing an > infinite explosion of interrupt-triggered errors that surfaces on > socket close, well after the offending code has run, and almost > un-debuggable because all you can interact through is the interrupt > menu. The only way I figured that one out is by asking Taylor to > tell me what I did wrong. :P Fascinating (as my hero would say, without a trace of sarcasm). What did you do wrong? One easy way is to close a channel that someone's waiting to do I/O on. _______________________________________________ MIT-Scheme-devel mailing list MIT-Scheme-devel@gnu.org https://lists.gnu.org/mailman/listinfo/mit-scheme-devel
