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For that matter, we can just provide Thread.ForkAll.<BR>
special implementation on pthreads.<BR>
Just call Unix.fork() on user threads.<BR>
No implementation for Win32.<BR>
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- Jay<BR>
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From: jay.krell@cornell.edu<BR>To: wagner@elegosoft.com; m3devel@elegosoft.com<BR>Date: Wed, 17 Mar 2010 11:02:02 +0000<BR>Subject: Re: [M3devel] cvsup<BR><BR>
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Another good option might be<BR>"RecreateThreadsAfterFork()"<BR> <BR>that cvsup can call. I'm trying that.<BR>If that doesn't work, I'll track down all of cvsup's thread creates.<BR> <BR> - Jay<BR> <BR>
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From: jay.krell@cornell.edu<BR>To: wagner@elegosoft.com; m3devel@elegosoft.com<BR>Date: Wed, 17 Mar 2010 10:50:31 +0000<BR>Subject: Re: [M3devel] cvsup<BR><BR>
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Here's a shorter more direct version.<BR><BR><BR>Please start here:<BR><A href="http://www.opengroup.org/onlinepubs/009695399/functions/pthread_atfork.html">http://www.opengroup.org/onlinepubs/009695399/functions/pthread_atfork.html</A><BR> "There are at least two serious problems with the semantics of <A href="http://www.opengroup.org/onlinepubs/009695399/functions/fork.html"><I>fork</I>()</A> in a multi-threaded program"<BR><BR> <BR>I have a good theory as to the problem and the fix.<BR> <BR> <BR>Problem:<BR> <BR>With user threads, when you fork(), all the threads keep running in the new child.<BR> Because the data that causes them to exist is carried forward.<BR> <BR> <BR>With kernel threads, they don't, just the caller of fork().<BR> <BR> <BR>Fix:<BR> A few small uses of pthread_atfork both in m3core and cvsup.<BR> Abstracted behind Thread.PThreadAtFork that does nothing for user threads and Win32.<BR> They would do things like "reinitialize globals" and "recreate worker threads".<BR> <BR> <BR>You can't just call all the module initializers over.<BR>That would ultimately I believe reset too much data.<BR> ?<BR> <BR> <BR>It might be possible, though, to setjmp, run the module initializers, longjmp.<BR>Something like, perhaps, a flag to RTLinker.InitRuntime that causes it to<BR>longjmp instead of calling main. However this would still e.g. give the initial thread<BR>the wrong stackbase and mess up garbage collection.<BR> <BR> <BR>I'm much more keen on selective use of pthread_atfork, in m3core and cvsup.<BR> <BR> <BR>A more conventional approach is the program to rerun itself with some flags<BR>that "push" it fast to "resume" point, but that somewhat defeats the<BR>purpose of the fork + do work model -- cheap reuse of already established state.<BR> <BR> <BR>Lingering problem:<BR> Any libraries that create worker threads need to use Thread.PThreadAtFork in order to be compatible with the fork + do more work pattern.<BR> <BR> <BR>fork + exec is fine.<BR> <BR> <BR> - Jay<BR> </body>
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