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Re: Serious problem with multithreaded I/O on Linux
Tom Tromey wrote:
> Bryce> Why are blocking IO calls not gc-safe, anyway?
>
> I don't think it wants to block all the threads (though I could be
> wrong as I haven't dug through all that code yet). Instead I believe
> it is changing the protection on the page so that the read() works.
> In incremental mode the Boehm GC write-protects pages to implement a
> write barrier.
Note that this only affects ports based on MPROTECT_VDB, such as
Linux/i386, FreeBSD and Irix. The Solaris port uses /proc to track
dirty pages.
I simply commented out "#define MPROTECT_VDB" at line 593 in
boehm-gc/config.h. Suddenly, my multithreaded tests run very well!
This ought to be filed as a GC bug, since incremental mode is
incompatible with pthreads, at least on Linux.
--
Jeff Sturm
jsturm@sigma6.com