Support Alpha architecture for processor_count #549
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Alpha machines with Linux do have /proc/cpuinfo but its format is different from normal Linux machines, and most specifically the processor entry is missing. Moreover, Alpha machines can be configured to compartimentalize their CPUs into different machines leading to further confusion when reading /proc/cpuinfo. Using /usr/bin/nproc seems to be the most reliable method of determining the number of processors on Alpha. Since reading /proc/cpuinfo is not reliable this patch places the nproc method before trying /proc/cpuinfo. For futher reference see our downstream bug report at https://bugs.gentoo.org/show_bug.cgi?id=587986
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graaff
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Nov 7, 2016
This re-orders the checks for the processor count so that forking is only done when needed. alpha-linux does not support the processor entry in /proc/cpuinfo so we must catch that case and fall back to using nproc which does work on alpha. This is a rework of ruby-concurrency#549 based on suggestions made in ruby-concurrency#576
pitr-ch
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Nov 10, 2016
This re-orders the checks for the processor count so that forking is only done when needed. alpha-linux does not support the processor entry in /proc/cpuinfo so we must catch that case and fall back to using nproc which does work on alpha. This is a rework of ruby-concurrency#549 based on suggestions made in ruby-concurrency#576
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Alpha machines with Linux do have /proc/cpuinfo but its format is
different from normal Linux machines, and most specifically the
processor entry is missing. Moreover, Alpha machines can be configured
to compartimentalize their CPUs into different machines leading to
further confusion when reading /proc/cpuinfo.
Using /usr/bin/nproc seems to be the most reliable method of determining
the number of processors on Alpha. Since reading /proc/cpuinfo is not
reliable this patch places the nproc method before trying /proc/cpuinfo.
For futher reference see our downstream bug report at
https://bugs.gentoo.org/show_bug.cgi?id=587986
I expect the choice of putting the nproc rule before /proc/cpuinfo may be controversial if only for the "start process" performance penalty on Linux, but given that /proc/cpuinfo returns "0" on alpha machines I didn't see another option apart from doing more rewriting.
Things that came to mind where to special-case alpha in a way similar to mingw/mswin, or to rewrite the /proc/cpuinfo check in a what tihat includes the check for /^processor/, or to rewrite the elsif mechanism to a set of separate if statements that continue as long as tentative_count = nil.
If you have preferences for any of these let me know and I can look at rewriting the PR.