[Bug-apl] Parallel progress

[Juergen Sauermann]

Hi,

there are some good news from the parallel front. I have replaced
the semaphores that control the fork() and join() off threads by a new,
busy-wait based, mechanism.

That has reduced the fork() and join() times considerably: from the 20,000 cycle ballpark to
less than 1000 cycles (the numbers still vary a lot due to caching). As a consequence, the
break-even point (where parallel is faster than sequential) for e.g. Z←A+B has dropped from
⍴,Z of some 1000s to some 50s.

I will now start to integrate the Parallel.cc prototype (see attachment) into GNU APL...

/// Jürgen

Parallel.cc
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plot_4
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Makefile
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