Then your rule of thumb is wrong. "Only require the unsafe modules you need in child threads" doesn't make sense. Requiring a module in one thread loads it for the entire process. Perhaps you misstated what you meant?

Or not: 

$ cat Mod.pm
package Mod;
print __PACKAGE__, "\n";
1;

$ perl -Mthreads -e'my @t = map { async { require Mod; }; } 1..2; $_->
+join() for @t;'
Mod
Mod

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In reply to Re^4: Semaphores failing to prevent race condition by ikegami
in thread Semaphores failing to prevent race condition by Llew_Llaw_Gyffes

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