What we found is that Perl is not thread-safe. Let me repeat that: PERL IS NOT THREAD-SAFE!

That sentance makes no sense at all.

Bizarre ARRAY copy in caller() at Common::Logger::log_stuff ...

Common::Logger is our internal logging package. log_stuff is the logging function. It calls CORE::caller(). This blew up.

Hmm. Did you report this 'bug'?

It's quite possible to generate the 'Bizarre ARRAY copy' bug in perfectly ordinary, non-threaded bad code. What's more, perl will often not give you much in the way of clues as to what you are doing wrong when it happens.

I don't know what version of Perl you were using, but it seems quite unlikely that using caller with threads is a problem. Set the loop counters in the following code to any values you like; or increase the depth of sub calls as far as you like, and it will run for as long as you let it without producing a "bizarre array copy error". Or any other error.

#! perl -slw
use strict;
use threads;

sub t1{
    printf "%3d:t1: %s\n", threads->tid, join '|', grep defined, calle
+r(1);
    return
}

sub t2 {
    t1();
    printf "%3d:t2: %s\n", threads->tid, ''; '|',  grep defined, calle
+r(1);
    return
}

sub t3 {
    for( 1 .. 100 ) {
        t2();
        printf "%3d:t3: %s\n", threads->tid, join '|',  grep defined, 
+caller(1);
    }
    return;
}

my @threads = map{ threads->create( \&t3 ) } 1 .. 100;
sleep 3;
$_->join for @threads;
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It seems much more likely that your Common::Logger class was not written to be called from multiple threads. Indeed, the most likely scenario is that you were passing objects between threads. That's a documented no no.

Most modern cars are pretty safe, but if you attempt to climb trees in them, it's likely to be unsuccessful; but saying cars are useless because your tree climbing attempt went ary, is unlikely to garner much support, even from the tree-hugging, cars-are-evil crowd.