multithreading - Perl:从并行线程派生

Question

下面的代码应该运行2个并行线程，每个线程执行fork()，等待子进程完成，然后线程应加入(完成)并打印结果。
实际上，第一个 fork 的子进程按预期完成，但是第二个 fork 卡在_mutex_lock()上试图退出，因此第二个线程永远不会加入，直到您用-9信号手动杀死第二个子进程为止。
有人可以解释为什么会发生这种情况，以及如何避免这种情况吗？

use strict;
use warnings;
use threads;
use Data::Dumper;

sub Run
{
    my $tid = threads->tid();
    my $log = {};
    $log->{"[$$:$tid]:00"} = "started";
    my $pid = fork();
    if ($pid == 0)
    {
         print "In child ($$): started\n";
         sleep 3;
         print "In child ($$): finished\n";
#         system("kill -9 $$");  -- brutal way
         exit 0;
    }
    waitpid($pid, 0);
    my $exitCode = $? >> 8;
    $log->{"[$$:$tid]:01"} = "finished, code=$exitCode";
    return $log;
}

my @threads = ();
foreach (1..2)
{
    push @threads, threads->new(sub { return Run() });
}
print Dumper($_->join()) for @threads;

Answer 1

在我的Linux机器上，可以使用POSIX中的_exit代替exit。但是，此解决方案可能无法移植到其他平台。

链接的文档说:

Note that when using threads and in Linux this is not a good way to exit a thread because in Linux processes and threads are kind of the same thing (Note: while this is the situation in early 2003 there are projects under way to have threads with more POSIXly semantics in Linux). If you want not to return from a thread, detach the thread.

同样， perlthrtut - Tutorial on threads in Perl说

Thinking of mixing fork() and threads? Please lie down and wait until the feeling passes. Be aware that the semantics of fork() vary between platforms. For example, some Unix systems copy all the current threads into the child process, while others only copy the thread that called fork(). You have been warned!