I can reproduce the problem with your client/server combo.  Running the server part under strace indicated the process had been "killed by SIGPIPE": 

...
[pid 27966] write(4, "58\n", 3)         = -1 EPIPE (Broken pipe)
[pid 27966] --- SIGPIPE (Broken pipe) @ 0 (0) ---
Process 27966 detached
[pid 27967] <... accept resumed> 0x4219cef0, [4096]) = ? ERESTARTSYS (
+To be restarted)
[pid 27967] +++ killed by SIGPIPE +++
Process 27967 detached
[pid 27968] <... accept resumed> 0x4299def0, [4096]) = ? ERESTARTSYS (
+To be restarted)
[pid 27968] +++ killed by SIGPIPE +++
Process 27968 detached
<... futex resumed> )                   = ? ERESTARTSYS (To be restart
+ed)
+++ killed by SIGPIPE +++

[download]

Adding $SIG{PIPE} = 'IGNORE' to the server code solved the issue for me.  You probably also want to check if the print $client "$second\n" failed, in which case you should close the connection properly (otherwise, the respective threads will remain busy for 60 seconds printing to nowhere...): 

    ...
        for ($second=60; $second>0; --$second) {
                sleep 1;
                last unless print $client "$second\n";
        }
        close $client;
    ...

[download]

In reply to Re: Is this a bug of perl threads? by almut
in thread SOLVED: Is this a bug of perl threads? by Ray.Zachary

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