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POSocket message hangs until thread completes in Perl
 

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  1. POSocket message hangs until thread completes in Perl
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    <p>I am trying to write Perl code that does two-way communication over a Unix socket. It needs to do the following things:</p> <ol> <li>Client code sends a request over the socket</li> <li>Server code reads the request</li> <li>Server performs any actions that should happen immediately</li> <li>Server creates a new thread to do additional actions that may take a long time</li> <li>Server sends response over the socket</li> <li>Client receives response</li> <li>The new thread continues to work after the response has been sent</li> </ol> <p>I have gotten most of this to work now, but with one problem. Steps 1 - 5 work fine, but at step 6, the client is unable to read the response until AFTER the thread has exited. (even though the response was sent more-or-less immediately) Any idea what I'm doing wrong?</p> <p>I'm using Perl 5.10.1 on Ubuntu Lucid.</p> <p>Here's an example:</p> <p><strong>Client code:</strong></p> <pre><code>#!/usr/bin/perl use strict; use Socket; my $socket_name = 'catsock'; my $client_message = "Hello server, this is the client."; my $SOCK; socket($SOCK, PF_UNIX, SOCK_STREAM, 0) or die "socket: $!"; connect($SOCK, sockaddr_un($socket_name)) or die "connect: $!"; $| = 1, select $_ for select $SOCK; # turn on autoflush print $SOCK $client_message; # send the message shutdown($SOCK,1); # finished writing print "sent: $client_message\n"; my $server_message = do { local $/; &lt;$SOCK&gt; }; # get the response print "recieved: $server_message\n\n"; </code></pre> <p><strong>Server code</strong></p> <pre><code>#!/usr/bin/perl use strict; use Socket; use threads; use threads::shared; sub threadfunc { print " waiting 5 seconds in new thread...\n"; sleep(5); print " exiting thread...\n\n"; } my $server_message = "Hello client, this is the server."; my $socket_name = 'catsock'; my $SERVER; my $CLIENT; socket($SERVER, PF_UNIX, SOCK_STREAM, 0) or die "socket: $!"; unlink($socket_name); bind($SERVER, sockaddr_un($socket_name)) or die "bind: $!"; chmod(0660, $socket_name); listen($SERVER, SOMAXCONN) or die "listen: $!"; print "server started on $socket_name\n\n"; while(1) { accept($CLIENT, $SERVER); my $client_message = do { local $/; &lt;$CLIENT&gt; }; # grab entire message print "recieved: $client_message\n"; print "creating new thread...\n"; my $thr = threads-&gt;create(\&amp;threadfunc); $thr-&gt;detach(); print $CLIENT $server_message; # send the response print "sent: $server_message\n\n"; close $CLIENT; } </code></pre> <p>When I run this, the following things happen:</p> <ol> <li>Client sends "Hello server, this is the client."</li> <li>Server receives client's message</li> <li>Server creates a new thread</li> <li>Server sends "Hello client, this is the server."</li> <li>Client should receive the message now, but it does not.</li> <li>New thread on server sleeps for 5 seconds</li> <li>Thread exits</li> <li><em>Now</em> the client receives the server's message, even though it was sent 5 seconds ago. Why?</li> </ol>
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    1. COset `$CLIENT` to autoflush after the accept?
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      1. USEric Strom
    2. COIs it possible that the server thread is blocking in the $thread->detach method and therefore the write on $CLIENT is not executing until the worker thread exits?
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      1. POSocket message hangs until thread completes in Perl
      1. USferoze
    3. CO@feroze - the extra thread keeps the connection open for 5 seconds (though I'm not sure exactly how -- the thread has a private copy of `$CLIENT` and the connection doesn't close until all the copies are out of scope, maybe), but it doesn't delay the write to `$CLIENT`.
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      1. POSocket message hangs until thread completes in Perl
      1. USmob
 

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