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PHP: How to use socket_select() and socket_read() correctly

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Old 08-26-2013
PHP: How to use socket_select() and socket_read() correctly

I have a multithreaded PHP application that uses sockets for communicating between threads. The communication works pretty well, except for one thing: when I call socket_select(), it works the first time after a new connection is made, but after that it always reports read handles ready, even after I've read all the data from them. Here's what I mean:

Main thread:
1. Setup socket, bind to port, listen
2. socket_select() (block, with null timeout to make it wait forever) on the socket from step 1
3. That call works fine: after the child thread connects, socket_select() tells me that the socket from step 1 is ready
4. Accept new connection, remember the handle returned by accept().
5. socket_select() on the main socket plus the new socket
6. After child thread writes, socket_select() reports that the new socket is ready
7. I read all the data from the socket, then go back to step 5.

At this point, socket_select() continues to report that the new socket is ready, even though the child thread has written no new data to it. What in the world am I doing wrong? Is it convention to close the new connection at this point and have the child thread reconnect? How can I get socket_select() to stop reporting that the new handle is ready to read?

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socket_create_pair - Creates a pair of indistinguishable sockets and stores them in an array

bool socket_create_pair (int $domain, int $type, int $protocol, array &$fd) DESCRIPTION
socket_create_pair(3) creates two connected and indistinguishable sockets, and stores them in $fd. This function is commonly used in IPC (InterProcess Communication). PARAMETERS
o $domain - The $domain parameter specifies the protocol family to be used by the socket. See socket_create(3) for the full list. o $type - The $type parameter selects the type of communication to be used by the socket. See socket_create(3) for the full list. o $protocol - The $protocol parameter sets the specific protocol within the specified $domain to be used when communicating on the returned socket. The proper value can be retrieved by name by using getprotobyname(3). If the desired protocol is TCP, or UDP the corre- sponding constants SOL_TCP, and SOL_UDP can also be used. See socket_create(3) for the full list of supported protocols. o $fd - Reference to an array in which the two socket resources will be inserted. RETURN VALUES
Returns TRUE on success or FALSE on failure. CHANGELOG
+--------+---------------------------------------------------+ |Version | | | | | | | Description | | | | +--------+---------------------------------------------------+ | 5.3.0 | | | | | | | This function is now re-enabled on Windows plat- | | | forms. | | | | | 4.3.0 | | | | | | | This function was due to a bug made unavailable | | | on Windows platforms. | | | | +--------+---------------------------------------------------+ EXAMPLES
Example #1 socket_create_pair(3) example <?php $sockets = array(); /* On Windows we need to use AF_INET */ $domain = (strtoupper(substr(PHP_OS, 0, 3)) == 'WIN' ? AF_INET : AF_UNIX); /* Setup socket pair */ if (socket_create_pair($domain, SOCK_STREAM, 0, $sockets) === false) { echo "socket_create_pair failed. Reason: ".socket_strerror(socket_last_error()); } /* Send and Recieve Data */ if (socket_write($sockets[0], "ABCdef123 ", strlen("ABCdef123 ")) === false) { echo "socket_write() failed. Reason: ".socket_strerror(socket_last_error($sockets[0])); } if (($data = socket_read($sockets[1], strlen("ABCdef123 "), PHP_BINARY_READ)) === false) { echo "socket_read() failed. Reason: ".socket_strerror(socket_last_error($sockets[1])); } var_dump($data); /* Close sockets */ socket_close($sockets[0]); socket_close($sockets[1]); ?> Example #2 socket_create_pair(3) IPC example <?php $ary = array(); $strone = 'Message From Parent.'; $strtwo = 'Message From Child.'; if (socket_create_pair(AF_UNIX, SOCK_STREAM, 0, $ary) === false) { echo "socket_create_pair() failed. Reason: ".socket_strerror(socket_last_error()); } $pid = pcntl_fork(); if ($pid == -1) { echo 'Could not fork Process.'; } elseif ($pid) { /*parent*/ socket_close($ary[0]); if (socket_write($ary[1], $strone, strlen($strone)) === false) { echo "socket_write() failed. Reason: ".socket_strerror(socket_last_error($ary[1])); } if (socket_read($ary[1], strlen($strtwo), PHP_BINARY_READ) == $strtwo) { echo "Recieved $strtwo "; } socket_close($ary[1]); } else { /*child*/ socket_close($ary[1]); if (socket_write($ary[0], $strtwo, strlen($strtwo)) === false) { echo "socket_write() failed. Reason: ".socket_strerror(socket_last_error($ary[0])); } if (socket_read($ary[0], strlen($strone), PHP_BINARY_READ) == $strone) { echo "Recieved $strone "; } socket_close($ary[0]); } ?> SEE ALSO
socket_create(3), socket_create_listen(3), socket_bind(3), socket_listen(3), socket_last_error(3), socket_strerror(3). PHP Documentation Group SOCKET_CREATE_PAIR(3)

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