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| <h4 class="subsection">16.9.3 Accepting Connections</h4> |
| |
| <p><a name="index-sockets_002c-accepting-connections-1800"></a><a name="index-accepting-connections-1801"></a> |
| When a server receives a connection request, it can complete the |
| connection by accepting the request. Use the function <code>accept</code> |
| to do this. |
| |
| <p>A socket that has been established as a server can accept connection |
| requests from multiple clients. The server's original socket |
| <em>does not become part of the connection</em>; instead, <code>accept</code> |
| makes a new socket which participates in the connection. |
| <code>accept</code> returns the descriptor for this socket. The server's |
| original socket remains available for listening for further connection |
| requests. |
| |
| <p>The number of pending connection requests on a server socket is finite. |
| If connection requests arrive from clients faster than the server can |
| act upon them, the queue can fill up and additional requests are refused |
| with an <code>ECONNREFUSED</code> error. You can specify the maximum length of |
| this queue as an argument to the <code>listen</code> function, although the |
| system may also impose its own internal limit on the length of this |
| queue. |
| |
| <!-- sys/socket.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>accept</b> (<var>int socket, struct sockaddr *addr, socklen_t *length_ptr</var>)<var><a name="index-accept-1802"></a></var><br> |
| <blockquote><p>This function is used to accept a connection request on the server |
| socket <var>socket</var>. |
| |
| <p>The <code>accept</code> function waits if there are no connections pending, |
| unless the socket <var>socket</var> has nonblocking mode set. (You can use |
| <code>select</code> to wait for a pending connection, with a nonblocking |
| socket.) See <a href="File-Status-Flags.html#File-Status-Flags">File Status Flags</a>, for information about nonblocking |
| mode. |
| |
| <p>The <var>addr</var> and <var>length-ptr</var> arguments are used to return |
| information about the name of the client socket that initiated the |
| connection. See <a href="Socket-Addresses.html#Socket-Addresses">Socket Addresses</a>, for information about the format |
| of the information. |
| |
| <p>Accepting a connection does not make <var>socket</var> part of the |
| connection. Instead, it creates a new socket which becomes |
| connected. The normal return value of <code>accept</code> is the file |
| descriptor for the new socket. |
| |
| <p>After <code>accept</code>, the original socket <var>socket</var> remains open and |
| unconnected, and continues listening until you close it. You can |
| accept further connections with <var>socket</var> by calling <code>accept</code> |
| again. |
| |
| <p>If an error occurs, <code>accept</code> returns <code>-1</code>. The following |
| <code>errno</code> error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>socket</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>ENOTSOCK</code><dd>The descriptor <var>socket</var> argument is not a socket. |
| |
| <br><dt><code>EOPNOTSUPP</code><dd>The descriptor <var>socket</var> does not support this operation. |
| |
| <br><dt><code>EWOULDBLOCK</code><dd><var>socket</var> has nonblocking mode set, and there are no pending |
| connections immediately available. |
| </dl> |
| |
| <p>This function is defined as a cancellation point in multi-threaded |
| programs, so one has to be prepared for this and make sure that |
| allocated resources (like memory, files descriptors, semaphores or |
| whatever) are freed even if the thread is canceled. |
| <!-- @xref{pthread_cleanup_push}, for a method how to do this. --> |
| </p></blockquote></div> |
| |
| <p>The <code>accept</code> function is not allowed for sockets using |
| connectionless communication styles. |
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