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.\" $Id: curl_multi_socket_action.3,v 1.1 2009-05-11 20:32:51 bagder Exp $
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.TH curl_multi_socket_action 3 "9 Jul 2006" "libcurl 7.16.0" "libcurl Manual"
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curl_multi_socket_action \- reads/writes available data given an action
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CURLMcode curl_multi_socket_action(CURLM * multi_handle,
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curl_socket_t sockfd, int ev_bitmask,
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int *running_handles);
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When the application has detected action on a socket handled by libcurl, it
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should call \fIcurl_multi_socket_action(3)\fP with the \fBsockfd\fP argument
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set to the socket with the action. When the events on a socket are known, they
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can be passed as an events bitmask \fBev_bitmask\fP by first setting
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\fBev_bitmask\fP to 0, and then adding using bitwise OR (|) any combination of
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events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT or
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CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0 instead, and
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libcurl will test the descriptor internally.
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At return, the integer \fBrunning_handles\fP points to will contain the number
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of still running easy handles within the multi handle. When this number
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reaches zero, all transfers are complete/done. Note that when you call
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\fIcurl_multi_socket_action(3)\fP on a specific socket and the counter
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decreases by one, it DOES NOT necessarily mean that this exact socket/transfer
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is the one that completed. Use \fIcurl_multi_info_read(3)\fP to figure out
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which easy handle that completed.
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The \fBcurl_multi_socket_action(3)\fP functions inform the application about
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updates in the socket (file descriptor) status by doing none, one, or multiple
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calls to the socket callback function set with the CURLMOPT_SOCKETFUNCTION
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option to \fIcurl_multi_setopt(3)\fP. They update the status with changes
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since the previous time the callback was called.
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Get the timeout time by setting the \fICURLMOPT_TIMERFUNCTION\fP option with
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\fIcurl_multi_setopt(3)\fP. Your application will then get called with
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information on how long to wait for socket actions at most before doing the
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timeout action: call the \fBcurl_multi_socket_action(3)\fP function with the
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\fBsockfd\fP argument set to CURL_SOCKET_TIMEOUT. You can also use the
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\fIcurl_multi_timeout(3)\fP function to poll the value at any given time, but
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for an event-based system using the callback is far better than relying on
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polling the timeout value.
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.SH "CALLBACK DETAILS"
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The socket \fBcallback\fP function uses a prototype like this
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int curl_socket_callback(CURL *easy, /* easy handle */
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curl_socket_t s, /* socket */
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int action, /* see values below */
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void *userp, /* private callback pointer */
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void *socketp); /* private socket pointer */
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The callback MUST return 0.
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The \fIeasy\fP argument is a pointer to the easy handle that deals with this
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particular socket. Note that a single handle may work with several sockets
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The \fIs\fP argument is the actual socket value as you use it within your
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The \fIaction\fP argument to the callback has one of five values:
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.IP "CURL_POLL_NONE (0)"
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register, not interested in readiness (yet)
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.IP "CURL_POLL_IN (1)"
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register, interested in read readiness
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.IP "CURL_POLL_OUT (2)"
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register, interested in write readiness
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.IP "CURL_POLL_INOUT (3)"
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register, interested in both read and write readiness
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.IP "CURL_POLL_REMOVE (4)"
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The \fIsocketp\fP argument is a private pointer you have previously set with
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\fIcurl_multi_assign(3)\fP to be associated with the \fIs\fP socket. If no
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pointer has been set, socketp will be NULL. This argument is of course a
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service to applications that want to keep certain data or structs that are
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strictly associated to the given socket.
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The \fIuserp\fP argument is a private pointer you have previously set with
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\fIcurl_multi_setopt(3)\fP and the CURLMOPT_SOCKETDATA option.
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CURLMcode type, general libcurl multi interface error code.
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Legacy: If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this basically means
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that you should call \fIcurl_multi_socket_action(3)\fP again, before you wait
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for more actions on libcurl's sockets. You don't have to do it immediately,
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but the return code means that libcurl may have more data available to return
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or that there may be more data to send off before it is "satisfied".
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In modern libcurls, \fICURLM_CALL_MULTI_PERFORM\fP or
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\fICURLM_CALL_MULTI_SOKCET\fP should not be returned and no application needs
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NOTE that the return code is for the whole multi stack. Problems still might have
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occurred on individual transfers even when one of these functions
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1. Create a multi handle
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2. Set the socket callback with CURLMOPT_SOCKETFUNCTION
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3. Set the timeout callback with CURLMOPT_TIMERFUNCTION, to get to know what
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timeout value to use when waiting for socket activities.
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4. Add easy handles with curl_multi_add_handle()
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5. Provide some means to manage the sockets libcurl is using, so you can check
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them for activity. This can be done through your application code, or by way
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of an external library such as libevent or glib.
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6. Wait for activity on any of libcurl's sockets, use the timeout value your
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callback has been told
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7, When activity is detected, call curl_multi_socket_action() for the
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socket(s) that got action. If no activity is detected and the timeout expires,
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call \fIcurl_multi_socket_action(3)\fP with \fICURL_SOCKET_TIMEOUT\fP
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8. Go back to step 6.
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This function was added in libcurl 7.15.4, and is deemed stable since 7.16.0.
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.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
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.BR curl_multi_fdset "(3), " curl_multi_info_read "(3), "
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.BR "the hiperfifo.c example"
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docs/libcurl/curl_multi_socket_action.3
