1curl_multi_socket_action(3) libcurl Manual curl_multi_socket_action(3)
2
6 curl_multi_socket_action - reads/writes available data given an action
7
9 #include <curl/curl.h>
10 CURLMcode curl_multi_socket_action(CURLM * multi_handle,
12 curl_socket_t sockfd, int ev_bitmask,
13 int *running_handles);
14
16 When the application has detected action on a socket handled by
17 libcurl, it should call curl_multi_socket_action(3) with the sockfd
18 argument set to the socket with the action. When the events on a socket
19 are known, they can be passed as an events bitmask ev_bitmask by first
20 setting ev_bitmask to 0, and then adding using bitwise OR (|) any com‐
21 bination of events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT
22 or CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0
23 instead, and libcurl will test the descriptor internally.
24 At return, the integer running_handles points to will contain the num‐
26 ber of still running easy handles within the multi handle. When this
27 number reaches zero, all transfers are complete/done. Note that when
28 you call curl_multi_socket_action(3) on a specific socket and the
29 counter decreases by one, it DOES NOT necessarily mean that this exact
30 socket/transfer is the one that completed. Use curl_multi_info_read(3)
31 to figure out which easy handle that completed.
32 The curl_multi_socket_action(3) functions inform the application about
34 updates in the socket (file descriptor) status by doing none, one, or
35 multiple calls to the socket callback function set with the CURL‐
36 MOPT_SOCKETFUNCTION option to curl_multi_setopt(3). They update the
37 status with changes since the previous time the callback was called.
38 Get the timeout time by setting the CURLMOPT_TIMERFUNCTION option with
40 curl_multi_setopt(3). Your application will then get called with infor‐
41 mation on how long to wait for socket actions at most before doing the
42 timeout action: call the curl_multi_socket_action(3) function with the
43 sockfd argument set to CURL_SOCKET_TIMEOUT. You can also use the
44 curl_multi_timeout(3) function to poll the value at any given time, but
45 for an event-based system using the callback is far better than relying
46 on polling the timeout value.
47
49 The socket callback function uses a prototype like this
50 int curl_socket_callback(CURL *easy, /* easy handle */
52 curl_socket_t s, /* socket */
53 int action, /* see values below */
54 void *userp, /* private callback pointer */
55 void *socketp); /* private socket pointer */
56 The callback MUST return 0.
58 The easy argument is a pointer to the easy handle that deals with this
60 particular socket. Note that a single handle may work with several
61 sockets simultaneously.
62 The s argument is the actual socket value as you use it within your
64 system.
65 The action argument to the callback has one of five values:
67 CURL_POLL_NONE (0)
69 register, not interested in readiness (yet)
70 CURL_POLL_IN (1)
72 register, interested in read readiness
73 CURL_POLL_OUT (2)
75 register, interested in write readiness
76 CURL_POLL_INOUT (3)
78 register, interested in both read and write readiness
79 CURL_POLL_REMOVE (4)
81 unregister
82 The socketp argument is a private pointer you have previously set with
84 curl_multi_assign(3) to be associated with the s socket. If no pointer
85 has been set, socketp will be NULL. This argument is of course a ser‐
86 vice to applications that want to keep certain data or structs that are
87 strictly associated to the given socket.
88 The userp argument is a private pointer you have previously set with
90 curl_multi_setopt(3) and the CURLMOPT_SOCKETDATA option.
91
93 CURLMcode type, general libcurl multi interface error code.
94 Legacy: If you receive CURLM_CALL_MULTI_PERFORM, this basically means
96 that you should call curl_multi_socket_action(3) again, before you wait
97 for more actions on libcurl's sockets. You don't have to do it immedi‐
98 ately, but the return code means that libcurl may have more data avail‐
99 able to return or that there may be more data to send off before it is
100 "satisfied".
101 In modern libcurls, CURLM_CALL_MULTI_PERFORM or CURLM_CALL_MULTI_SOKCET
103 should not be returned and no application needs to care about them.
104 NOTE that the return code is for the whole multi stack. Problems still
106 might have occurred on individual transfers even when one of these
107 functions return OK.
108
110 1. Create a multi handle
111 2. Set the socket callback with CURLMOPT_SOCKETFUNCTION
113 3. Set the timeout callback with CURLMOPT_TIMERFUNCTION, to get to know
115 what timeout value to use when waiting for socket activities.
116 4. Add easy handles with curl_multi_add_handle()
118 5. Provide some means to manage the sockets libcurl is using, so you
120 can check them for activity. This can be done through your application
121 code, or by way of an external library such as libevent or glib.
122 6. Wait for activity on any of libcurl's sockets, use the timeout value
124 your callback has been told
125 7, When activity is detected, call curl_multi_socket_action() for the
127 socket(s) that got action. If no activity is detected and the timeout
128 expires, call curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT
129 8. Go back to step 6.
131
133 This function was added in libcurl 7.15.4, and is deemed stable since
134 7.16.0.
135
137 curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3),
138 curl_multi_info_read(3), the hiperfifo.c example
139libcurl 7.16.0 9 Jul 2006 curl_multi_socket_action(3)