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,
13 int ev_bitmask,
14 int *running_handles);
15
17 When the application has detected action on a socket handled by
18 libcurl, it should call curl_multi_socket_action(3) with the sockfd
19 argument set to the socket with the action. When the events on a socket
20 are known, they can be passed as an events bitmask ev_bitmask by first
21 setting ev_bitmask to 0, and then adding using bitwise OR (|) any com‐
22 bination of events to be chosen from CURL_CSELECT_IN, CURL_CSELECT_OUT
23 or CURL_CSELECT_ERR. When the events on a socket are unknown, pass 0
24 instead, and libcurl will test the descriptor internally. It is also
25 permissible to pass CURL_SOCKET_TIMEOUT to the sockfd parameter in
26 order to initiate the whole process or when a timeout occurs.
27 At return, running_handles points to the number of running easy handles
29 within the multi handle. When this number reaches zero, all transfers
30 are complete/done. When you call curl_multi_socket_action(3) on a spe‐
31 cific socket and the counter decreases by one, it DOES NOT necessarily
32 mean that this exact socket/transfer is the one that completed. Use
33 curl_multi_info_read(3) to figure out which easy handle that completed.
34 The curl_multi_socket_action(3) functions inform the application about
36 updates in the socket (file descriptor) status by doing none, one, or
37 multiple calls to the socket callback function set with the CURL‐
38 MOPT_SOCKETFUNCTION(3) option to curl_multi_setopt(3). They update the
39 status with changes since the previous time the callback was called.
40 Get the timeout time by setting the CURLMOPT_TIMERFUNCTION(3) option
42 with curl_multi_setopt(3). Your application will then get called with
43 information on how long to wait for socket actions at most before doing
44 the timeout action: call the curl_multi_socket_action(3) function with
45 the sockfd argument set to CURL_SOCKET_TIMEOUT. You can also use the
46 curl_multi_timeout(3) function to poll the value at any given time, but
47 for an event-based system using the callback is far better than relying
48 on polling the timeout value.
49
51 The socket callback function uses a prototype like this
52 int curl_socket_callback(CURL *easy, /* easy handle */
54 curl_socket_t s, /* socket */
55 int action, /* see values below */
56 void *userp, /* private callback pointer */
57 void *socketp); /* private socket pointer,
58 NULL if not
59 previously assigned with
60 curl_multi_assign(3) */
61 The callback MUST return 0.
63 The easy argument is a pointer to the easy handle that deals with this
65 particular socket. Note that a single handle may work with several
66 sockets simultaneously.
67 The s argument is the actual socket value as you use it within your
69 system.
70 The action argument to the callback has one of five values:
72 CURL_POLL_NONE (0)
74 register, not interested in readiness (yet)
75 CURL_POLL_IN (1)
77 register, interested in read readiness
78 CURL_POLL_OUT (2)
80 register, interested in write readiness
81 CURL_POLL_INOUT (3)
83 register, interested in both read and write readiness
84 CURL_POLL_REMOVE (4)
86 unregister
87 The socketp argument is a private pointer you have previously set with
89 curl_multi_assign(3) to be associated with the s socket. If no pointer
90 has been set, socketp will be NULL. This argument is of course a ser‐
91 vice to applications that want to keep certain data or structs that are
92 strictly associated to the given socket.
93 The userp argument is a private pointer you have previously set with
95 curl_multi_setopt(3) and the CURLMOPT_SOCKETDATA(3) option.
96
98 CURLMcode type, general libcurl multi interface error code.
99 Before version 7.20.0: If you receive CURLM_CALL_MULTI_PERFORM, this
101 basically means that you should call curl_multi_socket_action(3) again
102 before you wait for more actions on libcurl's sockets. You don't have
103 to do it immediately, but the return code means that libcurl may have
104 more data available to return or that there may be more data to send
105 off before it is "satisfied".
106 The return code from this function is for the whole multi stack. Prob‐
108 lems still might have occurred on individual transfers even when one of
109 these functions return OK.
110
112 1. Create a multi handle
113 2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3)
115 3. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to
117 know what timeout value to use when waiting for socket activities.
118 4. Add easy handles with curl_multi_add_handle()
120 5. Provide some means to manage the sockets libcurl is using, so you
122 can check them for activity. This can be done through your application
123 code, or by way of an external library such as libevent or glib.
124 6. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...) to
126 kickstart everything. To get one or more callbacks called.
127 7. Wait for activity on any of libcurl's sockets, use the timeout value
129 your callback has been told.
130 8, When activity is detected, call curl_multi_socket_action() for the
132 socket(s) that got action. If no activity is detected and the timeout
133 expires, call curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT.
134
136 This function was added in libcurl 7.15.4, and is deemed stable since
137 7.16.0.
138
140 curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3),
141 curl_multi_info_read(3), the hiperfifo.c example
142libcurl 7.61.1 June 30, 2018 curl_multi_socket_action(3)