1curl_multi_socket_action(3) libcurl Manual curl_multi_socket_action(3)
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6 curl_multi_socket_action - reads/writes available data given an action
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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 ar‐
19 gument 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 or‐
26 der 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) function informs 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.
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51 1. Create a multi handle
52 2. Set the socket callback with CURLMOPT_SOCKETFUNCTION(3)
54 3. Set the timeout callback with CURLMOPT_TIMERFUNCTION(3), to get to
56 know what timeout value to use when waiting for socket activities.
57 4. Add easy handles with curl_multi_add_handle()
59 5. Provide some means to manage the sockets libcurl is using, so you
61 can check them for activity. This can be done through your application
62 code, or by way of an external library such as libevent or glib.
63 6. Call curl_multi_socket_action(..., CURL_SOCKET_TIMEOUT, 0, ...) to
65 kickstart everything. To get one or more callbacks called.
66 7. Wait for activity on any of libcurl's sockets, use the timeout value
68 your callback has been told.
69 8, When activity is detected, call curl_multi_socket_action() for the
71 socket(s) that got action. If no activity is detected and the timeout
72 expires, call curl_multi_socket_action(3) with CURL_SOCKET_TIMEOUT.
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75 This function was added in libcurl 7.15.4, and is deemed stable since
76 7.16.0.
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79 curl_multi_cleanup(3), curl_multi_init(3), curl_multi_fdset(3),
80 curl_multi_info_read(3), the hiperfifo.c example
81libcurl 7.76.1 November 05, 2020 curl_multi_socket_action(3)