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1---
2c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
3SPDX-License-Identifier: curl
4Title: curl_multi_poll
5Section: 3
6Source: libcurl
7See-also:
8  - curl_multi_fdset (3)
9  - curl_multi_perform (3)
10  - curl_multi_wait (3)
11  - curl_multi_wakeup (3)
12---
13
14# NAME
15
16curl_multi_poll - polls on all easy handles in a multi handle
17
18# SYNOPSIS
19
20~~~c
21#include <curl/curl.h>
22
23CURLMcode curl_multi_poll(CURLM *multi_handle,
24                          struct curl_waitfd extra_fds[],
25                          unsigned int extra_nfds,
26                          int timeout_ms,
27                          int *numfds);
28~~~
29
30# DESCRIPTION
31
32curl_multi_poll(3) polls all file descriptors used by the curl easy
33handles contained in the given multi handle set. It blocks until activity is
34detected on at least one of the handles or *timeout_ms* has passed.
35Alternatively, if the multi handle has a pending internal timeout that has a
36shorter expiry time than *timeout_ms*, that shorter time is used instead
37to make sure timeout accuracy is reasonably kept.
38
39The calling application may pass additional curl_waitfd structures which are
40similar to *poll(2)*'s *pollfd* structure to be waited on in the same
41call.
42
43On completion, if *numfds* is non-NULL, it gets populated with the total
44number of file descriptors on which interesting events occurred. This number
45can include both libcurl internal descriptors as well as descriptors provided
46in *extra_fds*.
47
48The curl_multi_wakeup(3) function can be used from another thread to
49wake up this function and return faster. This is one of the details
50that makes this function different than curl_multi_wait(3) which cannot
51be woken up this way.
52
53If no extra file descriptors are provided and libcurl has no file descriptor
54to offer to wait for, this function instead waits during *timeout_ms*
55milliseconds (or shorter if an internal timer indicates so). This is the other
56detail that makes this function different than curl_multi_wait(3).
57
58This function is encouraged to be used instead of select(3) when using the
59multi interface to allow applications to easier circumvent the common problem
60with 1024 maximum file descriptors.
61
62# curl_waitfd
63
64~~~c
65struct curl_waitfd {
66  curl_socket_t fd;
67  short events;
68  short revents;
69};
70~~~
71
72## CURL_WAIT_POLLIN
73
74Bit flag to curl_waitfd.events indicating the socket should poll on read
75events such as new data received.
76
77## CURL_WAIT_POLLPRI
78
79Bit flag to curl_waitfd.events indicating the socket should poll on high
80priority read events such as out of band data.
81
82## CURL_WAIT_POLLOUT
83
84Bit flag to curl_waitfd.events indicating the socket should poll on write
85events such as the socket being clear to write without blocking.
86
87# EXAMPLE
88
89~~~c
90int main(void)
91{
92  CURL *easy_handle;
93  CURLM *multi_handle;
94  int still_running = 0;
95
96  /* add the individual easy handle */
97  curl_multi_add_handle(multi_handle, easy_handle);
98
99  do {
100    CURLMcode mc;
101    int numfds;
102
103    mc = curl_multi_perform(multi_handle, &still_running);
104
105    if(mc == CURLM_OK) {
106      /* wait for activity or timeout */
107      mc = curl_multi_poll(multi_handle, NULL, 0, 1000, &numfds);
108    }
109
110    if(mc != CURLM_OK) {
111      fprintf(stderr, "curl_multi failed, code %d.\n", mc);
112      break;
113    }
114
115  } while(still_running);
116
117  curl_multi_remove_handle(multi_handle, easy_handle);
118}
119~~~
120
121# AVAILABILITY
122
123Added in 7.66.0.
124
125# RETURN VALUE
126
127CURLMcode type, general libcurl multi interface error code. See
128libcurl-errors(3)
129