curl_multi_wait(3)

1curl_multi_wait(3)              libcurl Manual              curl_multi_wait(3)
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NAME

6       curl_multi_wait - polls on all easy handles in a multi handle
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SYNOPSIS

9       #include <curl/curl.h>
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11       CURLMcode curl_multi_wait(CURLM *multi_handle,
12                                 struct curl_waitfd extra_fds[],
13                                 unsigned int extra_nfds,
14                                 int timeout_ms,
15                                 int *numfds);
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DESCRIPTION

18       curl_multi_wait(3)  polls  all  file  descriptors used by the curl easy
19       handles contained in the given multi handle set.  It will  block  until
20       activity  is  detected on at least one of the handles or timeout_ms has
21       passed.  Alternatively, if the multi  handle  has  a  pending  internal
22       timeout  that  has  a shorter expiry time than timeout_ms, that shorter
23       time will be used instead to make sure timeout accuracy  is  reasonably
24       kept.
25
26       The  calling  application  may  pass  additional curl_waitfd structures
27       which are similar to poll(2)'s pollfd structure to be waited on in  the
28       same call.
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30       On  completion,  if  numfds  is non-NULL, it will be populated with the
31       total number of file descriptors on which interesting events  occurred.
32       This  number  can  include both libcurl internal descriptors as well as
33       descriptors provided in extra_fds.
34
35       If no extra file descriptors are  provided  and  libcurl  has  no  file
36       descriptor to offer to wait for, this function will return immediately.
37       (Try curl_multi_poll(3) instead if you rather avoid this behavior.)
38
39       This function is encouraged to be used instead of select(3) when  using
40       the multi interface to allow applications to easier circumvent the com‐
41       mon problem with 1024 maximum file descriptors.
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curl_waitfd

44       struct curl_waitfd {
45         curl_socket_t fd;
46         short events;
47         short revents;
48       };
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50       CURL_WAIT_POLLIN
51              Bit flag to curl_waitfd.events indicating the socket should poll
52              on read events such as new data received.
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54       CURL_WAIT_POLLPRI
55              Bit flag to curl_waitfd.events indicating the socket should poll
56              on high priority read events such as out of band data.
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58       CURL_WAIT_POLLOUT
59              Bit flag to curl_waitfd.events indicating the socket should poll
60              on  write events such as the socket being clear to write without
61              blocking.
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EXAMPLE

64       CURL *easy_handle;
65       CURLM *multi_handle;
66
67       /* add the individual easy handle */
68       curl_multi_add_handle(multi_handle, easy_handle);
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70       do {
71         CURLMcode mc;
72         int numfds;
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74         mc = curl_multi_perform(multi_handle, &still_running);
75
76         if(mc == CURLM_OK ) {
77           /* wait for activity, timeout or "nothing" */
78           mc = curl_multi_wait(multi_handle, NULL, 0, 1000, &numfds);
79         }
80
81         if(mc != CURLM_OK) {
82           fprintf(stderr, "curl_multi failed, code %d.\n", mc);
83           break;
84         }
85
86         /* 'numfds' being zero means either a timeout or no file descriptors to
87            wait for. Try timeout on first occurrence, then assume no file
88            descriptors and no file descriptors to wait for means wait for 100
89            milliseconds. */
90
91         if(!numfds) {
92           repeats++; /* count number of repeated zero numfds */
93           if(repeats > 1) {
94             WAITMS(100); /* sleep 100 milliseconds */
95           }
96         }
97         else
98           repeats = 0;
99
100       } while(still_running);
101
102       curl_multi_remove_handle(multi_handle, easy_handle);
103

RETURN VALUE

105       CURLMcode  type,  general  libcurl  multi  interface  error  code.  See
106       libcurl-errors(3)
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AVAILABILITY

109       This function was added in libcurl 7.28.0.
110