129 lines
3.4 KiB
Markdown
129 lines
3.4 KiB
Markdown
---
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c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
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SPDX-License-Identifier: curl
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Title: curl_multi_poll
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Section: 3
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Source: libcurl
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See-also:
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- curl_multi_fdset (3)
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- curl_multi_perform (3)
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- curl_multi_wait (3)
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- curl_multi_wakeup (3)
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---
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# NAME
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curl_multi_poll - polls on all easy handles in a multi handle
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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CURLMcode curl_multi_poll(CURLM *multi_handle,
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struct curl_waitfd extra_fds[],
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unsigned int extra_nfds,
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int timeout_ms,
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int *numfds);
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~~~
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# DESCRIPTION
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curl_multi_poll(3) polls all file descriptors used by the curl easy
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handles contained in the given multi handle set. It blocks until activity is
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detected on at least one of the handles or *timeout_ms* has passed.
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Alternatively, if the multi handle has a pending internal timeout that has a
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shorter expiry time than *timeout_ms*, that shorter time is used instead
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to make sure timeout accuracy is reasonably kept.
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The calling application may pass additional curl_waitfd structures which are
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similar to *poll(2)*'s *pollfd* structure to be waited on in the same
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call.
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On completion, if *numfds* is non-NULL, it gets populated with the total
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number of file descriptors on which interesting events occurred. This number
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can include both libcurl internal descriptors as well as descriptors provided
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in *extra_fds*.
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The curl_multi_wakeup(3) function can be used from another thread to
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wake up this function and return faster. This is one of the details
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that makes this function different than curl_multi_wait(3) which cannot
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be woken up this way.
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If no extra file descriptors are provided and libcurl has no file descriptor
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to offer to wait for, this function instead waits during *timeout_ms*
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milliseconds (or shorter if an internal timer indicates so). This is the other
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detail that makes this function different than curl_multi_wait(3).
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This function is encouraged to be used instead of select(3) when using the
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multi interface to allow applications to easier circumvent the common problem
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with 1024 maximum file descriptors.
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# curl_waitfd
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~~~c
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struct curl_waitfd {
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curl_socket_t fd;
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short events;
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short revents;
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};
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~~~
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## CURL_WAIT_POLLIN
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Bit flag to curl_waitfd.events indicating the socket should poll on read
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events such as new data received.
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## CURL_WAIT_POLLPRI
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Bit flag to curl_waitfd.events indicating the socket should poll on high
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priority read events such as out of band data.
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## CURL_WAIT_POLLOUT
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Bit flag to curl_waitfd.events indicating the socket should poll on write
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events such as the socket being clear to write without blocking.
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# EXAMPLE
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~~~c
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int main(void)
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{
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CURL *easy_handle;
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CURLM *multi_handle;
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int still_running = 0;
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/* add the individual easy handle */
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curl_multi_add_handle(multi_handle, easy_handle);
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do {
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CURLMcode mc;
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int numfds;
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mc = curl_multi_perform(multi_handle, &still_running);
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if(mc == CURLM_OK) {
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/* wait for activity or timeout */
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mc = curl_multi_poll(multi_handle, NULL, 0, 1000, &numfds);
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}
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if(mc != CURLM_OK) {
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fprintf(stderr, "curl_multi failed, code %d.\n", mc);
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break;
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}
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} while(still_running);
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curl_multi_remove_handle(multi_handle, easy_handle);
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}
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~~~
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# AVAILABILITY
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Added in 7.66.0.
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# RETURN VALUE
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CURLMcode type, general libcurl multi interface error code. See
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libcurl-errors(3)
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