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3rd-party/curl-7.52.1/docs/libcurl/curl_multi_perform.3
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3rd-party/curl-7.52.1/docs/libcurl/curl_multi_perform.3
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.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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.\" * are also available at https://curl.haxx.se/docs/copyright.html.
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" **************************************************************************
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.TH curl_multi_perform 3 "1 March 2002" "libcurl 7.9.5" "libcurl Manual"
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.SH NAME
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curl_multi_perform - reads/writes available data from each easy handle
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.SH SYNOPSIS
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#include <curl/curl.h>
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CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles);
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.ad
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.SH DESCRIPTION
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This function handles transfers on all the added handles that need attention
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in an non-blocking fashion.
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When an application has found out there's data available for the multi_handle
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or a timeout has elapsed, the application should call this function to
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read/write whatever there is to read or write right now etc.
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\fIcurl_multi_perform(3)\fP returns as soon as the reads/writes are done. This
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function does not require that there actually is any data available for
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reading or that data can be written, it can be called just in case. It will
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write the number of handles that still transfer data in the second argument's
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integer-pointer.
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If the amount of \fIrunning_handles\fP is changed from the previous call (or
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is less than the amount of easy handles you've added to the multi handle), you
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know that there is one or more transfers less "running". You can then call
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\fIcurl_multi_info_read(3)\fP to get information about each individual
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completed transfer, and that returned info includes CURLcode and more. If an
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added handle fails very quickly, it may never be counted as a running_handle.
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When \fIrunning_handles\fP is set to zero (0) on the return of this function,
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there is no longer any transfers in progress.
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.SH EXAMPLE
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.nf
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#ifdef _WIN32
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#define SHORT_SLEEP Sleep(100)
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#else
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#define SHORT_SLEEP usleep(100000)
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#endif
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fd_set fdread;
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fd_set fdwrite;
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fd_set fdexcep;
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int maxfd = -1;
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long curl_timeo;
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curl_multi_timeout(multi_handle, &curl_timeo);
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if(curl_timeo < 0)
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curl_timeo = 1000;
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timeout.tv_sec = curl_timeo / 1000;
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timeout.tv_usec = (curl_timeo % 1000) * 1000;
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FD_ZERO(&fdread);
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FD_ZERO(&fdwrite);
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FD_ZERO(&fdexcep);
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/* get file descriptors from the transfers */
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mc = curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
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if(maxfd == -1) {
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SHORT_SLEEP;
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rc = 0;
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}
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else
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rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
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switch(rc) {
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case -1:
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/* select error */
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break;
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case 0:
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default:
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/* timeout or readable/writable sockets */
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curl_multi_perform(multi_handle, &still_running);
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break;
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}
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/* if there are still transfers, loop! */
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.fi
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.SH "RETURN VALUE"
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CURLMcode type, general libcurl multi interface error code.
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Before version 7.20.0: If you receive \fICURLM_CALL_MULTI_PERFORM\fP, this
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basically means that you should call \fIcurl_multi_perform(3)\fP again, before
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you select() on more actions. You don't have to do it immediately, but the
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return code means that libcurl may have more data available to return or that
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there may be more data to send off before it is "satisfied". Do note that
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\fIcurl_multi_perform(3)\fP will return \fICURLM_CALL_MULTI_PERFORM\fP only
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when it wants to be called again \fBimmediately\fP. When things are fine and
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there is nothing immediate it wants done, it'll return \fICURLM_OK\fP and you
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need to wait for \&"action" and then call this function again.
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This function only returns errors etc regarding the whole multi stack.
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Problems still might have occurred on individual transfers even when this
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function returns \fICURLM_OK\fP. Use \fIcurl_multi_info_read(3)\fP to figure
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out how individual transfers did.
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.SH "TYPICAL USAGE"
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Most applications will use \fIcurl_multi_fdset(3)\fP to get the multi_handle's
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file descriptors, and \fIcurl_multi_timeout(3)\fP to get a suitable timeout
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period, then it'll wait for action on the file descriptors using
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\fBselect(3)\fP. As soon as one or more file descriptor is ready,
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\fIcurl_multi_perform(3)\fP gets called.
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.SH "SEE ALSO"
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.BR curl_multi_cleanup "(3), " curl_multi_init "(3), "
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.BR curl_multi_wait "(3), "
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.BR curl_multi_fdset "(3), " curl_multi_info_read "(3), "
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.BR libcurl-errors "(3)"
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