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