108 lines
3.3 KiB
Markdown
108 lines
3.3 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_perform
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Section: 3
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Source: libcurl
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See-also:
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- curl_multi_add_handle (3)
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- curl_multi_cleanup (3)
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- curl_multi_fdset (3)
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- curl_multi_info_read (3)
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- curl_multi_init (3)
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- curl_multi_wait (3)
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- libcurl-errors (3)
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---
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# NAME
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curl_multi_perform - reads/writes available data from easy handles
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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_perform(CURLM *multi_handle, int *running_handles);
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~~~
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# DESCRIPTION
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This function performs transfers on all the added handles that need attention
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in a non-blocking fashion. The easy handles have previously been added to the
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multi handle with curl_multi_add_handle(3).
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When an application has found out there is 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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curl_multi_perform(3) 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 stores
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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 *running_handles* is changed from the previous call (or
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is less than the amount of easy handles you have added to the multi handle),
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you know that there is one or more transfers less "running". You can then call
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curl_multi_info_read(3) 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 quickly, it may never be counted as a running_handle. You
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could use curl_multi_info_read(3) to track actual status of the added
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handles in that case.
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When *running_handles* 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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When this function returns error, the state of all transfers are uncertain and
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they cannot be continued. curl_multi_perform(3) should not be called
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again on the same multi handle after an error has been returned, unless first
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removing all the handles and adding new ones.
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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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int still_running;
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CURL *multi = curl_multi_init();
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CURL *curl = curl_easy_init();
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if(curl) {
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curl_multi_add_handle(multi, curl);
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do {
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CURLMcode mc = curl_multi_perform(multi, &still_running);
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if(!mc && still_running)
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/* wait for activity, timeout or "nothing" */
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mc = curl_multi_poll(multi, NULL, 0, 1000, NULL);
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if(mc) {
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fprintf(stderr, "curl_multi_poll() failed, code %d.\n", (int)mc);
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break;
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}
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/* if there are still transfers, loop! */
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} while(still_running);
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}
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}
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~~~
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# AVAILABILITY
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Added in 7.9.6
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# RETURN VALUE
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CURLMcode type, general libcurl multi interface error code.
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This function returns errors regarding the whole multi stack. Problems on
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individual transfers may have occurred even when this function returns
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*CURLM_OK*. Use curl_multi_info_read(3) to figure out how individual
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transfers did.
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# TYPICAL USAGE
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Most applications use curl_multi_poll(3) to make libcurl wait for
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activity on any of the ongoing transfers. As soon as one or more file
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descriptor has activity or the function times out, the application calls
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curl_multi_perform(3).
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