1--- 2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3SPDX-License-Identifier: curl 4Title: curl_multi_perform 5Section: 3 6Source: libcurl 7See-also: 8 - curl_multi_add_handle (3) 9 - curl_multi_cleanup (3) 10 - curl_multi_fdset (3) 11 - curl_multi_info_read (3) 12 - curl_multi_init (3) 13 - curl_multi_wait (3) 14 - libcurl-errors (3) 15Protocol: 16 - All 17Added-in: 7.9.6 18--- 19 20# NAME 21 22curl_multi_perform - run all transfers until it would block 23 24# SYNOPSIS 25 26~~~c 27#include <curl/curl.h> 28 29CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles); 30~~~ 31 32# DESCRIPTION 33 34This function performs transfers on all the added handles that need attention 35in a non-blocking fashion. The easy handles have previously been added to the 36multi handle with curl_multi_add_handle(3). 37 38When an application has found out there is data available for the multi_handle 39or a timeout has elapsed, the application should call this function to 40read/write whatever there is to read or write right now etc. 41curl_multi_perform(3) returns as soon as the reads/writes are done. This 42function does not require that there actually is any data available for 43reading or that data can be written, it can be called just in case. It stores 44the number of handles that still transfer data in the second argument's 45integer-pointer. 46 47If the amount of *running_handles* is changed from the previous call (or 48is less than the amount of easy handles you have added to the multi handle), 49you know that there is one or more transfers less "running". You can then call 50curl_multi_info_read(3) to get information about each individual 51completed transfer, and that returned info includes CURLcode and more. If an 52added handle fails quickly, it may never be counted as a running_handle. You 53could use curl_multi_info_read(3) to track actual status of the added 54handles in that case. 55 56When *running_handles* is set to zero (0) on the return of this function, 57there is no longer any transfers in progress. 58 59When this function returns error, the state of all transfers are uncertain and 60they cannot be continued. curl_multi_perform(3) should not be called 61again on the same multi handle after an error has been returned, unless first 62removing all the handles and adding new ones. 63 64# %PROTOCOLS% 65 66# EXAMPLE 67 68~~~c 69int main(void) 70{ 71 int still_running; 72 CURLM *multi = curl_multi_init(); 73 CURL *curl = curl_easy_init(); 74 if(curl) { 75 curl_multi_add_handle(multi, curl); 76 do { 77 CURLMcode mc = curl_multi_perform(multi, &still_running); 78 79 if(!mc && still_running) 80 /* wait for activity, timeout or "nothing" */ 81 mc = curl_multi_poll(multi, NULL, 0, 1000, NULL); 82 83 if(mc) { 84 fprintf(stderr, "curl_multi_poll() failed, code %d.\n", (int)mc); 85 break; 86 } 87 88 /* if there are still transfers, loop */ 89 } while(still_running); 90 } 91} 92~~~ 93 94# %AVAILABILITY% 95 96# RETURN VALUE 97 98CURLMcode type, general libcurl multi interface error code. 99 100This function returns errors regarding the whole multi stack. Problems on 101individual transfers may have occurred even when this function returns 102*CURLM_OK*. Use curl_multi_info_read(3) to figure out how individual 103transfers did. 104 105# TYPICAL USAGE 106 107Most applications use curl_multi_poll(3) to make libcurl wait for 108activity on any of the ongoing transfers. As soon as one or more file 109descriptor has activity or the function times out, the application calls 110curl_multi_perform(3). 111
