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