curl_multi_perform

Syntax

#include <curl/curl.h>

CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles); 

Parameters

multi_handle Pointer to a curl multi handle.
running_handles Pointer to running handles.

Return Values

CURLMcode type, general libcurl multi interface error code.

Before version 7.20.0: If you receive CURLM_CALL_MULTI_PERFORM, this indicates that you should call curl_multi_perform again, before you select on more actions. You do not have to perform this call immediately, but the return code indicates 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 curl_multi_perform will return CURLM_CALL_MULTI_PERFORM only when it wants to be called again immediately. When things are fine and there is nothing immediate it wants done, it will return CURLM_OK 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 CURLM_OK.

Description

When the app deems there is data available for the multi_handle, it should call this function to read/write whatever there is to read or write at this time. curl_multi_perform 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.

When you call curl_multi_perform and the amount of running_handles is changed from the previous call (or is less than the amount of easy handles you have added to the multi-handle), you know that there is one or more transfers less "running". You can then call curl_multi_info_read to get information about each individual completed transfer, and that returned info includes CURLcode and more. If an added handle quickly fails, it may never be counted as a running_handle.

When running_handles is set to zero (0) on the return of this function, there is no longer any transfers in progress.

NOTE:
The resolver inside curl_multi_perform allocates memory from the user stack during name resolution. Refer to SOGetAddrInfo for the amount.

Typical Usage

Most applications will use curl_multi_fdset to get the multi_handle's file descriptors, then it will wait for action on them using select and as soon as one or more of them are ready, curl_multi_perform gets called.

Do Not Call From

None.

See Also

HTTP Client Library (libcurl)
libcurl API Functions
libcurl Error Codes
curl_multi_cleanup
curl_multi_init
curl_multi_fdset
curl_multi_info_read

Revision History

2014/04/07 Note about stack consumption.
2013/09/18 Conversion
2013/05/08 Automated cleanup pass.
2012/05/04 Initial version.


CONFIDENTIAL