CURLMOPT_RESOLVE_THREADS_MAX(3) Library Functions Manual
NAME
CURLMOPT_RESOLVE_THREADS_MAX - max threads for threaded DNS resolver
SYNOPSIS
#include <curl/curl.h>
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_RESOLVE_THREADS_MAX,
long amount);
DESCRIPTION
Pass a long for the amount. The set number is used as the maximum
number of threads to be used for the threaded DNS resolver. It has to
be a positive number in the range of 32 bits.
When libcurl is built with a threaded resolver, which is the default on
many systems, it uses a thread pool to lookup addresses and other
properties of hostnames so other transfers are not blocked by this.
Threads are started on demand to perform the resolving and shut down
again after a period of inactivity. When the maximum number of threads
is reached, outstanding resolves are held in a queue and served when a
thread becomes available.
The default maximum is expected to work fine for many situations.
Application may override it using this option for the multi handle.
Changing this value while there are resolves in progress is possible.
Increasing the value takes effect right away. Lowering the value does
not close down any resolves, but ends threads above the new maximum
once the resolving is done.
DEFAULT
20.
PROTOCOLS
This functionality affects all supported protocols
EXAMPLE
int main(void)
{
CURLM *m = curl_multi_init();
/* never use more than 5 threads for resolving */
curl_multi_setopt(m, CURLMOPT_RESOLVE_THREADS_MAX, 5L);
}
AVAILABILITY
Added in curl 8.20.0
RETURN VALUE
curl_multi_setopt(3) returns a CURLMcode indicating success or error.
CURLM_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_IPRESOLVE(3), CURLOPT_RESOLVE(3)
libcurl 2026-06-09 CURLMOPT_RESOLVE_THREADS_MAX(3)
curl 8.20.0 - Generated Wed Jun 10 19:15:47 CDT 2026