curl/docs/libcurl/opts/CURLSHOPT_LOCKFUNC.md

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---
c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
SPDX-License-Identifier: curl
Title: CURLSHOPT_LOCKFUNC
Section: 3
Source: libcurl
See-also:
- CURLSHOPT_UNLOCKFUNC (3)
- curl_share_cleanup (3)
- curl_share_init (3)
- curl_share_setopt (3)
---
# NAME
CURLSHOPT_LOCKFUNC - mutex lock callback
# SYNOPSIS
~~~c
#include <curl/curl.h>
void lockcb(CURL *handle, curl_lock_data data, curl_lock_access access,
void *clientp);
CURLSHcode curl_share_setopt(CURLSH *share, CURLSHOPT_LOCKFUNC, lockcb);
~~~
# DESCRIPTION
Set a mutex lock callback for the share object, to allow it to get used by
multiple threads concurrently. There is a corresponding
CURLSHOPT_UNLOCKFUNC(3) callback called when the mutex is again released.
The *lockcb* argument must be a pointer to a function matching the
prototype shown above. The arguments to the callback are:
*handle* is the currently active easy handle in use when the share object
is intended to get used.
The *data* argument tells what kind of data libcurl wants to lock. Make
sure that the callback uses a different lock for each kind of data.
*access* defines what access type libcurl wants, shared or single.
*clientp* is the private pointer you set with CURLSHOPT_USERDATA(3).
This pointer is not used by libcurl itself.
# PROTOCOLS
All
# EXAMPLE
~~~c
extern void mutex_lock(CURL *handle, curl_lock_data data,
curl_lock_access access, void *clientp);
int main(void)
{
CURLSHcode sh;
CURLSH *share = curl_share_init();
sh = curl_share_setopt(share, CURLSHOPT_LOCKFUNC, mutex_lock);
if(sh)
printf("Error: %s\n", curl_share_strerror(sh));
}
~~~
# AVAILABILITY
Added in 7.10
# RETURN VALUE
CURLSHE_OK (zero) means that the option was set properly, non-zero means an
error occurred. See libcurl-errors(3) for the full list with
descriptions.