---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.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)
Protocol:
  - All
---

# 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.

# 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.