---
name: "pthread_rwlock_init"
section: "3"
platform: "macos"
package: "libpthread"
version: "539.100.4"
release: "macOS 26.5"
platforms: ["freebsd", "macos"]
url: "https://new.carta.tech/pthread_rwlock_init"
---

# pthread\_rwlock\_init(3)

initialize a read/write lock

## NAME

**pthread\_rwlock\_init** – initialize a read/write lock

## SYNOPSIS

**#include \<pthread.h\>**

*int*\

**pthread\_rwlock\_init**(*pthread\_rwlock\_t \*lock*, *const pthread\_rwlockattr\_t \*attr*);

## DESCRIPTION

The **pthread\_rwlock\_init**() function is used to initialize a read/write lock, with attributes specified by *attr*. If *attr* is NULL, the default read/write lock attributes are used.

The results of calling **pthread\_rwlock\_init**() with an already initialized lock are undefined.

## RETURN VALUES

If successful, the **pthread\_rwlock\_init**() function will return zero. Otherwise an error number will be returned to indicate the error.

## ERRORS

The **pthread\_rwlock\_init**() function will fail if:

- \[EAGAIN\]

  The system lacked the necessary resources (other than memory) to initialize the lock.

- \[ENOMEM\]

  Insufficient memory exists to initialize the lock.

- \[EPERM\]

  The caller does not have sufficient privilege to perform the operation.

The **pthread\_rwlock\_init**() function may fail if:

- \[EBUSY\]

  The system has detected an attempt to re-initialize the object referenced by *lock*, a previously initialized but not yet destroyed read/write lock.

- \[EINVAL\]

  The value specified by *attr* is invalid.

## SEE ALSO

[pthread\_rwlock\_destroy(3)](/pthread_rwlock_destroy/3.md), [pthread\_rwlockattr\_init(3)](/pthread_rwlockattr_init/3.md), [pthread\_rwlockattr\_setpshared(3)](/pthread_rwlockattr_setpshared/3.md)

## STANDARDS

The **pthread\_rwlock\_init**() function is expected to conform to Version 2 of the Single UNIX Specification (“SUSv2”).

## HISTORY

The **pthread\_rwlock\_init**() function first appeared in FreeBSD 3.0.

## BUGS

The PTHREAD\_PROCESS\_SHARED attribute is not supported.