forksafe_mutex_init()

QNX SDP8.0C Library ReferenceAPIDeveloper

Initialize a forksafe mutex

Synopsis:

#include <forksafe_mutex.h>

forksafe_mutex_t mutex = FORKSAFE_MUTEX_INITIALIZER;

int forksafe_mutex_init(
            forksafe_mutex_t* mutex,
            const pthread_mutexattr_t* attr );

Arguments:

mutex: A pointer to the forksafe_mutex_t object that you want to initialize.
Note:
It's always safe, and typically faster, to assure that mutex is 32-bit aligned.
attr: NULL, or a pointer to a pthread_mutexattr_t object that specifies the attributes that you want to use for the mutex. For more information, see pthread_mutexattr_init().

Library:

libc, libforksafe_mutex

There are two versions of the forksafe_mutex_*() functions:

The functions in libc are declared as weak symbols and use a regular mutex, simply calling the corresponding pthread_mutex_*() functions. Use the -l c option to qcc to link against this library. This library is usually included automatically.
The functions in libforksafe_mutex use a forksafe mutex. Use the -l forksafe_mutex option to qcc to link against this library.

Description:

The forksafe_mutex_init() function initializes the given forksafe mutex object, using the attributes specified by the mutex attributes object attr. If attr is NULL, then the mutex is initialized with the default attributes (see pthread_mutexattr_init()). After initialization, the mutex is in an unlocked state.

CAUTION:

You should allocate synchronization objects only in normal memory mappings. On certain processors, atomic operations such as calls to forksafe_mutex_lock() will cause a fault if the control structure is allocated in uncached memory.

You can initialize a statically allocated mutex with the default attributes by assigning to it the macro FORKSAFE_MUTEX_INITIALIZER or FORKSAFE_RMUTEX_INITIALIZER (for recursive mutexes).

Note:

To destroy a mutex, call forksafe_mutex_destroy(). Once you've destroyed a mutex, don't reuse it without reinitializing it by calling forksafe_mutex_init().

For more information about forksafe mutexes, see Using fork() in a multithreaded process in the Processes and Threads chapter of Getting Started with the QNX OS.

Returns:

EOK: Success.
EFAULT: A fault occurred when the kernel tried to access mutex or attr.
EINVAL: The value specified by attr is invalid.
ENOMEM: All kernel synchronization objects are in use.

Classification:

QNX OS


Safety:
Cancellation point	No
Signal handler	Yes
Thread	Yes

Page updated: August 09, 2024