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
In QNX Neutrino 7.1 or later, 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 QNX Neutrino.
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 Neutrino
| Safety: |
|
|---|
| Cancellation point |
No |
| Interrupt handler |
No |
| Signal handler |
Yes |
| Thread |
Yes |