SyncTypeCreate(), SyncTypeCreate

Note: Don't use the SyncTypeCreate() or SyncTypeCreate_r() kernel call directly; instead, use the POSIX functions for synchronization objects (see pthread_cond_init(), pthread_mutex_init(), pthread_rwlock_init(), and sem_init()).

Synopsis:

#include <sys/neutrino.h>

int SyncTypeCreate( 
        unsigned type,
        sync_t * sync,
        const struct _sync_attr * attr );

int SyncTypeCreate_r( 
        unsigned type,
        sync_t * sync,
        const struct _sync_attr * attr );

Arguments:

type

One of the following:

_NTO_SYNC_MUTEX_FREE — create a mutex.
_NTO_SYNC_SEM — create a semaphore.
_NTO_SYNC_COND — create a condition variable.

sync

A pointer to a sync_t object that the kernel sets up for the synchronization object; you should treat this as an opaque structure.

Note: It's always safe, and typically faster, to assure that sync is 32-bit aligned.

attr

A pointer to a _sync_attr structure that specifies attributes for the object. This structure contains at least the following members:

int __protocol — PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT.
Note: If you use PTHREAD_PRIO_PROTECT and you want to change the priority ceiling to a value above the maximum permitted for unprivileged processes, your process must have the PROCMGR_AID_PRIORITY ability enabled. For more information, see procmgr_ability().

If attr is NULL, the default attributes (PTHREAD_PRIO_INHERIT) are assumed.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The SyncTypeCreate() and SyncTypeCreate_r() kernel calls create a synchronization object in the kernel and initializes sync for use in other synchronization kernel calls. These functions are similar, except for the way they indicate errors. See the Returns section for details.

CAUTION:

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

Synchronization objects can be used for mutexes, semaphores, or condition variables.

You can destroy the synchronization object by calling SyncDestroy().

Blocking states

These calls don't block.

Returns:

The only difference between these functions is the way they indicate errors:

SyncTypeCreate(): If an error occurs, the function returns -1 and sets errno. Any other value returned indicates success.
SyncTypeCreate_r(): Returns EOK on success. This function does NOT set errno. If an error occurs, the function can return any value in the Errors section.

Errors:

EAGAIN

All kernel synchronization objects are in use.

EBUSY

The synchronization object indicated by sync was previously initialized but hasn't been destroyed.

EFAULT

A fault occurred when the kernel tried to access sync or attr.

EINVAL

Either:

the type isn't one of _NTO_SYNC_COND, _NTO_SYNC_MUTEX_FREE or _NTO_SYNC_SEM
Or:
if the type is correct, and the synchronization object is:
- a mutex — the protocol isn't one of PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT.
- a mutex and PTHREAD_PRIO_PROTECT is specified — the ceiling priority isn't within the kernel priority range.
- a condvar — the clock type is invalid.
- a semaphore — the semaphore value exceeds SEM_VALUE_MAX.

Classification:

QNX Neutrino

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes

SyncTypeCreate(), SyncTypeCreate_r()