Create a synchronization object
#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 );
- One of the following:
- _NTO_SYNC_MUTEX_FREE — create a mutex.
- _NTO_SYNC_SEM — create a semaphore.
- _NTO_SYNC_COND — create a condition variable.
- A pointer to a sync_t that the kernel sets up for the synchronization object; see below.
- A pointer to a _sync_attr structure that specifies
attributes for the object.
This structure contains at least the following members:
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.
- int protocol — PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The SyncTypeCreate() and SyncTypeCreate_r() kernel calls create a synchronization object in the kernel and initializes sync for use in other synchronization kernel calls. The synchronization object is local to the process. These functions are similar, except for the way they indicate errors. See the Returns section for details.
Synchronization objects can be used for mutexes, semaphores, or condition variables.
The sync_t argument contains at least the following members:
- int __count
- The count for recursive mutexes and semaphores. The kernel sets this member when it creates the synchronization object.
- int __owner
- When a mutex is created, this member holds the thread ID of the thread that acquired the mutex. When unowned, the value is 0. It's set to zero when the synchronization object is created.
The current state of sync is summarized below:
|0||-1||Statically initialized; auto-created when used|
|count||>0||Recursive counter number of the mutex|
|count||<-1||If the high bit of count is set, it's a flag meaning others waiting|
|--||-256||Mutex is dead, waits for revival|
The synchronization object is destroyed by a call to SyncDestroy() .
These calls don't block.
The only difference between these functions is the way they indicate errors:
- If an error occurs, the function returns -1 and sets errno . Any other value returned indicates success.
- Returns EOK on success. This function does NOT set errno. If an error occurs, the function can return any value in the Errors section.
- All kernel synchronization objects are in use.
- A fault occurred when the kernel tried to access sync or attr.
- the type isn't one of
_NTO_SYNC_COND, _NTO_SYNC_MUTEX_FREE or _NTO_SYNC_SEM
- 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.
- the type isn't one of _NTO_SYNC_COND, _NTO_SYNC_MUTEX_FREE or _NTO_SYNC_SEM