pthread_mutexattr_settype()
Set a mutex type
Synopsis:
#include <pthread.h>
int pthread_mutexattr_settype(
pthread_mutexattr_t * attr,
int type );
Arguments:
- attr
- A pointer to the pthread_mutexattr_t object that you want to set the attribute in.
- type
- The new type; one of:
- PTHREAD_MUTEX_NORMAL
- PTHREAD_MUTEX_ERRORCHECK
- PTHREAD_MUTEX_RECURSIVE
- PTHREAD_MUTEX_DEFAULT
In QNX OS, PTHREAD_MUTEX_DEFAULT mutexes are treated in the same way as PTHREAD_MUTEX_ERRORCHECK ones.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The pthread_mutexattr_settype() function sets the mutex type in the mutex attribute object attr to the value given by type.
To make the mutext robust (PTHREAD_MUTEX_ROBUST) or nonrobust (PTHREAD_MUTEX_STALLED), call pthread_mutexattr_setrobust().
The type and the robustness govern the behavior of the mutex when you relock the mutex without first unlocking it, and when you try to unlock a mutex that you don't own or that isn't locked:
| Mutex type | Robustness | Relock | Unlock when not the owner |
|---|---|---|---|
| NORMAL | STALLED | Deadlock | Undefined behavior |
| NORMAL | ROBUST | Deadlock | pthread_mutex_unlock() returns EPERM |
| ERRORCHECK | Either | pthread_mutex_lock() and pthread_mutex_timedlock() return EDEADLK | pthread_mutex_unlock() returns EPERM |
| RECURSIVE | Either | The lock count is incremented. You must unlock it the same number of times before another thread can acquire the mutex. | pthread_mutex_unlock() returns EPERM |
| DEFAULT | Either | pthread_mutex_lock() and pthread_mutex_timedlock() return EDEADLK | pthread_mutex_unlock() returns EPERM |
Returns:
- EOK
- Success.
- EINVAL
- The value specified by attr or type is invalid.
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |
Caveats:
An application shouldn't use a PTHREAD_MUTEX_RECURSIVE mutex with condition variables because the implicit unlock performed for a pthread_cond_wait() or pthread_cond_timedwait() may not actually release the mutex (if it's been locked multiple times). If this happens, no other thread can satisfy the condition of the predicate.