sem_init()
Initialize an unnamed semaphore
Synopsis:
#include <semaphore.h> int sem_init( sem_t * sem, int pshared, unsigned value );
Arguments:
- sem
- A pointer to the sem_t object for the semaphore that you want to initialize.
- pshared
- Nonzero if you want the semaphore to be shared between processes via shared memory.
- value
- The initial value of the semaphore. A positive value (i.e. greater than zero) indicates an unlocked semaphore, and a value of 0 (zero) indicates a locked semaphore. This value must not exceed SEM_VALUE_MAX.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The sem_init() function initializes the unnamed semaphore referred to by the sem argument. The initial counter value of this semaphore is specified by the value argument.
You can use the initialized semaphore in subsequent calls to sem_wait() , sem_trywait() , sem_post() , and sem_destroy() . An initialized semaphore is valid until it's destroyed by the sem_destroy() function, or until the memory where the semaphore resides is released.
If the pshared argument is nonzero, then the semaphore can be shared between processes via shared memory. Any process can then use sem with the sem_wait(), sem_trywait(), sem_post() and sem_destroy() functions.
Returns:
- 0
- Success. The semaphore referred to by sem is initialized.
- -1
- An error occurred (errno is set).
Errors:
- EAGAIN
- A resource required to initialize the semaphore has been exhausted.
- EBUSY
- The given semaphore was previously initialized, and has not been destroyed.
- EINVAL
- The value argument exceeds SEM_VALUE_MAX.
- EPERM
- The process lacks the appropriate privileges to initialize the semaphore.
- ENOSPC
- A resource required to initialize the semaphore has been exhausted.
- ENOSYS
- The sem_init() function isn't supported.
Classification:
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | No |
Thread | Yes |
Caveats:
Don't initialize the same semaphore from more than one thread. It's best to set up semaphores before starting any threads.