11-06-2007
Would it not be "n-1" where each semaphore is effectively creating the synchronisation for one arrow?
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LEARN ABOUT OSF1
sem_trywait
sem_wait(3) Library Functions Manual sem_wait(3)
NAME
sem_wait, sem_trywait - Performs (or conditionally performs) a semaphore lock (P1003.1b)
LIBRARY
Realtime Library (librt.so, librt.a)
SYNOPSIS
#include <semaphore.h>
int sem_wait (
sem_t *sem);
int sem_trywait (
sem_t *sem);
PARAMETERS
sem Specifies a pointer to the semaphore to be locked.
DESCRIPTION
The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero,
the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.
The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait
function returns without locking the semaphore.
These functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains
locked until the process unlocks it with a call to the sem_post function.
Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.
RETURN VALUES
If the sem_wait or sem_trywait function returns successfully, a value of 0 (zero) is returned and the function executes the semaphore lock
operation.
On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains
unchanged.
ERRORS
The sem_wait and sem_trywait functions fail under the following conditions:
[EAGAIN] The semaphore was already locked and cannot be locked by the sem_trywait operation (sem_trywait only).
[EINTR] A signal interrupted this function.
[EINVAL] The sem argument does not refer to a valid semaphore.
RELATED INFORMATION
Functions: sem_post(3)
Guide to Realtime Programming delim off
sem_wait(3)