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/*
* -------------------------------------------------------------
*
* Module: semaphore.c
*
* Purpose:
* Semaphores aren't actually part of the PThreads standard.
* They are defined by the POSIX Standard:
*
* POSIX 1003.1b-1993 (POSIX.1b)
*
* They are supposed to follow the older UNIX convention for
* reporting errors. That is, on failure they are supposed
* to return a value of -1 and store the appropriate error
* number into 'errno'.
* HOWEVER,errno cannot be modified in a multithreaded
* program on WIN32; therefore, the value is returned as
* the function value.
* It is recommended that you compare for zero (0) for success
* instead of -1 for failure when checking the status of
* these functions.
*
* Contents:
* Public Methods Author
* -------------- ------
* sem_init John E. Bossom Mar 1998
* sem_destroy John E. Bossom Mar 1998
* sem_trywait John E. Bossom Mar 1998
* sem_wait John E. Bossom Mar 1998
* sem_post John E. Bossom Mar 1998
*
* Private Methods
* ---------------
*
* -------------------------------------------------------------
*/
#include <pthread.h>
#include <windows.h>
#include <process.h>
#include <errno.h>
#include <string.h>
#include "semaphore.h"
int
sem_init (sem_t * sem, int pshared, unsigned int value)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function initializes an unnamed semaphore. the
* initial value of the semaphore is 'value'
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
* pshared
* if zero, this semaphore may only be shared between
* threads in the same process.
* if nonzero, the semaphore can be shared between
* processes
*
* value
* initial value of the semaphore counter
*
* DESCRIPTION
* This function initializes an unnamed semaphore. The
* initial value of the semaphore is set to 'value'.
*
* RESULTS
* 0 successfully created semaphore,
* EINVAL 'sem' is not a valid semaphore,
* ENOSPC a required resource has been exhausted,
* ENOSYS semaphores are not supported,
* EPERM the process lacks appropriate privilege
*
* ------------------------------------------------------
*/
{
int result = 0;
if (pshared != 0)
{
/*
* Creating a semaphore that can be shared between
* processes
*/
result = EPERM;
}
else
{
/*
* NOTE: Taking advantage of the fact that
* sem_t is a simple structure with one entry;
* We don't have to allocate it...
*/
*sem = CreateSemaphore (
0,
value,
0x7FFFFFF,
NULL);
if (*sem == 0)
{
result = ENOSPC;
}
}
return (result);
} /* sem_init */
int
sem_destroy (sem_t * sem)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function destroys an unnamed semaphore.
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
* DESCRIPTION
* This function destroys an unnamed semaphore.
*
* RESULTS
* 0 successfully destroyed semaphore,
* EINVAL 'sem' is not a valid semaphore,
* ENOSYS semaphores are not supported,
* EBUSY threads (or processes) are currently
* blocked on 'sem'
*
* ------------------------------------------------------
*/
{
return ((sem == NULL)
? EINVAL
: (CloseHandle (*sem)
? 0
: EINVAL));
} /* sem_destroy */
int
sem_trywait (sem_t * sem)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function tries to wait on a semaphore.
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
* DESCRIPTION
* This function tries to wait on a semaphore. If the
* semaphore value is greater than zero, it decreases
* its value by one. If the semaphore value is zero, then
* this function returns immediately with the error EAGAIN
*
* RESULTS
* 0 successfully destroyed semaphore,
* EAGAIN the semaphore was already locked,
* EINVAL 'sem' is not a valid semaphore,
* ENOSYS semaphores are not supported,
* EINTR the function was interrupted by a signal,
* EDEADLK a deadlock condition was detected.
*
* ------------------------------------------------------
*/
{
return ((sem == NULL)
? EINVAL
: ((WaitForSingleObject (*sem, 0) == WAIT_TIMEOUT)
? EAGAIN
: 0));
} /* sem_trywait */
int
sem_wait (sem_t * sem)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function waits on a semaphore.
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
* DESCRIPTION
* This function waits on a semaphore. If the
* semaphore value is greater than zero, it decreases
* its value by one. If the semaphore value is zero, then
* the calling thread (or process) is blocked until it can
* successfully decrease the value or until interrupted by
* a signal.
*
* RESULTS
* 0 successfully destroyed semaphore,
* EINVAL 'sem' is not a valid semaphore,
* ENOSYS semaphores are not supported,
* EINTR the function was interrupted by a signal,
* EDEADLK a deadlock condition was detected.
*
* ------------------------------------------------------
*/
{
return ((sem == NULL)
? EINVAL
: pthreadCancelableWait (*sem)
);
} /* sem_wait */
int
sem_post (sem_t * sem)
/*
* ------------------------------------------------------
* DOCPUBLIC
* This function posts a wakeup to a semaphore.
*
* PARAMETERS
* sem
* pointer to an instance of sem_t
*
* DESCRIPTION
* This function posts a wakeup to a semaphore. If there
* are waiting threads (or processes), on is awakened;
* otherwise, the semaphore value is incremented by one.
*
* RESULTS
* 0 successfully destroyed semaphore,
* EINVAL 'sem' is not a valid semaphore,
* ENOSYS semaphores are not supported,
*
* ------------------------------------------------------
*/
{
return ((sem == NULL)
? EINVAL
: (ReleaseSemaphore (*sem, 1, 0)
? 0
: EINVAL));
} /* sem_post */

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