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/*
* Modification History
*
* 2001-January-11 Jason Rohrer
* Created.
*
* 2003-August-26 Jason Rohrer
* Added support for timeouts on wait.
*
* 2006-February-28 Jason Rohrer
* Fixed bug in sub-second timeout computation.
*/
#include "minorGems/system/BinarySemaphore.h"
#include "minorGems/system/Time.h"
#include <pthread.h>
/**
* Linux-specific implementation of the BinarySemaphore class member functions.
*
* May also be compatible with other POSIX-like systems.
*
* To compile:
* g++ -lpthread
*/
/**
* Native object pointer A is the condition variable.
* Pointer B is the mutex that must go along with it.
*/
BinarySemaphore::BinarySemaphore() :
mSemaphoreValue( 0 ) {
// allocate a condition variable structure on the heap
mNativeObjectPointerA = (void *)( new pthread_cond_t[1] );
// get a pointer to the cond
pthread_cond_t *condPointer =
(pthread_cond_t *)mNativeObjectPointerA;
// init the cond
pthread_cond_init( &( condPointer[0] ), NULL );
// allocate a mutex structure on the heap
mNativeObjectPointerB = (void *)( new pthread_mutex_t[1] );
// get a pointer to the mutex
pthread_mutex_t *mutexPointer =
(pthread_mutex_t *)mNativeObjectPointerB;
// init the mutex
pthread_mutex_init( &( mutexPointer[0] ), NULL );
}
BinarySemaphore::~BinarySemaphore() {
// get a pointer to the cond
pthread_cond_t *condPointer =
(pthread_cond_t *)mNativeObjectPointerA;
// destroy the cond
pthread_cond_destroy( &( condPointer[0] ) );
// de-allocate the cond structure from the heap
delete [] condPointer;
// get a pointer to the mutex
pthread_mutex_t *mutexPointer =
(pthread_mutex_t *)mNativeObjectPointerB;
// destroy the mutex
pthread_mutex_destroy( &( mutexPointer[0] ) );
// de-allocate the mutex structure from the heap
delete [] mutexPointer;
}
int BinarySemaphore::wait( int inTimeoutInMilliseconds ) {
int returnValue = 1;
// get a pointer to the cond
pthread_cond_t *condPointer =
(pthread_cond_t *)mNativeObjectPointerA;
// get a pointer to the mutex
pthread_mutex_t *mutexPointer =
(pthread_mutex_t *)mNativeObjectPointerB;
// lock the mutex
pthread_mutex_lock( &( mutexPointer[0] ) );
if( mSemaphoreValue == 0 ) {
// wait on condition variable, which automatically unlocks
// the passed-in mutex
if( inTimeoutInMilliseconds == -1 ) {
// no timeout
pthread_cond_wait( &( condPointer[0] ), &( mutexPointer[0] ) );
}
else {
// use timeout version
unsigned long nsecPerSecond = 1000000000;
unsigned long nsecPerMillisecond = 1000000;
unsigned long currentSec;
unsigned long currentMS;
Time::getCurrentTime( ¤tSec, ¤tMS );
unsigned long currentNS = currentMS * nsecPerMillisecond;
long timeoutSec = inTimeoutInMilliseconds / 1000;
long extraMS = inTimeoutInMilliseconds % 1000;
long extraNS = extraMS * nsecPerMillisecond;
unsigned long absTimeoutSec = currentSec + timeoutSec;
unsigned long absTimeoutNsec = currentNS + extraNS;
// check for nsec overflow
if( absTimeoutNsec > nsecPerSecond ) {
absTimeoutSec += 1;
absTimeoutNsec -= nsecPerSecond;
}
struct timespec abstime;
abstime.tv_sec = absTimeoutSec;
abstime.tv_nsec = absTimeoutNsec;
int result = pthread_cond_timedwait( &( condPointer[0] ),
&( mutexPointer[0] ),
&abstime );
if( result != 0 ) {
// timed out
returnValue = 0;
}
}
// mutex is apparently re-locked when we return from cond_wait
}
// decrement the semaphore value
mSemaphoreValue = 0;
// unlock the mutex again
pthread_mutex_unlock( &( mutexPointer[0] ) );
return returnValue;
}
void BinarySemaphore::signal() {
// get a pointer to the cond
pthread_cond_t *condPointer =
(pthread_cond_t *)mNativeObjectPointerA;
// get a pointer to the mutex
pthread_mutex_t *mutexPointer =
(pthread_mutex_t *)mNativeObjectPointerB;
// lock the mutex
pthread_mutex_lock( &( mutexPointer[0] ) );
// increment the semaphore value
mSemaphoreValue = 1;
pthread_cond_signal( &( condPointer[0] ) );
// unlock the mutex
pthread_mutex_unlock( &( mutexPointer[0] ) );
}
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