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C:/temp/src/j2k/nto/bak2/RWLock.cpp

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#ifndef __J2K__RWLock_CPP__
#define __J2K__RWLock_CPP__

#include <j2k/nto/RWLock.hpp>

//
// Classical Implementation of Reader/Writer lock using Mutex
// Don't use pthread_rwlock, since it's not implemented on every platforms;
// however, pthread_mutex is more common than pthread_rwlock, 
// so use it to implement the other.
//
// It's also simpler to code then to play with C structs...
//

 void RWLock::read() {
   readfail = 1;
   do {
     if ( loop ) sched_yield();
     loop = 1;
     mutex.lock();
     if ( readers >= 0 ) {
       readers++;
       readfail = 0;
     }
     mutex.unlock();
   } while( readfail );
 }

 void RWLock::releaseRead() {
   mutex.lock();
   if ( readers >= 0 ) {
     readers--;
   }   
   mutex.unlock();
 }

 void RWLock::releaseWrite() {
   mutex.lock();
   if ( readers < 0 ) {
     readers = 0;
   }   
   mutex.unlock();
 }

 void RWLock::write() {
   writefail = 1;
   do {
     if ( loop ) sched_yield();
     loop = 1;
     mutex.lock();
     if ( readers == 0 ) {
       readers   = -1;
       writefail = 0;
     }
     mutex.unlock();     
   } while( writefail );   
 }

#endif

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