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C:/temp/src/j2k/Posix/RWLock.hpp

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#ifndef __J2K__RWLock_HPP__
#define __J2K__RWLock_HPP__

#include <j2k/Fred/Standard.hpp>
#include <j2k/445/Posix/Mutex.hpp>

class RWLock {
public:
 inline RWLock() 
  : readers( 0 ), readfail( 0 ), writefail( 0 ), loop( 0 ) { }

 inline virtual ~RWLock() { }

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

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

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

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

private:
 // -1 = writing
 // 0  = NotUsed
 // 1+ = reading
 long  readers;
 int   readfail;
 int   writefail;
 int   loop;
 Mutex mutex;
};

#endif

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