RWMutex.cxx

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/* ====================================================================
 * The Vovida Software License, Version 1.0
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#include "RWMutex.hxx"
#include "Lock.hxx"
#include "rutil/ResipAssert.h"
 
using resip::RWMutex;
using resip::Lock;
 
RWMutex::RWMutex()
   :   mReaderCount(0),
       mWriterHasLock(false),
       mPendingWriterCount(0)
{
}
 
 
RWMutex::~RWMutex()
{
}
 
 
void
RWMutex::readlock()
{
   Lock    lock(mMutex);
 
   while ( mWriterHasLock || mPendingWriterCount > 0 )
   {
      mReadCondition.wait(lock);
   }
 
   mReaderCount++;
}
 
 
void
RWMutex::writelock()
{
   Lock    lock(mMutex);
 
   mPendingWriterCount++;
 
   while ( mWriterHasLock || mReaderCount > 0 )
   {
      mPendingWriteCondition.wait(lock);
   }
 
   mPendingWriterCount--;
 
   mWriterHasLock = true;
}
 
 
void
RWMutex::lock()
{
   writelock();
}
 
 
void
RWMutex::unlock()
{
   Lock    lock(mMutex);
 
   // Unlocking a write lock.
   //
   if ( mWriterHasLock )
   {
      resip_assert( mReaderCount == 0 );
 
      mWriterHasLock = false;
 
      // Pending writers have priority. Could potentially starve readers.
      //
      if ( mPendingWriterCount > 0 )
      {
         mPendingWriteCondition.notify_one();
      }
 
      // No writer, no pending writers, so all the readers can go.
      //
      else
      {
         mReadCondition.notify_all();
      }
 
   }
 
   // Unlocking a read lock.
   //
   else
   {
      resip_assert( mReaderCount > 0 );
 
      mReaderCount--;
 
      if ( mReaderCount == 0 && mPendingWriterCount > 0 )
      {
         mPendingWriteCondition.notify_one();
      }
   }
}
 
unsigned int
RWMutex::readerCount() const
{
   return ( mReaderCount );
}
 
unsigned int
RWMutex::pendingWriterCount() const
{
   return ( mPendingWriterCount );
}