1.1 --- a/PrivateQueue.c	Wed Dec 19 15:38:08 2012 +0100
     1.2 +++ b/PrivateQueue.c	Wed Mar 06 14:33:55 2013 +0100
     1.3 @@ -149,11 +149,17 @@
     1.4     void **extractPos = Q->extractPos;
     1.5  
     1.6        //if not empty -- (extract is just below insert when empty)
     1.7 -   if( insertPos - extractPos != 1 &&
     1.8 -       !(extractPos == endOfData && insertPos == startOfData))
     1.9 -    { 
    1.10 -      out = *(Q->extractPos + 1);
    1.11 -      return out;
    1.12 +       if (insertPos - extractPos != 1 &&
    1.13 +            !(extractPos == endOfData && insertPos == startOfData)) { //move before read
    1.14 +        if (extractPos == endOfData) //write new pos exactly once, correctly
    1.15 +        {
    1.16 +            out = *(startOfData); //can't overrun then fix it 'cause
    1.17 +        }// other thread might read bad pos
    1.18 +        else {
    1.19 +            out = *(Q->extractPos + 1);
    1.20 +        }
    1.21 +        
    1.22 +        return out;
    1.23      }
    1.24        //Q is empty
    1.25     return NULL;
    1.26 @@ -162,9 +168,6 @@
    1.27  /*Returns NULL when queue is empty
    1.28   */
    1.29  void* readPrivQ(PrivQueueStruc* Q) {
    1.30 -#ifdef DEBUG_PRIVATE_Q
    1.31 -    Q->numReads++;
    1.32 -#endif
    1.33      
    1.34      void *out = 0;
    1.35      void **startOfData = Q->startOfData;
    1.36 @@ -184,6 +187,10 @@
    1.37              Q->extractPos++;
    1.38          }
    1.39          out = *(Q->extractPos);
    1.40 +        //*(Q->extractPos) = NULL;
    1.41 +#ifdef DEBUG_PRIVATE_Q
    1.42 +        Q->numReads++;
    1.43 +#endif
    1.44          return out;
    1.45      }
    1.46      //Q is empty