/// A wait free alternative to offer which fails on CAS failure.
/// @param e new element, not null
/// @return 1 if next element cannot be filled, -1 if CAS failed, 0 if successful
public int WeakEnqueue(T e)
{
Contract.Requires(e != null);
long mask = this.Mask;
long capacity = mask + 1;
long currentTail = this.ProducerIndex; // LoadLoad
long consumerIndexCache = this.ConsumerIndexCache; // LoadLoad
long wrapPoint = currentTail - capacity;
if (consumerIndexCache <= wrapPoint)
{
long currHead = this.ConsumerIndex; // LoadLoad
if (currHead <= wrapPoint)
{
return(1); // FULL :(
}
else
{
this.ConsumerIndexCache = currHead; // StoreLoad
}
}
// look Ma, no loop!
if (!this.TrySetProducerIndex(currentTail, currentTail + 1))
{
return(-1); // CAS FAIL :(
}
// Won CAS, move on to storing
long offset = RefArrayAccessUtil.CalcElementOffset(currentTail, mask);
this.SoElement(offset, e);
return(0); // AWESOME :)
}
/// {@inheritDoc}
/// <br />
/// IMPLEMENTATION NOTES:
/// <br />
/// Lock free offer using a single CAS. As class name suggests access is permitted to many threads
/// concurrently.
/// @see java.util.Queue#offer(java.lang.Object)
public override bool TryEnqueue(T e)
{
Contract.Requires(e != null);
// use a cached view on consumer index (potentially updated in loop)
long mask = this.Mask;
long capacity = mask + 1;
long consumerIndexCache = this.ConsumerIndexCache; // LoadLoad
long currentProducerIndex;
do
{
currentProducerIndex = this.ProducerIndex; // LoadLoad
long wrapPoint = currentProducerIndex - capacity;
if (consumerIndexCache <= wrapPoint)
{
long currHead = this.ConsumerIndex; // LoadLoad
if (currHead <= wrapPoint)
{
return(false); // FULL :(
}
else
{
// update shared cached value of the consumerIndex
this.ConsumerIndexCache = currHead; // StoreLoad
// update on stack copy, we might need this value again if we lose the CAS.
consumerIndexCache = currHead;
}
}
}while (!this.TrySetProducerIndex(currentProducerIndex, currentProducerIndex + 1));
// NOTE: the new producer index value is made visible BEFORE the element in the array. If we relied on
// the index visibility to poll() we would need to handle the case where the element is not visible.
// Won CAS, move on to storing
long offset = RefArrayAccessUtil.CalcElementOffset(currentProducerIndex, mask);
this.SoElement(offset, e); // StoreStore
return(true); // AWESOME :)
}
/// @param index desirable element index /// @return the offset in bytes within the array for a given index. protected long CalcElementOffset(long index) => RefArrayAccessUtil.CalcElementOffset(index, this.Mask);