private void CleanUp()
{
if (null != workStealingQueue)
{
if (null != workQueue)
{
bool done = false;
while (!done)
{
// Ensure that we won't be aborted between LocalPop and Enqueue.
try { }
finally
{
IHeliosWorkItem cb = null;
if (workStealingQueue.LocalPop(out cb))
{
Contract.Assert(null != cb);
workQueue.Enqueue(cb, true);
}
else
{
done = true;
}
}
}
}
workQueue.allThreadQueues.Remove(workStealingQueue);
}
}
public bool TryEnqueue(IHeliosWorkItem node)
{
//
// If there's room in this segment, atomically increment the upper count (to reserve
// space for this node), then store the node.
// Note that this leaves a window where it will look like there is data in that
// array slot, but it hasn't been written yet. This is taken care of in TryDequeue
// with a busy-wait loop, waiting for the element to become non-null. This implies
// that we can never store null nodes in this data structure.
//
Contract.Assert(null != node);
int upper, lower;
GetIndexes(out upper, out lower);
while (true)
{
if (upper == nodes.Length)
{
return(false);
}
if (CompareExchangeIndexes(ref upper, upper + 1, ref lower, lower))
{
Contract.Assert(Volatile.Read(ref nodes[upper]) == null);
Volatile.Write(ref nodes[upper], node);
return(true);
}
}
}
public void Enqueue(IHeliosWorkItem callback, bool forceGlobal)
{
ThreadPoolWorkQueueThreadLocals tl = null;
if (!forceGlobal)
{
tl = ThreadPoolWorkQueueThreadLocals.threadLocals;
}
if (null != tl)
{
tl.workStealingQueue.LocalPush(callback);
}
else
{
QueueSegment head = queueHead;
while (!head.TryEnqueue(callback))
{
Interlocked.CompareExchange(ref head.Next, new QueueSegment(), null);
while (head.Next != null)
{
Interlocked.CompareExchange(ref queueHead, head.Next, head);
head = queueHead;
}
}
}
}
private bool TrySteal(out IHeliosWorkItem obj, ref bool missedSteal, int millisecondsTimeout)
{
obj = null;
while (true)
{
if (m_headIndex >= m_tailIndex)
{
return(false);
}
bool taken = false;
try
{
m_foreignLock.TryEnter(millisecondsTimeout, ref taken);
if (taken)
{
// Increment head, and ensure read of tail doesn't move before it (fence).
int head = m_headIndex;
Interlocked.Exchange(ref m_headIndex, head + 1);
if (head < m_tailIndex)
{
int idx = head & m_mask;
obj = Volatile.Read(ref m_array[idx]);
// Check for nulls in the array.
if (obj == null)
{
continue;
}
m_array[idx] = null;
return(true);
}
else
{
// Failed, restore head.
m_headIndex = head;
obj = null;
missedSteal = true;
}
}
else
{
missedSteal = true;
}
}
finally
{
if (taken)
{
m_foreignLock.Exit(false);
}
}
return(false);
}
}
public void Dequeue(ThreadPoolWorkQueueThreadLocals tl, out IHeliosWorkItem callback, out bool missedSteal)
{
callback = null;
missedSteal = false;
WorkStealingQueue wsq = tl.workStealingQueue;
if (wsq.LocalPop(out callback))
{
Contract.Assert(null != callback);
}
if (null == callback)
{
QueueSegment tail = queueTail;
while (true)
{
if (tail.TryDequeue(out callback))
{
Contract.Assert(null != callback);
break;
}
if (null == tail.Next || !tail.IsUsedUp())
{
break;
}
else
{
Interlocked.CompareExchange(ref queueTail, tail.Next, tail);
tail = queueTail;
}
}
}
if (null == callback)
{
WorkStealingQueue[] otherQueues = allThreadQueues.Current;
int i = tl.random.Next(otherQueues.Length);
int c = otherQueues.Length;
while (c > 0)
{
WorkStealingQueue otherQueue = Volatile.Read(ref otherQueues[i % otherQueues.Length]);
if (otherQueue != null &&
otherQueue != wsq &&
otherQueue.TrySteal(out callback, ref missedSteal))
{
Contract.Assert(null != callback);
break;
}
i++;
c--;
}
}
}
internal bool LocalFindAndPop(IHeliosWorkItem callback)
{
ThreadPoolWorkQueueThreadLocals tl = ThreadPoolWorkQueueThreadLocals.threadLocals;
if (null == tl)
{
return(false);
}
return(tl.workStealingQueue.LocalFindAndPop(callback));
}
public bool TryDequeue(out IHeliosWorkItem node)
{
//
// If there are nodes in this segment, increment the lower count, then take the
// element we find there.
//
int upper, lower;
GetIndexes(out upper, out lower);
while (true)
{
if (lower == upper)
{
node = null;
return(false);
}
if (CompareExchangeIndexes(ref upper, upper, ref lower, lower + 1))
{
// It's possible that a concurrent call to Enqueue hasn't yet
// written the node reference to the array. We need to spin until
// it shows up.
SpinWait spinner = new SpinWait();
while ((node = Volatile.Read(ref nodes[lower])) == null)
{
spinner.SpinOnce();
}
// Null-out the reference so the object can be GC'd earlier.
nodes[lower] = null;
return(true);
}
}
}
public bool TrySteal(out IHeliosWorkItem obj, ref bool missedSteal)
{
return(TrySteal(out obj, ref missedSteal, 0)); // no blocking by default.
}
public bool LocalPop(out IHeliosWorkItem obj)
{
while (true)
{
// Decrement the tail using a fence to ensure subsequent read doesn't come before.
int tail = m_tailIndex;
if (m_headIndex >= tail)
{
obj = null;
return(false);
}
tail -= 1;
Interlocked.Exchange(ref m_tailIndex, tail);
// If there is no interaction with a take, we can head down the fast path.
if (m_headIndex <= tail)
{
int idx = tail & m_mask;
obj = Volatile.Read(ref m_array[idx]);
// Check for nulls in the array.
if (obj == null)
{
continue;
}
m_array[idx] = null;
return(true);
}
else
{
// Interaction with takes: 0 or 1 elements left.
bool lockTaken = false;
try
{
m_foreignLock.Enter(ref lockTaken);
if (m_headIndex <= tail)
{
// Element still available. Take it.
int idx = tail & m_mask;
obj = Volatile.Read(ref m_array[idx]);
// Check for nulls in the array.
if (obj == null)
{
continue;
}
m_array[idx] = null;
return(true);
}
else
{
// We lost the ----, element was stolen, restore the tail.
m_tailIndex = tail + 1;
obj = null;
return(false);
}
}
finally
{
if (lockTaken)
{
m_foreignLock.Exit(false);
}
}
}
}
}
public bool LocalFindAndPop(IHeliosWorkItem obj)
{
// Fast path: check the tail. If equal, we can skip the lock.
if (m_array[(m_tailIndex - 1) & m_mask] == obj)
{
IHeliosWorkItem unused;
if (LocalPop(out unused))
{
Contract.Assert(unused == obj);
return(true);
}
return(false);
}
// Else, do an O(N) search for the work item. The theory of work stealing and our
// inlining logic is that most waits will happen on recently queued work. And
// since recently queued work will be close to the tail end (which is where we
// begin our search), we will likely find it quickly. In the worst case, we
// will traverse the whole local queue; this is typically not going to be a
// problem (although degenerate cases are clearly an issue) because local work
// queues tend to be somewhat shallow in length, and because if we fail to find
// the work item, we are about to block anyway (which is very expensive).
for (int i = m_tailIndex - 2; i >= m_headIndex; i--)
{
if (m_array[i & m_mask] == obj)
{
// If we found the element, block out steals to avoid interference.
// @
bool lockTaken = false;
try
{
m_foreignLock.Enter(ref lockTaken);
// If we lost the ----, bail.
if (m_array[i & m_mask] == null)
{
return(false);
}
// Otherwise, null out the element.
Volatile.Write(ref m_array[i & m_mask], null);
// And then check to see if we can fix up the indexes (if we're at
// the edge). If we can't, we just leave nulls in the array and they'll
// get filtered out eventually (but may lead to superflous resizing).
if (i == m_tailIndex)
{
m_tailIndex -= 1;
}
else if (i == m_headIndex)
{
m_headIndex += 1;
}
return(true);
}
finally
{
if (lockTaken)
{
m_foreignLock.Exit(false);
}
}
}
}
return(false);
}
public void LocalPush(IHeliosWorkItem obj)
{
int tail = m_tailIndex;
// We're going to increment the tail; if we'll overflow, then we need to reset our counts
if (tail == int.MaxValue)
{
bool lockTaken = false;
try
{
m_foreignLock.Enter(ref lockTaken);
if (m_tailIndex == int.MaxValue)
{
//
// Rather than resetting to zero, we'll just mask off the bits we don't care about.
// This way we don't need to rearrange the items already in the queue; they'll be found
// correctly exactly where they are. One subtlety here is that we need to make sure that
// if head is currently < tail, it remains that way. This happens to just fall out from
// the bit-masking, because we only do this if tail == int.MaxValue, meaning that all
// bits are set, so all of the bits we're keeping will also be set. Thus it's impossible
// for the head to end up > than the tail, since you can't set any more bits than all of
// them.
//
m_headIndex = m_headIndex & m_mask;
m_tailIndex = tail = m_tailIndex & m_mask;
Contract.Assert(m_headIndex <= m_tailIndex);
}
}
finally
{
if (lockTaken)
{
m_foreignLock.Exit(true);
}
}
}
// When there are at least 2 elements' worth of space, we can take the fast path.
if (tail < m_headIndex + m_mask)
{
Volatile.Write(ref m_array[tail & m_mask], obj);
m_tailIndex = tail + 1;
}
else
{
// We need to contend with foreign pops, so we lock.
bool lockTaken = false;
try
{
m_foreignLock.Enter(ref lockTaken);
int head = m_headIndex;
int count = m_tailIndex - m_headIndex;
// If there is still space (one left), just add the element.
if (count >= m_mask)
{
// We're full; expand the queue by doubling its size.
IHeliosWorkItem[] newArray = new IHeliosWorkItem[m_array.Length << 1];
for (int i = 0; i < m_array.Length; i++)
{
newArray[i] = m_array[(i + head) & m_mask];
}
// Reset the field values, incl. the mask.
m_array = newArray;
m_headIndex = 0;
m_tailIndex = tail = count;
m_mask = (m_mask << 1) | 1;
}
Volatile.Write(ref m_array[tail & m_mask], obj);
m_tailIndex = tail + 1;
}
finally
{
if (lockTaken)
{
m_foreignLock.Exit(false);
}
}
}
}
/// <summary>
/// Method run internally by each worker thread
/// </summary>
private bool Dispatch()
{
var workQueue = WorkQueue;
//
// Update our records to indicate that an outstanding request for a thread has now been fulfilled.
// From this point on, we are responsible for requesting another thread if we stop working for any
// reason, and we believe there might still be work in the queue.
MarkThreadRequestSatisfied();
bool needAnotherThread = true;
IHeliosWorkItem workItem = null;
try
{
//Set up thread-local data
ThreadPoolWorkQueueThreadLocals tl = workQueue.EnsureCurrentThreadHasQueue();
while (!_shutdownRequested && tl.ConsecutiveQueueMissCount < workQueue.QueueMissUpperLimit) //look for work until explicitly shut down or too many queue misses
{
bool missedSteal = false;
workQueue.Dequeue(tl, out workItem, out missedSteal);
try
{
}
finally
{
if (workItem == null)
{
//
// No work. We're going to return to the VM once we leave this protected region.
// If we missed a steal, though, there may be more work in the queue.
// Instead of looping around and trying again, we'll just request another thread. This way
// we won't starve other AppDomains while we spin trying to get locks, and hopefully the thread
// that owns the contended work-stealing queue will pick up its own workitems in the meantime,
// which will be more efficient than this thread doing it anyway.
//
needAnotherThread = missedSteal;
}
else
{
//
// If we found work, there may be more work. Ask for another thread so that the other work can be processed
// in parallel. Note that this will only ask for a max of #procs threads, so it's safe to call it for every dequeue.
//
EnsureThreadRequested();
}
}
if (workItem == null)
{
tl.IncrementQueueMiss();
}
else //execute our work
{
tl.ResetQueueMiss();
workItem.ExecuteWorkItem();
workItem = null;
}
}
return(true);
}
finally
{
//had an exception in the course of executing some work, and this thread is going to die.
if (needAnotherThread)
{
EnsureThreadRequested();
}
}
//should never hit this code, unless something catastrophically bad happened (like an aborted thread)
Contract.Assert(false);
return(true);
}
