/// <summary>
/// (asynchronously) block until there is a process available on the local queue, the rack queue
/// or the cluster queue, then return that process. If ShutDown is called, this returns null
/// immediately
/// </summary>
private async Task <Process> GetProcess()
{
// make a new waiter object to block on all the available queues until a Process is available
var waiter = new ProcessWaiter(this);
// get the actual blocker Task out of the waiter
var blocker = waiter.Initialize();
logger.Log("Computer " + name + " trying to find process on local queue");
// try to match with an available Process in the local queue. If AddWaiter returns false, there
// wasn't one, but by passing in waiter, we ensure that blocker will be unblocked if one
// turns up. If Peek returns true there was already a waiting Process to be paired with,
// blocker has been unblocked, and the await below will fall through immediately and return
// the process; in this case don't bother to add the waiter to the rack and cluster queues.
if (!localQueue.AddWaiter(waiter))
{
logger.Log("Computer " + name + " trying to find process on rack queue");
// there was no local process, so try to match with an available Process in the rack queue.
// If Peek returns false, there wasn't one, but by passing in waiter, we ensure that blocker
// will be unblocked if one turns up. If Peek returns true then blocker is already unblocked
// (because there was a Process in the rack queue, or by the localQueue we just put it in above)
// and matched with a waiting process, and the await below will fall through immediately.
if (!rackQueue.AddWaiter(waiter))
{
logger.Log("Computer " + name + " trying to find process on cluster queue");
// there was no local or rack process, so try to match with an available Process in the
// cluster queue.
clusterQueue.AddWaiter(waiter);
}
}
logger.Log("Computer " + name + " waiting for matched process");
// we want to wait either for waiter to be matched with a Process in one of the three queues, or
// for ShutDown to be called, so make an array of tasks and wait for the first one to be unblocked.
TaskCompletionSource <Process> thisWaiter = GetAsyncFinishWaiter();
var unblocked = await Task.WhenAny(blocker, thisWaiter.Task);
RemoveAsyncFinishWaiter(thisWaiter);
if (unblocked.Result != null)
{
logger.Log("Computer " + name + " matched process " + blocker.Result.Id);
}
else
{
logger.Log("Computer " + name + " unblocked by shutdown");
}
return(unblocked.Result);
}
/// <summary>
/// add a waiting computer. If there is an unclaimed process waiting, the
/// process will be assigned to the computer and the computer's Task will be
/// unblocked. Returns true if the waiter has been matched (by this call or
/// another asynchronous event in the meantime). Returns false if the computer
/// still needs to be matched.
/// </summary>
/// <param name="waiter">holder for the waiting computer</param>
/// <returns></returns>
public bool AddWaiter(ProcessWaiter waiter)
{
// process will exit the lock holding the value of the newly-claimed process, if
// any. process may be non-null exiting the lock even if there was no
// unclaimed process; the claimed flag below disambiguates
Process process = null;
// claimed will exit the lock set to true if and only if there was an unclaimed
// waiter, in which case waiter will be set to the value of the waiter
bool claimed = false;
// lock ordering discipline is Queue first, then waiter, then process
lock (this)
{
if (!active)
{
// the queue has been shut down so don't accept another waiter
lock (waiter)
{
if (waiter.Unclaimed)
{
waiter.Claim();
// this will make us Dispatch the waiter with a null process below
// which is correct since the queue has been shut down, and will cause
// the waiting computer's commandloop to exit if it hasn't already
claimed = true;
}
}
}
// even if there are processes, they may have been claimed by other computers
// already, so use a loop here
while (active && processQueue.Count > 0 && !claimed)
{
// get the next available process; don't dequeue it yet because
// we have to wait until we acquire the locks below to figure out
// if it's going to be matched to anything
process = processQueue.Peek();
// lock ordering discipline is Queue first, then waiter, then process
lock (waiter)
{
if (waiter.Unclaimed)
{
// lock ordering discipline is Queue first, then waiter, then process
lock (process)
{
// another queue might have turned up and claimed the Process
// while we were dithering; matching a process to a computer
// must be done while both are locked
if (process.Unclaimed)
{
// remove the process from the queue and match it to the computer
processQueue.Dequeue();
var computer = waiter.Claim();
process.Claim(computer);
// break out of the loop
claimed = true;
}
else
{
// the process that we Peek()ed above was already claimed so discard it
// and go around the loop again
processQueue.Dequeue();
}
}
}
else
{
// there's no point in continuing to look for a process for the waiter
// since it has been claimed by someone else.
// The process we Peek()ed is left in the queue for the next
// waiter to match
return true;
}
}
}
// there were no unclaimed processes, so add the waiter to the queue of
// waiting computers
if (!claimed)
{
waiterQueue.Enqueue(waiter);
}
}
// exit the lock before triggering the wakeup of the computer
if (claimed)
{
// this pairs the process with the computer
waiter.Dispatch(process);
return true;
}
else
{
return false;
}
}
/// <summary>
/// add a waiting computer. If there is an unclaimed process waiting, the
/// process will be assigned to the computer and the computer's Task will be
/// unblocked. Returns true if the waiter has been matched (by this call or
/// another asynchronous event in the meantime). Returns false if the computer
/// still needs to be matched.
/// </summary>
/// <param name="waiter">holder for the waiting computer</param>
/// <returns></returns>
public bool AddWaiter(ProcessWaiter waiter)
{
// process will exit the lock holding the value of the newly-claimed process, if
// any. process may be non-null exiting the lock even if there was no
// unclaimed process; the claimed flag below disambiguates
Process process = null;
// claimed will exit the lock set to true if and only if there was an unclaimed
// waiter, in which case waiter will be set to the value of the waiter
bool claimed = false;
// lock ordering discipline is Queue first, then waiter, then process
lock (this)
{
if (!active)
{
// the queue has been shut down so don't accept another waiter
lock (waiter)
{
if (waiter.Unclaimed)
{
waiter.Claim();
// this will make us Dispatch the waiter with a null process below
// which is correct since the queue has been shut down, and will cause
// the waiting computer's commandloop to exit if it hasn't already
claimed = true;
}
}
}
// even if there are processes, they may have been claimed by other computers
// already, so use a loop here
while (active && processQueue.Count > 0 && !claimed)
{
// get the next available process; don't dequeue it yet because
// we have to wait until we acquire the locks below to figure out
// if it's going to be matched to anything
process = processQueue.Peek();
// lock ordering discipline is Queue first, then waiter, then process
lock (waiter)
{
if (waiter.Unclaimed)
{
// lock ordering discipline is Queue first, then waiter, then process
lock (process)
{
// another queue might have turned up and claimed the Process
// while we were dithering; matching a process to a computer
// must be done while both are locked
if (process.Unclaimed)
{
// remove the process from the queue and match it to the computer
processQueue.Dequeue();
var computer = waiter.Claim();
process.Claim(computer);
// break out of the loop
claimed = true;
}
else
{
// the process that we Peek()ed above was already claimed so discard it
// and go around the loop again
processQueue.Dequeue();
}
}
}
else
{
// there's no point in continuing to look for a process for the waiter
// since it has been claimed by someone else.
// The process we Peek()ed is left in the queue for the next
// waiter to match
return(true);
}
}
}
// there were no unclaimed processes, so add the waiter to the queue of
// waiting computers
if (!claimed)
{
waiterQueue.Enqueue(waiter);
}
}
// exit the lock before triggering the wakeup of the computer
if (claimed)
{
// this pairs the process with the computer
waiter.Dispatch(process);
return(true);
}
else
{
return(false);
}
}
/// <summary>
/// add a schedulable process. If there is an unclaimed computer waiting, the
/// process will be assigned to the computer and the computer's Task will be
/// unblocked. Returns true if the process has been matched (by this call or
/// another asynchronous event in the meantime). Returns false if the process
/// still needs to be matched.
/// </summary>
public bool AddProcess(Process process)
{
// waiter will exit the lock holding the value of the newly-claimed waiter, if
// any. waiter may be non-null exiting the lock even if there was no
// unclaimed waiter; the claimed flag below disambiguates
ProcessWaiter waiter = null;
// claimed will exit the lock set to true if and only if there was an unclaimed
// waiter, in which case waiter will be set to the value of the waiter
bool claimed = false;
// lock ordering discipline is Queue first, then waiter, then process
lock (this)
{
// if we are shutting down, return immediately
if (!active)
{
return(false);
}
// even if there are waiters, they may have been claimed by processes
// already, so use a loop here
while (waiterQueue.Count > 0 && !claimed)
{
// get the next available waiter; don't dequeue it yet because
// we have to wait until we acquire the locks below to figure out
// if it's going to be matched to anything
waiter = waiterQueue.Peek();
// lock ordering discipline is Queue first, then waiter, then process
lock (waiter)
{
if (waiter.Unclaimed)
{
// lock ordering discipline is Queue first, then waiter, then process
lock (process)
{
// another queue might have turned up and claimed the Process
// while we were dithering; matching a process to a computer
// must be done while both are locked
if (process.Unclaimed)
{
// remove the waiter from the queue and match it to the process
waiterQueue.Dequeue();
var computer = waiter.Claim();
process.Claim(computer);
// break out of the loop
claimed = true;
}
else
{
// there's no point in continuing to try to add the process
// since it has been claimed by someone else.
// The waiter we Peek()ed is left in the queue for the next
// process to match
return(true);
}
}
}
else
{
// the waiter that we Peek()ed above was already claimed so discard it
// and go around the loop again
waiterQueue.Dequeue();
}
}
}
// there were no unclaimed waiters, so add the process to the queue of
// schedulable items while we're holding the queue lock
if (!claimed)
{
lock (process)
{
// let the process know it has been added to another queue
process.IncrementQueueCount();
}
processQueue.Enqueue(process);
}
}
// exit the lock before triggering the wakeup of the computer
if (claimed)
{
// this pairs the process with the computer
waiter.Dispatch(process);
return(true);
}
else
{
return(false);
}
}
