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//------------------------------------------------------------------------------
// <copyright file="RequestQueue.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
//
// Request Queue
// queues up the requests to avoid thread pool starvation,
// making sure that there are always available threads to process requests
//
namespace System.Web {
using System.Threading;
using System.Collections;
using System.Web.Util;
using System.Web.Hosting;
using System.Web.Configuration;
internal class RequestQueue {
// configuration params
private int _minExternFreeThreads;
private int _minLocalFreeThreads;
private int _queueLimit;
private TimeSpan _clientConnectedTime;
private bool _iis6;
// two queues -- one for local requests, one for external
private Queue _localQueue = new Queue();
private Queue _externQueue = new Queue();
// total count
private int _count;
// work items queued to pick up new work
private WaitCallback _workItemCallback;
private int _workItemCount;
private const int _workItemLimit = 2;
private bool _draining;
// timer to drain the queue
private readonly TimeSpan _timerPeriod = new TimeSpan(0, 0, 10); // 10 seconds
private Timer _timer;
// helpers
private static bool IsLocal(HttpWorkerRequest wr) {
String remoteAddress = wr.GetRemoteAddress();
// check if localhost
if (remoteAddress == "127.0.0.1" || remoteAddress == "::1")
return true;
// if unknown, assume not local
if (String.IsNullOrEmpty(remoteAddress))
return false;
// compare with local address
if (remoteAddress == wr.GetLocalAddress())
return true;
return false;
}
private void QueueRequest(HttpWorkerRequest wr, bool isLocal) {
lock (this) {
if (isLocal) {
_localQueue.Enqueue(wr);
}
else {
_externQueue.Enqueue(wr);
}
_count++;
}
PerfCounters.IncrementGlobalCounter(GlobalPerfCounter.REQUESTS_QUEUED);
PerfCounters.IncrementCounter(AppPerfCounter.REQUESTS_IN_APPLICATION_QUEUE);
if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Information, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_REQ_QUEUED, wr);
}
private HttpWorkerRequest DequeueRequest(bool localOnly) {
HttpWorkerRequest wr = null;
while (_count > 0) {
lock (this) {
if (_localQueue.Count > 0) {
wr = (HttpWorkerRequest)_localQueue.Dequeue();
_count--;
}
else if (!localOnly && _externQueue.Count > 0) {
wr = (HttpWorkerRequest)_externQueue.Dequeue();
_count--;
}
}
if (wr == null) {
break;
}
else {
PerfCounters.DecrementGlobalCounter(GlobalPerfCounter.REQUESTS_QUEUED);
PerfCounters.DecrementCounter(AppPerfCounter.REQUESTS_IN_APPLICATION_QUEUE);
if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Information, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_REQ_DEQUEUED, wr);
if (!CheckClientConnected(wr)) {
HttpRuntime.RejectRequestNow(wr, true);
wr = null;
PerfCounters.IncrementGlobalCounter(GlobalPerfCounter.REQUESTS_DISCONNECTED);
PerfCounters.IncrementCounter(AppPerfCounter.APP_REQUEST_DISCONNECTED);
}
else {
break;
}
}
}
return wr;
}
// This method will check to see if the client is still connected.
// The checks are only done if it's an in-proc Isapi request AND the request has been waiting
// more than the configured clientConenctedCheck time.
private bool CheckClientConnected(HttpWorkerRequest wr) {
if (DateTime.UtcNow - wr.GetStartTime() > _clientConnectedTime)
return wr.IsClientConnected();
else
return true;
}
// ctor
internal RequestQueue(int minExternFreeThreads, int minLocalFreeThreads, int queueLimit, TimeSpan clientConnectedTime) {
_minExternFreeThreads = minExternFreeThreads;
_minLocalFreeThreads = minLocalFreeThreads;
_queueLimit = queueLimit;
_clientConnectedTime = clientConnectedTime;
_workItemCallback = new WaitCallback(this.WorkItemCallback);
_timer = new Timer(new TimerCallback(this.TimerCompletionCallback), null, _timerPeriod, _timerPeriod);
_iis6 = HostingEnvironment.IsUnderIIS6Process;
// set the minimum number of requests that must be executing in order to detect a deadlock
int maxWorkerThreads, maxIoThreads;
ThreadPool.GetMaxThreads(out maxWorkerThreads, out maxIoThreads);
UnsafeNativeMethods.SetMinRequestsExecutingToDetectDeadlock(maxWorkerThreads - minExternFreeThreads);
}
// method called from HttpRuntime for incoming requests
internal HttpWorkerRequest GetRequestToExecute(HttpWorkerRequest wr) {
int workerThreads, ioThreads;
ThreadPool.GetAvailableThreads(out workerThreads, out ioThreads);
int freeThreads;
if (_iis6)
freeThreads = workerThreads; // ignore IO threads to avoid starvation from Indigo TCP requests
else
freeThreads = (ioThreads > workerThreads) ? workerThreads : ioThreads;
// fast path when there are threads available and nothing queued
if (freeThreads >= _minExternFreeThreads && _count == 0)
return wr;
bool isLocal = IsLocal(wr);
// fast path when there are threads for local requests available and nothing queued
if (isLocal && freeThreads >= _minLocalFreeThreads && _count == 0)
return wr;
// reject if queue limit exceeded
if (_count >= _queueLimit) {
HttpRuntime.RejectRequestNow(wr, false);
return null;
}
// can't execute the current request on the current thread -- need to queue
QueueRequest(wr, isLocal);
// maybe can execute a request previously queued
if (freeThreads >= _minExternFreeThreads) {
wr = DequeueRequest(false); // enough threads to process even external requests
}
else if (freeThreads >= _minLocalFreeThreads) {
wr = DequeueRequest(true); // enough threads to process only local requests
}
else {
wr = null; // not enough threads -> do nothing on this thread
ScheduleMoreWorkIfNeeded(); // try to schedule to worker thread
}
return wr;
}
// method called from HttpRuntime at the end of request
internal void ScheduleMoreWorkIfNeeded() {
// too late for more work if draining
if (_draining)
return;
// is queue empty?
if (_count == 0)
return;
// already scheduled enough work items
if (_workItemCount >= _workItemLimit)
return;
// enough worker threads?
int workerThreads, ioThreads;
ThreadPool.GetAvailableThreads(out workerThreads, out ioThreads);
if (workerThreads < _minLocalFreeThreads)
return;
// queue the work item
Interlocked.Increment(ref _workItemCount);
ThreadPool.QueueUserWorkItem(_workItemCallback);
}
// is empty property
internal bool IsEmpty {
get { return (_count == 0); }
}
// method called to pick up more work
private void WorkItemCallback(Object state) {
Interlocked.Decrement(ref _workItemCount);
// too late for more work if draining
if (_draining)
return;
// is queue empty?
if (_count == 0)
return;
int workerThreads, ioThreads;
ThreadPool.GetAvailableThreads(out workerThreads, out ioThreads);
// not enough worker threads to do anything
if (workerThreads < _minLocalFreeThreads)
return;
// pick up request from the queue
HttpWorkerRequest wr = DequeueRequest(workerThreads < _minExternFreeThreads);
if (wr == null)
return;
// let another work item through before processing the request
ScheduleMoreWorkIfNeeded();
// call the runtime to process request
HttpRuntime.ProcessRequestNow(wr);
}
// periodic timer to pick up more work
private void TimerCompletionCallback(Object state) {
ScheduleMoreWorkIfNeeded();
}
// reject all requests
internal void Drain() {
// set flag before killing timer to shorten the code path
// in the callback after the timer is disposed
_draining = true;
// stop the timer
if (_timer != null) {
((IDisposable)_timer).Dispose();
_timer = null;
}
// wait for all work items to finish
while (_workItemCount > 0)
Thread.Sleep(100);
// is queue empty?
if (_count == 0)
return;
// reject the remaining requests
for (;;) {
HttpWorkerRequest wr = DequeueRequest(false);
if (wr == null)
break;
HttpRuntime.RejectRequestNow(wr, false);
}
}
}
}
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