Modify the issue of premature thread exit caused by Monitor.Wait(). #95
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
Fixed, compare the following 2 pieces of code using System;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Collections.Concurrent;
class Program
{
static readonly object _locker = new object();
public class Client{
public int i;
}
public static ConcurrentClientQueue clientQueue = new ConcurrentClientQueue();
public class ConcurrentClientQueue
{
public ConcurrentQueue<Client> ClientQueue { get; }
public ConcurrentClientQueue(List<Client> clients)
{
ClientQueue = new ConcurrentQueue<Client>(clients);
}
public ConcurrentClientQueue()
{
ClientQueue = new ConcurrentQueue<Client>();
}
public void Add(Client client) => Return(client);
public void Return(Client client)
{
Monitor.Enter(ClientQueue);
ClientQueue.Enqueue(client);
Console.WriteLine("Return client {0} Time {1}", client.i, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
Monitor.Pulse(ClientQueue);
Monitor.Exit(ClientQueue);
Thread.Sleep(0);
}
int _ref = 0;
public void AddRef()
{
lock (this)
{
_ref++;
}
}
public int GetRef()
{
return _ref;
}
public void RemoveRef()
{
lock (this)
{
_ref--;
}
}
public int Timeout { get; set; } = 10;
public Client Take()
{
Client client = null;
Monitor.Enter(ClientQueue);
if (ClientQueue.IsEmpty)
{
Console.WriteLine("Queue empty, Thread {0} wait, time {1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
Monitor.Wait(ClientQueue, TimeSpan.FromSeconds(Timeout));
}
Console.WriteLine("Thread {0} wake up, time {1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
if (!ClientQueue.TryDequeue(out client))
{
Console.WriteLine("Thread {0} get client failed, time {1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
}
else
{
Console.WriteLine("Thread {0} get client {1} success, time {2}", Thread.CurrentThread.ManagedThreadId, client.i, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
}
Monitor.Exit(ClientQueue);
if (client == null)
{
throw new TimeoutException($"Connection pool is empty and wait time out({Timeout}s)!");
}
return client;
static void Main()
{
for(int i = 0; i < 1; i++){
clientQueue.Add(new Client(){i = i});
}
Thread t1 = new Thread(() => ThreadWork(1));
Thread t2 = new Thread(() => ThreadWork(2));
Thread t3 = new Thread(() => ThreadWork(3));
t1.Start();
t2.Start();
t3.Start();
t1.Join();
t2.Join();
t3.Join();
}
static void ThreadWork(int threadNumber)
{
var client = clientQueue.Take();
Console.WriteLine("Thread {0} took client {1} Time {2}", threadNumber, client.i, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
long useless = 0;
for(long i = 0; i < 4000000000;i++){
useless++;
}
clientQueue.Add(client);
}
}The following error occurs during the execution of the code because both Thread 2 and Thread 3 are waiting for Thread 1 to complete its task. However, Monitor.Pulse will only wake up one of the threads, allowing either Thread 2 or Thread 3 to acquire the resource and continue execution while the other thread continues to wait. As a result, when the total waiting time reaches 10 seconds, the waiting thread exits prematurely. In the second piece of code, we replace the Taken function with the following definition and replace public Client Take()
{
Client client = null;
Monitor.Enter(ClientQueue);
while(true){
bool timeout = false;
if (ClientQueue.IsEmpty)
{
Console.WriteLine("Queue empty, Thread {0} wait, time {1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
timeout = !Monitor.Wait(ClientQueue, TimeSpan.FromSeconds(Timeout));
}
Console.WriteLine("Thread {0} wake up, time {1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
if (!ClientQueue.TryDequeue(out client))
{
Console.WriteLine("Thread {0} get client failed, time {1}", Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
}
else
{
Console.WriteLine("Thread {0} get client {1} success, time {2}", Thread.CurrentThread.ManagedThreadId, client.i, DateTime.Now.ToString("HH:mm:ss.fff.ffff"));
}
if(client != null || timeout){
break;
}
}
Monitor.Exit(ClientQueue);
if (client == null)
{
throw new TimeoutException($"Connection pool is empty and wait time out({Timeout}s)!");
}
return client;
}This time, when the client returns, using Monitor.PulseAll will wake up all threads. When two threads compete for the client through ConcurrentClientQueue, the winner will exit while the loser refreshes its waiting time and continues to wait. Therefore, the error situation described earlier will not occur. |
Closed
|
👍 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
#93 Try to fix this issue, this occurs because multiple threads are waiting simultaneously, but only one of them will be awakened in the end, others will continue waiting, making the timeout period not the same as the time set by the user.