[英]C# Threading issue with AutoResetEvent
How to properly synchronize this? 如何正确同步? At the moment it is possible that SetData
is called after e.WaitOne()
has completed so d
could be already set to another value. 目前,在e.WaitOne()
完成后可能会调用SetData
因此d
可能已经设置为另一个值。 I tried to insert locks but it resulted into a deadlock. 我试图插入锁,但它导致死锁。
AutoResetEvent e = new AutoResetEvent(false);
public SetData(MyData d)
{
this.d=d;
e.Set(); // notify that new data is available
}
// This runs in separate thread and waits for d to be set to a new value
void Runner()
{
while (true)
{
e.WaitOne(); // waits for new data to process
DoLongOperationWith_d(d);
}
}
Will the best solution be to introduce a new boolean variable dataAlreadyBeenSetAndWaitingToBeProcessed
that is set in SetData
to true and at the end of DoLongOperationWith_d
it could be set to true, so if SetData
is called with this variable set to true it could just return? 最好的解决方案是将一个新的布尔变量dataAlreadyBeenSetAndWaitingToBeProcessed
在SetData
设置为true,并且在DoLongOperationWith_d
结束时它可以设置为true,所以如果调用SetData
并将此变量设置为true,它可能只返回?
This is untested, but is an elegant way to do this with the .net based primitives: 这是未经测试的,但使用基于.net的原语是一种优雅的方法:
class Processor<T> {
Action<T> action;
Queue<T> queue = new Queue<T>();
public Processor(Action<T> action) {
this.action = action;
new Thread(new ThreadStart(ThreadProc)).Start();
}
public void Queue(T data) {
lock (queue) {
queue.Enqueue(data);
Monitor.Pulse(queue);
}
}
void ThreadProc() {
Monitor.Enter(queue);
Queue<T> copy;
while (true) {
if (queue.Count == 0) {
Monitor.Wait(queue);
}
copy = new Queue<T>(queue);
queue.Clear();
Monitor.Exit(queue);
foreach (var item in copy) {
action(item);
}
Monitor.Enter(queue);
}
}
}
Example program: 示例程序:
class Program {
static void Main(string[] args) {
Processor<int> p = new Processor<int>((data) => { Console.WriteLine(data); });
p.Queue(1);
p.Queue(2);
Console.Read();
p.Queue(3);
}
}
This is a non-queue version, a queue version may be preferred: 这是一个非队列版本,可能首选队列版本:
object sync = new object();
AutoResetEvent e = new AutoResetEvent(false);
bool pending = false;
public SetData(MyData d)
{
lock(sync)
{
if (pending) throw(new CanNotSetDataException());
this.d=d;
pending = true;
}
e.Set(); // notify that new data is available
}
void Runner() // this runs in separate thread and waits for d to be set to a new value
{
while (true)
{
e.WaitOne(); // waits for new data to process
DoLongOperationWith_d(d);
lock(sync)
{
pending = false;
}
}
}
There are two possibly troubling scenarios here. 这里有两个可能令人不安的场景。
If that's your concern, I think you can relax. 如果这是你的担忧,我想你可以放松一下。 From the documentation , we see that 从文档中 ,我们看到了
If a thread calls WaitOne while the AutoResetEvent is in the signaled state, the thread does not block. 如果线程在AutoResetEvent处于信号状态时调用WaitOne,则线程不会阻塞。 The AutoResetEvent releases the thread immediately and returns to the non-signaled state. AutoResetEvent立即释放线程并返回到非信号状态。
So that's not a problem. 所以这不是问题。 However, depending on how and when SetData() is called, you may be dealing with the more serious 但是,根据调用SetData()的方式和时间,您可能会处理更严重的问题
If that's your problem, the simplest way to solve it is a concurrent queue. 如果这是你的问题,解决它的最简单方法是并发队列。 Implementations abound. 实施比比皆是。
You can use 2 events, 你可以使用2个活动,
AutoResetEvent e = new AutoResetEvent(false);
AutoResetEvent readyForMore = new AutoResetEvent(true); // Initially signaled
public SetData(MyData d)
{
// This will immediately determine if readyForMore is set or not.
if( readyForMore.WaitOne(0,true) ) {
this.d=d;
e.Set(); // notify that new data is available
}
// you could return a bool or something to indicate it bailed.
}
void Runner() // this runs in separate thread and waits for d to be set to a new value
{
while (true)
{
e.WaitOne(); // waits for new data to process
DoLongOperationWith_d(d);
readyForMore.Set();
}
}
One of the things you can do with this approach is have SetData take a timeout, and pass that into WaitOne
. 使用此方法可以执行的操作之一是让SetData超时,并将其传递给WaitOne
。 I think however you shoudl investigate ThreadPool.QueueUserWorkItem
. 不过我想你会调查ThreadPool.QueueUserWorkItem
。
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