根据MSDN,Stopwatch
类实例方法对于多线程访问并不安全。这也可以通过检查个别方法来确认。
但是,由于我在代码中的几个地方只需要简单的“经过时间”的定时器,我想知道它是否仍然可以无锁地完成,使用类似的东西:
public class ElapsedTimer : IElapsedTimer
{
/// Shared (static) stopwatch instance.
static readonly Stopwatch _stopwatch = Stopwatch.StartNew();
/// Stopwatch offset captured at last call to Reset
long _lastResetTime;
/// Each instance is immediately reset when created
public ElapsedTimer()
{
Reset();
}
/// Resets this instance.
public void Reset()
{
Interlocked.Exchange(ref _lastResetTime, _stopwatch.ElapsedMilliseconds);
}
/// Seconds elapsed since last reset.
public double SecondsElapsed
{
get
{
var resetTime = Interlocked.Read(ref _lastResetTime);
return (_stopwatch.ElapsedMilliseconds - resetTime) / 1000.0;
}
}
}
由于_stopwatch.ElapsedMilliseconds
基本上是对QueryPerformanceCounter
的调用,我假设从多个线程调用是安全的?与常规Stopwatch
的区别在于此类基本上一直在运行,所以我不需要保持任何附加状态(“运行”或“停止”),就像Stopwatch
那样
(适用更新)
在@Scott在下面的答案中提出建议之后,我意识到Stopwatch
提供了一个简单的静态GetTimestamp
方法,它返回原始QueryPerformanceCounter
刻度。换句话说,可以将代码修改为此,这是线程安全的:
public class ElapsedTimer : IElapsedTimer
{
static double Frequency = (double)Stopwatch.Frequency;
/// Stopwatch offset for last reset
long _lastResetTime;
public ElapsedTimer()
{
Reset();
}
/// Resets this instance.
public void Reset()
{
// must keep in mind that GetTimestamp ticks are NOT DateTime ticks
// (i.e. they must be divided by Stopwatch.Frequency to get seconds,
// and Stopwatch.Frequency is hw dependent)
Interlocked.Exchange(ref _lastResetTime, Stopwatch.GetTimestamp());
}
/// Seconds elapsed since last reset
public double SecondsElapsed
{
get
{
var resetTime = Interlocked.Read(ref _lastResetTime);
return (Stopwatch.GetTimestamp() - resetTime) / Frequency;
}
}
}
澄清这段代码的想法是:
我会使用它类似于:
private readonly ElapsedTimer _lastCommandReceiveTime = new ElapsedTimer();
// can be invoked by multiple threads (usually threadpool)
void Port_CommandReceived(Cmd command)
{
_lastCommandReceiveTime.Reset();
}
// also can be run from multiple threads
void DoStuff()
{
if (_lastCommandReceiveTime.SecondsElapsed > 10)
{
// must do something
}
}
答案 0 :(得分:1)
我建议的唯一更改是使用Interlocked.Exchange(ref _lastResetTime, _stopwatch.ElapsedTicks);
而不是毫秒,因为如果您处于高性能模式,则可以从QueryPerformanceCounter
获得亚毫秒的结果。
答案 1 :(得分:0)
我建议创建Stopwatch
的多个实例,并且只在同一个帖子上读取它。
我不知道您的异步代码是什么样的,但在psuedo代码中,我会这样做:
Stopwatch watch = Stopwatch.Startnew();
DoAsyncWork((err, result) =>
{
Console.WriteLine("Time Elapsed:" + (watch.ElapsedMilliseconds / 1000.0));
// process results...
});
或者:
public DoAsyncWork(callback) // called asynchronously
{
Stopwatch watch = Stopwatch.Startnew();
// do work
var time = watch.ElapsedMilliseconds / 1000.0;
callback(null, new { time: time });
}
第一个示例假设DoAsyncWork
工作在另一个线程中完成工作,然后在完成时调用回调,然后编组回调用者线程。
第二个例子假设调用者正在处理线程,这个函数自己完成所有的计时,并将结果传回给调用者。