C#事件:如何以并行方式处理事件

Question

我有一个我希望以并行方式处理的事件.我的想法是将每个回调添加到ThreadPool,effectivley有每个注册由ThreadPool处理的事件的方法.

我的试用代码如下所示:

Delegate[] delegates = myEvent.GetInvocationList();
IAsyncResult[] results = new IAsyncResult[ delegates.Count<Delegate>() ];

for ( int i = 0; i < delegates.Count<Delegate>(); i++ )
{
    IAsyncResult result = ( ( TestDelegate )delegates[ i ] ).BeginInvoke( "BeginInvoke/EndInvoke", null, null );
    results[ i ] = result;
}

for ( int i = 0; i < delegates.Length; i++ )
{
    ( ( TestDelegate )delegates[ i ] ).EndInvoke( results[ i ] );
}

这只是为了玩,因为我很好奇如何做到这一点.我相信有更好的方法可以做到这一点.我不喜欢有一个Func创建一个持有lambda的WaitCallback.此外,与直接调用委托相比,DynamicInvoke相当慢.我怀疑这种处理事件的方式比按顺序执行要快.

我的问题是:如何以并行方式处理事件,最好是使用ThreadPool？

由于我通常使用Mono,因此.NET 4.0或任务并行库都不是一个选项.

谢谢!

编辑: - 通过Earwickers答案更正了示例. - 更新了试用代码

Answer 1

我将使用DynamicMethod(LCG)和一个带有参数的状态对象,并跟踪调用(以便您可以等待它们完成).

代码:这样的 东西应该做(虽然没有通过测试,但在某些情况下可能会抛出一些讨厌的异常):

/// <summary>
/// Class for dynamic parallel invoking of a MulticastDelegate.
/// (C) 2009 Arsène von Wyss, avw@gmx.ch
/// No warranties of any kind, use at your own risk. Copyright notice must be kept in the source when re-used.
/// </summary>
public static class ParallelInvoke {
    private class ParallelInvokeContext<TDelegate> where TDelegate: class {
        private static readonly DynamicMethod invoker;
        private static readonly Type[] parameterTypes;

        static ParallelInvokeContext() {
            if (!typeof(Delegate).IsAssignableFrom(typeof(TDelegate))) {
                throw new InvalidOperationException("The TDelegate type must be a delegate");
            }
            Debug.Assert(monitor_enter != null, "Could not find the method Monitor.Enter()");
            Debug.Assert(monitor_pulse != null, "Could not find the method Monitor.Pulse()");
            Debug.Assert(monitor_exit != null, "Could not find the method Monitor.Exit()");
            FieldInfo parallelInvokeContext_activeCalls = typeof(ParallelInvokeContext<TDelegate>).GetField("activeCalls", BindingFlags.Instance|BindingFlags.NonPublic);
            Debug.Assert(parallelInvokeContext_activeCalls != null, "Could not find the private field ParallelInvokeContext.activeCalls");
            FieldInfo parallelInvokeContext_arguments = typeof(ParallelInvokeContext<TDelegate>).GetField("arguments", BindingFlags.Instance|BindingFlags.NonPublic);
            Debug.Assert(parallelInvokeContext_arguments != null, "Could not find the private field ParallelInvokeContext.arguments");
            MethodInfo delegate_invoke = typeof(TDelegate).GetMethod("Invoke", BindingFlags.Instance|BindingFlags.Public);
            Debug.Assert(delegate_invoke != null, string.Format("Could not find the method {0}.Invoke()", typeof(TDelegate).FullName));
            if (delegate_invoke.ReturnType != typeof(void)) {
                throw new InvalidOperationException("The TDelegate delegate must not have a return value");
            }
            ParameterInfo[] parameters = delegate_invoke.GetParameters();
            parameterTypes = new Type[parameters.Length];
            invoker = new DynamicMethod(string.Format("Invoker<{0}>", typeof(TDelegate).FullName), typeof(void), new[] {typeof(ParallelInvokeContext<TDelegate>), typeof(object)},
                                        typeof(ParallelInvokeContext<TDelegate>), true);
            ILGenerator il = invoker.GetILGenerator();
            LocalBuilder args = (parameters.Length > 2) ? il.DeclareLocal(typeof(object[])) : null;
            bool skipLoad = false;
            il.BeginExceptionBlock();
            il.Emit(OpCodes.Ldarg_1); // the delegate we are going to invoke
            if (args != null) {
                Debug.Assert(args.LocalIndex == 0);
                il.Emit(OpCodes.Ldarg_0);
                il.Emit(OpCodes.Ldfld, parallelInvokeContext_arguments);
                il.Emit(OpCodes.Dup);
                il.Emit(OpCodes.Stloc_0);
                skipLoad = true;
            }
            foreach (ParameterInfo parameter in parameters) {
                if (parameter.ParameterType.IsByRef) {
                    throw new InvalidOperationException("The TDelegate delegate must note have out or ref parameters");
                }
                parameterTypes[parameter.Position] = parameter.ParameterType;
                if (args == null) {
                    il.Emit(OpCodes.Ldarg_0);
                    il.Emit(OpCodes.Ldfld, parallelInvokeContext_arguments);
                } else if (skipLoad) {
                    skipLoad = false;
                } else {
                    il.Emit(OpCodes.Ldloc_0);
                }
                il.Emit(OpCodes.Ldc_I4, parameter.Position);
                il.Emit(OpCodes.Ldelem_Ref);
                if (parameter.ParameterType.IsValueType) {
                    il.Emit(OpCodes.Unbox_Any, parameter.ParameterType);
                }
            }
            il.Emit(OpCodes.Callvirt, delegate_invoke);
            il.BeginFinallyBlock();
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Call, monitor_enter);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Dup);
            il.Emit(OpCodes.Ldfld, parallelInvokeContext_activeCalls);
            il.Emit(OpCodes.Ldc_I4_1);
            il.Emit(OpCodes.Sub);
            il.Emit(OpCodes.Dup);
            Label noPulse = il.DefineLabel();
            il.Emit(OpCodes.Brtrue, noPulse);
            il.Emit(OpCodes.Stfld, parallelInvokeContext_activeCalls);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Call, monitor_pulse);
            Label exit = il.DefineLabel();
            il.Emit(OpCodes.Br, exit);
            il.MarkLabel(noPulse);
            il.Emit(OpCodes.Stfld, parallelInvokeContext_activeCalls);
            il.MarkLabel(exit);
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Call, monitor_exit);
            il.EndExceptionBlock();
            il.Emit(OpCodes.Ret);
        }

        [Conditional("DEBUG")]
        private static void VerifyArgumentsDebug(object[] args) {
            for (int i = 0; i < parameterTypes.Length; i++) {
                if (args[i] == null) {
                    if (parameterTypes[i].IsValueType) {
                        throw new ArgumentException(string.Format("The parameter {0} cannot be null, because it is a value type", i));
                    }
                } else if (!parameterTypes[i].IsAssignableFrom(args[i].GetType())) {
                    throw new ArgumentException(string.Format("The parameter {0} is not compatible", i));
                }
            }
        }

        private readonly object[] arguments;
        private readonly WaitCallback invokeCallback;
        private int activeCalls;

        public ParallelInvokeContext(object[] args) {
            if (parameterTypes.Length > 0) {
                if (args == null) {
                    throw new ArgumentNullException("args");
                }
                if (args.Length != parameterTypes.Length) {
                    throw new ArgumentException("The parameter count does not match");
                }
                VerifyArgumentsDebug(args);
                arguments = args;
            } else if ((args != null) && (args.Length > 0)) {
                throw new ArgumentException("This delegate does not expect any parameters");
            }
            invokeCallback = (WaitCallback)invoker.CreateDelegate(typeof(WaitCallback), this);
        }

        public void QueueInvoke(Delegate @delegate) {
            Debug.Assert(@delegate is TDelegate);
            activeCalls++;
            ThreadPool.QueueUserWorkItem(invokeCallback, @delegate);
        }
    }

    private static readonly MethodInfo monitor_enter;
    private static readonly MethodInfo monitor_exit;
    private static readonly MethodInfo monitor_pulse;

    static ParallelInvoke() {
        monitor_enter = typeof(Monitor).GetMethod("Enter", BindingFlags.Static|BindingFlags.Public, null, new[] {typeof(object)}, null);
        monitor_pulse = typeof(Monitor).GetMethod("Pulse", BindingFlags.Static|BindingFlags.Public, null, new[] {typeof(object)}, null);
        monitor_exit = typeof(Monitor).GetMethod("Exit", BindingFlags.Static|BindingFlags.Public, null, new[] {typeof(object)}, null);
    }

    public static void Invoke<TDelegate>(TDelegate @delegate) where TDelegate: class {
        Invoke(@delegate, null);
    }

    public static void Invoke<TDelegate>(TDelegate @delegate, params object[] args) where TDelegate: class {
        if (@delegate == null) {
            throw new ArgumentNullException("delegate");
        }
        ParallelInvokeContext<TDelegate> context = new ParallelInvokeContext<TDelegate>(args);
        lock (context) {
            foreach (Delegate invocationDelegate in ((Delegate)(object)@delegate).GetInvocationList()) {
                context.QueueInvoke(invocationDelegate);
            }
            Monitor.Wait(context);
        }
    }
}

用法:

ParallelInvoke.Invoke(yourDelegate, arguments);

笔记:

• 不处理事件处理程序中的异常(但IL代码最终会减少计数器,以便方法可以正确结束)并且这可能会导致麻烦.也可以在IL代码中捕获和传输异常.

• 除了继承之外的隐式转换(例如int到double)不会执行,并会引发异常.

• 使用的同步技术不分配OS等待句柄,这通常有利于提高性能.可以在Joseph Albahari的页面上找到有关Monitor工作的说明.

• 经过一些性能测试后,似乎这种方法比使用委托上的"本机"BeginInvoke/EndInvoke调用的任何方法都要好得多(至少在MS CLR中).