我可以把一个return语句里面锁 [英] Can I put a return statement inside a lock

问题描述

杜佩： 锁定程序中返回语句：内部或外部

标题是有点误导。我知道你可以做到这一点，但我想了解一下性能的影响。

The title is a little misleading. I know that you can do it, but I'm wondering about the performance implications.

考虑这些代码两个街区。 （没有错误处理）

consider these two blocks of code. (no error handling)

该模块具有收益锁

 public DownloadFile Dequeue()
 {
     DownloadFile toReturn = null;
     lock (QueueModifierLockObject)
     {
         toReturn = queue[0];
         queue.RemoveAt(0);
     }
     return toReturn;
 }

该模块具有收益声明的在的锁

 public DownloadFile Dequeue()
 {
     lock (QueueModifierLockObject)
     {
         DownloadFile toReturn = queue[0];
         queue.RemoveAt(0);

         return toReturn;
     }
 }

有没有代码有什么区别？据我所知，性能差异（如有）将是最小的，但我特别想知道是否会有顺序的锁定得到释放差异。

推荐答案

C＃编译器将移动return语句尝试/终于的外是锁定语句创建的。 。您的两个例子是相同的IL而言，编译器将发出他们

The C# compiler will move the return statement outside of the try/finally that is created for the lock statement. Both of your examples are identical in terms of the IL that the compiler will emit for them.

下面是一个简单的例子证明：

Here is a simple example proving that:

class Example
{
    static Object obj = new Object();

    static int Foo()
    {
    	lock (obj)
    	{
    		Console.WriteLine("Foo");
    		return 1;
    	}
    }

    static int Bar()
    {
    	lock (obj)
    	{
    		Console.WriteLine("Bar");
    	}
    	return 2;
    }
}

上面的代码被编译为以下内容：

The code above gets compiled to the following:

internal class Example
{
        private static object obj;

        static Example()
        {
                obj = new object();
                return;
        }

        public Example()
        {
                base..ctor();
                return;
        }

        private static int Bar()
        {
                int CS$1$0000;
                object CS$2$0001;
                Monitor.Enter(CS$2$0001 = obj);
        Label_000E:
                try
                {
                        Console.WriteLine("Bar");
                        goto Label_0025;
                }
                finally
                {
                Label_001D:
                        Monitor.Exit(CS$2$0001);
                }
        Label_0025:
                CS$1$0000 = 2;
        Label_002A:
                return CS$1$0000;
        }

        private static int Foo()
        {
                int CS$1$0000;
                object CS$2$0001;
                Monitor.Enter(CS$2$0001 = obj);
        Label_000E:
                try
                {
                        Console.WriteLine("Foo");
                        CS$1$0000 = 1;
                        goto Label_0026;
                }
                finally
                {
                Label_001E:
                        Monitor.Exit(CS$2$0001);
                }
        Label_0026:
                return CS$1$0000;
        }
}

正如你所看到的，编译器采取了libery在富移动return语句尝试/终于。

As you can see, the compiler has taken the libery of moving the return statement in Foo outside of the try/finally.

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