C# Does Lambda => generate garbage?

问题

Does using a lambda expression generate garbage for the GC opposed to the normal foreach loop?

// Lambda version
Foos.ForEach(f=>f.Update(gameTime));

// Normal approach:
foreach (Foo f in Foos)
{
  f.Update(gameTime);
}

The CLR profiler shows that I have 69.9% system.Action< T > and I suspect that being the lamba version of the foreach loop as above. Is that true?

EDIT: I used the Microsoft CLR profiler: http://download.microsoft.com/download/4/4/2/442d67c7-a1c1-4884-9715-803a7b485b82/clr%20profiler.exe or http://msdn.microsoft.com/en-us/library/ff650691.aspx

回答1:

Yes, a lambda will create garbage if the closure captures a variable from the local scope (i.e. gameTime in this context).

For example, the following C# function:

static void TestLambda(List<Foo> Foos, DateTime gameTime)
{
    Foos.ForEach(f => f.Update(gameTime));
}

Will get translated to this:

private static void TestLambda(List<Foo> Foos, DateTime gameTime)
{
    Program.<>c__DisplayClass1 <>c__DisplayClass = new Program.<>c__DisplayClass1();
    <>c__DisplayClass.gameTime = gameTime;
    Foos.ForEach(new Action<Foo>(<>c__DisplayClass.<TestLambda>b__0));
}

Note that there are two instances of new in the resulting code, meaning that there is not only Action objects being allocated (the closures), but also objects to hold the captured variables (escaping variable records).

回答2:

In this case I think that you are using a generic method (ForEach) which will generate a new type (assuming that Foo is a reference type, only one new type will be generated), and the lambda will be compiled as a regular anonymous method. Nothing about that suggests any sort of linear increase in memory usage.

As far as the profiler is concerned, you are not measuring anything about memory or the GC. You are measuring time spent executing the method, and the lambda should not be significantly slower than the 'regular' way.

来源：https://stackoverflow.com/questions/7133013/c-sharp-does-lambda-generate-garbage

标签

linq

garbage