Question

I am writing a C# app for a device with limited ram. (Mono on iPhone/iPad)

When I assign a large string:

string xml = "10 meg xml string from REST service";

then clear it

xml = null;

Is with the GC free up that memory asap? Is there a way to make sure it’s cleaned up. GC has a collect feature, but is this executed right away?

The problem is that I am downloading many large xml files in a loop and even though I am setting the string to null, memory use is growing.

Answer 1

In general GC does not happen immediately because garbage collection is relatively expensive. The runtime generally tries to do it while it’s not busy doing other things, but this clearly isn’t always possible. I ran into a non-deterministic out of memory error at one point because it was putting off GC too long (sometimes) while I was running a tight memory intensive loop. Lesson: Generally the collector knows what it is doing and you don’t need to tweak it. But not always.

To force a collection to happen, you need two lines:

GC.Collect();
GC.WaitForPendingFinalizers();

EDIT: Wrote this before I saw your note on what you were running on. This is written based on the desktop .NET machine. It may (or may not) be different on mono / iPad.