Run GC.Collect synchronously

Question

GC.Collect appears to start the garbage collection in a background thread, and then return immediately. How can I run GC.Collect synchronously -- i.e., wait for the garbage collection to complete?

This is in the context of NUnit tests. I tried adding the gcConcurrent setting to my test assembly's app.config file, and I tried the same with nunit.exe.config. Neither had any effect -- when I debug, I can still see the finalizer being run on the "GC Finalizer Thread", rather than the thread that called GC.Collect (NUnit's "TestRunnerThread"), and both threads are running concurrently.

Background: I want my tests to fail if they leak (don't call Dispose on) a particular class. So I've added a finalizer to that class that sets a static wasLeaked flag; then my test TearDown calls GC.Collect() and then throws if wasLeaked is true. But it's not failing deterministically, because when it reads wasLeaked, the finalizer usually hasn't even been called yet. (It fails some later test instead, after the garbage collection finally finishes.)

Answer 1

Finalizers are run on a dedicated, high-priority background thread. From the background in your post, I gather that you can simply do

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

The Collect() will schedule any non-rooted instances for finalization and then the thread will wait for the finalizer thread to complete.