Resource Management

Garbage collection

C# programmers don’t have to release allocated memory, the CLR takes care of it with the so called Garbage Collector.

Garbage collection has 2 Phases, Mark and sweep/Detection and Reclamation. Detection: The garbage collector searches for managed objects that are referenced in managed code. Reclamation: The garbage collector attempts to finalize objects that are unreachable. The garbage collector frees objects that are unmarked and reclaims their memory.

This example is a tracing, compacting ,stop the world , mark & sweep garbage collector. tracing = Follow references to decide reachability compacting = Free memory by compacting heap stop the world = Stop all threads during GC mark & sweep = GC in two phases

Runtime performs GC whenever it “feels like it”

Finalization/destructors

Prior to an object being released, the GC calls its finalizer/destructor. Collection can be forced with GC.Collect(). Runs on the finalizer thread (concurrent to the rest of the application) .NET provides the IDisposable interface then users can call Dispose() Objects also call Dispose on their child objects

public sealed class OSHandle : IDisposable
{
 private bool disposed;
 public OSHandle(IntPtr h) { handle = h; disposed = false ;}
 public void Dispose(){
  Dispose(true);
  GC.SuppressFinalize(this);
 }
 
 ~OSHandle(){
  Dispose(false);
 }
 
 protected void Dispose(bool disposing)
 {
  if(!disposed){
   if(disposing){
    /* safe to access references here */
   }
   disposed = true;
   // dispose unmanaged resources here
  }
  base.Dispose(disposing);
 }
}

Dispose() = Deterministic, Explicitly called by user, Free resources File handlers, locks, OS resources, ...)

Finalizers destructors = Non deterministic, Automatically called by GC, Free memory or as safety net

Dispose pattern combines best of both worlds