[Mono-dev] WeakReference problem

[Tobias Käs]

While trying to write a minimal test case I realized that mono actually 
never (?) returns false from WeakReference.TryGetTarget when the object 
has been collected, so this is pretty easy to reproduce and totally 
deterministic.


using System;
using System.Threading;

static class Program {
         static WeakReference<object> wr;

         static void Main(string[] args) {
                 Allocate();
                 GC.Collect();
                 GC.WaitForPendingFinalizers();
                 GC.Collect();
                 Check();
         }

         static void Allocate() {
                 wr = new WeakReference<object>(new object());
         }

         static void Check() {
                 object obj;
                 if(wr.TryGetTarget(out obj) && obj == null) {
                         throw new ApplicationException("assertion 
failed: object has been collected but TryGetTarget returned true");
                 }
         }
}


Am 29.01.2014 23:41, schrieb Rodrigo Kumpera:
> Please provide a test case that shows this behavior
>
>
> On Wed, Jan 29, 2014 at 5:00 PM, Tobias Käs <tobias.kaes at gmx.de 
> <mailto:tobias.kaes at gmx.de>> wrote:
>
>     Hi, the generic WeakReference<T> for .NET 4.5 sometimes returns
>     true from TryGetTarget even though the target has been collected
>     (the out-value is correctly set to null). All my WeakReferences
>     have been initialized with non-null values.
>
>     Looking at the source at github I can imagine that there is a race
>     between the handle.IsAllocated check and the handle.Target
>     retrieval, but I'm no expert. Should I file a bug on that one? I'm
>     not sure what the expected behavior is since MSDN documentation of
>     that method isn't so great, but if the caller has to check the
>     out-value against null anyways, then the return value becomes
>     kinda pointless in my opinion.
>
>     Regards,
>     Tobias
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