The CriticalHandle.ReleaseHandle method is guaranteed to be called only once, provided that you employ proper synchronization mechanisms to ensure that only one call to the CriticalHandle.Close or erload:System.Runtime.InteropServices.CriticalHandle.Dispose method is made. The CriticalHandle.ReleaseHandle method will not be called if the CriticalHandle.IsInvalid or CriticalHandle.IsClosed property is true. Implement this method in your System.Runtime.InteropServices.CriticalHandle derived classes to execute any code that is required to free the handle. Because one of the functions of System.Runtime.InteropServices.CriticalHandle is to guarantee prevention of resource leaks, the code in your implementation of CriticalHandle.ReleaseHandle must never fail. The garbage collector calls CriticalHandle.ReleaseHandle after normal finalizers have been run for objects that were garbage collected at the same time, and guarantees the resources to invoke it and that it will not be interrupted while it is in progress. This method will be prepared as a constrained execution region (CER) at instance construction time (along with all the methods in its statically determinable call graph). Although this prevents thread abort interrupts, you must still be careful not to introduce any fault paths in your overridden CriticalHandle.ReleaseHandle method. In particular, apply the System.Runtime.ConstrainedExecution.ReliabilityContractAttribute attribute to any methods you call from CriticalHandle.ReleaseHandle. In most cases this code should be:

ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)

Additionally, for simple cleanup (for example, calling the Win32 API CloseHandle on a file handle) you can check the return value for the single platform invoke call. For complex cleanup, you may have a lot of program logic and many method calls, some of which might fail. You must ensure that your program logic has fallback code for each of those cases.

If the CriticalHandle.ReleaseHandle method returns false for any reason, it generates a ReleaseHandleFailed Managed Debugging Assistant.