In C# will the Finally block be executed in a try, catch, finally if an unhandled exception is thrown? [duplicate]

Answer 1

Straight from MSDN:

The finally block is useful for cleaning up any resources allocated in the try block. Control is always passed to the finally block regardless of how the try block exits.

Whereas catch is used to handle exceptions that occur in a statement block, finally is used to guarantee a statement block of code executes regardless of how the preceding try block is exited.

http://msdn.microsoft.com/en-us/library/zwc8s4fz(VS.71,loband).aspx

Answer 2

'Finally' is executed regardless of whether an exception is thrown or not.

Its a good place to close any open connections. Successful or failed execution, you can still manage your connections or open files.

Answer 3

It is not totally true that finally will always be executed. See this answer from Haacked:

Two possibilities:

• StackOverflowException
• ExecutingEngineException

The finally block will not be executed when there's a StackOverflowException since there's no room on the stack to even execute any more code. It will also not be called when there's an ExecutingEngineException, which is very rare.

However, these two exceptions are exception you cannot recover from, so basically your process will exit anyway.

As mentioned by Mehrdad, a reliable try/catch/finally will have to use Constrained Execution Regions (CER). An example is provided by MSDN:

[StructLayout(LayoutKind.Sequential)]
struct MyStruct
{
    public IntPtr m_outputHandle;
}

sealed class MySafeHandle : SafeHandle
{
    // Called by P/Invoke when returning SafeHandles
    public MySafeHandle()
        : base(IntPtr.Zero, true)
    {
    }

    public MySafeHandle AllocateHandle()
    {
        // Allocate SafeHandle first to avoid failure later.
        MySafeHandle sh = new MySafeHandle();

        RuntimeHelpers.PrepareConstrainedRegions();
        try { }
        finally
        {
            MyStruct myStruct = new MyStruct();
            NativeAllocateHandle(ref myStruct);
            sh.SetHandle(myStruct.m_outputHandle);
        }

        return sh;
    }
}