Trapping COM exception in F#

Question

I have some F# code that calls a method on a COM Automation object. Sometimes that COM object throws an exception.

I tried wrapping the calls to the COM object in a try...with block:

  try
    do some COM stuff
  with _ ->
    Printf.printf "got an exn\r\n"

But the exception-handling code isn't called at all, the application just dies.

The message I see on the console is typically:

The message filter indicated that the application is busy. 
(Exception from HRESULT: 0x8001010A (RPC_E_SERVERCALL_RETRYLATER))

How can I trap the COM exception?

Answer 1

Hm, I would think this would work... are you calling from the STA (UI) thread? Do you have a simple repro case to share (what are you up to - Visual Studio automation or what)? It smells almost like the call is being marshalled to another background thread and that thread has the exception with no handler.

Answer 2

Sorry, my mistake.

It was a different COM call that was causing the error, and a different with-handler was catching the error, after all.

So try...with does the job.