Re: [Haskell-cafe] GHC.Conc.threadStatus - documentation of ThreadDied :: ThreadStatus

On Mon, 2022-03-07 at 23:04 -0500, Ben Gamari wrote:

Olaf Klinke writes:

...

Dear Cafe,

I had expected to see ThreadDied in the small example below. But when I compile with ghc --make -threaded -with-rtsopts=-N2 The output is:

threadStatus: user error (child thread is crashing!) The status of my child is: ThreadFinished

The output is not really a lie. But how do I determine whether a child thread has exited normally or not? Wouldn't you say a call to fail (or any other throwIO) should count as ThreadDied?

The documentation of GHC.Conc.forkIO says: "... passes all other exceptions to the uncaught exception handler." and the documentation for GHC.Conc.ThreadStatus says: ThreadDied -- the thread received an uncaught exception

One can provoke ThreadDied by using throwTo from the parent thread. So the emphasis in the documentation of ThreadDied should be on the word "received". This is a case of misleading documentation, in my humble opinion. The constructor should not be named ThreadDied because that suggests inclusion of internal reasons.

Thanks for reporting this, Olaf! Could you open a GHC ticket? [1]

Cheers,

- Ben

[1] https://gitlab.haskell.org/ghc/ghc/-/issues/new

Opened as https://gitlab.haskell.org/ghc/ghc/-/issues/21195 Regards Olaf