Sparks off a new thread to run the IO computation passed as the first argument, and returns the ThreadId of the newly created thread.
The new thread will be a lightweight thread; if you want to use a foreign library that uses thread-local storage, use Control.Concurrent.forkOS instead.
GHC note: the new thread inherits the masked state of the parent (see Control.Exception.mask).
The newly created thread has an exception handler that discards the exceptions BlockedIndefinitelyOnMVar, BlockedIndefinitelyOnSTM, and ThreadKilled, and passes all other exceptions to the uncaught exception handler (see setUncaughtExceptionHandler).
Like forkIO, but the child thread is created with asynchronous exceptions unmasked (see Control.Exception.mask).