I also note that the "forever" is in fact writing to a TVar. I'd be curious as to whether it's retrying for some reason, possibly related to the "lost" TVars confusing the STM machinery. I seem to recall it has some infelicities currently; and I have no idea how (or if) STM retries interact with thread yielding.

On Thu, Nov 29, 2018 at 2:25 PM Bryan Richter <b@chreekat.net> wrote:

On Thu, Nov 29, 2018, 20:51 Johannes Waldmann <johannes.waldmann@htwk-leipzig.de wrote:
On 11/29/18 7:48 PM, Brandon Allbery wrote:

> main thread exiting will kill the entire process,

The main thread does "forever $ something".

The process does not exit (I am not getting
the console prompt). I observe that the process
either prints and then hangs, or it hangs immediately.

Printing to the console still isn't a great test to see if something has "run", because of buffering that seems to behave unintuitively in these situations. Maybe try flushing stdout within the forked thread, to ensure the runtime is doing what you think it's doing?
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