What does this have to do with contention for stdout? Thread switching is unrelated; seeing individual output operations just gives more hints about when the thread switches happen. And with -fno-omit-yields it presumably can happen when putChar is evaluated, not because of I/O but because of function entry. On Thu, Nov 29, 2018 at 2:49 PM Johannes Waldmann < johannes.waldmann@htwk-leipzig.de> wrote:
so thread scheduling would be more obvious with individual characters being output instead of a single flush triggered by the final putChar.
Yes but in my example program, there is no contention for stdout, as only one thread is using it.
I am inclined to enter this into the GHC issue tracker as it seems there's no obvious explanation, and "lost TVars confusing the STM machinery" was mentioned. Do you mean that this a known thing? Searching the tracker for "lost TVar" does not turn up anything.
- J.W.
-- brandon s allbery kf8nh allbery.b@gmail.com