Race condition in yesod-bin

[psibi]

In some scenarios, yesod-bin (or the yesod executable) is always in the "compiling" state of the web application, even when the application has been compiled successfully. I verified this, by going to the random PORT which yesod-bin creates and reverse proxies to. Going to the random PORT, I can see the web application working properly. But the $DISPLAY_PORT was still in compilation "refreshing" page.

After doing lot of instrumentation in the yesod-bin code, I found the reason being this:

atomically (writeTVar appPortVar (-1))

In some scenarios, the above function was called even after yesod-devel/rebuild file was successfully generated.

My proposed fix for this is to call the function only when stack emits ExitFailure. I already have a private working branch where this solution is hugely relieving to me. I will send a PR once my other team members try out the solution and don't encounter any new bugs.

Meanwhile, I'm looking for feedback of the above proposed solution. Note that, I tried to fix this in various ways (going through MVar route for synchronization, etc) but at the end this seemed to be the most obvious way.

[psibi]

Fixed in #1381