What's the difference between Catch and CatchOnce?

[chris-martin]

The Handler constructors could use some documentation. In particular, I'm not sure what CatchOnce means.

[edsko]

+1

[hvr]

Yes, this should be documented better. The name CatchOnce implies that the signal handler is automatically reset (via SA_RESETHAND), as opposed to Catch which doesn't.

[edsko]

It's confusing also because Unix signal handlers typically need to be reinstalled after they are invoked, right? Also, there is a comment in the code someplace that says "it's impossible to get CatchOnce right". Would be good to document that too.

[hvr]

@edsko there's some history fun fact about that: SysV and BSD disagree on the semantics of signal(2) regarding whether it's one-shot or not. If you want to cry a little bit, read the gory details in https://linux.die.net/man/2/signal under the "Portability" heading (TLDR: use sigaction(2) which doesn't reset the handler by default if you want portable behaviour without CPP mess)... ;-)