[Interest] proper (silent) exit in response to SIGHUP?

René J. V. Bertin rjvbertin at gmail.com
Mon Oct 15 15:34:55 CEST 2018

Thiago Macieira wrote:

> You were complaining that pipes are too costly. Ok, so get your OS vendor to
> create an equivalent to Linux's eventfd()

Sure. Dear Apple (FreeBSD), please implement eventfd() (and a bunch of other 
Linux features because they make Linux so much better).

> Do you realise that the cost of starting a thread is much higher than the cost
> of a pipe? Not to mention that using QThread will create a pipe anyway, so
> you'd need to drop down to low-level primitives (pthread, Win32) to get away
> from it.

OK, that's an argument. I tried to figure that out and didn't see evidence that 
QThread *always* creates a pipe. Pity but thanks for confirming.

> "just allocate in the actual signal handler" is exactly what you mustn't do,
> since malloc() is not async-signal-safe. You can deadlock or corrupt memory if
> you try that.

The actual signal handler, the one that does the things you want to but cannot 
do in the, erm, signal handler. Sorry for the confusion.

> You could pre-allocate the event before the signal and then you can transfer
> ownership. But postEvent() still needs to manage a queue and that may need to

Exactly, which is what I realised when I saw it locking a mutex.


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