Implement os.SIGDFL and os.SIGIGN

[dkaszews]

Fixes: #4889

Allows user to reset the previously overwritten os.signal or ignore it completely (not passed to process, same as with { exclusive = true }.

Opens:

• More descriptive names like signal_default/reset and signal_ignore instead of Unix's SIGDFL and SIGIGN?
• Tests? May be tricky to test signals, would need to run xmake in a subprocess of its own.
• Add documentation

[waruqi]

More descriptive names like signal_default/reset and signal_ignore instead of Unix's SIGDFL and SIGIGN?

or we can use

os.signal(os.SIGINT, {reset = true})
os.signal(os.SIGINT, {ignore = true})

[waruqi]

Tests? May be tricky to test signals, would need to run xmake in a subprocess of its own.

If you can help to add some tests, it will be better.

[waruqi]

Add documentation

you can add doc in https://github.com/xmake-io/xmake-docs/blob/master/manual/builtin_modules.md#os

[dkaszews]

os.signal(os.SIGINT, {reset = true})
os.signal(os.SIGINT, {ignore = true})

I don't quite like using dictionary just for named value, it's easy to make a typo and not get any feedback. I think cleaner would be to create one function for each:

name	signal	xmake action	process signalled
os.set_signal(signo, fun)	fun	callback	yes
os.ignore_signal(signo)	SIG_IGN	no action	no
os.reset_signal(signo)	SIG_DLF	killed	yes(1)

Notes:

1. If traps and does not exit, then it's orphaned detached from I/O as per issue

[waruqi]

I wouldn't consider adding too much API to the os module for signal. please only use os.signal

Or use a separate signal module.

signal.register(signo, handler)
signal.ignore(signo)
signal.reset(signo)

[dkaszews]

Or use a separate signal module.

Understood, how about putting it in process since it's related and has relatively small API?

[waruqi]

Or use a separate signal module.

Understood, how about putting it in since it's related and has relatively small API?process

no, process is only used to run and manage a single child process.

[waruqi]

see #4908