Install a SIGCHLD handler, and allow wait() and also getting the exit code

[gaborcsardi]

The SIGCHLD handler will be incompatible with the parallel package, which just removes the old handler and installs a new one. So ideally, parallel needs a fix, too.

[gaborcsardi]

Of course this is only for Unix. I don't know how you would do this on Windows....

[gaborcsardi]

Btw. you definitely need a SIGCHLD handler, because currently sys leaves zombie processes around...

[gaborcsardi]

Related to this, I would like to have the exit status of the background process as well, without waiting on it, of course.

On Unix the SIGCHLD signal handler can get the exit status, and there is also a way to get it on Windows. But where should sys store the exit status? If we had process objects or some handle, then we could store it in the handle object. So how about making an exec_background version that returns a handle instead of a pid?

[gaborcsardi]

Another, slightly hackier solution is to return the pid, but add some attribute that will be essentially the handle. It should be an external pointer, so that it has reference semantics.

Personally I think that just having a new function that returns a handle is cleaner. exec_with_handle() or sg like that.

[gaborcsardi]

Just tell me which one to implement, and then I'll do it. :)

[jeroen]

Sorry I got silent, it was late. Reviewing now.

[jeroen]

In sys we temporarily block SIGCHLD for blocking calls, which ensures there are no side effects. Users that want more control should switch to processx.