use of daemon call in ported code

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Created Jul ’20

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daemon(int nochdir, int noclose) is marked as discouraged.

Will it work in straight unix ported code that doesn't use Apple libraries?

I wrestled with this discouragement in a previous life where I had to gradually shift calls to CF to one side of deamon or the other in order to prevent catastrophe.

The cost of moving to launchd as is non-trivial in this instance and I'd like to be sure it is going to be necessary before going farther down this path.

Answered by joconnor in 620750022

I got things working with dispatch and xpc, so this question isn't really relevant any longer for me. Glib has internal tests for the main thread and that made things congested. It turned out to be easier for the moment to simply avoid dispatch_main and let glib have the main thread.

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Answer 1

DTS Engineer OP

Apple

Jul ’20

Are you planning to use daemon in a daemon? If so, how is that daemon getting launched?

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Answer 2

joconnor OP

Jul ’20

On unix the process parses the command line utils and then based on them it daemonizes so that the command line util can terminate and the daemon hangs around indefinitely.

What I'm doing for macOS is have the command line util parse the params and then XPC them to a mach service registered with launchd.

XPC and dispatch are conflicting with the shared unix glib code for event loops and signal handling. I'm working on making glib use dispatch and dispatch_io with the side benefit of hopefully being more efficient, but I'm wondering if all of this is necessary since the immediate reason to do this is to avoid the daemon call.

Exactly how this will work in the finished product is unknown.

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Answer 3

DTS Engineer OP

Apple

Jul ’20

On unix the process parses the command line utils and then based on them it daemonizes …

But who runs the command-line tool? Do you expect the user to run it with privileges, like using sudo?

If so, that definitely won’t work on macOS. macOS has execution context above and beyond the traditional UNIX uid, gid, and so on, and there’s no good way for a process that starts in a user context to switch to a daemon context. For more background on this, see Technote 2083 Daemons and Agents.

What I'm doing for macOS is have the command line util parse the params and then XPC them to a mach service registered with launchd.

That’s definitely heading in the right direction.

XPC and dispatch are conflicting with the shared unix glib code for event loops and signal handling.

My usual approach for handling this is to run that event loop on a secondary thread and then use the main thread just for XPC. Most event loops like this have some way to route events into the loop from outside, and your XPC code can use that.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@apple.com"

1

Answer 4

joconnor OP

Jul ’20

Accepted Answer

I got things working with dispatch and xpc, so this question isn't really relevant any longer for me. Glib has internal tests for the main thread and that made things congested. It turned out to be easier for the moment to simply avoid dispatch_main and let glib have the main thread.

0