pid

Daemonize your go programs by locking the process id file. Simply put the following at the top of your main,

func main() {
    defer pid.Start("monokuma").Stop()
    // your code...
}

This will create a monokuma.pid file in /tmp with the process id (pid) of the go program when loaded by your operating system. When your main exits, the file will be cleaned up.

Using

As with any go library, get it through go,

go get -u -v github.com/thecsw/pid@v0.1.0

The versioning of this is arbitrary, it is not v1.0.0 because it hasn't been tested or used in production systems.

Motivation

This will prevent any other instances of your program running at the same time (say running a web server or overloading some resources). Say, when I run

λ ./monokuma

I can find the PID of it with (no line feed at the end),

λ cat /tmp/monokuma.pid
91100⏎

If I try to start the same program, I will be greeted by

λ ./monokuma
2023/05/17 23:03:03 your app with pid 91100 is already running

and exit with code 1 <- opiniated and expected behavior. Some edge-cases are handled below.

Caveats

There are multiple instances where we have to find edge-cases, say, your program failed and the cleanup of the pid didn't happen. What then?

pid will check for the pid file's existence and if it exists, we will read the pid value and try to find whether there is a running process with said pid. If there is none, it is considered a "stale" pid file and deleted. New pid file will be created.

However, if a pid from the file exists, we exit immediately with 1 like above. What if the running pid isn't actually your program but some other program that commandeered said pid? That shouldn't happen on Unix-like systems, because each pid is unique until the max value is reached (care to reboot your machine?)

On windows it's a different story, though. But hey, this pid library isn't supported on windows, so this little code is flawless. hah.

As of May 17th, 2023, os.FindProcess doesn't work on checking a running pid,

On Unix systems, FindProcess always succeeds and returns a Process for the given pid, regardless of whether the process exists.

Instead, I used fantastic gopsutil's PidExists.

TODO

Should we write to somewhere that is not /tmp? For security reasons, /var/run is locked behind special permissions or user id 0, which I don't want to touch.

How do we manage pids on windows? I know there is a way, but I usually use Unix-style machines.

LICENSE

Apache licensed, go wild.