Kraken HPC

What is Go-Fork?

https://github.com/kraken-hpc/go-fork

Go fork is a package to provide fork-like emulation for Go. In reality, it’s not very fork-like, but provides for a common thing fork() is used for, namely making a subroutine (goroutine) run in a new process spaces.

Go, by its natively threaded nature, is not fork-safe. This pkg does not implement a real fork.

Instead, this package makes a way to reroute go to execute a goroutine other than main() in a new process. This allows easy creation of some fork-like behaviors without actually using forks.

Moreover, while go-fork children do not share any memory space with go-fork parents, the parent can pass arbitrary data to go-fork via function arguments.

Here are a couple of particularly important diffierence between real forks and go-forks:

  • Go fork does not continue execution from the fork, but rather starts the specified goroutine from whatever point fork.Init() is called (usually early in main() or in init()).
  • Go fork doesn’t share memory, file pointers, mutexes, or really anything with the child process. It passes function arguments to the child by encoding them to/decoding them from a temporary file.

How it works

To use go-fork you must do two things:

  1. Register functions to be forkable (this must be done before trying to fork).b
  2. Call fork.Init() somewhere early in the code. If the process is a child, execution will be taken over from this point, and the code will os.Exit when it’s done, never returning execution to anything after fork.Init() is called.

It should be noted that go-fork is not able to detect function calling errors at build time. Errors like incorrect argument assignments are runtime errors.

go-fork determines that an run is a fork by looking for special values in its environment, which it will immediately unset once read.

go-fork passes arguments by encoding/gob endoding/decoding them in a temporary file. This fill will be cleaned up immediately after it is read.

Example:

func init() {
	fork.RegisterFunc("child", child)
	fork.Init()
}

func child(n int) {
	fmt.Printf("child(%d) pid: %d\n", n, os.Getpid())
}

func main() {
	fmt.Printf("main() pid: %d\n", os.Getpid())
	if err := fork.Fork("child", 1); err != nil {
		log.Fatalf("failed to fork: %v", err)
	}
}

This will output:

$ go run example/example.go 
main() pid: 164120
child(1) pid: 164125

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