Safely restart current process in golang.
By safely we mean it waits parent process to exit completely before the child process begins to allocate resources. The child process will inherit parent process' command line arguments and environment variables.
To put everything simple, we did NOT implement anything "graceful" such as pass network resources to child process to avoid service interruption because it's way too complicate for programs that is listening to multiple network ports or sockets.
This package is more suitable for an agent program that updates its own binary and requires to restart itself to complete the upgrade.
It's hard to write unit tests for a process keep restarting(exit/fork).
Here is how it can be tested:
- Build and start a parent process
go build -o ./bin/example ./example
./bin/example -any=arguments -we=want -inherited=to -be=tested
- Following message is to be expected
Current PID: 29539
29539 : this is a parent
29539 : have arguments [./bin/example -any=args]
kill -HUP 29539 -> to rollover(restart).
kill 29539 -> to quit
-
Run
kill -HUP 29539to initiate rollover(restart). -
Following message is to be expected
initiating rollover
child started runing, pid: 29544
- And after 3 second we should see parent cleaned up and exit
29539 : safely exit after clean up
- Also, following message is to be expected:
Current PID: 29544
29544 : this is a child
29544 : have arguments [./bin/example -any=args]
kill -HUP 29544 -> to rollover(restart).
kill 29544 -> to quit
-
Loop between step 3 to 6 to see if it works for multiple rollovers(restart).
-
Now we can kill the child by run
kill 29544
Q. Why kill the parent from child instead of quitting the parent when rollover.Restart()?
A. In case the child is failed to spawn.
Q. Why not put the syscall signal handler to the package?
A. It's caller's responsibility and privilege to decide when or under what condition to rollover(restart). There may be other ways such as by API calls or automatically happened when binary update finished.