最终流程和子流程

Question

I'm trying to properly terminate a command

c := exec.Command("omxplayer", "video.mp4")
c.Start()

// send kill signal to terminate command at later stage
time.Sleep(4*time.Second)
c.Process.Kill()
c.Wait() // should wait for program to fully exit

// start again with new video
c := exec.Command("omxplayer", "video2.mp4")
c.Start()

I'm trying to kill the current omxplayer process on my Raspberry-Pi so that I can start it again with a new video.

Once I send the Kill signal, I call c.Wait() to wait for the current command to end before starting a new command.

The Problem is that the first command is not stopping, but the next command is starting anyway. So I end up with multiple videos being played at the same time.

Answer 1

omxplayer is forking a new process. For omxplayer in particular, I can send the "q" string into its StdinPipe. That's like pressing the q key on the keyboard, which quits the program, ending both the parent and child processes:

c := exec.Command("omxplayer", "video.mp4")
c.Start()
p := c.StdinPipe()
_, err := p.Write([]byte("q")) // send 'q' to the Stdin of the process to quit omxplayer

c.Wait() // should wait for program to fully exit

// start again with new video
c := exec.Command("omxplayer", "video2.mp4")
c.Start()

Another more general option is to create a process group with both the parent and child processes and kill that:

c := exec.Command("omxplayer", "video.mp4")
// make the process group id the same as the pid
c.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
c.Start()

// sending a negative number as the PID sends the kill signal to the group
syscall.Kill(-c.Process.Pid, syscall.SIGKILL)

c.Wait()

Based on this Medium post