Put child processes in their own session

The core can be gracefully shutdown by sending a SIGINT to its process.
However, this signal is also propagated to all child processes, i.e. the
forked ffmpeg processes. They will also be stopped and might reconnect.
This is not wanted. The core has to stop these processes.

The child process will now get their own session ID with setsid() before
replacing themselves with ffmpeg. This way they will not receive a SIGINT
that was meant only for the parent.

internal/.gitignore

@@ -1,4 +1,5 @@
 testhelper/ignoresigint/ignoresigint
 testhelper/sigint/sigint
 testhelper/sigintwait/sigintwait
+testhelper/sigpropagate/sigpropagate
 testhelper/ffmpeg/ffmpeg

internal/testhelper/sigpropagate/sigpropagate.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+func main() {
+	if len(os.Args) == 1 {
+		cmd := exec.Command(os.Args[0], "x")
+		cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
+		stdout, _ := cmd.StdoutPipe()
+		cmd.Start()
+
+		go func() {
+			io.Copy(os.Stdout, stdout)
+		}()
+	}
+
+	sigcount := 0
+
+	// Wait for interrupt signal to gracefully shutdown the app
+	quit := make(chan os.Signal, 1)
+	signal.Notify(quit, os.Interrupt)
+
+	ticker := time.NewTicker(time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-quit:
+			fmt.Printf("[%d] got SIGINT\n", os.Getpid())
+			sigcount++
+
+			if sigcount > 5 {
+				return
+			}
+		case <-ticker.C:
+			fmt.Printf("[%d] hello\n", os.Getpid())
+		}
+	}
+}

process/process.go

@@ -564,6 +564,7 @@ func (p *process) start() error {
 	}
 
 	p.cmd = exec.Command(p.binary, args...)
+	p.cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
 	p.cmd.Env = []string{}
 
 	p.stdout, err = p.cmd.StderrPipe()