Add freebsd (#229)

Author: mdbenjam

pkg/proctree/proctree_freebsd.go

@@ -0,0 +1,25 @@
+//go:build freebsd
+
+package proctree
+
+import (
+	"syscall"
+)
+
+func startPlatform(p *ProcTree) error {
+	// Start the child in a new session (which also gives it a new process group
+	// with pgid == child's pid). That lets us signal the entire tree via -pid.
+	p.cmd.SysProcAttr = &syscall.SysProcAttr{
+		Setsid: true,
+	}
+	return p.cmd.Start()
+}
+
+func killPlatformTree(p *ProcTree) error {
+	if p.cmd.Process == nil {
+		return nil
+	}
+	// Signal the whole process group. Negative PID targets the PGID.
+	_ = syscall.Kill(-p.cmd.Process.Pid, syscall.SIGKILL)
+	return p.cmd.Process.Kill()
+}