From 44f52eb6a8cc035dc509bc42b81dc933b6db6899 Mon Sep 17 00:00:00 2001
From: Charles Moog <moogcharlie@gmail.com>
Date: Sat, 24 Oct 2020 12:07:48 -0500
Subject: [PATCH] Allow package users to set the child process priority (#17)

---
 localexec.go      | 2 ++
 localexec_unix.go | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/localexec.go b/localexec.go
index 8f1ed86..bdb7237 100644
--- a/localexec.go
+++ b/localexec.go
@@ -9,6 +9,8 @@ import (
 
 // LocalExecer executes command on the local system.
 type LocalExecer struct {
+	// ChildProcessPriority overrides the default niceness of all child processes launch by LocalExecer.
+	ChildProcessPriority *int
 }
 
 func (l *localProcess) Stdin() io.WriteCloser {
diff --git a/localexec_unix.go b/localexec_unix.go
index a40b127..b1f8fd8 100644
--- a/localexec_unix.go
+++ b/localexec_unix.go
@@ -91,6 +91,15 @@ func (l LocalExecer) Start(ctx context.Context, c Command) (Process, error) {
 		if err != nil {
 			return nil, xerrors.Errorf("start command: %w", err)
 		}
+
+		if l.ChildProcessPriority != nil {
+			pid := process.cmd.Process.Pid
+			niceness := *l.ChildProcessPriority
+			err := syscall.Setpriority(syscall.PRIO_PROCESS, pid, niceness)
+			if err != nil {
+				return nil, xerrors.Errorf("set process (pid: %d) priority to (niceness: %d): %w", pid, niceness, err)
+			}
+		}
 	}
 
 	return &process, nil