From fe91af5e09b802cec76d7c5cd6a646c38e9bbfa9 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 14 Oct 2022 15:06:11 +0530
Subject: [PATCH] Go stdlib doesnt even have a way to lock files

---
 tools/utils/filelock.go | 48 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 tools/utils/filelock.go

diff --git a/tools/utils/filelock.go b/tools/utils/filelock.go
new file mode 100644
index 000000000..69c566603
--- /dev/null
+++ b/tools/utils/filelock.go
@@ -0,0 +1,48 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"syscall"
+)
+
+var _ = fmt.Print
+
+func lock(fd, op int, path string) (err error) {
+	for {
+		err = syscall.Flock(fd, op)
+		if err != syscall.EINTR {
+			break
+		}
+	}
+	if err != nil {
+		opname := "exclusive flock()"
+		switch op {
+		case syscall.LOCK_UN:
+			opname = "unlock flock()"
+		case syscall.LOCK_SH:
+			opname = "shared flock()"
+		}
+		return &fs.PathError{
+			Op:   opname,
+			Path: path,
+			Err:  err,
+		}
+	}
+	return nil
+}
+
+func LockFileShared(f *os.File) error {
+	return lock(int(f.Fd()), syscall.LOCK_SH, f.Name())
+}
+
+func LockFileExclusive(f *os.File) error {
+	return lock(int(f.Fd()), syscall.LOCK_EX, f.Name())
+}
+
+func UnlockFile(f *os.File) error {
+	return lock(int(f.Fd()), syscall.LOCK_UN, f.Name())
+}