From 58366ce64d21f3b0d2d061f1c9fe52e9d908ab7e Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Fri, 18 Mar 2022 20:29:17 +0900
Subject: [PATCH] internal/glfw: make the file operation atomic

If multiple Ebiten processes start at the same time, the file operation
can cause a race condition. Add a file lock to avoid this.
---
 go.mod                                  | 2 ++
 go.sum                                  | 9 +++++++++
 internal/glfw/notexternaldll_windows.go | 6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/go.mod b/go.mod
index f38f9da99..51ea248a5 100644
--- a/go.mod
+++ b/go.mod
@@ -4,6 +4,7 @@ go 1.15
 
 require (
 	github.com/go-gl/glfw/v3.3/glfw v0.0.0-20211213063430-748e38ca8aec
+	github.com/gofrs/flock v0.8.1
 	github.com/hajimehoshi/bitmapfont/v2 v2.2.0
 	github.com/hajimehoshi/file2byteslice v0.0.0-20210813153925-5340248a8f41
 	github.com/hajimehoshi/go-mp3 v0.3.2
@@ -16,4 +17,5 @@ require (
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
 	golang.org/x/sys v0.0.0-20220128215802-99c3d69c2c27
 	golang.org/x/tools v0.1.8-0.20211022200916-316ba0b74098
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 )
diff --git a/go.sum b/go.sum
index 293b68ed8..99d5f6a68 100644
--- a/go.sum
+++ b/go.sum
@@ -1,6 +1,8 @@
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20211213063430-748e38ca8aec h1:3FLiRYO6PlQFDpUU7OEFlWgjGD1jnBIVSJ5SYRWk+9c=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20211213063430-748e38ca8aec/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
+github.com/gofrs/flock v0.8.1 h1:+gYjHKf32LDeiEEFhQaotPbLuUXjY5ZqxKgXy7n59aw=
+github.com/gofrs/flock v0.8.1/go.mod h1:F1TvTiK9OcQqauNUHlbJvyl9Qa1QvF/gOUDKA14jxHU=
 github.com/hajimehoshi/bitmapfont/v2 v2.2.0 h1:E6vzlchynZj6OVohVKFqWkKW348EmDW62K5zPXDi7A8=
 github.com/hajimehoshi/bitmapfont/v2 v2.2.0/go.mod h1:Llj2wTYXMuCTJEw2ATNIO6HbFPOoBYPs08qLdFAxOsQ=
 github.com/hajimehoshi/file2byteslice v0.0.0-20210813153925-5340248a8f41 h1:s01qIIRG7vN/5ndLwkDktjx44ulFk6apvAjVBYR50Yo=
@@ -19,6 +21,11 @@ github.com/jfreymuth/oggvorbis v1.0.3 h1:MLNGGyhOMiVcvea9Dp5+gbs2SAwqwQbtrWnonYa
 github.com/jfreymuth/oggvorbis v1.0.3/go.mod h1:1U4pqWmghcoVsCJJ4fRBKv9peUJMBHixthRlBeD6uII=
 github.com/jfreymuth/vorbis v1.0.2 h1:m1xH6+ZI4thH927pgKD8JOH4eaGRm18rEE9/0WKjvNE=
 github.com/jfreymuth/vorbis v1.0.2/go.mod h1:DoftRo4AznKnShRl1GxiTFCseHr4zR9BN3TWXyuzrqQ=
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/pkg/browser v0.0.0-20210911075715-681adbf594b8/go.mod h1:HKlIX3XHQyzLZPlr7++PzdhaXEj94dEiJgZDTsxEqUI=
 github.com/yuin/goldmark v1.4.0/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
@@ -69,3 +76,5 @@ golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8T
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
diff --git a/internal/glfw/notexternaldll_windows.go b/internal/glfw/notexternaldll_windows.go
index 8edd2b343..6761693a5 100644
--- a/internal/glfw/notexternaldll_windows.go
+++ b/internal/glfw/notexternaldll_windows.go
@@ -24,6 +24,7 @@ import (
 	"os"
 	"path/filepath"
 
+	"github.com/gofrs/flock"
 	"golang.org/x/sys/windows"
 )
 
@@ -57,6 +58,11 @@ func loadDLL() (*dll, error) {
 		return nil, err
 	}
 
+	// Make the file operation atomic among multiple processes.
+	fl := flock.New(filepath.Join(dir, glfwDLLHash+".lock"))
+	fl.Lock()
+	defer fl.Unlock()
+
 	fn := filepath.Join(dir, glfwDLLHash+".dll")
 	if _, err := os.Stat(fn); err != nil {
 		if !os.IsNotExist(err) {