From 288fcb82182282b02102015d988f2d674851e489 Mon Sep 17 00:00:00 2001
From: Ian Gudger <ian@iangudger.com>
Date: Sat, 15 Oct 2022 23:31:11 -0700
Subject: [PATCH] Use standard library sync.Mutex.TryLock.
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The standard library sync.Mutex has included a TryLock method since Go 1.18.
There is no longer a need to implement a parallel version with unsafe. Using
the standard library version reduces the ongoing maintenance cost of this
package.

https://pkg.go.dev/sync#Mutex.TryLock
https://tip.golang.org/doc/go1.18#minor_library_changes
---
 .github/workflows/go.yml |  2 +-
 pkg/sync/BUILD           |  1 -
 pkg/sync/mutex_test.go   | 72 ----------------------------------------
 pkg/sync/mutex_unsafe.go | 35 +++----------------
 4 files changed, 5 insertions(+), 105 deletions(-)
 delete mode 100644 pkg/sync/mutex_test.go

diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 32aa1845f..eff0447b7 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -45,7 +45,7 @@ jobs:
         fetch-depth: 0
     - uses: actions/setup-go@v2
       with:
-        go-version: 1.17
+        go-version: 1.18
     - run: tools/go_branch.sh
     - run: git checkout go && git clean -xf . && go build ./...
     - if: github.event_name == 'push'
diff --git a/pkg/sync/BUILD b/pkg/sync/BUILD
index d105e9436..78d50f8d9 100644
--- a/pkg/sync/BUILD
+++ b/pkg/sync/BUILD
@@ -42,7 +42,6 @@ go_test(
     size = "small",
     srcs = [
         "gate_test.go",
-        "mutex_test.go",
         "rwmutex_test.go",
         "seqcount_test.go",
     ],
diff --git a/pkg/sync/mutex_test.go b/pkg/sync/mutex_test.go
deleted file mode 100644
index 4122b2e82..000000000
--- a/pkg/sync/mutex_test.go
+++ /dev/null
@@ -1,72 +0,0 @@
-// Copyright 2019 The gVisor Authors.
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +checkalignedignore
-package sync
-
-import (
-	"sync"
-	"testing"
-	"unsafe"
-)
-
-// TestStructSize verifies that syncMutex's size hasn't drifted from the
-// standard library's version.
-//
-// The correctness of this package relies on these remaining in sync.
-func TestStructSize(t *testing.T) {
-	const (
-		got  = unsafe.Sizeof(syncMutex{})
-		want = unsafe.Sizeof(sync.Mutex{})
-	)
-	if got != want {
-		t.Errorf("got sizeof(syncMutex) = %d, want = sizeof(sync.Mutex) = %d", got, want)
-	}
-}
-
-// TestFieldValues verifies that the semantics of syncMutex.state from the
-// standard library's implementation.
-//
-// The correctness of this package relies on these remaining in sync.
-func TestFieldValues(t *testing.T) {
-	var m Mutex
-	m.Lock()
-	if got := *m.m.state(); got != mutexLocked {
-		t.Errorf("got locked sync.Mutex.state = %d, want = %d", got, mutexLocked)
-	}
-	m.Unlock()
-	if got := *m.m.state(); got != mutexUnlocked {
-		t.Errorf("got unlocked sync.Mutex.state = %d, want = %d", got, mutexUnlocked)
-	}
-}
-
-func TestDoubleTryLock(t *testing.T) {
-	var m Mutex
-	if !m.TryLock() {
-		t.Fatal("failed to aquire lock")
-	}
-	if m.TryLock() {
-		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
-	}
-}
-
-func TestTryLockAfterLock(t *testing.T) {
-	var m Mutex
-	m.Lock()
-	if m.TryLock() {
-		t.Fatal("unexpectedly succeeded in aquiring locked mutex")
-	}
-}
-
-func TestTryLockUnlock(t *testing.T) {
-	var m Mutex
-	if !m.TryLock() {
-		t.Fatal("failed to aquire lock")
-	}
-	m.Unlock() // +checklocksforce
-	if !m.TryLock() {
-		t.Fatal("failed to aquire lock after unlock")
-	}
-}
diff --git a/pkg/sync/mutex_unsafe.go b/pkg/sync/mutex_unsafe.go
index f0a471da4..9bf412700 100644
--- a/pkg/sync/mutex_unsafe.go
+++ b/pkg/sync/mutex_unsafe.go
@@ -3,62 +3,35 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.13 && !go1.21
-// +build go1.13,!go1.21
-
-// When updating the build constraint (above), check that syncMutex matches the
-// standard library sync.Mutex definition.
-
 package sync
 
 import (
 	"sync"
-	"sync/atomic"
 	"unsafe"
 )
 
 // CrossGoroutineMutex is equivalent to Mutex, but it need not be unlocked by a
 // the same goroutine that locked the mutex.
 type CrossGoroutineMutex struct {
-	sync.Mutex
-}
-
-type syncMutex struct {
-	state int32
-	sema  uint32
-}
-
-func (m *CrossGoroutineMutex) state() *int32 {
-	return &(*syncMutex)(unsafe.Pointer(&m.Mutex)).state
+	m sync.Mutex
 }
 
 // Lock locks the underlying Mutex.
 // +checklocksignore
 func (m *CrossGoroutineMutex) Lock() {
-	m.Mutex.Lock()
+	m.m.Lock()
 }
 
 // Unlock unlocks the underlying Mutex.
 // +checklocksignore
 func (m *CrossGoroutineMutex) Unlock() {
-	m.Mutex.Unlock()
+	m.m.Unlock()
 }
 
-const (
-	mutexUnlocked = 0
-	mutexLocked   = 1
-)
-
 // TryLock tries to acquire the mutex. It returns true if it succeeds and false
 // otherwise. TryLock does not block.
 func (m *CrossGoroutineMutex) TryLock() bool {
-	if atomic.CompareAndSwapInt32(m.state(), mutexUnlocked, mutexLocked) {
-		if RaceEnabled {
-			RaceAcquire(unsafe.Pointer(&m.Mutex))
-		}
-		return true
-	}
-	return false
+	return m.m.TryLock()
 }
 
 // Mutex is a mutual exclusion lock. The zero value for a Mutex is an unlocked