TMutex based on sync.Mutex.

Updates #231

PiperOrigin-RevId: 290854399

1 files changed, 49 insertions, 0 deletions

diff --git a/pkg/sync/tmutex_unsafe.go b/pkg/sync/tmutex_unsafe.go
new file mode 100644
index 000000000..3c32f8371
--- /dev/null
+++ b/pkg/sync/tmutex_unsafe.go
@@ -0,0 +1,49 @@
+// 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.
+
+// +build go1.13
+// +build !go1.15
+
+// When updating the build constraint (above), check that syncMutex matches the
+// standard library sync.Mutex definition.
+
+package sync
+
+import (
+	"sync"
+	"sync/atomic"
+	"unsafe"
+)
+
+// TMutex is a try lock.
+type TMutex struct {
+	sync.Mutex
+}
+
+type syncMutex struct {
+	state int32
+	sema  uint32
+}
+
+func (m *TMutex) state() *int32 {
+	return &(*syncMutex)(unsafe.Pointer(&m.Mutex)).state
+}
+
+const (
+	mutexUnlocked = 0
+	mutexLocked   = 1
+)
+
+// TryLock tries to aquire the mutex. It returns true if it succeeds and false
+// otherwise. TryLock does not block.
+func (m *TMutex) TryLock() bool {
+	if atomic.CompareAndSwapInt32(m.state(), mutexUnlocked, mutexLocked) {
+		if RaceEnabled {
+			RaceAcquire(unsafe.Pointer(&m.Mutex))
+		}
+		return true
+	}
+	return false
+}