sync: Add Locker type

sync/locker.go

@@ -0,0 +1,36 @@
+package usync
+
+import "sync"
+
+// Locker guards access to a value
+type Locker[T any] struct {
+	value T
+	mutex sync.Mutex
+}
+
+// NewLocker creates a new locker with the specified value.
+func NewLocker[T any] (value T) Locker[T] {
+	return Locker[T] {
+		value: value,
+	}
+}
+
+// Set sets the value of the locker.
+func (this *Locker[T]) Set (value T) {
+	this.mutex.Lock()
+	defer this.mutex.Unlock()
+	this.value = value
+}
+
+// Borrow borrows the value from the locker, and returns a function that must
+// immediately be deferred, like this:
+//
+//   value, done := locker.Borrow()
+//   defer done()
+//
+// From the time Borrow is called to the time the done function is called, it is
+// safe to access the locked object from within the current goroutine.
+func (this *Locker[T]) Borrow () (T, func ()) {
+	this.mutex.Lock()
+	return this.value, this.mutex.Unlock
+}