sync: Add monitor tests

sync/monitor.go

@@ -25,7 +25,7 @@ func (this *Monitor[T]) Set (value T) {
 // Borrow borrows the value from the Monitor, and returns a function that must
 // immediately be deferred, like this:
 //
-//   value, done := Monitor.Borrow()
+//   value, done := monitor.Borrow()
 //   defer done()
 //
 // From the time Borrow is called to the time the done function is called, it is
@@ -35,6 +35,19 @@ func (this *Monitor[T]) Borrow () (T, func ()) {
 	return this.value, this.mutex.Unlock
 }
 
+// BorrowReturn is like borrow, but returns a "done" function that takes in an
+// updated value. The intended use of this function is like this:
+//
+//   value, done := monitor.BorrowReturn()
+//   defer done(value)
+func (this *Monitor[T]) BorrowReturn () (T, func (T)) {
+	this.mutex.Lock()
+	return this.value, func (value T) {
+		defer this.mutex.Unlock()
+		this.value = value
+	}
+}
+
 // RWMonitor guards separate read/write access to a value.
 type RWMonitor[T any] struct {
 	value T
@@ -59,7 +72,7 @@ func (this *RWMonitor[T]) Set (value T) {
 // Borrow borrows the value from the Monitor for write access, and returns a
 // function that must immediately be deferred, like this:
 //
-//   value, done := Monitor.Borrow()
+//   value, done := monitor.Borrow()
 //   defer done()
 //
 // From the time Borrow is called to the time the done function is called, it is
@@ -69,6 +82,19 @@ func (this *RWMonitor[T]) Borrow () (T, func ()) {
 	return this.value, this.mutex.Unlock
 }
 
+// BorrowReturn is like borrow, but returns a "done" function that takes in an
+// updated value. The intended use of this function is like this:
+//
+//   value, done := monitor.BorrowReturn()
+//   defer done(value)
+func (this *RWMonitor[T]) BorrowReturn () (T, func (T)) {
+	this.mutex.Lock()
+	return this.value, func (value T) {
+		defer this.mutex.Unlock()
+		this.value = value
+	}
+}
+
 // RBorrow is like Borrow, but returns the item for read access only. Do not
 // under any circumstances modify anything returned by this method.
 func (this *RWMonitor[T]) RBorrow () (T, func ()) {

sync/monitor_test.go

@@ -0,0 +1,47 @@
+package usync
+
+import "testing"
+import "math/rand"
+
+func TestMonitor (test *testing.T) {
+	mon := NewMonitor(9)
+	func () {
+		value, done := mon.Borrow()
+		defer done()
+		test.Log(value)
+		if value != 9 { test.Fatal("not equal") }
+	} ()
+	func () {
+		value, done := mon.BorrowReturn()
+		value += 3
+		defer done(value)
+	} ()
+	func () {
+		value, done := mon.Borrow()
+		defer done()
+		test.Log(value)
+		if value != 12 { test.Fatal("not equal") }
+	} ()
+	mon.Set(11)
+	func () {
+		value, done := mon.Borrow()
+		defer done()
+		test.Log(value)
+		if value != 11 { test.Fatal("not equal") }
+	} ()
+}
+
+func TestMonitorConcurrent (test *testing.T) {
+	mon := NewMonitor(map[int] int { })
+	for index := 0; index < 16; index ++ {
+		go func () {
+			for index := 0; index < 8192; index ++ {
+				func () {
+					value, done := mon.Borrow()
+					defer done()
+					value[rand.Int()] = rand.Int()
+				} ()
+			}
+		} ()
+	}
+}