State Change Callback in circuit breaker

hystrix/callback/callback.go

@@ -0,0 +1,34 @@
+package callback
+
+var circuitCallback map[string]stateFunc
+
+//State is a type to hold Circuit-state this will be used while calling stateFunc on State change
+type State string
+
+const (
+	//Open is a state to indicate that Circuit state is Open
+	Open = "Open"
+	//Close is a state to indicate that Circuit state is Close
+	Close = "Close"
+	//AllowSingle is a state to indicate that Circuit state is AllowSingle or trying to Open Circuit
+	AllowSingle = "Allow Single"
+)
+
+type stateFunc func(name string, state State)
+
+func init() {
+	circuitCallback = make(map[string]stateFunc)
+}
+
+//Register adds callback for a circuit
+func Register(name string, callbackFunc stateFunc) {
+	circuitCallback[name] = callbackFunc
+}
+
+//Invoke is a function to invoke Callback function in a goroutine on State change
+func Invoke(name string, state State) {
+	callbackFunc, _ := circuitCallback[name]
+	if callbackFunc != nil {
+		go callbackFunc(name, state)
+	}
+}

hystrix/callback/callback_test.go

@@ -0,0 +1,57 @@
+package callback
+
+import (
+	"testing"
+	"time"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestRegister(t *testing.T) {
+	Convey("Register a command", t, func() {
+		Register("Test-Command", func(name string, state State) {})
+
+		Convey("Read Callback function for Registered Command", func() {
+			callbackFunc, _ := circuitCallback["Test-Command"]
+			So(callbackFunc, ShouldNotBeNil)
+		})
+		Convey("Read Callback function for unknown Command", func() {
+			callbackFunc, _ := circuitCallback["Command"]
+			So(callbackFunc, ShouldBeNil)
+		})
+	})
+}
+
+func TestInvoke(t *testing.T) {
+	Convey("Register a command", t, func() {
+		var callbackInvoked bool
+		var callbackState State = Close
+		Register("TestInvokeCommand", func(name string, state State) {
+			callbackInvoked = true
+			callbackState = state
+		})
+
+		Invoke("TestInvokeCommand", Open)
+		time.Sleep(2 * time.Second)
+		Convey("Invoke Callback for Registered Command", func() {
+			So(callbackInvoked, ShouldBeTrue)
+			So(callbackState, ShouldEqual, Open)
+		})
+	})
+
+	Convey("Register a Invoke command", t, func() {
+		var callbackInvoked = false
+		var callbackState State = Close
+		Register("TestInvokeCommand", func(name string, state State) {
+			callbackInvoked = true
+			callbackState = state
+		})
+
+		Invoke("Command", Open)
+
+		Convey("Read Callback function for unknown Command", func() {
+			So(callbackInvoked, ShouldBeFalse)
+			So(callbackState, ShouldEqual, Close)
+		})
+	})
+}

hystrix/circuit.go

@@ -5,6 +5,8 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+
+	"github.com/ContinuumLLC/hystrix-go/hystrix/callback"
 )
 
 // CircuitBreaker is created for each ExecutorPool to track whether requests
@@ -128,6 +130,8 @@ func (circuit *CircuitBreaker) allowSingleTest() bool {
 		swapped := atomic.CompareAndSwapInt64(&circuit.openedOrLastTestedTime, openedOrLastTestedTime, now)
 		if swapped {
 			log.Printf("hystrix-go: allowing single test to possibly close circuit %v", circuit.Name)
+
+			callback.Invoke(circuit.Name, callback.AllowSingle)
 		}
 		return swapped
 	}
@@ -144,9 +148,11 @@ func (circuit *CircuitBreaker) setOpen() {
 	}
 
 	log.Printf("hystrix-go: opening circuit %v", circuit.Name)
-
 	circuit.openedOrLastTestedTime = time.Now().UnixNano()
 	circuit.open = true
+
+	callback.Invoke(circuit.Name, callback.Open)
+
 }
 
 func (circuit *CircuitBreaker) setClose() {
@@ -161,6 +167,9 @@ func (circuit *CircuitBreaker) setClose() {
 
 	circuit.open = false
 	circuit.metrics.Reset()
+
+	callback.Invoke(circuit.Name, callback.Close)
+
 }
 
 // ReportEvent records command metrics for tracking recent error rates and exposing data to the dashboard.

hystrix/settings.go

@@ -20,6 +20,7 @@ var (
 	DefaultLogger = NoopLogger{}
 )
 
+//Settings is used to tune circuit settings
 type Settings struct {
 	Timeout                time.Duration
 	MaxConcurrentRequests  int
@@ -106,6 +107,7 @@ func getSettings(name string) *Settings {
 	return s
 }
 
+//GetCircuitSettings returns Circuit Settings for each command
 func GetCircuitSettings() map[string]*Settings {
 	copy := make(map[string]*Settings)