Add Flag util

utils/flag.go

@@ -0,0 +1,84 @@
+package utils
+
+import (
+	"sync"
+
+	"github.com/tevino/abool"
+)
+
+// FlagController is a simple system to broadcast a flag value.
+type FlagController struct {
+	flag   *abool.AtomicBool
+	signal chan struct{}
+	lock   sync.Mutex
+}
+
+// Flag receives changes from its FlagController.
+// A Flag must only be used in one goroutine and is not concurrency safe,
+// but fast.
+type Flag struct {
+	flag       *abool.AtomicBool
+	signal     chan struct{}
+	controller *FlagController
+}
+
+// NewFlagController returns a new FlagController.
+// In the initial state, the flag is not set and the singal does not trigger.
+func NewFlagController() *FlagController {
+	return &FlagController{
+		flag:   abool.New(),
+		signal: make(chan struct{}),
+		lock:   sync.Mutex{},
+	}
+}
+
+// NewFlag returns a new Flag controlled by this controller.
+// In the initial state, the flag is set and the singal triggers.
+// You can call Refresh immediately to get the current state from the
+// controller.
+func (cfc *FlagController) NewFlag() *Flag {
+	newFlag := &Flag{
+		flag:       abool.NewBool(true),
+		signal:     make(chan struct{}),
+		controller: cfc,
+	}
+	close(newFlag.signal)
+	return newFlag
+}
+
+// NotifyAndReset notifies all flags of this controller and resets the
+// controller state.
+func (cfc *FlagController) NotifyAndReset() {
+	cfc.lock.Lock()
+	defer cfc.lock.Unlock()
+
+	// Notify all flags of the change.
+	cfc.flag.Set()
+	close(cfc.signal)
+
+	// Reset
+	cfc.flag = abool.New()
+	cfc.signal = make(chan struct{})
+}
+
+// Signal returns a channel that waits for the flag to be set. This does not
+// reset the Flag itself, you'll need to call Refresh for that.
+func (cf *Flag) Signal() <-chan struct{} {
+	return cf.signal
+}
+
+// IsSet returns whether the flag was set since the last Refresh.
+// This does not reset the Flag itself, you'll need to call Refresh for that.
+func (cf *Flag) IsSet() bool {
+	return cf.flag.IsSet()
+}
+
+// Refresh fetches the current state from the controller.
+func (cf *Flag) Refresh() {
+	cf.controller.lock.Lock()
+	defer cf.controller.lock.Unlock()
+
+	// Copy current flag and signal from the controller.
+	cf.flag = cf.controller.flag
+	cf.signal = cf.controller.signal
+}