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listener.go
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listener.go
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// Copyright (C) 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package status
import (
"context"
"fmt"
"runtime"
"sync"
)
var listeners = map[int]Listener{}
var listenerMutex sync.RWMutex
var nextListenerID int
// EventScope defines the scope for a particular event
type EventScope int
const (
// TaskScope is an event that applies to the current task
TaskScope EventScope = iota
// ProcessScope is an event that only applies to this process
ProcessScope
// GlobalScope is an event that applies globally
GlobalScope
)
func (s EventScope) String() string {
switch s {
case TaskScope:
return "Task"
case ProcessScope:
return "Process"
case GlobalScope:
return "Global"
default:
return "Unknown"
}
}
// Listener is the interface implemented by types that want to listen to
// application status messages.
type Listener interface {
OnTaskStart(context.Context, *Task)
OnTaskProgress(context.Context, *Task)
OnTaskFinish(context.Context, *Task)
OnEvent(context.Context, *Task, string, EventScope)
OnMemorySnapshot(context.Context, runtime.MemStats)
OnTaskBlock(context.Context, *Task)
OnTaskUnblock(context.Context, *Task)
}
// Unregister is the function returned by RegisterListener and is used to
// unregister the listenenr.
type Unregister func()
// RegisterListener registers l for status updates
func RegisterListener(l Listener) Unregister {
listenerMutex.Lock()
defer listenerMutex.Unlock()
id := nextListenerID
nextListenerID++
listeners[id] = l
return func() {
listenerMutex.Lock()
defer listenerMutex.Unlock()
delete(listeners, id)
}
}
func onTaskStart(ctx context.Context, t *Task) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
for _, l := range listeners {
l.OnTaskStart(ctx, t)
}
}
func onTaskProgress(ctx context.Context, t *Task) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
for _, l := range listeners {
l.OnTaskProgress(ctx, t)
}
}
func onBlock(ctx context.Context, t *Task) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
for _, l := range listeners {
l.OnTaskBlock(ctx, t)
}
}
func onUnblock(ctx context.Context, t *Task) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
for _, l := range listeners {
l.OnTaskUnblock(ctx, t)
}
}
func onTaskFinish(ctx context.Context, t *Task) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
for _, l := range listeners {
l.OnTaskFinish(ctx, t)
}
}
func onEvent(ctx context.Context, t *Task, scope EventScope, name string, args []interface{}) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
if len(listeners) > 0 {
msg := fmt.Sprintf(name, args...)
for _, l := range listeners {
l.OnEvent(ctx, t, msg, scope)
}
}
}
func onMemorySnapshot(ctx context.Context, snapshot runtime.MemStats) {
listenerMutex.RLock()
defer listenerMutex.RUnlock()
for _, l := range listeners {
l.OnMemorySnapshot(ctx, snapshot)
}
}