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// Copyright 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 interrupt provides an interrupt helper.
package interrupt
import (
"fmt"
"sync"
)
// Receiver receives interrupt notifications from a Forwarder.
type Receiver interface {
// NotifyInterrupt is called when the Receiver receives an interrupt.
NotifyInterrupt()
}
// Forwarder is a helper for delivering delayed signal interruptions.
//
// This helps platform implementations with Interrupt semantics.
type Forwarder struct {
// mu protects the below.
mu sync.Mutex
// dst is the function to be called when NotifyInterrupt() is called. If
// dst is nil, pending will be set instead, causing the next call to
// Enable() to return false.
dst Receiver
pending bool
}
// Enable attempts to enable interrupt forwarding to r. If f has already
// received an interrupt, Enable does nothing and returns false. Otherwise,
// future calls to f.NotifyInterrupt() cause r.NotifyInterrupt() to be called,
// and Enable returns true.
//
// Usage:
//
// if !f.Enable(r) {
// // There was an interrupt.
// return
// }
// defer f.Disable()
//
// Preconditions: r must not be nil. f must not already be forwarding
// interrupts to a Receiver.
func (f *Forwarder) Enable(r Receiver) bool {
if r == nil {
panic("nil Receiver")
}
f.mu.Lock()
if f.dst != nil {
f.mu.Unlock()
panic(fmt.Sprintf("already forwarding interrupts to %+v", f.dst))
}
if f.pending {
f.pending = false
f.mu.Unlock()
return false
}
f.dst = r
f.mu.Unlock()
return true
}
// Disable stops interrupt forwarding. If interrupt forwarding is already
// disabled, Disable is a no-op.
func (f *Forwarder) Disable() {
f.mu.Lock()
f.dst = nil
f.mu.Unlock()
}
// NotifyInterrupt implements Receiver.NotifyInterrupt. If interrupt forwarding
// is enabled, the configured Receiver will be notified. Otherwise the
// interrupt will be delivered to the next call to Enable.
func (f *Forwarder) NotifyInterrupt() {
f.mu.Lock()
if f.dst != nil {
f.dst.NotifyInterrupt()
} else {
f.pending = true
}
f.mu.Unlock()
}
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