src/os/signal/signal.go - go - Git at Google

 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package signal

 import (
 	"context"
 	"os"
 	"sync"
 )

 var handlers struct {
 	sync.Mutex
 	// Map a channel to the signals that should be sent to it.
 	m map[chan<- os.Signal]*handler
 	// Map a signal to the number of channels receiving it.
 	ref [numSig]int64
 	// Map channels to signals while the channel is being stopped.
 	// Not a map because entries live here only very briefly.
 	// We need a separate container because we need m to correspond to ref
 	// at all times, and we also need to keep track of the *handler
 	// value for a channel being stopped. See the Stop function.
 	stopping []stopping
 }

 type stopping struct {
 	c chan<- os.Signal
 	h *handler
 }

 type handler struct {
 	mask [(numSig + 31) / 32]uint32
 }

 func (h *handler) want(sig int) bool {
 	return (h.mask[sig/32]>>uint(sig&31))&1 != 0
 }

 func (h *handler) set(sig int) {
 	h.mask[sig/32] |= 1 << uint(sig&31)
 }

 func (h *handler) clear(sig int) {
 	h.mask[sig/32] &^= 1 << uint(sig&31)
 }

 // Stop relaying the signals, sigs, to any channels previously registered to
 // receive them and either reset the signal handlers to their original values
 // (action=disableSignal) or ignore the signals (action=ignoreSignal).
 func cancel(sigs []os.Signal, action func(int)) {
 	handlers.Lock()
 	defer handlers.Unlock()

 	remove := func(n int) {
 		var zerohandler handler

 		for c, h := range handlers.m {
 			if h.want(n) {
 				handlers.ref[n]--
 				h.clear(n)
 				if h.mask == zerohandler.mask {
 					delete(handlers.m, c)
 				}
 			}
 		}

 		action(n)
 	}

 	if len(sigs) == 0 {
 		for n := 0; n < numSig; n++ {
 			remove(n)
 		}
 	} else {
 		for _, s := range sigs {
 			remove(signum(s))
 		}
 	}
 }

 // Ignore causes the provided signals to be ignored. If they are received by
 // the program, nothing will happen. Ignore undoes the effect of any prior
 // calls to Notify for the provided signals.
 // If no signals are provided, all incoming signals will be ignored.
 func Ignore(sig ...os.Signal) {
 	cancel(sig, ignoreSignal)
 }

 // Ignored reports whether sig is currently ignored.
 func Ignored(sig os.Signal) bool {
 	sn := signum(sig)
 	return sn >= 0 && signalIgnored(sn)
 }

 var (
 	// watchSignalLoopOnce guards calling the conditionally
 	// initialized watchSignalLoop. If watchSignalLoop is non-nil,
 	// it will be run in a goroutine lazily once Notify is invoked.
 	// See Issue 21576.
 	watchSignalLoopOnce sync.Once
 	watchSignalLoop     func()
 )

 // Notify causes package signal to relay incoming signals to c.
 // If no signals are provided, all incoming signals will be relayed to c.
 // Otherwise, just the provided signals will.
 //
 // Package signal will not block sending to c: the caller must ensure
 // that c has sufficient buffer space to keep up with the expected
 // signal rate. For a channel used for notification of just one signal value,
 // a buffer of size 1 is sufficient.
 //
 // It is allowed to call Notify multiple times with the same channel:
 // each call expands the set of signals sent to that channel.
 // The only way to remove signals from the set is to call Stop.
 //
 // It is allowed to call Notify multiple times with different channels
 // and the same signals: each channel receives copies of incoming
 // signals independently.
 func Notify(c chan<- os.Signal, sig ...os.Signal) {
 	if c == nil {
 		panic("os/signal: Notify using nil channel")
 	}

 	handlers.Lock()
 	defer handlers.Unlock()

 	h := handlers.m[c]
 	if h == nil {
 		if handlers.m == nil {
 			handlers.m = make(map[chan<- os.Signal]*handler)
 		}
 		h = new(handler)
 		handlers.m[c] = h
 	}

 	add := func(n int) {
 		if n < 0 {
 			return
 		}
 		if !h.want(n) {
 			h.set(n)
 			if handlers.ref[n] == 0 {
 				enableSignal(n)

 				// The runtime requires that we enable a
 				// signal before starting the watcher.
 				watchSignalLoopOnce.Do(func() {
 					if watchSignalLoop != nil {
 						go watchSignalLoop()
 					}
 				})
 			}
 			handlers.ref[n]++
 		}
 	}

 	if len(sig) == 0 {
 		for n := 0; n < numSig; n++ {
 			add(n)
 		}
 	} else {
 		for _, s := range sig {
 			add(signum(s))
 		}
 	}
 }

 // Reset undoes the effect of any prior calls to Notify for the provided
 // signals.
 // If no signals are provided, all signal handlers will be reset.
 func Reset(sig ...os.Signal) {
 	cancel(sig, disableSignal)
 }

 // Stop causes package signal to stop relaying incoming signals to c.
 // It undoes the effect of all prior calls to Notify using c.
 // When Stop returns, it is guaranteed that c will receive no more signals.
 func Stop(c chan<- os.Signal) {
 	handlers.Lock()

 	h := handlers.m[c]
 	if h == nil {
 		handlers.Unlock()
 		return
 	}
 	delete(handlers.m, c)

 	for n := 0; n < numSig; n++ {
 		if h.want(n) {
 			handlers.ref[n]--
 			if handlers.ref[n] == 0 {
 				disableSignal(n)
 			}
 		}
 	}

 	// Signals will no longer be delivered to the channel.
 	// We want to avoid a race for a signal such as SIGINT:
 	// it should be either delivered to the channel,
 	// or the program should take the default action (that is, exit).
 	// To avoid the possibility that the signal is delivered,
 	// and the signal handler invoked, and then Stop deregisters
 	// the channel before the process function below has a chance
 	// to send it on the channel, put the channel on a list of
 	// channels being stopped and wait for signal delivery to
 	// quiesce before fully removing it.

 	handlers.stopping = append(handlers.stopping, stopping{c, h})

 	handlers.Unlock()

 	signalWaitUntilIdle()

 	handlers.Lock()

 	for i, s := range handlers.stopping {
 		if s.c == c {
 			handlers.stopping = append(handlers.stopping[:i], handlers.stopping[i+1:]...)
 			break
 		}
 	}

 	handlers.Unlock()
 }

 // Wait until there are no more signals waiting to be delivered.
 // Defined by the runtime package.
 func signalWaitUntilIdle()

 func process(sig os.Signal) {
 	n := signum(sig)
 	if n < 0 {
 		return
 	}

 	handlers.Lock()
 	defer handlers.Unlock()

 	for c, h := range handlers.m {
 		if h.want(n) {
 			// send but do not block for it
 			select {
 			case c <- sig:
 			default:
 			}
 		}
 	}

 	// Avoid the race mentioned in Stop.
 	for _, d := range handlers.stopping {
 		if d.h.want(n) {
 			select {
 			case d.c <- sig:
 			default:
 			}
 		}
 	}
 }

 // NotifyContext returns a copy of the parent context that is marked done
 // (its Done channel is closed) when one of the listed signals arrives,
 // when the returned stop function is called, or when the parent context's
 // Done channel is closed, whichever happens first.
 //
 // The stop function unregisters the signal behavior, which, like signal.Reset,
 // may restore the default behavior for a given signal. For example, the default
 // behavior of a Go program receiving os.Interrupt is to exit. Calling
 // NotifyContext(parent, os.Interrupt) will change the behavior to cancel
 // the returned context. Future interrupts received will not trigger the default
 // (exit) behavior until the returned stop function is called.
 //
 // The stop function releases resources associated with it, so code should
 // call stop as soon as the operations running in this Context complete and
 // signals no longer need to be diverted to the context.
 func NotifyContext(parent context.Context, signals ...os.Signal) (ctx context.Context, stop context.CancelFunc) {
 	ctx, cancel := context.WithCancel(parent)
 	c := &signalCtx{
 		Context: ctx,
 		cancel:  cancel,
 		signals: signals,
 	}
 	c.ch = make(chan os.Signal, 1)
 	Notify(c.ch, c.signals...)
 	if ctx.Err() == nil {
 		go func() {
 			select {
 			case <-c.ch:
 				c.cancel()
 			case <-c.Done():
 			}
 		}()
 	}
 	return c, c.stop
 }

 type signalCtx struct {
 	context.Context

 	cancel  context.CancelFunc
 	signals []os.Signal
 	ch      chan os.Signal
 }

 func (c *signalCtx) stop() {
 	c.cancel()
 	Stop(c.ch)
 }

 type stringer interface {
 	String() string
 }

 func (c *signalCtx) String() string {
 	var buf []byte
 	// We know that the type of c.Context is context.cancelCtx, and we know that the
 	// String method of cancelCtx returns a string that ends with ".WithCancel".
 	name := c.Context.(stringer).String()
 	name = name[:len(name)-len(".WithCancel")]
 	buf = append(buf, "signal.NotifyContext("+name...)
 	if len(c.signals) != 0 {
 		buf = append(buf, ", ["...)
 		for i, s := range c.signals {
 			buf = append(buf, s.String()...)
 			if i != len(c.signals)-1 {
 				buf = append(buf, ' ')
 			}
 		}
 		buf = append(buf, ']')
 	}
 	buf = append(buf, ')')
 	return string(buf)
 }
	// Copyright 2012 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package signal

	import (
	"context"
	"os"
	"sync"
	)

	var handlers struct {
	sync.Mutex
	// Map a channel to the signals that should be sent to it.
	m map[chan<- os.Signal]*handler
	// Map a signal to the number of channels receiving it.
	ref [numSig]int64
	// Map channels to signals while the channel is being stopped.
	// Not a map because entries live here only very briefly.
	// We need a separate container because we need m to correspond to ref
	// at all times, and we also need to keep track of the *handler
	// value for a channel being stopped. See the Stop function.
	stopping []stopping
	}

	type stopping struct {
	c chan<- os.Signal
	h *handler
	}

	type handler struct {
	mask [(numSig + 31) / 32]uint32
	}

	func (h *handler) want(sig int) bool {
	return (h.mask[sig/32]>>uint(sig&31))&1 != 0
	}

	func (h *handler) set(sig int) {
	h.mask[sig/32] \|= 1 << uint(sig&31)
	}

	func (h *handler) clear(sig int) {
	h.mask[sig/32] &^= 1 << uint(sig&31)
	}

	// Stop relaying the signals, sigs, to any channels previously registered to
	// receive them and either reset the signal handlers to their original values
	// (action=disableSignal) or ignore the signals (action=ignoreSignal).
	func cancel(sigs []os.Signal, action func(int)) {
	handlers.Lock()
	defer handlers.Unlock()

	remove := func(n int) {
	var zerohandler handler

	for c, h := range handlers.m {
	if h.want(n) {
	handlers.ref[n]--
	h.clear(n)
	if h.mask == zerohandler.mask {
	delete(handlers.m, c)
	}
	}
	}

	action(n)
	}

	if len(sigs) == 0 {
	for n := 0; n < numSig; n++ {
	remove(n)
	}
	} else {
	for _, s := range sigs {
	remove(signum(s))
	}
	}
	}

	// Ignore causes the provided signals to be ignored. If they are received by
	// the program, nothing will happen. Ignore undoes the effect of any prior
	// calls to Notify for the provided signals.
	// If no signals are provided, all incoming signals will be ignored.
	func Ignore(sig ...os.Signal) {
	cancel(sig, ignoreSignal)
	}

	// Ignored reports whether sig is currently ignored.
	func Ignored(sig os.Signal) bool {
	sn := signum(sig)
	return sn >= 0 && signalIgnored(sn)
	}

	var (
	// watchSignalLoopOnce guards calling the conditionally
	// initialized watchSignalLoop. If watchSignalLoop is non-nil,
	// it will be run in a goroutine lazily once Notify is invoked.
	// See Issue 21576.
	watchSignalLoopOnce sync.Once
	watchSignalLoop func()
	)

	// Notify causes package signal to relay incoming signals to c.
	// If no signals are provided, all incoming signals will be relayed to c.
	// Otherwise, just the provided signals will.
	//
	// Package signal will not block sending to c: the caller must ensure
	// that c has sufficient buffer space to keep up with the expected
	// signal rate. For a channel used for notification of just one signal value,
	// a buffer of size 1 is sufficient.
	//
	// It is allowed to call Notify multiple times with the same channel:
	// each call expands the set of signals sent to that channel.
	// The only way to remove signals from the set is to call Stop.
	//
	// It is allowed to call Notify multiple times with different channels
	// and the same signals: each channel receives copies of incoming
	// signals independently.
	func Notify(c chan<- os.Signal, sig ...os.Signal) {
	if c == nil {
	panic("os/signal: Notify using nil channel")
	}

	handlers.Lock()
	defer handlers.Unlock()

	h := handlers.m[c]
	if h == nil {
	if handlers.m == nil {
	handlers.m = make(map[chan<- os.Signal]*handler)
	}
	h = new(handler)
	handlers.m[c] = h
	}

	add := func(n int) {
	if n < 0 {
	return
	}
	if !h.want(n) {
	h.set(n)
	if handlers.ref[n] == 0 {
	enableSignal(n)

	// The runtime requires that we enable a
	// signal before starting the watcher.
	watchSignalLoopOnce.Do(func() {
	if watchSignalLoop != nil {
	go watchSignalLoop()
	}
	})
	}
	handlers.ref[n]++
	}
	}

	if len(sig) == 0 {
	for n := 0; n < numSig; n++ {
	add(n)
	}
	} else {
	for _, s := range sig {
	add(signum(s))
	}
	}
	}

	// Reset undoes the effect of any prior calls to Notify for the provided
	// signals.
	// If no signals are provided, all signal handlers will be reset.
	func Reset(sig ...os.Signal) {
	cancel(sig, disableSignal)
	}

	// Stop causes package signal to stop relaying incoming signals to c.
	// It undoes the effect of all prior calls to Notify using c.
	// When Stop returns, it is guaranteed that c will receive no more signals.
	func Stop(c chan<- os.Signal) {
	handlers.Lock()

	h := handlers.m[c]
	if h == nil {
	handlers.Unlock()
	return
	}
	delete(handlers.m, c)

	for n := 0; n < numSig; n++ {
	if h.want(n) {
	handlers.ref[n]--
	if handlers.ref[n] == 0 {
	disableSignal(n)
	}
	}
	}

	// Signals will no longer be delivered to the channel.
	// We want to avoid a race for a signal such as SIGINT:
	// it should be either delivered to the channel,
	// or the program should take the default action (that is, exit).
	// To avoid the possibility that the signal is delivered,
	// and the signal handler invoked, and then Stop deregisters
	// the channel before the process function below has a chance
	// to send it on the channel, put the channel on a list of
	// channels being stopped and wait for signal delivery to
	// quiesce before fully removing it.

	handlers.stopping = append(handlers.stopping, stopping{c, h})

	handlers.Unlock()

	signalWaitUntilIdle()

	handlers.Lock()

	for i, s := range handlers.stopping {
	if s.c == c {
	handlers.stopping = append(handlers.stopping[:i], handlers.stopping[i+1:]...)
	break
	}
	}

	handlers.Unlock()
	}

	// Wait until there are no more signals waiting to be delivered.
	// Defined by the runtime package.
	func signalWaitUntilIdle()

	func process(sig os.Signal) {
	n := signum(sig)
	if n < 0 {
	return
	}

	handlers.Lock()
	defer handlers.Unlock()

	for c, h := range handlers.m {
	if h.want(n) {
	// send but do not block for it
	select {
	case c <- sig:
	default:
	}
	}
	}

	// Avoid the race mentioned in Stop.
	for _, d := range handlers.stopping {
	if d.h.want(n) {
	select {
	case d.c <- sig:
	default:
	}
	}
	}
	}

	// NotifyContext returns a copy of the parent context that is marked done
	// (its Done channel is closed) when one of the listed signals arrives,
	// when the returned stop function is called, or when the parent context's
	// Done channel is closed, whichever happens first.
	//
	// The stop function unregisters the signal behavior, which, like signal.Reset,
	// may restore the default behavior for a given signal. For example, the default
	// behavior of a Go program receiving os.Interrupt is to exit. Calling
	// NotifyContext(parent, os.Interrupt) will change the behavior to cancel
	// the returned context. Future interrupts received will not trigger the default
	// (exit) behavior until the returned stop function is called.
	//
	// The stop function releases resources associated with it, so code should
	// call stop as soon as the operations running in this Context complete and
	// signals no longer need to be diverted to the context.
	func NotifyContext(parent context.Context, signals ...os.Signal) (ctx context.Context, stop context.CancelFunc) {
	ctx, cancel := context.WithCancel(parent)
	c := &signalCtx{
	Context: ctx,
	cancel: cancel,
	signals: signals,
	}
	c.ch = make(chan os.Signal, 1)
	Notify(c.ch, c.signals...)
	if ctx.Err() == nil {
	go func() {
	select {
	case <-c.ch:
	c.cancel()
	case <-c.Done():
	}
	}()
	}
	return c, c.stop
	}

	type signalCtx struct {
	context.Context

	cancel context.CancelFunc
	signals []os.Signal
	ch chan os.Signal
	}

	func (c *signalCtx) stop() {
	c.cancel()
	Stop(c.ch)
	}

	type stringer interface {
	String() string
	}

	func (c *signalCtx) String() string {
	var buf []byte
	// We know that the type of c.Context is context.cancelCtx, and we know that the
	// String method of cancelCtx returns a string that ends with ".WithCancel".
	name := c.Context.(stringer).String()
	name = name[:len(name)-len(".WithCancel")]
	buf = append(buf, "signal.NotifyContext("+name...)
	if len(c.signals) != 0 {
	buf = append(buf, ", ["...)
	for i, s := range c.signals {
	buf = append(buf, s.String()...)
	if i != len(c.signals)-1 {
	buf = append(buf, ' ')
	}
	}
	buf = append(buf, ']')
	}
	buf = append(buf, ')')
	return string(buf)
	}