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// 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 (
"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)
}
// 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)
}
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:
}
}
}
}