src/runtime/sigqueue.go - go - Git at Google

 // Copyright 2009 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.

 // This file implements runtime support for signal handling.
 //
 // Most synchronization primitives are not available from
 // the signal handler (it cannot block, allocate memory, or use locks)
 // so the handler communicates with a processing goroutine
 // via struct sig, below.
 //
 // sigsend is called by the signal handler to queue a new signal.
 // signal_recv is called by the Go program to receive a newly queued signal.
 // Synchronization between sigsend and signal_recv is based on the sig.state
 // variable. It can be in 4 states: sigIdle, sigReceiving, sigSending and sigFixup.
 // sigReceiving means that signal_recv is blocked on sig.Note and there are no
 // new pending signals.
 // sigSending means that sig.mask *may* contain new pending signals,
 // signal_recv can't be blocked in this state.
 // sigIdle means that there are no new pending signals and signal_recv is not blocked.
 // sigFixup is a transient state that can only exist as a short
 // transition from sigReceiving and then on to sigIdle: it is
 // used to ensure the AllThreadsSyscall()'s mDoFixup() operation
 // occurs on the sleeping m, waiting to receive a signal.
 // Transitions between states are done atomically with CAS.
 // When signal_recv is unblocked, it resets sig.Note and rechecks sig.mask.
 // If several sigsends and signal_recv execute concurrently, it can lead to
 // unnecessary rechecks of sig.mask, but it cannot lead to missed signals
 // nor deadlocks.

 // +build !plan9

 package runtime

 import (
 	"runtime/internal/atomic"
 	_ "unsafe" // for go:linkname
 )

 // sig handles communication between the signal handler and os/signal.
 // Other than the inuse and recv fields, the fields are accessed atomically.
 //
 // The wanted and ignored fields are only written by one goroutine at
 // a time; access is controlled by the handlers Mutex in os/signal.
 // The fields are only read by that one goroutine and by the signal handler.
 // We access them atomically to minimize the race between setting them
 // in the goroutine calling os/signal and the signal handler,
 // which may be running in a different thread. That race is unavoidable,
 // as there is no connection between handling a signal and receiving one,
 // but atomic instructions should minimize it.
 var sig struct {
 	note       note
 	mask       [(_NSIG + 31) / 32]uint32
 	wanted     [(_NSIG + 31) / 32]uint32
 	ignored    [(_NSIG + 31) / 32]uint32
 	recv       [(_NSIG + 31) / 32]uint32
 	state      uint32
 	delivering uint32
 	inuse      bool
 }

 const (
 	sigIdle = iota
 	sigReceiving
 	sigSending
 	sigFixup
 )

 // sigsend delivers a signal from sighandler to the internal signal delivery queue.
 // It reports whether the signal was sent. If not, the caller typically crashes the program.
 // It runs from the signal handler, so it's limited in what it can do.
 func sigsend(s uint32) bool {
 	bit := uint32(1) << uint(s&31)
 	if !sig.inuse || s >= uint32(32*len(sig.wanted)) {
 		return false
 	}

 	atomic.Xadd(&sig.delivering, 1)
 	// We are running in the signal handler; defer is not available.

 	if w := atomic.Load(&sig.wanted[s/32]); w&bit == 0 {
 		atomic.Xadd(&sig.delivering, -1)
 		return false
 	}

 	// Add signal to outgoing queue.
 	for {
 		mask := sig.mask[s/32]
 		if mask&bit != 0 {
 			atomic.Xadd(&sig.delivering, -1)
 			return true // signal already in queue
 		}
 		if atomic.Cas(&sig.mask[s/32], mask, mask|bit) {
 			break
 		}
 	}

 	// Notify receiver that queue has new bit.
 Send:
 	for {
 		switch atomic.Load(&sig.state) {
 		default:
 			throw("sigsend: inconsistent state")
 		case sigIdle:
 			if atomic.Cas(&sig.state, sigIdle, sigSending) {
 				break Send
 			}
 		case sigSending:
 			// notification already pending
 			break Send
 		case sigReceiving:
 			if atomic.Cas(&sig.state, sigReceiving, sigIdle) {
 				if GOOS == "darwin" || GOOS == "ios" {
 					sigNoteWakeup(&sig.note)
 					break Send
 				}
 				notewakeup(&sig.note)
 				break Send
 			}
 		case sigFixup:
 			// nothing to do - we need to wait for sigIdle.
 			mDoFixupAndOSYield()
 		}
 	}

 	atomic.Xadd(&sig.delivering, -1)
 	return true
 }

 // sigRecvPrepareForFixup is used to temporarily wake up the
 // signal_recv() running thread while it is blocked waiting for the
 // arrival of a signal. If it causes the thread to wake up, the
 // sig.state travels through this sequence: sigReceiving -> sigFixup
 // -> sigIdle -> sigReceiving and resumes. (This is only called while
 // GC is disabled.)
 //go:nosplit
 func sigRecvPrepareForFixup() {
 	if atomic.Cas(&sig.state, sigReceiving, sigFixup) {
 		notewakeup(&sig.note)
 	}
 }

 // Called to receive the next queued signal.
 // Must only be called from a single goroutine at a time.
 //go:linkname signal_recv os/signal.signal_recv
 func signal_recv() uint32 {
 	for {
 		// Serve any signals from local copy.
 		for i := uint32(0); i < _NSIG; i++ {
 			if sig.recv[i/32]&(1<<(i&31)) != 0 {
 				sig.recv[i/32] &^= 1 << (i & 31)
 				return i
 			}
 		}

 		// Wait for updates to be available from signal sender.
 	Receive:
 		for {
 			switch atomic.Load(&sig.state) {
 			default:
 				throw("signal_recv: inconsistent state")
 			case sigIdle:
 				if atomic.Cas(&sig.state, sigIdle, sigReceiving) {
 					if GOOS == "darwin" || GOOS == "ios" {
 						sigNoteSleep(&sig.note)
 						break Receive
 					}
 					notetsleepg(&sig.note, -1)
 					noteclear(&sig.note)
 					if !atomic.Cas(&sig.state, sigFixup, sigIdle) {
 						break Receive
 					}
 					// Getting here, the code will
 					// loop around again to sleep
 					// in state sigReceiving. This
 					// path is taken when
 					// sigRecvPrepareForFixup()
 					// has been called by another
 					// thread.
 				}
 			case sigSending:
 				if atomic.Cas(&sig.state, sigSending, sigIdle) {
 					break Receive
 				}
 			}
 		}

 		// Incorporate updates from sender into local copy.
 		for i := range sig.mask {
 			sig.recv[i] = atomic.Xchg(&sig.mask[i], 0)
 		}
 	}
 }

 // signalWaitUntilIdle waits until the signal delivery mechanism is idle.
 // This is used to ensure that we do not drop a signal notification due
 // to a race between disabling a signal and receiving a signal.
 // This assumes that signal delivery has already been disabled for
 // the signal(s) in question, and here we are just waiting to make sure
 // that all the signals have been delivered to the user channels
 // by the os/signal package.
 //go:linkname signalWaitUntilIdle os/signal.signalWaitUntilIdle
 func signalWaitUntilIdle() {
 	// Although the signals we care about have been removed from
 	// sig.wanted, it is possible that another thread has received
 	// a signal, has read from sig.wanted, is now updating sig.mask,
 	// and has not yet woken up the processor thread. We need to wait
 	// until all current signal deliveries have completed.
 	for atomic.Load(&sig.delivering) != 0 {
 		Gosched()
 	}

 	// Although WaitUntilIdle seems like the right name for this
 	// function, the state we are looking for is sigReceiving, not
 	// sigIdle.  The sigIdle state is really more like sigProcessing.
 	for atomic.Load(&sig.state) != sigReceiving {
 		Gosched()
 	}
 }

 // Must only be called from a single goroutine at a time.
 //go:linkname signal_enable os/signal.signal_enable
 func signal_enable(s uint32) {
 	if !sig.inuse {
 		// This is the first call to signal_enable. Initialize.
 		sig.inuse = true // enable reception of signals; cannot disable
 		if GOOS == "darwin" || GOOS == "ios" {
 			sigNoteSetup(&sig.note)
 		} else {
 			noteclear(&sig.note)
 		}
 	}

 	if s >= uint32(len(sig.wanted)*32) {
 		return
 	}

 	w := sig.wanted[s/32]
 	w |= 1 << (s & 31)
 	atomic.Store(&sig.wanted[s/32], w)

 	i := sig.ignored[s/32]
 	i &^= 1 << (s & 31)
 	atomic.Store(&sig.ignored[s/32], i)

 	sigenable(s)
 }

 // Must only be called from a single goroutine at a time.
 //go:linkname signal_disable os/signal.signal_disable
 func signal_disable(s uint32) {
 	if s >= uint32(len(sig.wanted)*32) {
 		return
 	}
 	sigdisable(s)

 	w := sig.wanted[s/32]
 	w &^= 1 << (s & 31)
 	atomic.Store(&sig.wanted[s/32], w)
 }

 // Must only be called from a single goroutine at a time.
 //go:linkname signal_ignore os/signal.signal_ignore
 func signal_ignore(s uint32) {
 	if s >= uint32(len(sig.wanted)*32) {
 		return
 	}
 	sigignore(s)

 	w := sig.wanted[s/32]
 	w &^= 1 << (s & 31)
 	atomic.Store(&sig.wanted[s/32], w)

 	i := sig.ignored[s/32]
 	i |= 1 << (s & 31)
 	atomic.Store(&sig.ignored[s/32], i)
 }

 // sigInitIgnored marks the signal as already ignored. This is called at
 // program start by initsig. In a shared library initsig is called by
 // libpreinit, so the runtime may not be initialized yet.
 //go:nosplit
 func sigInitIgnored(s uint32) {
 	i := sig.ignored[s/32]
 	i |= 1 << (s & 31)
 	atomic.Store(&sig.ignored[s/32], i)
 }

 // Checked by signal handlers.
 //go:linkname signal_ignored os/signal.signal_ignored
 func signal_ignored(s uint32) bool {
 	i := atomic.Load(&sig.ignored[s/32])
 	return i&(1<<(s&31)) != 0
 }
	// Copyright 2009 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.

	// This file implements runtime support for signal handling.
	//
	// Most synchronization primitives are not available from
	// the signal handler (it cannot block, allocate memory, or use locks)
	// so the handler communicates with a processing goroutine
	// via struct sig, below.
	//
	// sigsend is called by the signal handler to queue a new signal.
	// signal_recv is called by the Go program to receive a newly queued signal.
	// Synchronization between sigsend and signal_recv is based on the sig.state
	// variable. It can be in 4 states: sigIdle, sigReceiving, sigSending and sigFixup.
	// sigReceiving means that signal_recv is blocked on sig.Note and there are no
	// new pending signals.
	// sigSending means that sig.mask may contain new pending signals,
	// signal_recv can't be blocked in this state.
	// sigIdle means that there are no new pending signals and signal_recv is not blocked.
	// sigFixup is a transient state that can only exist as a short
	// transition from sigReceiving and then on to sigIdle: it is
	// used to ensure the AllThreadsSyscall()'s mDoFixup() operation
	// occurs on the sleeping m, waiting to receive a signal.
	// Transitions between states are done atomically with CAS.
	// When signal_recv is unblocked, it resets sig.Note and rechecks sig.mask.
	// If several sigsends and signal_recv execute concurrently, it can lead to
	// unnecessary rechecks of sig.mask, but it cannot lead to missed signals
	// nor deadlocks.

	// +build !plan9

	package runtime

	import (
	"runtime/internal/atomic"
	_ "unsafe" // for go:linkname
	)

	// sig handles communication between the signal handler and os/signal.
	// Other than the inuse and recv fields, the fields are accessed atomically.
	//
	// The wanted and ignored fields are only written by one goroutine at
	// a time; access is controlled by the handlers Mutex in os/signal.
	// The fields are only read by that one goroutine and by the signal handler.
	// We access them atomically to minimize the race between setting them
	// in the goroutine calling os/signal and the signal handler,
	// which may be running in a different thread. That race is unavoidable,
	// as there is no connection between handling a signal and receiving one,
	// but atomic instructions should minimize it.
	var sig struct {
	note note
	mask [(_NSIG + 31) / 32]uint32
	wanted [(_NSIG + 31) / 32]uint32
	ignored [(_NSIG + 31) / 32]uint32
	recv [(_NSIG + 31) / 32]uint32
	state uint32
	delivering uint32
	inuse bool
	}

	const (
	sigIdle = iota
	sigReceiving
	sigSending
	sigFixup
	)

	// sigsend delivers a signal from sighandler to the internal signal delivery queue.
	// It reports whether the signal was sent. If not, the caller typically crashes the program.
	// It runs from the signal handler, so it's limited in what it can do.
	func sigsend(s uint32) bool {
	bit := uint32(1) << uint(s&31)
	if !sig.inuse \|\| s >= uint32(32*len(sig.wanted)) {
	return false
	}

	atomic.Xadd(&sig.delivering, 1)
	// We are running in the signal handler; defer is not available.

	if w := atomic.Load(&sig.wanted[s/32]); w&bit == 0 {
	atomic.Xadd(&sig.delivering, -1)
	return false
	}

	// Add signal to outgoing queue.
	for {
	mask := sig.mask[s/32]
	if mask&bit != 0 {
	atomic.Xadd(&sig.delivering, -1)
	return true // signal already in queue
	}
	if atomic.Cas(&sig.mask[s/32], mask, mask\|bit) {
	break
	}
	}

	// Notify receiver that queue has new bit.
	Send:
	for {
	switch atomic.Load(&sig.state) {
	default:
	throw("sigsend: inconsistent state")
	case sigIdle:
	if atomic.Cas(&sig.state, sigIdle, sigSending) {
	break Send
	}
	case sigSending:
	// notification already pending
	break Send
	case sigReceiving:
	if atomic.Cas(&sig.state, sigReceiving, sigIdle) {
	if GOOS == "darwin" \|\| GOOS == "ios" {
	sigNoteWakeup(&sig.note)
	break Send
	}
	notewakeup(&sig.note)
	break Send
	}
	case sigFixup:
	// nothing to do - we need to wait for sigIdle.
	mDoFixupAndOSYield()
	}
	}

	atomic.Xadd(&sig.delivering, -1)
	return true
	}

	// sigRecvPrepareForFixup is used to temporarily wake up the
	// signal_recv() running thread while it is blocked waiting for the
	// arrival of a signal. If it causes the thread to wake up, the
	// sig.state travels through this sequence: sigReceiving -> sigFixup
	// -> sigIdle -> sigReceiving and resumes. (This is only called while
	// GC is disabled.)
	//go:nosplit
	func sigRecvPrepareForFixup() {
	if atomic.Cas(&sig.state, sigReceiving, sigFixup) {
	notewakeup(&sig.note)
	}
	}

	// Called to receive the next queued signal.
	// Must only be called from a single goroutine at a time.
	//go:linkname signal_recv os/signal.signal_recv
	func signal_recv() uint32 {
	for {
	// Serve any signals from local copy.
	for i := uint32(0); i < _NSIG; i++ {
	if sig.recv[i/32]&(1<<(i&31)) != 0 {
	sig.recv[i/32] &^= 1 << (i & 31)
	return i
	}
	}

	// Wait for updates to be available from signal sender.
	Receive:
	for {
	switch atomic.Load(&sig.state) {
	default:
	throw("signal_recv: inconsistent state")
	case sigIdle:
	if atomic.Cas(&sig.state, sigIdle, sigReceiving) {
	if GOOS == "darwin" \|\| GOOS == "ios" {
	sigNoteSleep(&sig.note)
	break Receive
	}
	notetsleepg(&sig.note, -1)
	noteclear(&sig.note)
	if !atomic.Cas(&sig.state, sigFixup, sigIdle) {
	break Receive
	}
	// Getting here, the code will
	// loop around again to sleep
	// in state sigReceiving. This
	// path is taken when
	// sigRecvPrepareForFixup()
	// has been called by another
	// thread.
	}
	case sigSending:
	if atomic.Cas(&sig.state, sigSending, sigIdle) {
	break Receive
	}
	}
	}

	// Incorporate updates from sender into local copy.
	for i := range sig.mask {
	sig.recv[i] = atomic.Xchg(&sig.mask[i], 0)
	}
	}
	}

	// signalWaitUntilIdle waits until the signal delivery mechanism is idle.
	// This is used to ensure that we do not drop a signal notification due
	// to a race between disabling a signal and receiving a signal.
	// This assumes that signal delivery has already been disabled for
	// the signal(s) in question, and here we are just waiting to make sure
	// that all the signals have been delivered to the user channels
	// by the os/signal package.
	//go:linkname signalWaitUntilIdle os/signal.signalWaitUntilIdle
	func signalWaitUntilIdle() {
	// Although the signals we care about have been removed from
	// sig.wanted, it is possible that another thread has received
	// a signal, has read from sig.wanted, is now updating sig.mask,
	// and has not yet woken up the processor thread. We need to wait
	// until all current signal deliveries have completed.
	for atomic.Load(&sig.delivering) != 0 {
	Gosched()
	}

	// Although WaitUntilIdle seems like the right name for this
	// function, the state we are looking for is sigReceiving, not
	// sigIdle. The sigIdle state is really more like sigProcessing.
	for atomic.Load(&sig.state) != sigReceiving {
	Gosched()
	}
	}

	// Must only be called from a single goroutine at a time.
	//go:linkname signal_enable os/signal.signal_enable
	func signal_enable(s uint32) {
	if !sig.inuse {
	// This is the first call to signal_enable. Initialize.
	sig.inuse = true // enable reception of signals; cannot disable
	if GOOS == "darwin" \|\| GOOS == "ios" {
	sigNoteSetup(&sig.note)
	} else {
	noteclear(&sig.note)
	}
	}

	if s >= uint32(len(sig.wanted)*32) {
	return
	}

	w := sig.wanted[s/32]
	w \|= 1 << (s & 31)
	atomic.Store(&sig.wanted[s/32], w)

	i := sig.ignored[s/32]
	i &^= 1 << (s & 31)
	atomic.Store(&sig.ignored[s/32], i)

	sigenable(s)
	}

	// Must only be called from a single goroutine at a time.
	//go:linkname signal_disable os/signal.signal_disable
	func signal_disable(s uint32) {
	if s >= uint32(len(sig.wanted)*32) {
	return
	}
	sigdisable(s)

	w := sig.wanted[s/32]
	w &^= 1 << (s & 31)
	atomic.Store(&sig.wanted[s/32], w)
	}

	// Must only be called from a single goroutine at a time.
	//go:linkname signal_ignore os/signal.signal_ignore
	func signal_ignore(s uint32) {
	if s >= uint32(len(sig.wanted)*32) {
	return
	}
	sigignore(s)

	w := sig.wanted[s/32]
	w &^= 1 << (s & 31)
	atomic.Store(&sig.wanted[s/32], w)

	i := sig.ignored[s/32]
	i \|= 1 << (s & 31)
	atomic.Store(&sig.ignored[s/32], i)
	}

	// sigInitIgnored marks the signal as already ignored. This is called at
	// program start by initsig. In a shared library initsig is called by
	// libpreinit, so the runtime may not be initialized yet.
	//go:nosplit
	func sigInitIgnored(s uint32) {
	i := sig.ignored[s/32]
	i \|= 1 << (s & 31)
	atomic.Store(&sig.ignored[s/32], i)
	}

	// Checked by signal handlers.
	//go:linkname signal_ignored os/signal.signal_ignored
	func signal_ignored(s uint32) bool {
	i := atomic.Load(&sig.ignored[s/32])
	return i&(1<<(s&31)) != 0
	}