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-rw-r--r--src/runtime/sigqueue.go275
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diff --git a/src/runtime/sigqueue.go b/src/runtime/sigqueue.go
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+// 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 three states:
+// * 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.
+//
+// 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.
+
+//go: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 atomic.Uint32
+ delivering atomic.Uint32
+ inuse bool
+}
+
+const (
+ sigIdle = iota
+ sigReceiving
+ sigSending
+)
+
+// 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 s >= uint32(32*len(sig.wanted)) {
+ return false
+ }
+
+ sig.delivering.Add(1)
+ // We are running in the signal handler; defer is not available.
+
+ if w := atomic.Load(&sig.wanted[s/32]); w&bit == 0 {
+ sig.delivering.Add(-1)
+ return false
+ }
+
+ // Add signal to outgoing queue.
+ for {
+ mask := sig.mask[s/32]
+ if mask&bit != 0 {
+ sig.delivering.Add(-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 sig.state.Load() {
+ default:
+ throw("sigsend: inconsistent state")
+ case sigIdle:
+ if sig.state.CompareAndSwap(sigIdle, sigSending) {
+ break Send
+ }
+ case sigSending:
+ // notification already pending
+ break Send
+ case sigReceiving:
+ if sig.state.CompareAndSwap(sigReceiving, sigIdle) {
+ if GOOS == "darwin" || GOOS == "ios" {
+ sigNoteWakeup(&sig.note)
+ break Send
+ }
+ notewakeup(&sig.note)
+ break Send
+ }
+ }
+ }
+
+ sig.delivering.Add(-1)
+ return true
+}
+
+// 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 sig.state.Load() {
+ default:
+ throw("signal_recv: inconsistent state")
+ case sigIdle:
+ if sig.state.CompareAndSwap(sigIdle, sigReceiving) {
+ if GOOS == "darwin" || GOOS == "ios" {
+ sigNoteSleep(&sig.note)
+ break Receive
+ }
+ notetsleepg(&sig.note, -1)
+ noteclear(&sig.note)
+ break Receive
+ }
+ case sigSending:
+ if sig.state.CompareAndSwap(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 sig.delivering.Load() != 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 sig.state.Load() != 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
+}