1 files changed, 275 insertions, 0 deletions
diff --git a/src/runtime/sigqueue.go b/src/runtime/sigqueue.go
new file mode 100644
index 0000000..51e424d
--- /dev/null
+++ b/src/runtime/sigqueue.go
@@ -0,0 +1,275 @@
+// 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
+}