From 657c8e4f02ad6c6c3cc97256b7529fe5514c0945 Mon Sep 17 00:00:00 2001
From: Yawning Angel <yawning@torproject.org>
Date: Sat, 28 Mar 2015 02:49:07 +0000
Subject: Clean up/refactor the shutdown/termination handling code.

This combines the old signal processing code with the parent monitor,
into a new termination monitor structure, which also now handles keeping
track of outstanding sessions.
---
 obfs4proxy/termmon.go | 119 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 obfs4proxy/termmon.go

(limited to 'obfs4proxy/termmon.go')

diff --git a/obfs4proxy/termmon.go b/obfs4proxy/termmon.go
new file mode 100644
index 0000000..eac7e20
--- /dev/null
+++ b/obfs4proxy/termmon.go
@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2015, Yawning Angel <yawning at torproject dot org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *  * Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ *
+ *  * Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package main
+
+import (
+	"os"
+	"os/signal"
+	"runtime"
+	"syscall"
+	"time"
+)
+
+var termMonitorOSInit func(*termMonitor) error
+
+type termMonitor struct {
+	sigChan     chan os.Signal
+	handlerChan chan int
+	numHandlers int
+}
+
+func (m *termMonitor) onHandlerStart() {
+	m.handlerChan <- 1
+}
+
+func (m *termMonitor) onHandlerFinish() {
+	m.handlerChan <- -1
+}
+
+func (m *termMonitor) wait(termOnNoHandlers bool) os.Signal {
+	// Block until a signal has been received, or (optionally) the
+	// number of pending handlers has hit 0.  In the case of the
+	// latter, treat it as if a SIGTERM has been received.
+	for {
+		select {
+		case n := <-m.handlerChan:
+			m.numHandlers += n
+		case sig := <-m.sigChan:
+			return sig
+		}
+		if termOnNoHandlers && m.numHandlers == 0 {
+			return syscall.SIGTERM
+		}
+	}
+}
+
+func (m *termMonitor) termOnPPIDChange(ppid int) {
+	// Under most if not all U*IX systems, the parent PID will change
+	// to that of init once the parent dies.  There are several notable
+	// exceptions (Slowlaris/Android), but the parent PID changes
+	// under those platforms as well.
+	//
+	// Naturally we lose if the parent has died by the time when the
+	// Getppid() call was issued in our parent, but, this is better
+	// than nothing.
+
+	const ppidPollInterval = 1 * time.Second
+	for ppid == os.Getppid() {
+		time.Sleep(ppidPollInterval)
+	}
+
+	// Treat the parent PID changing as the same as having received
+	// a SIGTERM.
+	noticef("Parent pid changed: %d (was %d)", os.Getppid(), ppid)
+	m.sigChan <- syscall.SIGTERM
+}
+
+func newTermMonitor() *termMonitor {
+	ppid := os.Getppid()
+	m := new(termMonitor)
+	m.sigChan = make(chan os.Signal)
+	m.handlerChan = make(chan int)
+	signal.Notify(m.sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	// Until #15435 is implemented, there is no reliable way to see if
+	// the parent has died that is portable/platform independent/reliable.
+	//
+	// Do the next best thing and use various kludges and hacks:
+	//  * Linux - Platform specific code that should always work.
+	//  * Other U*IX - Somewhat generic code, that works unless the parent
+	//    dies before the monitor is initialized.
+	//  * Windows - Don't specifically monitor for parent termination.
+	if termMonitorOSInit != nil {
+		// Errors here are non-fatal, since it might still be possible
+		// to fall back to a generic implementation.
+		if err := termMonitorOSInit(m); err == nil {
+			return m
+		}
+	}
+	if runtime.GOOS != "windows" {
+		go m.termOnPPIDChange(ppid)
+	}
+
+	return m
+}
-- 
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