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/*
* 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 termmon
import (
"io"
"io/ioutil"
"os"
"os/signal"
"runtime"
"syscall"
"time"
"github.com/OperatorFoundation/shapeshifter-dispatcher/common/log"
"github.com/OperatorFoundation/shapeshifter-dispatcher/common/pt_extras"
)
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) termOnStdinClose() {
_, err := io.Copy(ioutil.Discard, os.Stdin)
// io.Copy() will return a nil on EOF, since reaching EOF is
// expected behavior. No matter what, if this unblocks, assume
// that stdin is closed, and treat that as having received a
// SIGTERM.
log.Noticef("Stdin is closed or unreadable: %v", err)
m.sigChan <- 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.
log.Noticef("Parent pid changed: %d (was %d)", os.Getppid(), ppid)
m.sigChan <- syscall.SIGTERM
}
func NewTermMonitor(exitOnStdinClose bool) (m *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)
// If tor supports feature #15435, we can use Stdin being closed as an
// indication that tor has died, or wants the PT to shutdown for any
// reason.
if exitOnStdinClose || pt_extras.PtShouldExitOnStdinClose() {
go m.termOnStdinClose()
} else {
// Instead of feature #15435, 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.
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
}
}
if runtime.GOOS != "windows" {
go m.termOnPPIDChange(ppid)
}
}
return
}
|
