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go/src/os/wait_waitid.go

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os: on GNU/Linux use waitid to avoid wait/kill race On systems that support the POSIX.1-2008 waitid function, we can use it to block until a wait will succeed. This avoids a possible race condition: if a program calls p.Kill/p.Signal and p.Wait from two different goroutines, then it is possible for the wait to complete just before the signal is sent. In that case, it is possible that the system will start a new process using the same PID between the wait and the signal, causing the signal to be sent to the wrong process. The Process.isdone field attempts to avoid that race, but there is a small gap of time between when wait returns and isdone is set when the race can occur. This CL avoids that race by using waitid to wait until the process has exited without actually collecting the PID. Then it sets isdone, then waits for any active signals to complete, and only then collects the PID. No test because any plausible test would require starting enough processes to recycle all the process IDs. Update #13987. Update #16028. Change-Id: Id2939431991d3b355dfb22f08793585fc0568ce8 Reviewed-on: https://go-review.googlesource.com/23967 Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-06-09 23:24:40 -06:00
// Copyright 2016 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.
os: use waitid to avoid wait/kill race on darwin This change is a followup to https://go-review.googlesource.com/23967 for Darwin. Updates #13987. Updates #16028. Change-Id: Ib1fb9f957fafd0f91da6fceea56620e29ad82b00 Reviewed-on: https://go-review.googlesource.com/24020 Reviewed-by: Ian Lance Taylor <iant@golang.org>
2016-06-11 04:36:17 -06:00
// +build darwin linux
os: on GNU/Linux use waitid to avoid wait/kill race On systems that support the POSIX.1-2008 waitid function, we can use it to block until a wait will succeed. This avoids a possible race condition: if a program calls p.Kill/p.Signal and p.Wait from two different goroutines, then it is possible for the wait to complete just before the signal is sent. In that case, it is possible that the system will start a new process using the same PID between the wait and the signal, causing the signal to be sent to the wrong process. The Process.isdone field attempts to avoid that race, but there is a small gap of time between when wait returns and isdone is set when the race can occur. This CL avoids that race by using waitid to wait until the process has exited without actually collecting the PID. Then it sets isdone, then waits for any active signals to complete, and only then collects the PID. No test because any plausible test would require starting enough processes to recycle all the process IDs. Update #13987. Update #16028. Change-Id: Id2939431991d3b355dfb22f08793585fc0568ce8 Reviewed-on: https://go-review.googlesource.com/23967 Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-06-09 23:24:40 -06:00
package os
import (
"runtime"
"syscall"
"unsafe"
)
const _P_PID = 1
// blockUntilWaitable attempts to block until a call to p.Wait will
// succeed immediately, and returns whether it has done so.
// It does not actually call p.Wait.
func (p *Process) blockUntilWaitable() (bool, error) {
os: use waitid to avoid wait/kill race on darwin This change is a followup to https://go-review.googlesource.com/23967 for Darwin. Updates #13987. Updates #16028. Change-Id: Ib1fb9f957fafd0f91da6fceea56620e29ad82b00 Reviewed-on: https://go-review.googlesource.com/24020 Reviewed-by: Ian Lance Taylor <iant@golang.org>
2016-06-11 04:36:17 -06:00
// The waitid system call expects a pointer to a siginfo_t,
// which is 128 bytes on all GNU/Linux systems.
// On Darwin, it requires greater than or equal to 64 bytes
// for darwin/{386,arm} and 104 bytes for darwin/amd64.
// We don't care about the values it returns.
os: on GNU/Linux use waitid to avoid wait/kill race On systems that support the POSIX.1-2008 waitid function, we can use it to block until a wait will succeed. This avoids a possible race condition: if a program calls p.Kill/p.Signal and p.Wait from two different goroutines, then it is possible for the wait to complete just before the signal is sent. In that case, it is possible that the system will start a new process using the same PID between the wait and the signal, causing the signal to be sent to the wrong process. The Process.isdone field attempts to avoid that race, but there is a small gap of time between when wait returns and isdone is set when the race can occur. This CL avoids that race by using waitid to wait until the process has exited without actually collecting the PID. Then it sets isdone, then waits for any active signals to complete, and only then collects the PID. No test because any plausible test would require starting enough processes to recycle all the process IDs. Update #13987. Update #16028. Change-Id: Id2939431991d3b355dfb22f08793585fc0568ce8 Reviewed-on: https://go-review.googlesource.com/23967 Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Austin Clements <austin@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
2016-06-09 23:24:40 -06:00
var siginfo [128]byte
psig := &siginfo[0]
_, _, e := syscall.Syscall6(syscall.SYS_WAITID, _P_PID, uintptr(p.Pid), uintptr(unsafe.Pointer(psig)), syscall.WEXITED|syscall.WNOWAIT, 0, 0)
runtime.KeepAlive(psig)
if e != 0 {
return false, NewSyscallError("waitid", e)
}
return true, nil
}
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