1// Copyright 2016 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// We used to use this code for Darwin, but according to issue #19314
6// waitid returns if the process is stopped, even when using WEXITED.
7
8//go:build linux
9
10package os
11
12import (
13	"runtime"
14	"syscall"
15	"unsafe"
16)
17
18const _P_PID = 1
19
20// blockUntilWaitable attempts to block until a call to p.Wait will
21// succeed immediately, and reports whether it has done so.
22// It does not actually call p.Wait.
23func (p *Process) blockUntilWaitable() (bool, error) {
24	// The waitid system call expects a pointer to a siginfo_t,
25	// which is 128 bytes on all Linux systems.
26	// On darwin/amd64, it requires 104 bytes.
27	// We don't care about the values it returns.
28	var siginfo [16]uint64
29	psig := &siginfo[0]
30	var e syscall.Errno
31	for {
32		_, _, e = syscall.Syscall6(syscall.SYS_WAITID, _P_PID, uintptr(p.Pid), uintptr(unsafe.Pointer(psig)), syscall.WEXITED|syscall.WNOWAIT, 0, 0)
33		if e != syscall.EINTR {
34			break
35		}
36	}
37	runtime.KeepAlive(p)
38	if e != 0 {
39		// waitid has been available since Linux 2.6.9, but
40		// reportedly is not available in Ubuntu on Windows.
41		// See issue 16610.
42		if e == syscall.ENOSYS {
43			return false, nil
44		}
45		return false, NewSyscallError("waitid", e)
46	}
47	return true, nil
48}
49