// the standard library should never take a read
		// lock on ForkLock.

		forkingLock.Unlock()

		ForkLock.RLock()
		ForkLock.RUnlock()

		forkingLock.Lock()

		// Readers got a chance, so now take the write lock.

		if forking == 0 {
			ForkLock.Lock()
		}
	}

	forking++
}

// releaseForkLock releases the conceptual write lock on ForkLock
// acquired by acquireForkLock.
func releaseForkLock() {

// descriptor as nonblocking and close-on-exec.
func sysSocket(family, sotype, proto int) (int, error) {
	// See ../syscall/exec_unix.go for description of ForkLock.
	syscall.ForkLock.RLock()
	s, err := socketFunc(family, sotype, proto)
	if err == nil {
		syscall.CloseOnExec(s)
	}
	syscall.ForkLock.RUnlock()
	if err != nil {
		return -1, os.NewSyscallError("socket", err)
	}
	if err = syscall.SetNonblock(s, true); err != nil {

		if err != nil {
			return -1, os.NewSyscallError("socket", err)
		}
		return s, nil
	}

	// See ../syscall/exec_unix.go for description of ForkLock.
	syscall.ForkLock.RLock()
	s, err := socketFunc(family, sotype, proto)
	if err == nil {
		syscall.CloseOnExec(s)
	}
	syscall.ForkLock.RUnlock()
	if err != nil {
		return -1, os.NewSyscallError("socket", err)
	}
	if err = syscall.SetNonblock(s, true); err != nil {

	var p [2]int

	// See ../syscall/exec.go for description of lock.
	syscall.ForkLock.RLock()
	e := syscall.Pipe(p[0:])
	if e != nil {
		syscall.ForkLock.RUnlock()
		return nil, nil, NewSyscallError("pipe", e)
	}
	syscall.CloseOnExec(p[0])
	syscall.CloseOnExec(p[1])
	syscall.ForkLock.RUnlock()

	return newFile(p[0], "|0", kindPipe, false), newFile(p[1], "|1", kindPipe, false), nil

		}
		return ns, sa, "", nil
	}

	// See ../syscall/exec_unix.go for description of ForkLock.
	// It is probably okay to hold the lock across syscall.Accept
	// because we have put fd.sysfd into non-blocking mode.
	// However, a call to the File method will put it back into
	// blocking mode. We can't take that risk, so no use of ForkLock here.
	ns, sa, err := AcceptFunc(s)
	if err == nil {
		syscall.CloseOnExec(ns)
	}

	}
	_, err = fcntl(p[0], F_SETFD, FD_CLOEXEC)
	if err != nil {
		return err
	}
	_, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
	return err
}

func acquireForkLock() {
	ForkLock.Lock()
}

func releaseForkLock() {
	ForkLock.Unlock()

// non-blocking I/O to accept on a listening socket.
// The rules for which file descriptor-creating operations use the
// ForkLock are as follows:
//
//   - [Pipe]. Use pipe2 if available. Otherwise, does not block,
//     so use ForkLock.
//   - [Socket]. Use SOCK_CLOEXEC if available. Otherwise, does not
//     block, so use ForkLock.
//   - [Open]. Use [O_CLOEXEC] if available. Otherwise, may block,
//     so live with the race.

func accept(s int) (int, syscall.Sockaddr, string, error) {
	// See ../syscall/exec_unix.go for description of ForkLock.
	// It is probably okay to hold the lock across syscall.Accept
	// because we have put fd.sysfd into non-blocking mode.
	// However, a call to the File method will put it back into
	// blocking mode. We can't take that risk, so no use of ForkLock here.
	ns, sa, err := AcceptFunc(s)
	if err == nil {
		syscall.CloseOnExec(ns)
	}

	}

	// See ../syscall/exec_unix.go for description of ForkLock.
	// It is probably okay to hold the lock across syscall.Accept
	// because we have put fd.sysfd into non-blocking mode.
	// However, a call to the File method will put it back into
	// blocking mode. We can't take that risk, so no use of ForkLock here.
	ns, sa, err = AcceptFunc(s)
	if err == nil {
		syscall.CloseOnExec(ns)
	}

	return CloseFunc(fd)
}

// dupCloseOnExecOld is the traditional way to dup an fd and
// set its O_CLOEXEC bit, using two system calls.
func dupCloseOnExecOld(fd int) (int, string, error) {
	syscall.ForkLock.RLock()
	defer syscall.ForkLock.RUnlock()
	newfd, err := syscall.Dup(fd)
	if err != nil {
		return -1, "dup", err
	}
	syscall.CloseOnExec(newfd)
	return newfd, "", nil
}

// Fchdir wraps syscall.Fchdir.