Backported from X.org:

 commit 6178b1c91cfc9e860914acc6f0be2f2d2e07a124
 Author: Adam Jackson <ajax@redhat.com>
 Date:   Tue Jun 7 15:52:11 2016 -0400

    dix: Use OsSignal() not signal()

    As the man page for the latter states:

        The effects of signal() in a multithreaded process are unspecified.

    We already have an interface to call sigaction() instead, use it.
Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Keith Packard <keithp@keithp.com>

 commit e10ba9e4b52269b2ac75c4802dce4ca47d169657
 Author: Keith Packard <keithp@keithp.com>
 Date:   Wed Nov 11 22:02:01 2015 -0800

    Remove non-smart scheduler. Don't require setitimer.

    This allows the server to call GetTimeInMillis() after each request is
    processed to avoid needing setitimer. -dumbSched now turns off the
    setitimer.
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

 commit 1f915e8b524dd02011158aa038935970684c7630
 Author: Daniel Drake <drake@endlessm.com>
 Date:   Wed May 20 13:16:12 2015 -0600

    Keep SIGALRM restart flag after Popen

    Commit 94ab7455 added SA_RESTART to the SIGALRM handler.  However, the
    Popen code tears down and recreates the SIGALRM handler via OsSignal(),
    and this flag is dropped at this time.

    Clean the code to use just a single codepath for creating this signal
    handler, always applying SA_RESTART.

    [ajax: Fixed commit id]
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Drake <drake@endlessm.com>

 commit 94ab7455abc213fc96760e29ab2e943ec682fb22
 Author: Daniel Drake <drake@endlessm.com>
 Date:   Tue May 12 16:39:22 2015 -0600

    Allow system call restarts upon signal interruption

    The X server frequently deals with SIGIO and SIGALRM interruptions.
    If process execution is inside certain blocking system calls
    when these signals arrive, e.g. with the kernel blocked on
    a contended semaphore, the system calls will be interrupted.

    Some system calls are automatically restartable (the kernel re-executes
    them with the same parameters once the signal handler returns) but
    only if the signal handler allows it.

    Set SA_RESTART on the signal handlers to enable this convenient
    behaviour.
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Drake <drake@endlessm.com>

 commit a6c71ce5d2d2fe89e07a2ef5041c915acc3dc686
 Author: Tiago Vignatti <tiago.vignatti@nokia.com>
 Date:   Mon Mar 28 19:21:28 2011 +0300

    os: fix memory and fd leaks in Popen
Signed-off-by: Tiago Vignatti <tiago.vignatti@nokia.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Nicolas Peninguy <nico@lostgeeks.org>

 commit c9051b684b524549eab6d5b88ee3e195a6f6fbe8
 Author: Alan Coopersmith <alan.coopersmith@sun.com>
 Date:   Wed Nov 5 18:25:57 2008 -0800

    Use OsSignal in Popen/Pclose to avoid SysV signal() stupidity

 commit 0e9ef65fa583bf2393dd0fda82df6f092387b425
 Author: Keith Packard <keithp@koto.keithp.com>
 Date:   Wed Nov 7 16:33:10 2007 -0800

    Don't frob timers unless SmartSchedule is running

 commit 2338d5c9914e2a43c3a4f7ee0f4355ad0a1ad9e7
 Author: Arjan van de Ven <arjan@linux.intel.com>
 Date:   Sun Oct 28 09:37:52 2007 +0100

    reduce wakeups from smart scheduler

    The smart scheduler itimer currently always fires after each request
    (which in turn causes the CPU to wake out of idle, burning precious
    power). Rather than doing this, just stop the timer before going into
    the select() portion of the WaitFor loop. It's a cheap system call, and
    it will only get called if there's no more commands batched up from the
    active fd.

    This change also allows some of the functions to be simplified;
    setitimer() will only fail if it's passed invalid data, and we don't do
    that... so make it void and remove all the conditional code that deals
    with failure.

    The change also allows us to remove a few variables that were used for
    housekeeping between the signal handler and the main loop.
Signed-off-by: Keith Packard <keithp@koto.keithp.com>

 **Note**: The above change also required ABI changes in hw/nxagent/.

 commit abe0a51f3f790f8c055289465e130177c4b647cc
 Author: Ben Byer <bbyer@bbyer.apple.com>
 Date:   Fri Sep 21 17:07:36 2007 -0700

    So, like, checking return codes of system calls (signal, etc) is good.
    Also, only restore an old signal handler if one was actually set
    (prevents the server from dying on OS X).

 commit 6da39c67905500ab2db00a45cda4a9f756cdde96
 Author: Eric Anholt <eric@anholt.net>
 Date:   Wed Sep 12 13:23:13 2007 +0000

    Fix build on FreeBSD after Popen changes.

 commit a5b8053606d6e786cdcf6734f271acc05f9cc588
 Author: Adam Jackson <ajax@benzedrine.nwnk.net>
 Date:   Tue Sep 11 11:37:06 2007 -0400

    Ignore - not just block - SIGALRM around Popen()/Pclose().

    Because our "popen" implementation uses stdio, and because nobody's stdio
    library is capable of surviving signals, we need to make absolutely sure
    that we hide the SIGALRM from the smart scheduler.  Otherwise, when you
    open a menu in openoffice, and it recompiles XKB to deal with the
    accelerators, and you popen xkbcomp because we suck, then the scheduler
    will tell you you're taking forever doing something stupid, and the
    wait() code will get confused, and input will hang and your CPU usage
    slams to 100%.  Down, not across.
Backported-to-NX-by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>