[PATCH v5 0/3] box: implement on_shutdown triggers

[Serge Petrenko]

This patchset adds on_shutdown triggers which can be registered from lua 
via box.ctl.on_shutdown() and are run on tarantool shutdown.

Issue: https://github.com/tarantool/tarantool/issues/1607
Branch: https://github.com/tarantool/tarantool/tree/sp/gh-1607-on-exit-triggers

Changes in v2: 
  - added 3rd patch which passes signals to triggers.
  - run on_shutdown triggers even if box is not configured.
  - add a documentation request to the 3rd patch.

Changes in v3: 
  - remove the patch which passes signals to the trigger, since
    the triggers are not run on fatal signals at all, and doing
    this for SIGTERM or SIGINT is not of much use.
  - Add a new patch which moves tarantool_free() from atexit()
    to end of main(). Only close the journal and restore terminal state
    (if needed) in atexit handlers. Also in signal handler create
    a new fiber which breaks the event loop. on_shutdown triggers will
    be run from this fiber before ev loop break.
  - add tests that on_shutdown triggers can yield to the third patch.

Changes in v4: 
  - squashed 2nd and 3rd patches
  - review fixes as per review by @locker
  - made 1st and 2nd patches independent.
    1st patch may be dropped if we decide not to
    implement it. 

Changes in v5:
  - patched os.exit() to call on_shutdown triggers
  - some minor fixes as per review by @locker
  - the patch which removes atexit() registration for
    cleanup routines is moved last. It is now completely
    trivial thanks to the os.exit() patch.

The first patch implements on_shutdown triggers. The triggers are run from
a fiber before ev_loop break, and the last executed trigger breaks ev_loop.
The triggers are exposed to lua via box.ctl.on_shutdown().

The second patch alters os.exit() to call on_shutdown triggers. Now behaviour
after os.exit() is identical to the behaviour after receiving SIGINT.
(Except that exit code is changed).

The third patch removes cleanup routines from atexit to the end of main().
This can be done thanks to the first two patches, which ensure that during
normal termination control always reaches end of main().

Serge Petrenko (3):
  box: implement on_shutdown triggers
  lua: patch os.exit() to execute on_shutdown triggers.
  box: get rid of atexit() for calling cleanup routines

 extra/exports          |  1 +
 src/box/box.cc         |  2 ++
 src/box/box.h          |  3 ++
 src/box/lua/ctl.c      |  8 +++++
 src/lua/init.lua       |  7 ++++
 src/lua/trigger.c      |  5 ++-
 src/main.cc            | 60 +++++++++++++++++++++++++++++++----
 src/main.h             |  3 ++
 test/box/misc.result   | 72 ++++++++++++++++++++++++++++++++++++++++++
 test/box/misc.test.lua | 32 +++++++++++++++++++
 10 files changed, 185 insertions(+), 8 deletions(-)

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2.17.2 (Apple Git-113)