[PATCH v4 2/2] box: implement on_shutdown triggers

[Serge Petrenko <sergepetrenko@tarantool.org>]

Add on_shutdown triggers which are run by a preallocated fiber on
shutdown and make it possible to register them via box.ctl.on_shutdown()
Make use of the new triggers: now dedicate an on_shutdown trigger to
break event loop instead of doing it explicitly from signal handler.
The trigger is run last, so that all other on_shutdown triggers may
yield, sleep and so on.
Also make sure we can register lbox_triggers without push_event function
in case we don't need one.

Closes #1607

@TarantoolBot document
Title: Document box.ctl.on_shutdown triggers
on_shutdown triggers may be set similar to space:on_replace triggers:
```
box.ctl.on_shutdown(new_trigger, old_trigger)
```
The triggers will be run when tarantool exits due to receiving one of
the signals: `SIGTERM`, `SIGINT`, `SIGHUP`.

Note that the triggers will not be run if you exit tarantool by typing
`os.exit()` to the lua console or if tarantool receives a fatal signal:
`SIGSEGV`, `SIGABORT` or any signal causing immediate program
termination.
---
 src/box/box.cc         |  2 ++
 src/box/box.h          |  3 ++
 src/box/lua/ctl.c      |  8 +++++
 src/lua/trigger.c      |  5 ++-
 src/main.cc            | 51 ++++++++++++++++++++++++++++--
 test/box/misc.result   | 72 ++++++++++++++++++++++++++++++++++++++++++
 test/box/misc.test.lua | 32 +++++++++++++++++++
 7 files changed, 170 insertions(+), 3 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index 9642364f6..049ed234f 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -79,6 +79,8 @@ static char status[64] = "unknown";
 /** box.stat rmean */
 struct rmean *rmean_box;
 
+struct rlist box_on_shutdown = RLIST_HEAD_INITIALIZER(box_on_shutdown);
+
 static void title(const char *new_status)
 {
 	snprintf(status, sizeof(status), "%s", new_status);
diff --git a/src/box/box.h b/src/box/box.h
index cb9a512be..16adc4135 100644
--- a/src/box/box.h
+++ b/src/box/box.h
@@ -64,6 +64,9 @@ struct vclock;
  */
 extern const struct vclock *box_vclock;
 
+/** Invoked on box shutdown. */
+extern struct rlist box_on_shutdown;
+
 /*
  * Initialize box library
  * @throws C++ exception
diff --git a/src/box/lua/ctl.c b/src/box/lua/ctl.c
index 9a105ed5c..7010be138 100644
--- a/src/box/lua/ctl.c
+++ b/src/box/lua/ctl.c
@@ -37,6 +37,7 @@
 #include <lualib.h>
 
 #include "lua/utils.h"
+#include "lua/trigger.h"
 
 #include "box/box.h"
 
@@ -64,9 +65,16 @@ lbox_ctl_wait_rw(struct lua_State *L)
 	return 0;
 }
 
+static int
+lbox_ctl_on_shutdown(struct lua_State *L)
+{
+	return lbox_trigger_reset(L, 2, &box_on_shutdown, NULL, NULL);
+}
+
 static const struct luaL_Reg lbox_ctl_lib[] = {
 	{"wait_ro", lbox_ctl_wait_ro},
 	{"wait_rw", lbox_ctl_wait_rw},
+	{"on_shutdown", lbox_ctl_on_shutdown},
 	{NULL, NULL}
 };
 
diff --git a/src/lua/trigger.c b/src/lua/trigger.c
index 2c2ede212..ec4d8aab3 100644
--- a/src/lua/trigger.c
+++ b/src/lua/trigger.c
@@ -91,7 +91,10 @@ lbox_trigger_run(struct trigger *ptr, void *event)
 	}
 	int top = lua_gettop(L);
 	lua_rawgeti(L, LUA_REGISTRYINDEX, trigger->ref);
-	int nargs = trigger->push_event(L, event);
+	int nargs = 0;
+	if (trigger->push_event != NULL) {
+		nargs = trigger->push_event(L, event);
+	}
 	if (luaT_call(L, nargs, LUA_MULTRET)) {
 		luaL_unref(tarantool_L, LUA_REGISTRYINDEX, coro_ref);
 		diag_raise();
diff --git a/src/main.cc b/src/main.cc
index 4303fb32c..a6bdac5d8 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -89,6 +89,10 @@ static const int ev_sig_count = sizeof(ev_sigs)/sizeof(*ev_sigs);
 
 static double start_time;
 
+/** A preallocated fiber to run on_shutdown triggers. */
+static struct fiber *on_exit_fiber = NULL;
+static bool is_shutting_down = false;
+
 double
 tarantool_uptime(void)
 {
@@ -119,9 +123,32 @@ sig_checkpoint(ev_loop * /* loop */, struct ev_signal * /* w */,
 	fiber_wakeup(f);
 }
 
+static int
+on_exit_f(va_list ap)
+{
+	(void) ap;
+	trigger_run(&box_on_shutdown, NULL);
+	return 0;
+}
+
+void
+tarantool_exit(void)
+{
+	if (is_shutting_down)
+		/*
+		 * We are already running on_shutdown triggers,
+		 * and will exit as soon as they'll finish.
+		 * Do not execute them twice.
+		 */
+		return;
+	is_shutting_down = true;
+	fiber_wakeup(on_exit_fiber);
+}
+
 static void
 signal_cb(ev_loop *loop, struct ev_signal *w, int revents)
 {
+	(void) loop;
 	(void) w;
 	(void) revents;
 
@@ -135,8 +162,7 @@ signal_cb(ev_loop *loop, struct ev_signal *w, int revents)
 	if (pid_file)
 		say_crit("got signal %d - %s", w->signum, strsignal(w->signum));
 	start_loop = false;
-	/* Terminate the main event loop */
-	ev_break(loop, EVBREAK_ALL);
+	tarantool_exit();
 }
 
 static void
@@ -636,6 +662,12 @@ print_help(const char *program)
 	puts("to see online documentation, submit bugs or contribute a patch.");
 }
 
+void
+break_loop(struct trigger *, void *)
+{
+	ev_break(loop(), EVBREAK_ALL);
+}
+
 int
 main(int argc, char **argv)
 {
@@ -759,6 +791,21 @@ main(int argc, char **argv)
 	try {
 		box_init();
 		box_lua_init(tarantool_L);
+		/* Reserve a fiber to run on_shutdown triggers. */
+		on_exit_fiber = fiber_new("on_exit", on_exit_f);
+		if (on_exit_fiber == NULL)
+			diag_raise();
+		/*
+		 * Register a on_shutdown trigger which will break the
+		 * main event loop. The trigger will be the last to run
+		 * since it's the first one we register.
+		 */
+		struct trigger *trig = (struct trigger *)malloc(sizeof(*trig));
+		if (trig == NULL)
+			tnt_raise(OutOfMemory, sizeof(*trig),
+				  "malloc", "struct trigger");
+		trigger_create(trig, break_loop, NULL, NULL);
+		trigger_add(&box_on_shutdown, trig);
 
 		atexit(tarantool_atexit);
 
diff --git a/test/box/misc.result b/test/box/misc.result
index 9fecbce76..9ffc11b88 100644
--- a/test/box/misc.result
+++ b/test/box/misc.result
@@ -1249,3 +1249,75 @@ box.cfg{too_long_threshold = too_long_threshold}
 s:drop()
 ---
 ...
+--
+-- gh-1607: on_shutdown triggers.
+--
+f = function() print('on_shutdown 1') end
+---
+...
+g = function() print('on_shutdown 2') end
+---
+...
+h = function() print('on_shutdown 3') end
+---
+...
+-- Check that on_shutdown triggers may yield
+-- and perform some complicated actions.
+fiber = require('fiber')
+---
+...
+test_run:cmd("setopt delimiter ';'")
+---
+- true
+...
+trig = function()
+    fiber.sleep(0.01)
+    fiber.yield()
+    box.schema.space.create("shutdown")
+    box.space.shutdown:create_index("pk")
+    box.space.shutdown:insert{1,2,3}
+    print('on_shutdown 4')
+end;
+---
+...
+test_run:cmd("setopt delimiter ''");
+---
+- true
+...
+_ = box.ctl.on_shutdown(f)
+---
+...
+_ = box.ctl.on_shutdown(g)
+---
+...
+-- Check that replacing triggers works
+_ = box.ctl.on_shutdown(h, g)
+---
+...
+_ = box.ctl.on_shutdown(trig)
+---
+...
+test_run:cmd('restart server default')
+test_run:grep_log('default', 'on_shutdown 1', nil, {noreset=true})
+---
+- on_shutdown 1
+...
+test_run:grep_log('default', 'on_shutdown 2', nil, {noreset=true})
+---
+- null
+...
+test_run:grep_log('default', 'on_shutdown 3', nil, {noreset=true})
+---
+- on_shutdown 3
+...
+test_run:grep_log('default', 'on_shutdown 4', nil, {noreset=true})
+---
+- on_shutdown 4
+...
+box.space.shutdown:select{}
+---
+- - [1, 2, 3]
+...
+box.space.shutdown:drop()
+---
+...
diff --git a/test/box/misc.test.lua b/test/box/misc.test.lua
index cc6cb34fb..f1c9d8e8c 100644
--- a/test/box/misc.test.lua
+++ b/test/box/misc.test.lua
@@ -352,3 +352,35 @@ rows == expected_rows
 lsn == expected_lsn
 box.cfg{too_long_threshold = too_long_threshold}
 s:drop()
+
+--
+-- gh-1607: on_shutdown triggers.
+--
+f = function() print('on_shutdown 1') end
+g = function() print('on_shutdown 2') end
+h = function() print('on_shutdown 3') end
+-- Check that on_shutdown triggers may yield
+-- and perform some complicated actions.
+fiber = require('fiber')
+test_run:cmd("setopt delimiter ';'")
+trig = function()
+    fiber.sleep(0.01)
+    fiber.yield()
+    box.schema.space.create("shutdown")
+    box.space.shutdown:create_index("pk")
+    box.space.shutdown:insert{1,2,3}
+    print('on_shutdown 4')
+end;
+test_run:cmd("setopt delimiter ''");
+_ = box.ctl.on_shutdown(f)
+_ = box.ctl.on_shutdown(g)
+-- Check that replacing triggers works
+_ = box.ctl.on_shutdown(h, g)
+_ = box.ctl.on_shutdown(trig)
+test_run:cmd('restart server default')
+test_run:grep_log('default', 'on_shutdown 1', nil, {noreset=true})
+test_run:grep_log('default', 'on_shutdown 2', nil, {noreset=true})
+test_run:grep_log('default', 'on_shutdown 3', nil, {noreset=true})
+test_run:grep_log('default', 'on_shutdown 4', nil, {noreset=true})
+box.space.shutdown:select{}
+box.space.shutdown:drop()
-- 
2.17.2 (Apple Git-113)