[Tarantool-patches] [PATCH v3 10/10] box.ctl: rename clear_synchro_queue to promote

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

New function name will be `box.ctl.promote()`. It's much shorter and
closer to the function's now enriched functionality.

Old name `box.ctl.clear_synchro_queue()` remains in Lua for the sake of
backward compatibility.

Follow-up #5445
Closes #3055

@TarantoolBot document
Title: deprecate `box.ctl.clear_synchro_queue()` in favor of `box.ctl.promote()`

Replace all the mentions of `box.ctl.clear_synchro_queue()` with
`box.ctl.promote()` and add a note that `box.ctl.clear_synchro_queue()`
is a deprecated alias to `box.ctl.promote()`
---
 changelogs/unreleased/box-ctl-promote.md      |   8 ++
 src/box/box.cc                                |  20 ++--
 src/box/box.h                                 |   2 +-
 src/box/lua/ctl.c                             |   8 +-
 src/box/raft.c                                |   4 +-
 test/replication/election_basic.result        |  25 +++++
 test/replication/election_basic.test.lua      |  10 ++
 .../gh-3055-election-promote.result           | 105 ++++++++++++++++++
 .../gh-3055-election-promote.test.lua         |  43 +++++++
 test/replication/suite.cfg                    |   1 +
 10 files changed, 210 insertions(+), 16 deletions(-)
 create mode 100644 changelogs/unreleased/box-ctl-promote.md
 create mode 100644 test/replication/gh-3055-election-promote.result
 create mode 100644 test/replication/gh-3055-election-promote.test.lua

diff --git a/changelogs/unreleased/box-ctl-promote.md b/changelogs/unreleased/box-ctl-promote.md
new file mode 100644
index 000000000..15f6fb206
--- /dev/null
+++ b/changelogs/unreleased/box-ctl-promote.md
@@ -0,0 +1,8 @@
+## feature/replication
+
+* Introduce `box.ctl.promote()` and the concept of manual elections (enabled
+  with `election_mode='manual'`). Once the instance is in `manual` election
+  mode, it acts like a `voter` most of the time, but may trigger elections and
+  become a leader, once `box.ctl.promote()` is called.
+  When `election_mode ~= 'manual'`, `box.ctl.promote()` replaces
+  `box.ctl.clear_synchro_queue()`, which is now deprecated (gh-3055).
diff --git a/src/box/box.cc b/src/box/box.cc
index 9b663f54a..0b0c38cd5 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -1509,12 +1509,12 @@ box_wait_quorum(uint32_t lead_id, int64_t target_lsn, int quorum,
 }
 
 int
-box_clear_synchro_queue(void)
+box_promote(void)
 {
 	/* A guard to block multiple simultaneous function invocations. */
-	static bool in_clear_synchro_queue = false;
-	if (in_clear_synchro_queue) {
-		diag_set(ClientError, ER_UNSUPPORTED, "clear_synchro_queue",
+	static bool in_promote = false;
+	if (in_promote) {
+		diag_set(ClientError, ER_UNSUPPORTED, "box.ctl.promote",
 			 "simultaneous invocations");
 		return -1;
 	}
@@ -1567,7 +1567,7 @@ box_clear_synchro_queue(void)
 	int64_t wait_lsn = txn_limbo.confirmed_lsn;
 	int rc = 0;
 	int quorum = replication_synchro_quorum;
-	in_clear_synchro_queue = true;
+	in_promote = true;
 
 	if (run_elections) {
 		/*
@@ -1584,13 +1584,13 @@ box_clear_synchro_queue(void)
 		raft_cfg_is_candidate(box_raft(), false, false);
 		if (!box_raft()->is_enabled) {
 			diag_set(ClientError, ER_RAFT_DISABLED);
-			in_clear_synchro_queue = false;
+			in_promote = false;
 			return -1;
 		}
 		if (box_raft()->state != RAFT_STATE_LEADER) {
 			diag_set(ClientError, ER_INTERFERING_PROMOTE,
 				 box_raft()->leader);
-			in_clear_synchro_queue = false;
+			in_promote = false;
 			return -1;
 		}
 	}
@@ -1614,13 +1614,13 @@ box_clear_synchro_queue(void)
 		if (former_leader_id != txn_limbo.owner_id) {
 			diag_set(ClientError, ER_INTERFERING_PROMOTE,
 				 txn_limbo.owner_id);
-			in_clear_synchro_queue = false;
+			in_promote = false;
 			return -1;
 		}
 	}
 
 	/*
-	 * clear_synchro_queue() is a no-op on the limbo owner, so all the rows
+	 * promote() is a no-op on the limbo owner, so all the rows
 	 * in the limbo must've come through the applier meaning they already
 	 * have an lsn assigned, even if their WAL write hasn't finished yet.
 	 */
@@ -1657,7 +1657,7 @@ promote:
 						req.term);
 		}
 	}
-	in_clear_synchro_queue = false;
+	in_promote = false;
 	return rc;
 }
 
diff --git a/src/box/box.h b/src/box/box.h
index 90facd189..04bdd397d 100644
--- a/src/box/box.h
+++ b/src/box/box.h
@@ -274,7 +274,7 @@ extern "C" {
 typedef struct tuple box_tuple_t;
 
 int
-box_clear_synchro_queue(void);
+box_promote(void);
 
 /* box_select is private and used only by FFI */
 API_EXPORT int
diff --git a/src/box/lua/ctl.c b/src/box/lua/ctl.c
index 5b8d0d0e4..368b9ab60 100644
--- a/src/box/lua/ctl.c
+++ b/src/box/lua/ctl.c
@@ -82,9 +82,9 @@ lbox_ctl_on_schema_init(struct lua_State *L)
 }
 
 static int
-lbox_ctl_clear_synchro_queue(struct lua_State *L)
+lbox_ctl_promote(struct lua_State *L)
 {
-	if (box_clear_synchro_queue() != 0)
+	if (box_promote() != 0)
 		return luaT_error(L);
 	return 0;
 }
@@ -124,7 +124,9 @@ static const struct luaL_Reg lbox_ctl_lib[] = {
 	{"wait_rw", lbox_ctl_wait_rw},
 	{"on_shutdown", lbox_ctl_on_shutdown},
 	{"on_schema_init", lbox_ctl_on_schema_init},
-	{"clear_synchro_queue", lbox_ctl_clear_synchro_queue},
+	{"promote", lbox_ctl_promote},
+	/* An old alias. */
+	{"clear_synchro_queue", lbox_ctl_promote},
 	{"is_recovery_finished", lbox_ctl_is_recovery_finished},
 	{"set_on_shutdown_timeout", lbox_ctl_set_on_shutdown_timeout},
 	{NULL, NULL}
diff --git a/src/box/raft.c b/src/box/raft.c
index e8c9f3d2c..e357772a5 100644
--- a/src/box/raft.c
+++ b/src/box/raft.c
@@ -89,14 +89,14 @@ box_raft_update_synchro_queue(struct raft *raft)
 	assert(raft == box_raft());
 	/*
 	 * In case these are manual elections, we are already in the middle of a
-	 * `clear_synchro_queue` call. No need to call it once again.
+	 * `promote` call. No need to call it once again.
 	 */
 	if (raft->state == RAFT_STATE_LEADER &&
 	    box_election_mode != ELECTION_MODE_MANUAL) {
 		int rc = 0;
 		uint32_t errcode = 0;
 		do {
-			rc = box_clear_synchro_queue();
+			rc = box_promote();
 			if (rc != 0) {
 				struct error *err = diag_last_error(diag_get());
 				errcode = box_error_code(err);
diff --git a/test/replication/election_basic.result b/test/replication/election_basic.result
index d5320b3ff..78c911245 100644
--- a/test/replication/election_basic.result
+++ b/test/replication/election_basic.result
@@ -108,6 +108,31 @@ assert(box.info.election.leader == box.info.id)
  | - true
  | ...
 
+-- Manual election mode. A voter most of the time, a leader once
+-- `box.ctl.promote()` is called.
+box.cfg{election_mode = 'manual'}
+ | ---
+ | ...
+
+assert(box.info.election.state == 'follower')
+ | ---
+ | - true
+ | ...
+term = box.info.election.term
+ | ---
+ | ...
+box.ctl.promote()
+ | ---
+ | ...
+assert(box.info.election.state == 'leader')
+ | ---
+ | - error: assertion failed!
+ | ...
+assert(box.info.election.term > term)
+ | ---
+ | - error: assertion failed!
+ | ...
+
 box.cfg{                                                                        \
     election_mode = 'off',                                                      \
     election_timeout = old_election_timeout                                     \
diff --git a/test/replication/election_basic.test.lua b/test/replication/election_basic.test.lua
index 821f73cea..5fc398848 100644
--- a/test/replication/election_basic.test.lua
+++ b/test/replication/election_basic.test.lua
@@ -39,6 +39,16 @@ assert(box.info.election.term > term)
 assert(box.info.election.vote == box.info.id)
 assert(box.info.election.leader == box.info.id)
 
+-- Manual election mode. A voter most of the time, a leader once
+-- `box.ctl.promote()` is called.
+box.cfg{election_mode = 'manual'}
+
+assert(box.info.election.state == 'follower')
+term = box.info.election.term
+box.ctl.promote()
+assert(box.info.election.state == 'leader')
+assert(box.info.election.term > term)
+
 box.cfg{                                                                        \
     election_mode = 'off',                                                      \
     election_timeout = old_election_timeout                                     \
diff --git a/test/replication/gh-3055-election-promote.result b/test/replication/gh-3055-election-promote.result
new file mode 100644
index 000000000..6f5af13bc
--- /dev/null
+++ b/test/replication/gh-3055-election-promote.result
@@ -0,0 +1,105 @@
+-- test-run result file version 2
+test_run = require('test_run').new()
+ | ---
+ | ...
+
+--
+-- gh-3055 box.ctl.promote(). Call on instance with election_mode='manual'
+-- in order to promote it to leader.
+SERVERS = {'election_replica1', 'election_replica2', 'election_replica3'}
+ | ---
+ | ...
+-- Start in candidate state in order for bootstrap to work.
+test_run:create_cluster(SERVERS, 'replication', {args='2 0.1 candidate'})
+ | ---
+ | ...
+test_run:wait_fullmesh(SERVERS)
+ | ---
+ | ...
+
+cfg_set_manual =\
+    "box.cfg{election_mode='manual'} "..\
+    "assert(box.info.election.state == 'follower') "..\
+    "assert(box.info.ro)"
+ | ---
+ | ...
+
+for _, server in pairs(SERVERS) do\
+    ok, res = test_run:eval(server, cfg_set_manual)\
+    assert(ok)\
+end
+ | ---
+ | ...
+
+-- Promote without living leader.
+test_run:switch('election_replica1')
+ | ---
+ | - true
+ | ...
+assert(box.info.election.state == 'follower')
+ | ---
+ | - true
+ | ...
+term = box.info.election.term
+ | ---
+ | ...
+box.ctl.promote()
+ | ---
+ | ...
+assert(box.info.election.state == 'leader')
+ | ---
+ | - true
+ | ...
+assert(not box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.election.term > term)
+ | ---
+ | - true
+ | ...
+
+-- Test promote when there's a live leader.
+test_run:switch('election_replica2')
+ | ---
+ | - true
+ | ...
+term = box.info.election.term
+ | ---
+ | ...
+assert(box.info.election.state == 'follower')
+ | ---
+ | - true
+ | ...
+assert(box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.election.leader ~= 0)
+ | ---
+ | - true
+ | ...
+box.ctl.promote()
+ | ---
+ | ...
+assert(box.info.election.state == 'leader')
+ | ---
+ | - true
+ | ...
+assert(not box.info.ro)
+ | ---
+ | - true
+ | ...
+assert(box.info.election.term > term)
+ | ---
+ | - true
+ | ...
+
+-- Cleanup.
+test_run:switch('default')
+ | ---
+ | - true
+ | ...
+test_run:drop_cluster(SERVERS)
+ | ---
+ | ...
diff --git a/test/replication/gh-3055-election-promote.test.lua b/test/replication/gh-3055-election-promote.test.lua
new file mode 100644
index 000000000..cbc3ed206
--- /dev/null
+++ b/test/replication/gh-3055-election-promote.test.lua
@@ -0,0 +1,43 @@
+test_run = require('test_run').new()
+
+--
+-- gh-3055 box.ctl.promote(). Call on instance with election_mode='manual'
+-- in order to promote it to leader.
+SERVERS = {'election_replica1', 'election_replica2', 'election_replica3'}
+-- Start in candidate state in order for bootstrap to work.
+test_run:create_cluster(SERVERS, 'replication', {args='2 0.1 candidate'})
+test_run:wait_fullmesh(SERVERS)
+
+cfg_set_manual =\
+    "box.cfg{election_mode='manual'} "..\
+    "assert(box.info.election.state == 'follower') "..\
+    "assert(box.info.ro)"
+
+for _, server in pairs(SERVERS) do\
+    ok, res = test_run:eval(server, cfg_set_manual)\
+    assert(ok)\
+end
+
+-- Promote without living leader.
+test_run:switch('election_replica1')
+assert(box.info.election.state == 'follower')
+term = box.info.election.term
+box.ctl.promote()
+assert(box.info.election.state == 'leader')
+assert(not box.info.ro)
+assert(box.info.election.term > term)
+
+-- Test promote when there's a live leader.
+test_run:switch('election_replica2')
+term = box.info.election.term
+assert(box.info.election.state == 'follower')
+assert(box.info.ro)
+assert(box.info.election.leader ~= 0)
+box.ctl.promote()
+assert(box.info.election.state == 'leader')
+assert(not box.info.ro)
+assert(box.info.election.term > term)
+
+-- Cleanup.
+test_run:switch('default')
+test_run:drop_cluster(SERVERS)
diff --git a/test/replication/suite.cfg b/test/replication/suite.cfg
index 8b185ce7e..dc39e2f74 100644
--- a/test/replication/suite.cfg
+++ b/test/replication/suite.cfg
@@ -2,6 +2,7 @@
     "anon.test.lua": {},
     "anon_register_gap.test.lua": {},
     "gh-2991-misc-asserts-on-update.test.lua": {},
+    "gh-3055-election-promote.test.lua": {},
     "gh-3111-misc-rebootstrap-from-ro-master.test.lua": {},
     "gh-3160-misc-heartbeats-on-master-changes.test.lua": {},
     "gh-3247-misc-iproto-sequence-value-not-replicated.test.lua": {},
-- 
2.24.3 (Apple Git-128)