[Tarantool-patches] [PATCH v2 07/16] raft: stop using replicaset.vclock

[Vladislav Shpilevoy]

Raft is being moved to a separate library in src/lib. It means,
it can't depend on anything from box/.

The patch makes raft stop using replicaset.vclock.

Instead, it has a new option 'vclock'. It is stored inside struct
raft by pointer and should be configured using raft_cfg_vclock().

Box configures it to point at replicaset.vclock like before. But
now raftlib code does not depend on it explicitly.

Vclock is stored in Raft by pointer instead of by value so as not
to update it for each transaction. It would be too high price to
pay for Raft independence from box.

Part of #5303
---
 src/box/box.cc    |  1 +
 src/box/raftlib.c | 15 +++++++++++----
 src/box/raftlib.h | 16 ++++++++++++++++
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index 043a37658..837fbd2e5 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -2768,6 +2768,7 @@ box_cfg_xc(void)
 	 */
 	if (!replication_anon)
 		raft_cfg_instance_id(box_raft(), instance_id);
+	raft_cfg_vclock(box_raft(), &replicaset.vclock);
 
 	if (box_set_election_timeout() != 0)
 		diag_raise();
diff --git a/src/box/raftlib.c b/src/box/raftlib.c
index 78164bf91..ab2e27fd8 100644
--- a/src/box/raftlib.c
+++ b/src/box/raftlib.c
@@ -125,8 +125,7 @@ raft_new_random_election_shift(const struct raft *raft)
 static inline bool
 raft_can_vote_for(const struct raft *raft, const struct vclock *v)
 {
-	(void)raft;
-	int cmp = vclock_compare_ignore0(v, &replicaset.vclock);
+	int cmp = vclock_compare_ignore0(v, raft->vclock);
 	return cmp == 0 || cmp == 1;
 }
 
@@ -597,7 +596,7 @@ raft_worker_handle_broadcast(struct raft *raft)
 	req.state = raft->state;
 	if (req.state == RAFT_STATE_CANDIDATE) {
 		assert(raft->vote == raft->self);
-		req.vclock = &replicaset.vclock;
+		req.vclock = raft->vclock;
 	}
 	replicaset_foreach(replica)
 		relay_push_raft(replica->relay, &req);
@@ -865,7 +864,7 @@ raft_serialize_for_network(const struct raft *raft, struct raft_request *req)
 	 * Vclock is sent out only by candidate instances.
 	 */
 	if (req->state == RAFT_STATE_CANDIDATE)
-		req->vclock = &replicaset.vclock;
+		req->vclock = raft->vclock;
 }
 
 void
@@ -984,6 +983,14 @@ raft_cfg_instance_id(struct raft *raft, uint32_t instance_id)
 	raft->self = instance_id;
 }
 
+void
+raft_cfg_vclock(struct raft *raft, const struct vclock *vclock)
+{
+	assert(raft->vclock == NULL);
+	assert(vclock != NULL);
+	raft->vclock = vclock;
+}
+
 void
 raft_new_term(struct raft *raft)
 {
diff --git a/src/box/raftlib.h b/src/box/raftlib.h
index 2da3cec86..8d0d03da0 100644
--- a/src/box/raftlib.h
+++ b/src/box/raftlib.h
@@ -154,6 +154,15 @@ struct raft {
 	int vote_count;
 	/** Number of votes necessary for successful election. */
 	int election_quorum;
+	/**
+	 * Vclock of the Raft node owner. Raft never changes it, only watches,
+	 * and makes decisions based on it. The value is not stored by copy so
+	 * as to avoid frequent updates. If every transaction would need to
+	 * update several vclocks in different places, it would be too
+	 * expensive. So they update only one vclock, which is shared between
+	 * subsystems, such as Raft.
+	 */
+	const struct vclock *vclock;
 	/** State machine timed event trigger. */
 	struct ev_timer timer;
 	/** Worker fiber to execute blocking tasks like IO. */
@@ -250,6 +259,13 @@ raft_cfg_death_timeout(struct raft *raft, double death_timeout);
 void
 raft_cfg_instance_id(struct raft *raft, uint32_t instance_id);
 
+/**
+ * Configure vclock of the given Raft instance. The vclock is not copied, so the
+ * caller must keep it valid.
+ */
+void
+raft_cfg_vclock(struct raft *raft, const struct vclock *vclock);
+
 /**
  * Bump the term. When it is persisted, the node checks if there is a leader,
  * and if there is not, a new election is started. That said, this function can
-- 
2.24.3 (Apple Git-128)