[Tarantool-patches] [PATCH 3/8] wal: don't touch box.cfg.wal_dir more than once

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Relay.cc and box.cc obtained box.cfg.wal_dir value using
cfg_gets() call. To initialize WAL and create struct recovery
objects.

That is not only a bit dangerous (cfg_gets() uses Lua API and can
throw a Lua error) and slow, but also not necessary - wal_dir
parameter is constant, it can't be changed after instance start.

It means, the value can be stored somewhere one time and then used
without Lua.

Main motivation is that the WAL directory path will be needed
inside relay threads to restart their recovery iterators in the
Raft patch. They can't use cfg_gets(), because Lua lives in TX
thread. But can access a constant global variable, introduced in
this patch (it existed before, but now has a method to get it).

Needed for #1146
---
 src/box/box.cc   | 9 ++++-----
 src/box/relay.cc | 7 ++-----
 src/box/wal.c    | 6 ++++++
 src/box/wal.h    | 7 +++++++
 4 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/src/box/box.cc b/src/box/box.cc
index 0813603c0..eeb00d5e2 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -2395,8 +2395,7 @@ local_recovery(const struct tt_uuid *instance_uuid,
 	wal_stream_create(&wal_stream);
 
 	struct recovery *recovery;
-	recovery = recovery_new(cfg_gets("wal_dir"),
-				cfg_geti("force_recovery"),
+	recovery = recovery_new(wal_dir(), cfg_geti("force_recovery"),
 				checkpoint_vclock);
 
 	/*
@@ -2469,7 +2468,7 @@ local_recovery(const struct tt_uuid *instance_uuid,
 		recovery_follow_local(recovery, &wal_stream.base, "hot_standby",
 				      cfg_getd("wal_dir_rescan_delay"));
 		while (true) {
-			if (path_lock(cfg_gets("wal_dir"), &wal_dir_lock))
+			if (path_lock(wal_dir(), &wal_dir_lock))
 				diag_raise();
 			if (wal_dir_lock >= 0)
 				break;
@@ -2616,7 +2615,7 @@ box_cfg_xc(void)
 	 * Lock the write ahead log directory to avoid multiple
 	 * instances running in the same dir.
 	 */
-	if (path_lock(cfg_gets("wal_dir"), &wal_dir_lock) < 0)
+	if (path_lock(wal_dir(), &wal_dir_lock) < 0)
 		diag_raise();
 	if (wal_dir_lock < 0) {
 		/**
@@ -2625,7 +2624,7 @@ box_cfg_xc(void)
 		 * WAL dir must contain at least one xlog.
 		 */
 		if (!cfg_geti("hot_standby") || checkpoint == NULL)
-			tnt_raise(ClientError, ER_ALREADY_RUNNING, cfg_gets("wal_dir"));
+			tnt_raise(ClientError, ER_ALREADY_RUNNING, wal_dir());
 	}
 
 	struct journal bootstrap_journal;
diff --git a/src/box/relay.cc b/src/box/relay.cc
index a7843a8c2..124b0f52f 100644
--- a/src/box/relay.cc
+++ b/src/box/relay.cc
@@ -34,7 +34,6 @@
 #include "tt_static.h"
 #include "scoped_guard.h"
 #include "cbus.h"
-#include "cfg.h"
 #include "errinj.h"
 #include "fiber.h"
 #include "say.h"
@@ -369,8 +368,7 @@ relay_final_join(int fd, uint64_t sync, struct vclock *start_vclock,
 		relay_delete(relay);
 	});
 
-	relay->r = recovery_new(cfg_gets("wal_dir"), false,
-			       start_vclock);
+	relay->r = recovery_new(wal_dir(), false, start_vclock);
 	vclock_copy(&relay->stop_vclock, stop_vclock);
 
 	int rc = cord_costart(&relay->cord, "final_join",
@@ -731,8 +729,7 @@ relay_subscribe(struct replica *replica, int fd, uint64_t sync,
 	});
 
 	vclock_copy(&relay->local_vclock_at_subscribe, &replicaset.vclock);
-	relay->r = recovery_new(cfg_gets("wal_dir"), false,
-			        replica_clock);
+	relay->r = recovery_new(wal_dir(), false, replica_clock);
 	vclock_copy(&relay->tx.vclock, replica_clock);
 	relay->version_id = replica_version_id;
 
diff --git a/src/box/wal.c b/src/box/wal.c
index 045006b60..e181e58d9 100644
--- a/src/box/wal.c
+++ b/src/box/wal.c
@@ -201,6 +201,12 @@ wal_mode(void)
 	return wal_writer_singleton.wal_mode;
 }
 
+const char *
+wal_dir(void)
+{
+	return wal_writer_singleton.wal_dir.dirname;
+}
+
 static void
 wal_write_to_disk(struct cmsg *msg);
 
diff --git a/src/box/wal.h b/src/box/wal.h
index 9d0cada46..581306fe9 100644
--- a/src/box/wal.h
+++ b/src/box/wal.h
@@ -98,6 +98,13 @@ wal_enable(void);
 void
 wal_free(void);
 
+/**
+ * Get WAL directory path. The value never changes after box is
+ * configured first time. Safe to use from multiple threads.
+ */
+const char *
+wal_dir(void);
+
 struct wal_watcher_msg {
 	struct cmsg cmsg;
 	struct wal_watcher *watcher;
-- 
2.21.1 (Apple Git-122.3)