MDEV-4984: Implement MASTER_GTID_WAIT() and @@LAST_GTID.

Rewrite the gtid_waiting::wait_for_gtid() function.
The code was rubbish (and buggy). Now the logic is
much clearer.

Also fix a missing slave sync that could cause test failure.

mysql-test/suite/rpl/r/rpl_gtid_basic.result

@@ -131,6 +131,7 @@ include/stop_slave.inc
 CHANGE MASTER TO master_host = '127.0.0.1', master_port = SERVER_MYPORT_3;
 include/start_slave.inc
 DROP TABLE t1,t2;
+include/save_master_gtid.inc
 *** A few more checks for BINLOG_GTID_POS function ***
 SELECT BINLOG_GTID_POS();
 ERROR 42000: Incorrect parameter count in the call to native function 'BINLOG_GTID_POS'
@@ -167,6 +168,7 @@ NULL
 Warnings:
 Warning	1916	Got overflow when converting '18446744073709551616' to INT. Value truncated.
 *** Some tests of @@GLOBAL.gtid_binlog_state ***
+include/sync_with_master_gtid.inc
 include/stop_slave.inc
 SET @old_state= @@GLOBAL.gtid_binlog_state;
 SET GLOBAL gtid_binlog_state = '';

mysql-test/suite/rpl/t/rpl_gtid_basic.test

@@ -139,6 +139,7 @@ eval CHANGE MASTER TO master_host = '127.0.0.1', master_port = $SERVER_MYPORT_3;
 
 connection server_1;
 DROP TABLE t1,t2;
+--source include/save_master_gtid.inc
 
 --echo *** A few more checks for BINLOG_GTID_POS function ***
 --let $valid_binlog_name = query_get_value(SHOW BINARY LOGS,Log_name,1)
@@ -160,6 +161,7 @@ eval SELECT BINLOG_GTID_POS('$valid_binlog_name',18446744073709551616);
 
 --echo *** Some tests of @@GLOBAL.gtid_binlog_state ***
 --connection server_2
+--source include/sync_with_master_gtid.inc
 --source include/stop_slave.inc
 
 --connection server_1

sql/rpl_gtid.h

@@ -40,6 +40,57 @@ enum enum_gtid_skip_type {
 };
 
 
+/*
+  Structure to keep track of threads waiting in MASTER_GTID_WAIT().
+
+  Since replication is (mostly) single-threaded, we want to minimise the
+  performance impact on that from MASTER_GTID_WAIT(). To achieve this, we
+  are careful to keep the common lock between replication threads and
+  MASTER_GTID_WAIT threads held for as short as possible. We keep only
+  a single thread waiting to be notified by the replication threads; this
+  thread then handles all the (potentially heavy) lifting of dealing with
+  all current waiting threads.
+*/
+struct gtid_waiting {
+  /* Elements in the hash, basically a priority queue for each domain. */
+  struct hash_element {
+    QUEUE queue;
+    uint32 domain_id;
+  };
+  /* A priority queue to handle waiters in one domain in seq_no order. */
+  struct queue_element {
+    uint64 wait_seq_no;
+    THD *thd;
+    int queue_idx;
+    /*
+      do_small_wait is true if we have responsibility for ensuring that there
+      is a small waiter.
+    */
+    bool do_small_wait;
+    /*
+      The flag `done' is set when the wait is completed (either due to reaching
+      the position waited for, or due to timeout or kill). The queue_element
+      is in the queue if and only if `done' is true.
+    */
+    bool done;
+  };
+
+  mysql_mutex_t LOCK_gtid_waiting;
+  HASH hash;
+
+  void init();
+  void destroy();
+  hash_element *get_entry(uint32 domain_id);
+  int wait_for_pos(THD *thd, String *gtid_str, longlong timeout_us);
+  void promote_new_waiter(gtid_waiting::hash_element *he);
+  int wait_for_gtid(THD *thd, rpl_gtid *wait_gtid, struct timespec *wait_until);
+  void process_wait_hash(uint64 wakeup_seq_no, gtid_waiting::hash_element *he);
+  int register_in_wait_queue(THD *thd, rpl_gtid *wait_gtid, hash_element *he,
+                             queue_element *elem);
+  void remove_from_wait_queue(hash_element *he, queue_element *elem);
+};
+
+
 /*
   Replication slave state.
 
@@ -68,9 +119,14 @@ struct rpl_slave_state
     /* Highest seq_no seen so far in this domain. */
     uint64 highest_seq_no;
     /*
-      If min_wait_seq_no is non-zero, then it is the smallest seq_no in this
-      domain that someone is doing MASTER_GTID_WAIT() on. When we reach this
-      seq_no, we need to signal the waiter on COND_wait_gtid.
+      If this is non-NULL, then it is the waiter responsible for the small
+      wait in MASTER_GTID_WAIT().
+    */
+    gtid_waiting::queue_element *gtid_waiter;
+    /*
+      If gtid_waiter is non-NULL, then this is the seq_no that its
+      MASTER_GTID_WAIT() is waiting on. When we reach this seq_no, we need to
+      signal the waiter on COND_wait_gtid.
     */
     uint64 min_wait_seq_no;
     mysql_cond_t COND_wait_gtid;
@@ -215,48 +271,6 @@ struct slave_connection_state
 };
 
 
-/*
-  Structure to keep track of threads waiting in MASTER_GTID_WAIT().
-
-  Since replication is (mostly) single-threaded, we want to minimise the
-  performance impact on that from MASTER_GTID_WAIT(). To achieve this, we
-  are careful to keep the common lock between replication threads and
-  MASTER_GTID_WAIT threads held for as short as possible. We keep only
-  a single thread waiting to be notified by the replication threads; this
-  thread then handles all the (potentially heavy) lifting of dealing with
-  all current waiting threads.
-*/
-
-struct gtid_waiting {
-  /* Elements in the hash, basically a priority queue for each domain. */
-  struct hash_element {
-    QUEUE queue;
-    uint32 domain_id;
-  };
-  /* A priority queue to handle waiters in one domain in seq_no order. */
-  struct queue_element {
-    uint64 wait_seq_no;
-    THD *thd;
-    int queue_idx;
-    enum { DONE, TAKEOVER } wakeup_reason;
-  };
-
-  mysql_mutex_t LOCK_gtid_waiting;
-  HASH hash;
-
-  void init();
-  void destroy();
-  hash_element *get_entry(uint32 domain_id);
-  int wait_for_pos(THD *thd, String *gtid_str, longlong timeout_us);
-  void promote_new_waiter(gtid_waiting::hash_element *he);
-  int wait_for_gtid(THD *thd, rpl_gtid *wait_gtid, struct timespec *wait_until);
-  void process_wait_hash(uint64 wakeup_seq_no, gtid_waiting::hash_element *he);
-  hash_element *register_in_wait_hash(THD *thd, rpl_gtid *wait_gtid,
-                                      queue_element *elem);
-  void remove_from_wait_hash(hash_element *e, queue_element *elem);
-};
-
-
 extern bool rpl_slave_state_tostring_helper(String *dest, const rpl_gtid *gtid,
                                             bool *first);
 extern int gtid_check_rpl_slave_state_table(TABLE *table);