Method xlock

phx_percona/percona/sql/binlog.cc:7742–7771

void MYSQL_BIN_LOG::xlock(void)
{
  mysql_mutex_lock(&LOCK_log);

  DBUG_ASSERT(!snapshot_lock_acquired);

  /*
    We must ensure that no writes to binlog and no commits to storage engines
    occur after function is called for START TRANSACTION FOR CONSISTENT
    SNAPSHOT. With binlog_order_commits=1 (the default) flushing to binlog is
    performed under the LOCK_log mutex and commits are done under the
    LOCK_commit mutex, both in the stage leader thread. So acquiring those 2
    mutexes is sufficient to guarantee atomicity.

    With binlog_order_commits=0 commits are performed in parallel by separate
    threads with each acquiring a shared lock on LOCK_consistent_snapshot.

    binlog_order_commits is a dynamic variable, so we have to keep track what
    primitives should be used in xunlock().
  */
  if (opt_binlog_order_commits)
  {
    mysql_mutex_lock(&LOCK_commit);
  }
  else
  {
    snapshot_lock_acquired= true;
    mysql_rwlock_wrlock(&LOCK_consistent_snapshot);
  }
}


void MYSQL_BIN_LOG::xunlock(void)