MWL#116: Code simplifications for TC_LOG_MMAP.

Make TC_LOG_MMAP (and TC_LOG_DUMMY) derive directly from TC_LOG, avoiding the
inheritance hierarchy TC_LOG_queued->TC_LOG_unordered.

Put the wakeup facility for commit_ordered() calls into the THD class.

Some renaming to get better names.

sql/log.cc

@@ -5778,43 +5778,12 @@ TC_LOG_queued::reverse_queue(TC_LOG_queued::TC_group_commit_entry *queue)
   return prev;
 }
 
-void
-TC_LOG_queued::group_commit_wait_for_wakeup(TC_group_commit_entry *entry)
-{
-  THD *thd= entry->thd;
-  pthread_mutex_lock(&thd->LOCK_commit_ordered);
-  while (!entry->group_commit_ready)
-    pthread_cond_wait(&thd->COND_commit_ordered,
-                      &thd->LOCK_commit_ordered);
-  pthread_mutex_unlock(&thd->LOCK_commit_ordered);
-}
-
-void
-TC_LOG_queued::group_commit_wakeup_other(TC_group_commit_entry *other)
-{
-  THD *thd= other->thd;
-  pthread_mutex_lock(&thd->LOCK_commit_ordered);
-  other->group_commit_ready= TRUE;
-  pthread_cond_signal(&thd->COND_commit_ordered);
-  pthread_mutex_unlock(&thd->LOCK_commit_ordered);
-}
-
-TC_LOG_unordered::TC_LOG_unordered() : group_commit_queue_busy(0)
-{
-  pthread_cond_init(&COND_queue_busy, 0);
-}
-
-TC_LOG_unordered::~TC_LOG_unordered()
-{
-  pthread_cond_destroy(&COND_queue_busy);
-}
-
-int TC_LOG_unordered::log_and_order(THD *thd, my_xid xid, bool all,
-                                    bool need_prepare_ordered,
-                                    bool need_commit_ordered)
+int TC_LOG_MMAP::log_and_order(THD *thd, my_xid xid, bool all,
+                               bool need_prepare_ordered,
+                               bool need_commit_ordered)
 {
   int cookie;
-  struct TC_group_commit_entry entry;
+  struct commit_entry entry;
   bool is_group_commit_leader;
   LINT_INIT(is_group_commit_leader);
 
@@ -5828,18 +5797,18 @@ int TC_LOG_unordered::log_and_order(THD *thd, my_xid xid, bool all,
         Must put us in queue so we can run_commit_ordered() in same sequence
         as we did run_prepare_ordered().
       */
+      thd->clear_wakeup_ready();
       entry.thd= thd;
-      entry.group_commit_ready= false;
-      TC_group_commit_entry *previous_queue= group_commit_queue;
+      commit_entry *previous_queue= commit_ordered_queue;
       entry.next= previous_queue;
-      group_commit_queue= &entry;
+      commit_ordered_queue= &entry;
       is_group_commit_leader= (previous_queue == NULL);
     }
     pthread_mutex_unlock(&LOCK_prepare_ordered);
   }
 
   if (xid)
-    cookie= log_xid(thd, xid);
+    cookie= log_one_transaction(xid);
   else
     cookie= 0;
 
@@ -5859,24 +5828,32 @@ int TC_LOG_unordered::log_and_order(THD *thd, my_xid xid, bool all,
       {
         /* The first in queue starts the ball rolling. */
         pthread_mutex_lock(&LOCK_prepare_ordered);
-        while (group_commit_queue_busy)
+        while (commit_ordered_queue_busy)
           pthread_cond_wait(&COND_queue_busy, &LOCK_prepare_ordered);
-        TC_group_commit_entry *queue= group_commit_queue;
-        group_commit_queue= NULL;
+        commit_entry *queue= commit_ordered_queue;
+        commit_ordered_queue= NULL;
         /*
           Mark the queue busy while we bounce it from one thread to the
           next.
         */
-        group_commit_queue_busy= TRUE;
+        commit_ordered_queue_busy= true;
         pthread_mutex_unlock(&LOCK_prepare_ordered);
 
-        queue= reverse_queue(queue);
-        DBUG_ASSERT(queue == &entry && queue->thd == thd);
+        /* Reverse the queue list so we get correct order. */
+        commit_entry *prev= NULL;
+        while (queue)
+        {
+          commit_entry *next= queue->next;
+          queue->next= prev;
+          prev= queue;
+          queue= next;
+        }
+        DBUG_ASSERT(prev == &entry && prev->thd == thd);
       }
       else
       {
         /* Not first in queue; just wait until previous thread wakes us up. */
-        group_commit_wait_for_wakeup(&entry);
+        thd->wait_for_wakeup_ready();
       }
     }
 
@@ -5890,15 +5867,15 @@ int TC_LOG_unordered::log_and_order(THD *thd, my_xid xid, bool all,
 
     if (need_prepare_ordered)
     {
-      TC_group_commit_entry *next= entry.next;
+      commit_entry *next= entry.next;
       if (next)
       {
-        group_commit_wakeup_other(next);
+        next->thd->signal_wakeup_ready();
       }
       else
       {
         pthread_mutex_lock(&LOCK_prepare_ordered);
-        group_commit_queue_busy= FALSE;
+        commit_ordered_queue_busy= false;
         pthread_cond_signal(&COND_queue_busy);
         pthread_mutex_unlock(&LOCK_prepare_ordered);
       }
@@ -5940,9 +5917,9 @@ int TC_LOG_group_commit::log_and_order(THD *thd, my_xid xid, bool all,
   struct TC_group_commit_entry entry;
   bool is_group_commit_leader;
 
+  thd->clear_wakeup_ready();
   entry.thd= thd;
   entry.all= all;
-  entry.group_commit_ready= false;
   entry.xid_error= 0;
 
   pthread_mutex_lock(&LOCK_prepare_ordered);
@@ -6019,7 +5996,7 @@ int TC_LOG_group_commit::log_and_order(THD *thd, my_xid xid, bool all,
       */
       TC_group_commit_entry *next= current->next;
       if (current != &entry)                    // Don't wake up ourself
-        group_commit_wakeup_other(current);
+        current->thd->signal_wakeup_ready();
       current= next;
     } while (current != NULL);
     DEBUG_SYNC(thd, "commit_after_group_run_commit_ordered");
@@ -6029,7 +6006,7 @@ int TC_LOG_group_commit::log_and_order(THD *thd, my_xid xid, bool all,
   else
   {
     /* If not leader, just wait until leader wakes us up. */
-    group_commit_wait_for_wakeup(&entry);
+    thd->wait_for_wakeup_ready();
   }
 
   /*
@@ -6181,6 +6158,7 @@ int TC_LOG_MMAP::open(const char *opt_name)
   pthread_mutex_init(&LOCK_pool,    MY_MUTEX_INIT_FAST);
   pthread_cond_init(&COND_active, 0);
   pthread_cond_init(&COND_pool, 0);
+  pthread_cond_init(&COND_queue_busy, 0);
 
   inited=6;
 
@@ -6188,6 +6166,8 @@ int TC_LOG_MMAP::open(const char *opt_name)
   active=pages;
   pool=pages+1;
   pool_last=pages+npages-1;
+  commit_ordered_queue= NULL;
+  commit_ordered_queue_busy= false;
 
   return 0;
 
@@ -6293,7 +6273,7 @@ int TC_LOG_MMAP::overflow()
     to the position in memory where xid was logged to.
 */
 
-int TC_LOG_MMAP::log_xid(THD *thd, my_xid xid)
+int TC_LOG_MMAP::log_one_transaction(my_xid xid)
 {
   int err;
   PAGE *p;
@@ -6462,6 +6442,8 @@ void TC_LOG_MMAP::close()
     pthread_mutex_destroy(&LOCK_active);
     pthread_mutex_destroy(&LOCK_pool);
     pthread_cond_destroy(&COND_pool);
+    pthread_cond_destroy(&COND_active);
+    pthread_cond_destroy(&COND_queue_busy);
   case 5:
     data[0]='A'; // garble the first (signature) byte, in case my_delete fails
   case 4:

sql/log.h

@@ -91,11 +91,6 @@ protected:
     THD *thd;
     /* This is the `all' parameter for ha_commit_trans() etc. */
     bool all;
-    /*
-      Flag set true when it is time for this thread to wake up after group
-      commit. Used with THD::LOCK_commit_ordered and THD::COND_commit_ordered.
-    */
-    bool group_commit_ready;
     /*
       Set by TC_LOG_group_commit::group_log_xid(), to return per-thd error and
       cookie.
@@ -105,9 +100,6 @@ protected:
 
   TC_group_commit_entry * reverse_queue(TC_group_commit_entry *queue);
 
-  void group_commit_wait_for_wakeup(TC_group_commit_entry *entry);
-  void group_commit_wakeup_other(TC_group_commit_entry *other);
-
   /*
     This is a queue of threads waiting for being allowed to commit.
     Access to the queue must be protected by LOCK_prepare_ordered.
@@ -115,36 +107,6 @@ protected:
   TC_group_commit_entry *group_commit_queue;
 };
 
-class TC_LOG_unordered: public TC_LOG_queued
-{
-public:
-  TC_LOG_unordered();
-  ~TC_LOG_unordered();
-
-  int log_and_order(THD *thd, my_xid xid, bool all,
-                    bool need_prepare_ordered, bool need_commit_ordered);
-
-protected:
-  virtual int log_xid(THD *thd, my_xid xid)=0;
-
-private:
-  /*
-    This flag and condition is used to reserve the queue while threads in it
-    each run the commit_ordered() methods one after the other. Only once the
-    last commit_ordered() in the queue is done can we start on a new queue
-    run.
-
-    Since we start this process in the first thread in the queue and finish in
-    the last (and possibly different) thread, we need a condition variable for
-    this (we cannot unlock a mutex in a different thread than the one who
-    locked it).
-
-    The condition is used together with the LOCK_prepare_ordered mutex.
-  */
-  my_bool group_commit_queue_busy;
-  pthread_cond_t COND_queue_busy;
-};
-
 class TC_LOG_group_commit: public TC_LOG_queued
 {
 public:
@@ -206,18 +168,28 @@ private:
   pthread_mutex_t LOCK_group_commit;
 };
 
-class TC_LOG_DUMMY: public TC_LOG_unordered // use it to disable the logging
+class TC_LOG_DUMMY: public TC_LOG // use it to disable the logging
 {
 public:
   TC_LOG_DUMMY() {}
   int open(const char *opt_name)        { return 0; }
   void close()                          { }
-  int log_xid(THD *thd, my_xid xid)         { return 1; }
+  /*
+    TC_LOG_DUMMY is only used when there are <= 1 XA-capable engines, and we
+    only use internal XA during commit when >= 2 XA-capable engines
+    participate.
+  */
+  int log_and_order(THD *thd, my_xid xid, bool all,
+                    bool need_prepare_ordered, bool need_commit_ordered)
+  {
+    DBUG_ASSERT(0 /* Internal error - TC_LOG_DUMMY::log_and_order() called */);
+    return 1;
+  }
   void unlog(ulong cookie, my_xid xid)  { }
 };
 
 #ifdef HAVE_MMAP
-class TC_LOG_MMAP: public TC_LOG_unordered
+class TC_LOG_MMAP: public TC_LOG
 {
   public:                // only to keep Sun Forte on sol9x86 happy
   typedef enum {
@@ -238,6 +210,13 @@ class TC_LOG_MMAP: public TC_LOG_unordered
     pthread_cond_t  cond; // to wait for a sync
   } PAGE;
 
+  /* List of THDs for which to invoke commit_ordered(), in order. */
+  struct commit_entry
+  {
+    struct commit_entry *next;
+    THD *thd;
+  };
+
   char logname[FN_REFLEN];
   File fd;
   my_off_t file_length;
@@ -252,16 +231,38 @@ class TC_LOG_MMAP: public TC_LOG_unordered
   */
   pthread_mutex_t LOCK_active, LOCK_pool, LOCK_sync;
   pthread_cond_t COND_pool, COND_active;
+  /*
+    Queue of threads that need to call commit_ordered().
+    Access to this queue must be protected by LOCK_prepare_ordered.
+  */
+  commit_entry *commit_ordered_queue;
+  /*
+    This flag and condition is used to reserve the queue while threads in it
+    each run the commit_ordered() methods one after the other. Only once the
+    last commit_ordered() in the queue is done can we start on a new queue
+    run.
+
+    Since we start this process in the first thread in the queue and finish in
+    the last (and possibly different) thread, we need a condition variable for
+    this (we cannot unlock a mutex in a different thread than the one who
+    locked it).
+
+    The condition is used together with the LOCK_prepare_ordered mutex.
+  */
+  my_bool commit_ordered_queue_busy;
+  pthread_cond_t COND_queue_busy;
 
   public:
   TC_LOG_MMAP(): inited(0) {}
   int open(const char *opt_name);
   void close();
-  int log_xid(THD *thd, my_xid xid);
+  int log_and_order(THD *thd, my_xid xid, bool all,
+                    bool need_prepare_ordered, bool need_commit_ordered);
   void unlog(ulong cookie, my_xid xid);
   int recover();
 
   private:
+  int log_one_transaction(my_xid xid);
   void get_active_from_pool();
   int sync();
   int overflow();

sql/sql_class.cc

@@ -704,8 +704,8 @@ THD::THD()
   active_vio = 0;
 #endif
   pthread_mutex_init(&LOCK_thd_data, MY_MUTEX_INIT_FAST);
-  pthread_mutex_init(&LOCK_commit_ordered, MY_MUTEX_INIT_FAST);
-  pthread_cond_init(&COND_commit_ordered, 0);
+  pthread_mutex_init(&LOCK_wakeup_ready, MY_MUTEX_INIT_FAST);
+  pthread_cond_init(&COND_wakeup_ready, 0);
 
   /* Variables with default values */
   proc_info="login";
@@ -1037,8 +1037,8 @@ THD::~THD()
   free_root(&transaction.mem_root,MYF(0));
 #endif
   mysys_var=0;					// Safety (shouldn't be needed)
-  pthread_cond_destroy(&COND_commit_ordered);
-  pthread_mutex_destroy(&LOCK_commit_ordered);
+  pthread_cond_destroy(&COND_wakeup_ready);
+  pthread_mutex_destroy(&LOCK_wakeup_ready);
   pthread_mutex_destroy(&LOCK_thd_data);
 #ifndef DBUG_OFF
   dbug_sentry= THD_SENTRY_GONE;
@@ -4009,6 +4009,25 @@ int THD::binlog_query(THD::enum_binlog_query_type qtype, char const *query_arg,
   DBUG_RETURN(0);
 }
 
+void
+THD::wait_for_wakeup_ready()
+{
+  pthread_mutex_lock(&LOCK_wakeup_ready);
+  while (!wakeup_ready)
+    pthread_cond_wait(&COND_wakeup_ready, &LOCK_wakeup_ready);
+  pthread_mutex_unlock(&LOCK_wakeup_ready);
+}
+
+void
+THD::signal_wakeup_ready()
+{
+  pthread_mutex_lock(&LOCK_wakeup_ready);
+  wakeup_ready= true;
+  pthread_cond_signal(&COND_wakeup_ready);
+  pthread_mutex_unlock(&LOCK_wakeup_ready);
+}
+
+
 bool Discrete_intervals_list::append(ulonglong start, ulonglong val,
                                  ulonglong incr)
 {

sql/sql_class.h

@@ -1447,10 +1447,6 @@ public:
   /* container for handler's private per-connection data */
   Ha_data ha_data[MAX_HA];
 
-  /* Mutex and condition for waking up threads after group commit. */
-  pthread_mutex_t LOCK_commit_ordered;
-  pthread_cond_t COND_commit_ordered;
-
 #ifndef MYSQL_CLIENT
   int binlog_setup_trx_data();
 
@@ -2380,6 +2376,14 @@ public:
   LEX_STRING get_invoker_user() { return invoker_user; }
   LEX_STRING get_invoker_host() { return invoker_host; }
   bool has_invoker() { return invoker_user.length > 0; }
+  void clear_wakeup_ready() { wakeup_ready= false; }
+  /*
+    Sleep waiting for others to wake us up with signal_wakeup_ready().
+    Must call clear_wakeup_ready() before waiting.
+  */
+  void wait_for_wakeup_ready();
+  /* Wake this thread up from wait_for_wakeup_ready(). */
+  void signal_wakeup_ready();
 private:
   /** The current internal error handler for this thread, or NULL. */
   Internal_error_handler *m_internal_handler;
@@ -2418,6 +2422,16 @@ private:
    */
   LEX_STRING invoker_user;
   LEX_STRING invoker_host;
+  /*
+    Flag, mutex and condition for a thread to wait for a signal from another
+    thread.
+
+    Currently used to wait for group commit to complete, can also be used for
+    other purposes.
+  */
+  bool wakeup_ready;
+  pthread_mutex_t LOCK_wakeup_ready;
+  pthread_cond_t COND_wakeup_ready;
 };