libitm: Improve method reinit and choice.

libitm/
	* dispatch.h (GTM::abi_dispatch::supports): New.
	(GTM::method_group::reinit): New.
	* retry.cc (GTM::gtm_thread::decide_retry_strategy): Use reinit().
	(GTM::gtm_thread::number_of_threads_changed): Check that the method
	supports the current situation.

From-SVN: r184211

libitm/ChangeLog

@@ -1,3 +1,11 @@
+2012-02-14  Torvald Riegel  <triegel@redhat.com>
+
+	* dispatch.h (GTM::abi_dispatch::supports): New.
+	(GTM::method_group::reinit): New.
+	* retry.cc (GTM::gtm_thread::decide_retry_strategy): Use reinit().
+	(GTM::gtm_thread::number_of_threads_changed): Check that the method
+	supports the current situation.
+
 2012-02-14  Torvald Riegel  <triegel@redhat.com>
 
 	* util.cc (GTM::xcalloc): New.

libitm/dispatch.h

@@ -245,6 +245,12 @@ struct method_group
   // Stop using any method from this group for now. This can be used to
   // destruct meta data as soon as this method group is not used anymore.
   virtual void fini() = 0;
+  // This can be overriden to implement more light-weight re-initialization.
+  virtual void reinit()
+  {
+    fini();
+    init();
+  }
 };
 
 
@@ -290,6 +296,10 @@ public:
   // method on begin of a nested transaction without committing or restarting
   // the parent method.
   virtual abi_dispatch* closed_nesting_alternative() { return 0; }
+  // Returns true iff this method group supports the current situation.
+  // NUMBER_OF_THREADS is the current number of threads that might execute
+  // transactions.
+  virtual bool supports(unsigned number_of_threads) { return true; }
 
   bool read_only () const { return m_read_only; }
   bool write_through() const { return m_write_through; }

libitm/retry.cc

@@ -58,11 +58,8 @@ GTM::gtm_thread::decide_retry_strategy (gtm_restart_reason r)
 	  serial_lock.read_unlock(this);
 	  serial_lock.write_lock();
 	  if (disp->get_method_group() == default_dispatch->get_method_group())
-	    {
+	    // Still the same method group.
-	      // Still the same method group.
+	    disp->get_method_group()->reinit();
-	      disp->get_method_group()->fini();
-	      disp->get_method_group()->init();
-	    }
 	  serial_lock.write_unlock();
 	  serial_lock.read_lock(this);
 	  if (disp->get_method_group() != default_dispatch->get_method_group())
@@ -72,11 +69,8 @@ GTM::gtm_thread::decide_retry_strategy (gtm_restart_reason r)
 	    }
 	}
       else
-	{
+	// We are a serial transaction already, which makes things simple.
-	  // We are a serial transaction already, which makes things simple.
+	disp->get_method_group()->reinit();
-	  disp->get_method_group()->fini();
-	  disp->get_method_group()->init();
-	}
     }
 
   bool retry_irr = (r == RESTART_SERIAL_IRR);
@@ -249,7 +243,7 @@ GTM::gtm_thread::number_of_threads_changed(unsigned previous, unsigned now)
       // Only one thread, so use a serializing method.
       // ??? If we don't have a fast serial mode implementation, it might be
       // better to use the global lock method set here.
-      if (default_dispatch_user)
+      if (default_dispatch_user && default_dispatch_user->supports(now))
 	set_default_dispatch(default_dispatch_user);
       else
 	set_default_dispatch(dispatch_serialirr());
@@ -257,9 +251,16 @@ GTM::gtm_thread::number_of_threads_changed(unsigned previous, unsigned now)
   else if (now > 1 && previous <= 1)
     {
       // More than one thread, use the default method.
-      if (default_dispatch_user)
+      if (default_dispatch_user && default_dispatch_user->supports(now))
 	set_default_dispatch(default_dispatch_user);
       else
-	set_default_dispatch(dispatch_serialirr_onwrite());
+	{
+	  abi_dispatch* a = dispatch_serialirr_onwrite();
+	  if (a->supports(now))
+	    set_default_dispatch(a);
+	  else
+	    // Serial-irrevocable mode always works.
+	    set_default_dispatch(dispatch_serialirr());
+	}
     }
 }