[pypy-commit] pypy stm-gc: A quick try to see the cost associated with locking this mutex:

[arigo]

Author: Armin Rigo <arigo at tunes.org>
Branch: stm-gc
Changeset: r52680:b104b62668bd
Date: 2012-02-20 18:19 +0100
http://bitbucket.org/pypy/pypy/changeset/b104b62668bd/

Log:	A quick try to see the cost associated with locking this mutex: add
	a fast-path if pending.run() adds exactly one new transaction.

diff --git a/pypy/module/transaction/fifo.py b/pypy/module/transaction/fifo.py
--- a/pypy/module/transaction/fifo.py
+++ b/pypy/module/transaction/fifo.py
@@ -16,6 +16,9 @@
         assert (self.first is None) == (self.last is None)
         return self.first is None
 
+    def is_of_length_1(self):
+        return self.first is not None and self.first is self.last
+
     def popleft(self):
         item = self.first
         self.first = item.next
diff --git a/pypy/module/transaction/interp_transaction.py b/pypy/module/transaction/interp_transaction.py
--- a/pypy/module/transaction/interp_transaction.py
+++ b/pypy/module/transaction/interp_transaction.py
@@ -247,7 +247,15 @@
             if state.pending.is_empty():
                 state.lock_no_tasks_pending()
             state.unlock()
-            pending.run()
+            #
+            while True:
+                pending.run()
+                # for now, always break out of this loop, unless
+                # 'my_transactions_pending' contains precisely one item
+                if not my_transactions_pending.is_of_length_1():
+                    break
+                pending = my_transactions_pending.popleft()
+            #
             state.lock()
             _add_list(my_transactions_pending)
     #