Author: Armin Rigo <[email protected]>
Branch:
Changeset: r1080:9b94866e95da
Date: 2014-03-20 08:27 +0100
http://bitbucket.org/pypy/stmgc/changeset/9b94866e95da/
Log: This contention management policy is much better. Document the
problem with the previous one.
diff --git a/c7/stm/contention.c b/c7/stm/contention.c
--- a/c7/stm/contention.c
+++ b/c7/stm/contention.c
@@ -69,6 +69,14 @@
__attribute__((unused))
static void cm_always_wait_for_other_thread(struct contmgr_s *cm)
{
+ /* we tried this contention management, but it seems to have
+ very bad cases: if thread 1 always reads an object in every
+ transaction, and thread 2 wants to write this object just
+ once, then thread 2 will pause when it tries to commit;
+ it will wait until thread 1 committed; but by the time
+ thread 2 resumes again, thread 1 has already started the
+ next transaction and read the object again.
+ */
cm_abort_the_younger(cm);
cm->try_sleep = true;
}
@@ -110,7 +118,7 @@
#ifdef STM_TESTS
cm_abort_the_younger(&contmgr);
#else
- cm_always_wait_for_other_thread(&contmgr);
+ cm_pause_if_younger(&contmgr);
#endif
/* Fix the choices that are found incorrect due to TS_INEVITABLE
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