From: Arnaud Giersch <arnaud.giersch@iut-bm.univ-fcomte.fr>
Date: Wed, 8 Feb 2012 16:03:36 +0000 (+0100)
Subject: Fix a race condition in _XBT_LOG_ISENABLEDV().
X-Git-Tag: exp_20120216~42^2
X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/commitdiff_plain/599c51d596d1b8cec905af3e219023cf3bd51417

Fix a race condition in _XBT_LOG_ISENABLEDV().

Without this change, catv.threshold can be initialized by another
thread, between the test for priority being great enough, and
that for catv.threshold being initialized, leading to a false
positive answer.

Hypothesis
==========
  Initially, catv.threshold == xbt_log_priority_unititialized == -1
  After initialization, priority < catv.threshold
  Two threads running _XBT_LOG_ISENABLEDV() for the same
  category, and the same priority.

Thread A                                Thread B
========                                ========

                                        priority >= cat.threshold
                                          is TRUE
priority >= catv.threshold
  is TRUE

catv.threshold != x.l.p._uninitialized
  is FALSE

call xbt_log_cat_init(...)
  returns FALSE
                                        catv.threshold != x.l.p._uninitialized
                                          is TRUE

=> _XBT_LOG_ISENABLEDV(...)             => _XBT_LOG_ISENABLEDV(...)
     is FALSE                                is TRUE
---

diff --git a/include/xbt/log.h b/include/xbt/log.h
index 5df2d0777f..ad7e612225 100644
--- a/include/xbt/log.h
+++ b/include/xbt/log.h
@@ -365,9 +365,9 @@ extern xbt_log_layout_t xbt_log_default_layout;
  */
 #define _XBT_LOG_ISENABLEDV(catv, priority)                  \
        (priority >= XBT_LOG_STATIC_THRESHOLD                 \
-        && priority >= catv.threshold                         \
         && (catv.threshold != xbt_log_priority_uninitialized \
-            || _xbt_log_cat_init(&catv, priority)) )
+            || _xbt_log_cat_init(&catv, priority))           \
+        && priority >= catv.threshold)
 
 /*
  * Internal Macros