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[Help-smalltalk] [PATCH] Fix ephemeron bug

From: Paolo Bonzini
Subject: [Help-smalltalk] [PATCH] Fix ephemeron bug
Date: Wed, 14 May 2008 11:21:30 +0200
User-agent: Thunderbird (Macintosh/20080421)

Ephemeron objects are treated specially in that the objects that are only reachable from them are marked later in the GC. This however does not apply to the class object. For this reason: 1) all ephemerons are added to a buffer for later processing; 2) tail recursion is used to mark the class object.

However, the case of tail recursion is very rare because it happens only if the ephemeron class has not already been marked before -- and all classes usually are marked very early when the Smalltalk dictionary is marked. It is so rare that it was buggy. :-) In the latest master, the bug was triggered by loading the ANSI testsuite. Luckily, it's trivial to fix and the only struggling was to find that the bug was caused by an ephemeron not in the buffer.

Committed to master and stable-3.0.

diff --git a/libgst/ChangeLog b/libgst/ChangeLog
index 7bfab36..ff87720 100644
--- a/libgst/ChangeLog
+++ b/libgst/ChangeLog
@@ -1,3 +1,9 @@
+2008-05-14  Paolo Bonzini  <address@hidden>
+       * libgst/oop.c: Add ephemerons to buffer before marking their class
+       (else, if the class actually has to be marked, we won't add them to the
+       buffer at all).
 2008-05-13  Paolo Bonzini  <address@hidden>
        * libgst/callin.h: Add _gst_oop_indexed_base and _gst_oop_indexed_kind.
diff --git a/libgst/oop.c b/libgst/oop.c
index 3eb1fb7..96c57cf 100644
--- a/libgst/oop.c
+++ b/libgst/oop.c
@@ -2197,14 +2197,14 @@ _gst_mark_an_oop_internal (OOP oop,
          else if UNCOMMON (oop->flags & (F_EPHEMERON | F_WEAK))
+             if (oop->flags & F_EPHEMERON)
+               _gst_add_buf_pointer (oop);
              /* In general, there will be many instances of a class,
                 but only the first time will it be unmarked.  So I'm
                 marking this as uncommon.  */
              if UNCOMMON (!IS_OOP_MARKED (objClass))
                TAIL_MARK_OOP (objClass);
-             if (oop->flags & F_EPHEMERON)
-               _gst_add_buf_pointer (oop);

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