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March 2009

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Code review request: 6810698: G1: _expanded flag on sparse RSets not cleared correctly (XXXS)
by Tony Printezis 02 Mar '09

02 Mar '09

From the CR blurb: Each sparse RSet has two tables: cur and next. At the beginning, both tables are the same (i.e., the two references _cur and _next point to the same table). When a sparse table needs to be expanded during a GC, the flag _expanded on the table is set, a new table is created (pointed to by _next) and the RSet is added to the expanded list. After the collection (in fact, at the beginning of the next collection), we iterate over the expanded list, we get rid of the _cur tables, and set _cur to point to _next (so the _next table basically replaces the _cur table). Unfortunately, at that time, the _expanded flag is not reset. So, if the sparse table is expanded again, it is not added to the expanded list (that operation is conditional on !_expanded, so that the table is not added twice during the same GC). As a result, some of the sparse tables are left in an inconsistent state, which causes some entries not to be scanned correctly during a GC. http://cr.openjdk.java.net/~tonyp/6810698/webrev.00/ (one line change!!!) Tony -- ---------------------------------------------------------------------- | Tony Printezis, Staff Engineer | Sun Microsystems Inc. | | | MS BUR02-311 | | e-mail: tony.printezis(a)sun.com | 35 Network Drive | | office: +1 781 442 0998 (x20998) | Burlington, MA01803-0902, USA | ---------------------------------------------------------------------- e-mail client: Thunderbird (Solaris)

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