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6948538: CMS: BOT walkers can fall into object allocation and initialization cracks

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GC workers now recognize an intermediate transient state of blocks which are allocated but have not yet completed initialization. blk_start() calls do not attempt to determine the size of a block in the transient state, rather waiting for the block to become initialized so that it is safe to query its size. Audited and ensured the order of initialization of object fields (klass, free bit and size) to respect block state transition protocol. Also included some new assertion checking code enabled in debug mode.

Reviewed-by: chrisphi, johnc, poonam
This commit is contained in:
Y. Srinivas Ramakrishna 2010-08-16 15:58:42 -07:00
parent becf7cffb3
commit 77f845359a
12 changed files with 318 additions and 123 deletions
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14
hotspot/src/share/vm/memory/blockOffsetTable.inline.hpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2000, 2002, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -55,10 +55,22 @@ inline HeapWord* BlockOffsetSharedArray::address_for_index(size_t index) const {
return result;
}
inline void BlockOffsetSharedArray::check_reducing_assertion(bool reducing) {
assert(reducing || !SafepointSynchronize::is_at_safepoint() || init_to_zero() ||
Thread::current()->is_VM_thread() ||
Thread::current()->is_ConcurrentGC_thread() ||
((!Thread::current()->is_ConcurrentGC_thread()) &&
ParGCRareEvent_lock->owned_by_self()), "Crack");
}
//////////////////////////////////////////////////////////////////////////
// BlockOffsetArrayNonContigSpace inlines
//////////////////////////////////////////////////////////////////////////
inline void BlockOffsetArrayNonContigSpace::freed(HeapWord* blk,
size_t size) {
freed(blk, blk + size);
}
inline void BlockOffsetArrayNonContigSpace::freed(HeapWord* blk_start,
HeapWord* blk_end) {
// Verify that the BOT shows [blk_start, blk_end) to be one block.