| /* |
| * Copyright (c) 2001, 2015, 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 |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| #ifndef SHARE_VM_GC_CMS_FREECHUNK_HPP |
| #define SHARE_VM_GC_CMS_FREECHUNK_HPP |
| |
| #include "memory/allocation.hpp" |
| #include "memory/memRegion.hpp" |
| #include "oops/markOop.hpp" |
| #include "runtime/mutex.hpp" |
| #include "runtime/orderAccess.hpp" |
| #include "utilities/debug.hpp" |
| #include "utilities/globalDefinitions.hpp" |
| #include "utilities/ostream.hpp" |
| |
| // |
| // Free block maintenance for Concurrent Mark Sweep Generation |
| // |
| // The main data structure for free blocks are |
| // . an indexed array of small free blocks, and |
| // . a dictionary of large free blocks |
| // |
| |
| // No virtuals in FreeChunk (don't want any vtables). |
| |
| // A FreeChunk is merely a chunk that can be in a doubly linked list |
| // and has a size field. NOTE: FreeChunks are distinguished from allocated |
| // objects in two ways (by the sweeper), depending on whether the VM is 32 or |
| // 64 bits. |
| // In 32 bits or 64 bits without CompressedOops, the second word (prev) has the |
| // LSB set to indicate a free chunk; allocated objects' klass() pointers |
| // don't have their LSB set. The corresponding bit in the CMSBitMap is |
| // set when the chunk is allocated. There are also blocks that "look free" |
| // but are not part of the free list and should not be coalesced into larger |
| // free blocks. These free blocks have their two LSB's set. |
| |
| class FreeChunk VALUE_OBJ_CLASS_SPEC { |
| friend class VMStructs; |
| // For 64 bit compressed oops, the markOop encodes both the size and the |
| // indication that this is a FreeChunk and not an object. |
| volatile size_t _size; |
| FreeChunk* _prev; |
| FreeChunk* _next; |
| |
| markOop mark() const volatile { return (markOop)_size; } |
| void set_mark(markOop m) { _size = (size_t)m; } |
| |
| public: |
| NOT_PRODUCT(static const size_t header_size();) |
| |
| // Returns "true" if the address indicates that the block represents |
| // a free chunk. |
| static bool indicatesFreeChunk(const HeapWord* addr) { |
| // Force volatile read from addr because value might change between |
| // calls. We really want the read of _mark and _prev from this pointer |
| // to be volatile but making the fields volatile causes all sorts of |
| // compilation errors. |
| return ((volatile FreeChunk*)addr)->is_free(); |
| } |
| |
| bool is_free() const volatile { |
| LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else) |
| return (((intptr_t)_prev) & 0x1) == 0x1; |
| } |
| bool cantCoalesce() const { |
| assert(is_free(), "can't get coalesce bit on not free"); |
| return (((intptr_t)_prev) & 0x2) == 0x2; |
| } |
| void dontCoalesce() { |
| // the block should be free |
| assert(is_free(), "Should look like a free block"); |
| _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2); |
| } |
| FreeChunk* prev() const { |
| return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); |
| } |
| |
| debug_only(void* prev_addr() const { return (void*)&_prev; }) |
| debug_only(void* next_addr() const { return (void*)&_next; }) |
| debug_only(void* size_addr() const { return (void*)&_size; }) |
| |
| size_t size() const volatile { |
| LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else ) |
| return _size; |
| } |
| void set_size(size_t sz) { |
| LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else ) |
| _size = sz; |
| } |
| |
| FreeChunk* next() const { return _next; } |
| |
| void link_after(FreeChunk* ptr) { |
| link_next(ptr); |
| if (ptr != NULL) ptr->link_prev(this); |
| } |
| void link_next(FreeChunk* ptr) { _next = ptr; } |
| void link_prev(FreeChunk* ptr) { |
| LP64_ONLY(if (UseCompressedOops) _prev = ptr; else) |
| _prev = (FreeChunk*)((intptr_t)ptr | 0x1); |
| } |
| void clear_next() { _next = NULL; } |
| void markNotFree() { |
| // Set _prev (klass) to null before (if) clearing the mark word below |
| _prev = NULL; |
| #ifdef _LP64 |
| if (UseCompressedOops) { |
| OrderAccess::storestore(); |
| set_mark(markOopDesc::prototype()); |
| } |
| #endif |
| assert(!is_free(), "Error"); |
| } |
| |
| // Return the address past the end of this chunk |
| uintptr_t* end() const { return ((uintptr_t*) this) + size(); } |
| |
| // debugging |
| void verify() const PRODUCT_RETURN; |
| void verifyList() const PRODUCT_RETURN; |
| void mangleAllocated(size_t size) PRODUCT_RETURN; |
| void mangleFreed(size_t size) PRODUCT_RETURN; |
| |
| void print_on(outputStream* st); |
| }; |
| |
| extern size_t MinChunkSize; |
| |
| |
| #endif // SHARE_VM_GC_CMS_FREECHUNK_HPP |