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hotspot/src/share/vm/gc_implementation/parallelScavenge/objectStartArray.hpp

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+/*
+ * Copyright 2001-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+//
+// This class can be used to locate the beginning of an object in the
+// covered region.
+//
+
+class ObjectStartArray : public CHeapObj {
+ friend class VerifyObjectStartArrayClosure;
+
+ private:
+  PSVirtualSpace  _virtual_space;
+  MemRegion       _reserved_region;
+  MemRegion       _covered_region;
+  MemRegion       _blocks_region;
+  jbyte*          _raw_base;
+  jbyte*          _offset_base;
+
+ public:
+
+  enum BlockValueConstants {
+    clean_block                  = -1
+  };
+
+  enum BlockSizeConstants {
+    block_shift                  = 9,
+    block_size                   = 1 << block_shift,
+    block_size_in_words          = block_size / sizeof(HeapWord)
+  };
+
+ protected:
+
+  // Mapping from address to object start array entry
+  jbyte* block_for_addr(void* p) const {
+    assert(_covered_region.contains(p),
+           "out of bounds access to object start array");
+    jbyte* result = &_offset_base[uintptr_t(p) >> block_shift];
+    assert(_blocks_region.contains(result),
+           "out of bounds result in byte_for");
+    return result;
+  }
+
+  // Mapping from object start array entry to address of first word
+  HeapWord* addr_for_block(jbyte* p) {
+    assert(_blocks_region.contains(p),
+           "out of bounds access to object start array");
+    size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
+    HeapWord* result = (HeapWord*) (delta << block_shift);
+    assert(_covered_region.contains(result),
+           "out of bounds accessor from card marking array");
+    return result;
+  }
+
+  // Mapping that includes the derived offset.
+  // If the block is clean, returns the last address in the covered region.
+  // If the block is < index 0, returns the start of the covered region.
+  HeapWord* offset_addr_for_block (jbyte* p) const {
+    // We have to do this before the assert
+    if (p < _raw_base) {
+      return _covered_region.start();
+    }
+
+    assert(_blocks_region.contains(p),
+           "out of bounds access to object start array");
+
+    if (*p == clean_block) {
+      return _covered_region.end();
+    }
+
+    size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
+    HeapWord* result = (HeapWord*) (delta << block_shift);
+    result += *p;
+
+    assert(_covered_region.contains(result),
+           "out of bounds accessor from card marking array");
+
+    return result;
+  }
+
+ public:
+
+  // This method is in lieu of a constructor, so that this class can be
+  // embedded inline in other classes.
+  void initialize(MemRegion reserved_region);
+
+  void set_covered_region(MemRegion mr);
+
+  void reset();
+
+  MemRegion covered_region() { return _covered_region; }
+
+  void allocate_block(HeapWord* p) {
+    assert(_covered_region.contains(p), "Must be in covered region");
+    jbyte* block = block_for_addr(p);
+    HeapWord* block_base = addr_for_block(block);
+    size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*));
+    assert(offset < 128, "Sanity");
+    // When doing MT offsets, we can't assert this.
+    //assert(offset > *block, "Found backwards allocation");
+    *block = (jbyte)offset;
+
+    // tty->print_cr("[%p]", p);
+  }
+
+  // Optimized for finding the first object that crosses into
+  // a given block. The blocks contain the offset of the last
+  // object in that block. Scroll backwards by one, and the first
+  // object hit should be at the begining of the block
+  HeapWord* object_start(HeapWord* addr) const {
+    assert(_covered_region.contains(addr), "Must be in covered region");
+    jbyte* block = block_for_addr(addr);
+    HeapWord* scroll_forward = offset_addr_for_block(block--);
+    while (scroll_forward > addr) {
+      scroll_forward = offset_addr_for_block(block--);
+    }
+
+    HeapWord* next = scroll_forward;
+    while (next <= addr) {
+      scroll_forward = next;
+      next += oop(next)->size();
+    }
+    assert(scroll_forward <= addr, "wrong order for current and arg");
+    assert(addr <= next, "wrong order for arg and next");
+    return scroll_forward;
+  }
+
+  bool is_block_allocated(HeapWord* addr) {
+    assert(_covered_region.contains(addr), "Must be in covered region");
+    jbyte* block = block_for_addr(addr);
+    if (*block == clean_block)
+      return false;
+
+    return true;
+  }
+
+  // Return true if an object starts in the range of heap addresses.
+  // If an object starts at an address corresponding to
+  // "start", the method will return true.
+  bool object_starts_in_range(HeapWord* start_addr, HeapWord* end_addr) const;
+};