HeadlessMixedObjectScanner.hpp

/*******************************************************************************
 * Copyright IBM Corp. and others 2019
 *
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which accompanies this
 * distribution and is available at https://www.eclipse.org/legal/epl-2.0/
 * or the Apache License, Version 2.0 which accompanies this distribution and
 * is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * This Source Code may also be made available under the following
 * Secondary Licenses when the conditions for such availability set
 * forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
 * General Public License, version 2 with the GNU Classpath
 * Exception [1] and GNU General Public License, version 2 with the
 * OpenJDK Assembly Exception [2].
 *
 * [1] https://www.gnu.org/software/classpath/license.html
 * [2] https://openjdk.org/legal/assembly-exception.html
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0-only WITH Classpath-exception-2.0 OR GPL-2.0-only WITH OpenJDK-assembly-exception-1.0
 *******************************************************************************/

#if !defined(HEADLESSMIXEDOBJECTSCANNER_HPP_)
#define HEADLESSMIXEDOBJECTSCANNER_HPP_

#include "j9.h"

#include "ObjectScanner.hpp"

class GC_HeadlessMixedObjectScanner : public GC_ObjectScanner
{
	/* Data Members */
private:

protected:
	fomrobject_t *_endPtr; /**< end scan pointer */
	fomrobject_t *_mapPtr; /**< pointer to first slot in current scan segment */
	uintptr_t *_descriptionPtr; /**< current description pointer */
#if defined(J9VM_GC_LEAF_BITS)
	uintptr_t *_leafPtr; /**< current leaf description pointer */
#endif /* J9VM_GC_LEAF_BITS */

public:

	/* Member Functions */
private:

protected:

public:

	/**
	 * @param env The scanning thread environment
	 * @param scanPtr Pointer to the start of the object
	 * @param size The instance size
	 * @param flags Scanning context flags
	 */
	MMINLINE GC_HeadlessMixedObjectScanner(MM_EnvironmentBase *env, fomrobject_t *scanPtr, uintptr_t size, uintptr_t flags)
		: GC_ObjectScanner(env, scanPtr, 0, flags)
		, _endPtr((fomrobject_t *)((uintptr_t)scanPtr + size))
		, _mapPtr(scanPtr)
		, _descriptionPtr(NULL)
#if defined(J9VM_GC_LEAF_BITS)
		, _leafPtr(NULL)
#endif /* J9VM_GC_LEAF_BITS */
	{
		_typeId = __FUNCTION__;
	}

	MMINLINE void
	initialize(MM_EnvironmentBase *env, uintptr_t *descriptionPtr, uintptr_t *leafPtr)
	{
		GC_ObjectScanner::initialize(env);

		/* Initialize the slot map from description bits */
		_scanMap = (uintptr_t)descriptionPtr;
#if defined(J9VM_GC_LEAF_BITS)
		_leafMap = (uintptr_t)leafPtr;
#endif /* J9VM_GC_LEAF_BITS */
		if (_scanMap & 1) {
			_scanMap >>= 1;
			_descriptionPtr = NULL;
#if defined(J9VM_GC_LEAF_BITS)
			_leafMap >>= 1;
			_leafPtr = NULL;
#endif /* J9VM_GC_LEAF_BITS */
			setNoMoreSlots();
		} else {
			_descriptionPtr = (uintptr_t *)_scanMap;
			_scanMap = *_descriptionPtr;
			_descriptionPtr += 1;
#if defined(J9VM_GC_LEAF_BITS)
			_leafPtr = (uintptr_t *)_leafMap;
			_leafMap = *_leafPtr;
			_leafPtr += 1;
#endif /* J9VM_GC_LEAF_BITS */
		}
	}

	MMINLINE void
	initialize(MM_EnvironmentBase *env, uintptr_t *descriptionPtr)
	{
		initialize(env, descriptionPtr, NULL);
	}

	MMINLINE uintptr_t getBytesRemaining() { return (uintptr_t)_endPtr - (uintptr_t)_scanPtr; }

	/**
	 * Return base pointer and slot bit map for next block of contiguous slots to be scanned. The
	 * base pointer must be fomrobject_t-aligned. Bits in the bit map are scanned in order of
	 * increasing significance, and the least significant bit maps to the slot at the returned
	 * base pointer.
	 *
	 * @param[out] scanMap the bit map for the slots contiguous with the returned base pointer
	 * @param[out] hasNextSlotMap set this to true if this method should be called again, false if this map is known to be last
	 * @return a pointer to the first slot mapped by the least significant bit of the map, or NULL if no more slots
	 */
	virtual fomrobject_t *
	getNextSlotMap(uintptr_t *slotMap, bool *hasNextSlotMap)
	{
		bool const compressed = compressObjectReferences();
		fomrobject_t *result = NULL;
		*slotMap = 0;
		*hasNextSlotMap = false;
		_mapPtr = GC_SlotObject::addToSlotAddress(_mapPtr, _bitsPerScanMap, compressed);
		while (_endPtr > _mapPtr) {
			*slotMap = *_descriptionPtr;
			_descriptionPtr += 1;
			if (0 != *slotMap) {
				*hasNextSlotMap = _bitsPerScanMap < GC_SlotObject::subtractSlotAddresses(_endPtr, _mapPtr, compressed);
				result = _mapPtr;
				break;
			}
			_mapPtr = GC_SlotObject::addToSlotAddress(_mapPtr, _bitsPerScanMap, compressed);
		}
		return result;
	}

#if defined(J9VM_GC_LEAF_BITS)
	/**
	 * Return base pointer and slot bit map for next block of contiguous slots to be scanned. The
	 * base pointer must be fomrobject_t-aligned. Bits in the bit map are scanned in order of
	 * increasing significance, and the least significant bit maps to the slot at the returned
	 * base pointer.
	 *
	 * @param[out] scanMap the bit map for the slots contiguous with the returned base pointer
	 * @param[out] leafMap the leaf bit map for the slots contiguous with the returned base pointer
	 * @param[out] hasNextSlotMap set this to true if this method should be called again, false if this map is known to be last
	 * @return a pointer to the first slot mapped by the least significant bit of the map, or NULL if no more slots
	 */
	virtual fomrobject_t *
	getNextSlotMap(uintptr_t *slotMap, uintptr_t *leafMap, bool *hasNextSlotMap)
	{
		bool const compressed = compressObjectReferences();
		fomrobject_t *result = NULL;
		*slotMap = 0;
		*leafMap = 0;
		*hasNextSlotMap = false;
		_mapPtr = GC_SlotObject::addToSlotAddress(_mapPtr, _bitsPerScanMap, compressed);
		while (_endPtr > _mapPtr) {
			*slotMap = *_descriptionPtr;
			_descriptionPtr += 1;
			*leafMap = *_leafPtr;
			_leafPtr += 1;
			if (0 != *slotMap) {
				*hasNextSlotMap = _bitsPerScanMap < GC_SlotObject::subtractSlotAddresses(_endPtr, _mapPtr, compressed);
				result = _mapPtr;
				break;
			}
			_mapPtr = GC_SlotObject::addToSlotAddress(_mapPtr, _bitsPerScanMap, compressed);
		}
		return result;
	}
#endif /* J9VM_GC_LEAF_BITS */
};

#endif /* HEADLESSMIXEDOBJECTSCANNER_HPP_ */