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// Copyright (C) 2008 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "heap_bitmap.h"
#include <sys/mman.h>
#include "UniquePtr.h"
#include "logging.h"
#include "utils.h"
namespace art {
HeapBitmap* HeapBitmap::Create(const char* name, byte* base, size_t length) {
UniquePtr<HeapBitmap> bitmap(new HeapBitmap(base, length));
if (!bitmap->Init(name, base, length)) {
return NULL;
} else {
return bitmap.release();
}
}
// Initialize a HeapBitmap so that it points to a bitmap large enough
// to cover a heap at <base> of <max_size> bytes, where objects are
// guaranteed to be kAlignment-aligned.
bool HeapBitmap::Init(const char* name, const byte* base, size_t max_size) {
CHECK(base != NULL);
size_t length = HB_OFFSET_TO_INDEX(max_size) * kWordSize;
mem_map_.reset(MemMap::MapAnonymous(name, NULL, length, PROT_READ | PROT_WRITE));
if (mem_map_.get() == NULL) {
return false;
}
words_ = reinterpret_cast<word*>(mem_map_->GetAddress());
num_bytes_ = length;
base_ = reinterpret_cast<uintptr_t>(base);
max_ = base_ - 1;
return true;
}
// Clean up any resources associated with the bitmap.
HeapBitmap::~HeapBitmap() {}
// Fill the bitmap with zeroes. Returns the bitmap's memory to the
// system as a side-effect.
void HeapBitmap::Clear() {
if (words_ != NULL) {
// This returns the memory to the system. Successive page faults
// will return zeroed memory.
int result = madvise(words_, num_bytes_, MADV_DONTNEED);
if (result == -1) {
PLOG(WARNING) << "madvise failed";
}
max_ = base_ - 1;
}
}
// Return true iff <obj> is within the range of pointers that this
// bitmap could potentially cover, even if a bit has not been set for
// it.
bool HeapBitmap::HasAddress(const void* obj) const {
if (obj != NULL) {
const uintptr_t offset = (uintptr_t)obj - base_;
const size_t index = HB_OFFSET_TO_INDEX(offset);
return index < num_bytes_ / kWordSize;
}
return false;
}
void HeapBitmap::VisitRange(uintptr_t base, uintptr_t max, Callback* visitor, void* arg) const {
size_t start = HB_OFFSET_TO_INDEX(base - base_);
size_t end = HB_OFFSET_TO_INDEX(max - base_ - 1);
for (size_t i = start; i <= end; i++) {
word w = words_[i];
if (w != 0) {
word high_bit = 1 << (kBitsPerWord - 1);
uintptr_t ptr_base = HB_INDEX_TO_OFFSET(i) + base_;
while (w != 0) {
const int shift = CLZ(w);
Object* obj = reinterpret_cast<Object*>(ptr_base + shift * kAlignment);
(*visitor)(obj, arg);
w &= ~(high_bit >> shift);
}
}
}
}
// Visits set bits in address order. The callback is not permitted to
// change the bitmap bits or max during the traversal.
void HeapBitmap::Walk(HeapBitmap::Callback* callback, void* arg) {
CHECK(words_ != NULL);
CHECK(callback != NULL);
uintptr_t end = HB_OFFSET_TO_INDEX(max_ - base_);
for (uintptr_t i = 0; i <= end; ++i) {
word w = words_[i];
if (UNLIKELY(w != 0)) {
word high_bit = 1 << (kBitsPerWord - 1);
uintptr_t ptr_base = HB_INDEX_TO_OFFSET(i) + base_;
while (w != 0) {
const int shift = CLZ(w);
Object* obj = reinterpret_cast<Object*>(ptr_base + shift * kAlignment);
(*callback)(obj, arg);
w &= ~(high_bit >> shift);
}
}
}
}
// Similar to Walk but the callback routine is permitted to change the
// bitmap bits and max during traversal. Used by the the root marking
// scan exclusively.
//
// The callback is invoked with a finger argument. The finger is a
// pointer to an address not yet visited by the traversal. If the
// callback sets a bit for an address at or above the finger, this
// address will be visited by the traversal. If the callback sets a
// bit for an address below the finger, this address will not be
// visited.
void HeapBitmap::ScanWalk(uintptr_t base, uintptr_t max, ScanCallback* callback, void* arg) {
CHECK(words_ != NULL);
CHECK(callback != NULL);
CHECK_LE(base, max);
CHECK_GE(base, base_);
size_t start = HB_OFFSET_TO_INDEX(base - base_);
if (max < max_) {
// The end of the space we're looking at is before the current maximum bitmap PC, scan to that
// and don't recompute end on each iteration
size_t end = HB_OFFSET_TO_INDEX(max - base_ - 1);
for (size_t i = start; i <= end; i++) {
word w = words_[i];
if (UNLIKELY(w != 0)) {
word high_bit = 1 << (kBitsPerWord - 1);
uintptr_t ptr_base = HB_INDEX_TO_OFFSET(i) + base_;
void* finger = reinterpret_cast<void*>(HB_INDEX_TO_OFFSET(i + 1) + base_);
while (w != 0) {
const int shift = CLZ(w);
Object* obj = reinterpret_cast<Object*>(ptr_base + shift * kAlignment);
(*callback)(obj, finger, arg);
w &= ~(high_bit >> shift);
}
}
}
} else {
size_t end = HB_OFFSET_TO_INDEX(max_ - base_);
for (size_t i = start; i <= end; i++) {
word w = words_[i];
if (UNLIKELY(w != 0)) {
word high_bit = 1 << (kBitsPerWord - 1);
uintptr_t ptr_base = HB_INDEX_TO_OFFSET(i) + base_;
void* finger = reinterpret_cast<void*>(HB_INDEX_TO_OFFSET(i + 1) + base_);
while (w != 0) {
const int shift = CLZ(w);
Object* obj = reinterpret_cast<Object*>(ptr_base + shift * kAlignment);
(*callback)(obj, finger, arg);
w &= ~(high_bit >> shift);
}
}
end = HB_OFFSET_TO_INDEX(max_ - base_);
}
}
}
// Walk through the bitmaps in increasing address order, and find the
// object pointers that correspond to garbage objects. Call
// <callback> zero or more times with lists of these object pointers.
//
// The callback is not permitted to increase the max of either bitmap.
void HeapBitmap::SweepWalk(const HeapBitmap& live_bitmap,
const HeapBitmap& mark_bitmap,
uintptr_t base, uintptr_t max,
HeapBitmap::SweepCallback* callback, void* arg) {
CHECK(live_bitmap.words_ != NULL);
CHECK(mark_bitmap.words_ != NULL);
CHECK_EQ(live_bitmap.base_, mark_bitmap.base_);
CHECK_EQ(live_bitmap.num_bytes_, mark_bitmap.num_bytes_);
CHECK(callback != NULL);
CHECK_LE(base, max);
CHECK_GE(base, live_bitmap.base_);
max = std::min(max - 1, live_bitmap.max_);
if (live_bitmap.max_ < live_bitmap.base_) {
// Easy case; both are obviously empty.
// TODO: this should never happen
return;
}
// TODO: rewrite the callbacks to accept a std::vector<void*> rather than a void**?
std::vector<void*> pointer_buf(4 * kBitsPerWord);
void** pb = &pointer_buf[0];
size_t start = HB_OFFSET_TO_INDEX(base - live_bitmap.base_);
size_t end = HB_OFFSET_TO_INDEX(max - live_bitmap.base_);
word* live = live_bitmap.words_;
word* mark = mark_bitmap.words_;
for (size_t i = start; i <= end; i++) {
word garbage = live[i] & ~mark[i];
if (UNLIKELY(garbage != 0)) {
word high_bit = 1 << (kBitsPerWord - 1);
uintptr_t ptr_base = HB_INDEX_TO_OFFSET(i) + live_bitmap.base_;
while (garbage != 0) {
int shift = CLZ(garbage);
garbage &= ~(high_bit >> shift);
*pb++ = reinterpret_cast<void*>(ptr_base + shift * kAlignment);
}
// Make sure that there are always enough slots available for an
// entire word of one bits.
if (pb >= &pointer_buf[pointer_buf.size() - kBitsPerWord]) {
(*callback)(pb - &pointer_buf[0], &pointer_buf[0], arg);
pb = &pointer_buf[0];
}
}
}
if (pb > &pointer_buf[0]) {
(*callback)(pb - &pointer_buf[0], &pointer_buf[0], arg);
}
}
} // namespace art
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