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apache / cassandra / f66adb0278aa56e8c2696db6f3fe24d311bf7b44 / . / src / java / org / apache / cassandra / utils / memory / BufferPool.java
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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
package org.apache.cassandra.utils.memory;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.ArrayDeque;
import java.util.Collections;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.LongAdder;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.function.BiPredicate;
import java.util.function.Consumer;
import java.util.function.Supplier;
import com.google.common.annotations.VisibleForTesting;
import net.nicoulaj.compilecommand.annotations.Inline;
import org.apache.cassandra.concurrent.InfiniteLoopExecutor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import io.netty.util.concurrent.FastThreadLocal;
import org.apache.cassandra.io.compress.BufferType;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.metrics.BufferPoolMetrics;
import org.apache.cassandra.utils.NoSpamLogger;
import org.apache.cassandra.utils.concurrent.Ref;
import static com.google.common.collect.ImmutableList.of;
import static org.apache.cassandra.utils.ExecutorUtils.*;
import static org.apache.cassandra.utils.FBUtilities.prettyPrintMemory;
import static org.apache.cassandra.utils.memory.MemoryUtil.isExactlyDirect;
/**
* A pool of ByteBuffers that can be recycled to reduce system direct memory fragmentation and improve buffer allocation
* performance.
* <p/>
*
* Each {@link BufferPool} instance has one {@link GlobalPool} which allocates two kinds of chunks:
* <ul>
* <li>Macro Chunk
* <ul>
* <li>A memory slab that has size of MACRO_CHUNK_SIZE which is 64 * NORMAL_CHUNK_SIZE</li>
* <li>Used to allocate normal chunk with size of NORMAL_CHUNK_SIZE</li>
* </ul>
* </li>
* <li>Normal Chunk
* <ul>
* <li>Used by {@link LocalPool} to serve buffer allocation</li>
* <li>Minimum allocation unit is NORMAL_CHUNK_SIZE / 64</li>
* </ul>
* </li>
* </ul>
*
* {@link GlobalPool} maintains two kinds of freed chunks, fully freed chunks where all buffers are released, and
* partially freed chunks where some buffers are not released, eg. held by {@link org.apache.cassandra.cache.ChunkCache}.
* Partially freed chunks are used to improve cache utilization and have lower priority compared to fully freed chunks.
*
* <p/>
*
* {@link LocalPool} is a thread local pool to serve buffer allocation requests. There are two kinds of local pool:
* <ul>
* <li>Normal Pool:
* <ul>
* <li>used to serve allocation size that is larger than half of NORMAL_ALLOCATION_UNIT but less than NORMAL_CHUNK_SIZE</li>
* <li>when there is insufficient space in the local queue, it will request global pool for more normal chunks</li>
* <li>when normal chunk is recycled either fully or partially, it will be passed to global pool to be used by other pools</li>
* </ul>
* </li>
* <li>Tiny Pool:
* <ul>
* <li>used to serve allocation size that is less than NORMAL_ALLOCATION_UNIT</li>
* <li>when there is insufficient space in the local queue, it will request parent normal pool for more tiny chunks</li>
* <li>when tiny chunk is fully freed, it will be passed to paretn normal pool and corresponding buffer in the parent normal chunk is freed</li>
* </ul>
* </li>
* </ul>
*
* Note: even though partially freed chunks improves cache utilization when chunk cache holds outstanding buffer for
* arbitrary period, there is still fragmentation in the partially freed chunk because of non-uniform allocation size.
* <p/>
*
* The lifecycle of a normal Chunk:
* <pre>
* new acquire release recycle
* ────────→ in GlobalPool ──────────────→ in LocalPool ──────────────→ EVICTED ──────────────────┐
* owner = null owner = LocalPool owner = null │
* status = IN_USE status = IN_USE status = EVICTED │
* ready serves get / free serves free only │
* ↑ │
* └────────────────────────────────────────────────────────────────────────────────┘
* </pre>
*/
public class BufferPool
{
/** The size of a page aligned buffer, 128KiB */
public static final int NORMAL_CHUNK_SIZE = 128 << 10;
public static final int NORMAL_ALLOCATION_UNIT = NORMAL_CHUNK_SIZE / 64;
public static final int TINY_CHUNK_SIZE = NORMAL_ALLOCATION_UNIT;
public static final int TINY_ALLOCATION_UNIT = TINY_CHUNK_SIZE / 64;
public static final int TINY_ALLOCATION_LIMIT = TINY_CHUNK_SIZE / 2;
private static final Logger logger = LoggerFactory.getLogger(BufferPool.class);
private static final NoSpamLogger noSpamLogger = NoSpamLogger.getLogger(logger, 15L, TimeUnit.MINUTES);
private static final ByteBuffer EMPTY_BUFFER = ByteBuffer.allocateDirect(0);
private volatile Debug debug = Debug.NO_OP;
protected final String name;
protected final BufferPoolMetrics metrics;
private final long memoryUsageThreshold;
private final String readableMemoryUsageThreshold;
/**
* Size of unpooled buffer being allocated outside of buffer pool in bytes.
*/
private final LongAdder overflowMemoryUsage = new LongAdder();
/**
* Size of buffer being used in bytes, including pooled buffer and unpooled buffer.
*/
private final LongAdder memoryInUse = new LongAdder();
/**
* Size of allocated buffer pool slabs in bytes
*/
private final AtomicLong memoryAllocated = new AtomicLong();
/** A global pool of chunks (page aligned buffers) */
private final GlobalPool globalPool;
/** Allow partially freed chunk to be recycled for allocation*/
private final boolean recyclePartially;
/** A thread local pool of chunks, where chunks come from the global pool */
private final FastThreadLocal<LocalPool> localPool = new FastThreadLocal<LocalPool>()
{
@Override
protected LocalPool initialValue()
{
return new LocalPool();
}
protected void onRemoval(LocalPool value)
{
value.release();
}
};
private final Set<LocalPoolRef> localPoolReferences = Collections.newSetFromMap(new ConcurrentHashMap<>());
private final ReferenceQueue<Object> localPoolRefQueue = new ReferenceQueue<>();
private final InfiniteLoopExecutor localPoolCleaner;
public BufferPool(String name, long memoryUsageThreshold, boolean recyclePartially)
{
this.name = name;
this.memoryUsageThreshold = memoryUsageThreshold;
this.readableMemoryUsageThreshold = prettyPrintMemory(memoryUsageThreshold);
this.globalPool = new GlobalPool();
this.metrics = new BufferPoolMetrics(name, this);
this.recyclePartially = recyclePartially;
this.localPoolCleaner = new InfiniteLoopExecutor("LocalPool-Cleaner-" + name, this::cleanupOneReference).start();
}
/**
* @return a local pool instance and caller is responsible to release the pool
*/
public LocalPool create()
{
return new LocalPool();
}
public ByteBuffer get(int size, BufferType bufferType)
{
if (bufferType == BufferType.ON_HEAP)
return allocate(size, bufferType);
else
return localPool.get().get(size);
}
public ByteBuffer getAtLeast(int size, BufferType bufferType)
{
if (bufferType == BufferType.ON_HEAP)
return allocate(size, bufferType);
else
return localPool.get().getAtLeast(size);
}
/** Unlike the get methods, this will return null if the pool is exhausted */
public ByteBuffer tryGet(int size)
{
return localPool.get().tryGet(size, false);
}
public ByteBuffer tryGetAtLeast(int size)
{
return localPool.get().tryGet(size, true);
}
private ByteBuffer allocate(int size, BufferType bufferType)
{
updateOverflowMemoryUsage(size);
return bufferType == BufferType.ON_HEAP
? ByteBuffer.allocate(size)
: ByteBuffer.allocateDirect(size);
}
public void put(ByteBuffer buffer)
{
if (isExactlyDirect(buffer))
localPool.get().put(buffer);
else
updateOverflowMemoryUsage(-buffer.capacity());
}
public void putUnusedPortion(ByteBuffer buffer)
{
if (isExactlyDirect(buffer))
{
LocalPool pool = localPool.get();
if (buffer.limit() > 0)
pool.putUnusedPortion(buffer);
else
pool.put(buffer);
}
}
private void updateOverflowMemoryUsage(int size)
{
overflowMemoryUsage.add(size);
}
public void setRecycleWhenFreeForCurrentThread(boolean recycleWhenFree)
{
localPool.get().recycleWhenFree(recycleWhenFree);
}
/**
* @return buffer size being allocated, including pooled buffers and unpooled buffers
*/
public long sizeInBytes()
{
return memoryAllocated.get() + overflowMemoryUsage.longValue();
}
/**
* @return buffer size being used, including used pooled buffers and unpooled buffers
*/
public long usedSizeInBytes()
{
return memoryInUse.longValue() + overflowMemoryUsage.longValue();
}
/**
* @return unpooled buffer size being allocated outside of buffer pool.
*/
public long overflowMemoryInBytes()
{
return overflowMemoryUsage.longValue();
}
/**
* @return maximum pooled buffer size in bytes
*/
public long memoryUsageThreshold()
{
return memoryUsageThreshold;
}
@VisibleForTesting
public GlobalPool globalPool()
{
return globalPool;
}
/**
* Forces to recycle free local chunks back to the global pool.
* This is needed because if buffers were freed by a different thread than the one
* that allocated them, recycling might not have happened and the local pool may still own some
* fully empty chunks.
*/
@VisibleForTesting
public void releaseLocal()
{
localPool.get().release();
}
interface Debug
{
public static Debug NO_OP = new Debug()
{
@Override
public void registerNormal(Chunk chunk) {}
@Override
public void acquire(Chunk chunk) {}
@Override
public void recycleNormal(Chunk oldVersion, Chunk newVersion) {}
@Override
public void recyclePartial(Chunk chunk) { }
};
void registerNormal(Chunk chunk);
void acquire(Chunk chunk);
void recycleNormal(Chunk oldVersion, Chunk newVersion);
void recyclePartial(Chunk chunk);
}
public void debug(Debug setDebug)
{
assert setDebug != null;
this.debug = setDebug;
}
interface Recycler
{
/**
* Recycle a fully freed chunk
*/
void recycle(Chunk chunk);
/**
* @return true if chunk can be reused before fully freed.
*/
boolean canRecyclePartially();
/**
* Recycle a partially freed chunk
*/
void recyclePartially(Chunk chunk);
}
/**
* A queue of page aligned buffers, the chunks, which have been sliced from bigger chunks,
* the macro-chunks, also page aligned. Macro-chunks are allocated as long as we have not exceeded the
* memory maximum threshold, MEMORY_USAGE_THRESHOLD and are never released.
*
* This class is shared by multiple thread local pools and must be thread-safe.
*/
final class GlobalPool implements Supplier<Chunk>, Recycler
{
/** The size of a bigger chunk, 1 MiB, must be a multiple of NORMAL_CHUNK_SIZE */
static final int MACRO_CHUNK_SIZE = 64 * NORMAL_CHUNK_SIZE;
private final String READABLE_MACRO_CHUNK_SIZE = prettyPrintMemory(MACRO_CHUNK_SIZE);
private final Queue<Chunk> macroChunks = new ConcurrentLinkedQueue<>();
// TODO (future): it would be preferable to use a CLStack to improve cache occupancy; it would also be preferable to use "CoreLocal" storage
// It contains fully free chunks and when it runs out, partially freed chunks will be used.
private final Queue<Chunk> chunks = new ConcurrentLinkedQueue<>();
// Partially freed chunk which is recirculated whenever chunk has free spaces to
// improve buffer utilization when chunk cache is holding a piece of buffer for a long period.
// Note: fragmentation still exists, as holes are with different sizes.
private final Queue<Chunk> partiallyFreedChunks = new ConcurrentLinkedQueue<>();
/** Used in logging statements to lazily build a human-readable current memory usage. */
private final Object readableMemoryUsage =
new Object() { @Override public String toString() { return prettyPrintMemory(sizeInBytes()); } };
public GlobalPool()
{
assert Integer.bitCount(NORMAL_CHUNK_SIZE) == 1; // must be a power of 2
assert Integer.bitCount(MACRO_CHUNK_SIZE) == 1; // must be a power of 2
assert MACRO_CHUNK_SIZE % NORMAL_CHUNK_SIZE == 0; // must be a multiple
}
/** Return a chunk, the caller will take owership of the parent chunk. */
public Chunk get()
{
Chunk chunk = getInternal();
if (chunk != null)
debug.acquire(chunk);
return chunk;
}
private Chunk getInternal()
{
Chunk chunk = chunks.poll();
if (chunk != null)
return chunk;
chunk = allocateMoreChunks();
if (chunk != null)
return chunk;
// another thread may have just allocated last macro chunk, so make one final attempt before returning null
chunk = chunks.poll();
// try to use partially freed chunk if there is no more fully freed chunk.
return chunk == null ? partiallyFreedChunks.poll() : chunk;
}
/**
* This method might be called by multiple threads and that's fine if we add more
* than one chunk at the same time as long as we don't exceed the MEMORY_USAGE_THRESHOLD.
*/
private Chunk allocateMoreChunks()
{
while (true)
{
long cur = memoryAllocated.get();
if (cur + MACRO_CHUNK_SIZE > memoryUsageThreshold)
{
if (memoryUsageThreshold > 0)
{
noSpamLogger.info("Maximum memory usage reached ({}) for {} buffer pool, cannot allocate chunk of {}",
readableMemoryUsageThreshold, name, READABLE_MACRO_CHUNK_SIZE);
}
return null;
}
if (memoryAllocated.compareAndSet(cur, cur + MACRO_CHUNK_SIZE))
break;
}
// allocate a large chunk
Chunk chunk;
try
{
chunk = new Chunk(null, allocateDirectAligned(MACRO_CHUNK_SIZE));
}
catch (OutOfMemoryError oom)
{
noSpamLogger.error("{} buffer pool failed to allocate chunk of {}, current size {} ({}). " +
"Attempting to continue; buffers will be allocated in on-heap memory which can degrade performance. " +
"Make sure direct memory size (-XX:MaxDirectMemorySize) is large enough to accommodate off-heap memtables and caches.",
name, READABLE_MACRO_CHUNK_SIZE, readableMemoryUsage, oom.getClass().getName());
return null;
}
chunk.acquire(null);
macroChunks.add(chunk);
final Chunk callerChunk = new Chunk(this, chunk.get(NORMAL_CHUNK_SIZE));
debug.registerNormal(callerChunk);
for (int i = NORMAL_CHUNK_SIZE; i < MACRO_CHUNK_SIZE; i += NORMAL_CHUNK_SIZE)
{
Chunk add = new Chunk(this, chunk.get(NORMAL_CHUNK_SIZE));
chunks.add(add);
debug.registerNormal(add);
}
return callerChunk;
}
@Override
public void recycle(Chunk chunk)
{
Chunk recycleAs = new Chunk(chunk);
debug.recycleNormal(chunk, recycleAs);
chunks.add(recycleAs);
}
@Override
public void recyclePartially(Chunk chunk)
{
debug.recyclePartial(chunk);
partiallyFreedChunks.add(chunk);
}
@Override
public boolean canRecyclePartially()
{
return recyclePartially;
}
/** This is not thread safe and should only be used for unit testing. */
@VisibleForTesting
void unsafeFree()
{
while (!chunks.isEmpty())
chunks.poll().unsafeFree();
while (!partiallyFreedChunks.isEmpty())
partiallyFreedChunks.poll().unsafeFree();
while (!macroChunks.isEmpty())
macroChunks.poll().unsafeFree();
}
@VisibleForTesting
boolean isPartiallyFreed(Chunk chunk)
{
return partiallyFreedChunks.contains(chunk);
}
@VisibleForTesting
boolean isFullyFreed(Chunk chunk)
{
return chunks.contains(chunk);
}
}
private static class MicroQueueOfChunks
{
// a microqueue of Chunks:
// * if any are null, they are at the end;
// * new Chunks are added to the last null index
// * if no null indexes available, the smallest is swapped with the last index, and this replaced
// * this results in a queue that will typically be visited in ascending order of available space, so that
// small allocations preferentially slice from the Chunks with the smallest space available to furnish them
// WARNING: if we ever change the size of this, we must update removeFromLocalQueue, and addChunk
private Chunk chunk0, chunk1, chunk2;
private int count;
// add a new chunk, if necessary evicting the chunk with the least available memory (returning the evicted chunk)
private Chunk add(Chunk chunk)
{
switch (count)
{
case 0:
chunk0 = chunk;
count = 1;
break;
case 1:
chunk1 = chunk;
count = 2;
break;
case 2:
chunk2 = chunk;
count = 3;
break;
case 3:
{
Chunk release;
int chunk0Free = chunk0.freeSlotCount();
int chunk1Free = chunk1.freeSlotCount();
int chunk2Free = chunk2.freeSlotCount();
if (chunk0Free < chunk1Free)
{
if (chunk0Free < chunk2Free)
{
release = chunk0;
chunk0 = chunk;
}
else
{
release = chunk2;
chunk2 = chunk;
}
}
else
{
if (chunk1Free < chunk2Free)
{
release = chunk1;
chunk1 = chunk;
}
else
{
release = chunk2;
chunk2 = chunk;
}
}
return release;
}
default:
throw new IllegalStateException();
}
return null;
}
private void remove(Chunk chunk)
{
// since we only have three elements in the queue, it is clearer, easier and faster to just hard code the options
if (chunk0 == chunk)
{ // remove first by shifting back second two
chunk0 = chunk1;
chunk1 = chunk2;
}
else if (chunk1 == chunk)
{ // remove second by shifting back last
chunk1 = chunk2;
}
else if (chunk2 != chunk)
{
return;
}
// whatever we do, the last element must be null
chunk2 = null;
--count;
}
ByteBuffer get(int size, boolean sizeIsLowerBound, ByteBuffer reuse)
{
ByteBuffer buffer;
if (null != chunk0)
{
if (null != (buffer = chunk0.get(size, sizeIsLowerBound, reuse)))
return buffer;
if (null != chunk1)
{
if (null != (buffer = chunk1.get(size, sizeIsLowerBound, reuse)))
return buffer;
if (null != chunk2 && null != (buffer = chunk2.get(size, sizeIsLowerBound, reuse)))
return buffer;
}
}
return null;
}
private void forEach(Consumer<Chunk> consumer)
{
forEach(consumer, count, chunk0, chunk1, chunk2);
}
private void clearForEach(Consumer<Chunk> consumer)
{
int oldCount = count;
Chunk chunk0 = this.chunk0, chunk1 = this.chunk1, chunk2 = this.chunk2;
count = 0;
this.chunk0 = this.chunk1 = this.chunk2 = null;
forEach(consumer, oldCount, chunk0, chunk1, chunk2);
}
private static void forEach(Consumer<Chunk> consumer, int count, Chunk chunk0, Chunk chunk1, Chunk chunk2)
{
switch (count)
{
case 3:
consumer.accept(chunk2);
case 2:
consumer.accept(chunk1);
case 1:
consumer.accept(chunk0);
}
}
private <T> void removeIf(BiPredicate<Chunk, T> predicate, T value)
{
// do not release matching chunks before we move null chunks to the back of the queue;
// because, with current buffer release from another thread, "chunk#release()" may eventually come back to
// "removeIf" causing NPE as null chunks are not at the back of the queue.
Chunk toRelease0 = null, toRelease1 = null, toRelease2 = null;
try
{
switch (count)
{
case 3:
if (predicate.test(chunk2, value))
{
--count;
toRelease2 = chunk2;
chunk2 = null;
}
case 2:
if (predicate.test(chunk1, value))
{
--count;
toRelease1 = chunk1;
chunk1 = null;
}
case 1:
if (predicate.test(chunk0, value))
{
--count;
toRelease0 = chunk0;
chunk0 = null;
}
break;
case 0:
return;
}
switch (count)
{
case 2:
// Find the only null item, and shift non-null so that null is at chunk2
if (chunk0 == null)
{
chunk0 = chunk1;
chunk1 = chunk2;
chunk2 = null;
}
else if (chunk1 == null)
{
chunk1 = chunk2;
chunk2 = null;
}
break;
case 1:
// Find the only non-null item, and shift it to chunk0
if (chunk1 != null)
{
chunk0 = chunk1;
chunk1 = null;
}
else if (chunk2 != null)
{
chunk0 = chunk2;
chunk2 = null;
}
break;
}
}
finally
{
if (toRelease0 != null)
toRelease0.release();
if (toRelease1 != null)
toRelease1.release();
if (toRelease2 != null)
toRelease2.release();
}
}
private void release()
{
clearForEach(Chunk::release);
}
private void unsafeRecycle()
{
clearForEach(Chunk::unsafeRecycle);
}
}
/**
* A thread local class that grabs chunks from the global pool for this thread allocations.
* Only one thread can do the allocations but multiple threads can release the allocations.
*/
public final class LocalPool implements Recycler
{
private final Queue<ByteBuffer> reuseObjects;
private final Supplier<Chunk> parent;
private final LocalPoolRef leakRef;
private final MicroQueueOfChunks chunks = new MicroQueueOfChunks();
private final Thread owningThread = Thread.currentThread();
/**
* If we are on outer LocalPool, whose chunks are == NORMAL_CHUNK_SIZE, we may service allocation requests
* for buffers much smaller than
*/
private LocalPool tinyPool;
private final int tinyLimit;
private boolean recycleWhenFree = true;
public LocalPool()
{
this.parent = globalPool;
this.tinyLimit = TINY_ALLOCATION_LIMIT;
this.reuseObjects = new ArrayDeque<>();
localPoolReferences.add(leakRef = new LocalPoolRef(this, localPoolRefQueue));
}
/**
* Invoked by an existing LocalPool, to create a child pool
*/
private LocalPool(LocalPool parent)
{
this.parent = () -> {
ByteBuffer buffer = parent.tryGetInternal(TINY_CHUNK_SIZE, false);
return buffer == null ? null : new Chunk(parent, buffer);
};
this.tinyLimit = 0; // we only currently permit one layer of nesting (which brings us down to 32 byte allocations, so is plenty)
this.reuseObjects = parent.reuseObjects; // we share the same ByteBuffer object reuse pool, as we both have the same exclusive access to it
localPoolReferences.add(leakRef = new LocalPoolRef(this, localPoolRefQueue));
}
private LocalPool tinyPool()
{
if (tinyPool == null)
tinyPool = new LocalPool(this).recycleWhenFree(recycleWhenFree);
return tinyPool;
}
public void put(ByteBuffer buffer)
{
Chunk chunk = Chunk.getParentChunk(buffer);
int size = buffer.capacity();
if (chunk == null)
{
FileUtils.clean(buffer);
updateOverflowMemoryUsage(-size);
}
else
{
put(buffer, chunk);
memoryInUse.add(-size);
}
}
private void put(ByteBuffer buffer, Chunk chunk)
{
LocalPool owner = chunk.owner;
if (owner != null && owner == tinyPool)
{
tinyPool.put(buffer, chunk);
return;
}
long free = chunk.free(buffer);
if (free == -1L && owner == this && owningThread == Thread.currentThread() && recycleWhenFree)
{
// The chunk was fully freed, and we're the owner - let's release the chunk from this pool
// and give it back to the parent.
//
// We can remove the chunk from our local queue only if we're the owner of the chunk,
// and we're running this code on the thread that owns this local pool
// because the local queue is not thread safe.
//
// Please note that we may end up running `put` on a different thread when we're called
// from chunk.tryRecycle() on a child chunk which was previously owned by tinyPool of this pool.
// Such tiny chunk will point to this pool with its recycler reference. Thanks to the recycler, a thread
// that returns the tiny chunk can end up here in a LocalPool that's not neccessarily local to the
// calling thread, as there is no guarantee a child chunk is returned to the pool
// by the same thread that originally allocated it.
// It is ok we skip recycling in such case, and it does not cause
// a leak because those chunks are still referenced by the local pool.
remove(chunk);
chunk.release();
}
else if (chunk.owner == null)
{
// The chunk has no owner, so we can attempt to recycle it from any thread because we don't need
// to remove it from the local pool.
// For normal chunk this would recycle the chunk fully or partially if not already recycled.
// For tiny chunk, this would recycle the tiny chunk back to the parent chunk,
// if this chunk is completely free.
chunk.tryRecycle();
}
if (owner == this && owningThread == Thread.currentThread())
{
MemoryUtil.setAttachment(buffer, null);
MemoryUtil.setDirectByteBuffer(buffer, 0, 0);
reuseObjects.add(buffer);
}
}
public void putUnusedPortion(ByteBuffer buffer)
{
Chunk chunk = Chunk.getParentChunk(buffer);
int originalCapacity = buffer.capacity();
int size = originalCapacity - buffer.limit();
if (chunk == null)
{
updateOverflowMemoryUsage(-size);
return;
}
chunk.freeUnusedPortion(buffer);
// Calculate the actual freed bytes which may be different from `size` when pooling is involved
memoryInUse.add(buffer.capacity() - originalCapacity);
}
public ByteBuffer get(int size)
{
return get(size, false);
}
public ByteBuffer getAtLeast(int size)
{
return get(size, true);
}
private ByteBuffer get(int size, boolean sizeIsLowerBound)
{
ByteBuffer ret = tryGet(size, sizeIsLowerBound);
if (ret != null)
return ret;
if (size > NORMAL_CHUNK_SIZE)
{
if (logger.isTraceEnabled())
logger.trace("Requested buffer size {} is bigger than {}; allocating directly",
prettyPrintMemory(size),
prettyPrintMemory(NORMAL_CHUNK_SIZE));
}
else
{
if (logger.isTraceEnabled())
logger.trace("Requested buffer size {} has been allocated directly due to lack of capacity", prettyPrintMemory(size));
}
return allocate(size, BufferType.OFF_HEAP);
}
private ByteBuffer tryGet(int size, boolean sizeIsLowerBound)
{
LocalPool pool = this;
if (size <= tinyLimit)
{
if (size <= 0)
{
if (size == 0)
return EMPTY_BUFFER;
throw new IllegalArgumentException("Size must be non-negative (" + size + ')');
}
pool = tinyPool();
}
else if (size > NORMAL_CHUNK_SIZE)
{
metrics.misses.mark();
return null;
}
ByteBuffer ret = pool.tryGetInternal(size, sizeIsLowerBound);
if (ret != null)
{
metrics.hits.mark();
memoryInUse.add(ret.capacity());
}
else
{
metrics.misses.mark();
}
return ret;
}
@Inline
private ByteBuffer tryGetInternal(int size, boolean sizeIsLowerBound)
{
ByteBuffer reuse = this.reuseObjects.poll();
ByteBuffer buffer = chunks.get(size, sizeIsLowerBound, reuse);
if (buffer != null)
{
return buffer;
}
// else ask the global pool
Chunk chunk = addChunkFromParent();
if (chunk != null)
{
ByteBuffer result = chunk.get(size, sizeIsLowerBound, reuse);
if (result != null)
return result;
}
if (reuse != null)
this.reuseObjects.add(reuse);
return null;
}
// recycle entire tiny chunk from tiny pool back to local pool
@Override
public void recycle(Chunk chunk)
{
ByteBuffer buffer = chunk.slab;
Chunk parentChunk = Chunk.getParentChunk(buffer);
assert parentChunk != null; // tiny chunk always has a parent chunk
put(buffer, parentChunk);
}
@Override
public void recyclePartially(Chunk chunk)
{
throw new UnsupportedOperationException("Tiny chunk doesn't support partial recycle.");
}
@Override
public boolean canRecyclePartially()
{
// tiny pool doesn't support partial recycle, as we want to have tiny chunk fully freed and put back to
// parent normal chunk.
return false;
}
private void remove(Chunk chunk)
{
chunks.remove(chunk);
if (tinyPool != null)
tinyPool.chunks.removeIf((child, parent) -> Chunk.getParentChunk(child.slab) == parent, chunk);
}
private Chunk addChunkFromParent()
{
Chunk chunk = parent.get();
if (chunk == null)
return null;
addChunk(chunk);
return chunk;
}
private void addChunk(Chunk chunk)
{
chunk.acquire(this);
Chunk evict = chunks.add(chunk);
if (evict != null)
{
if (tinyPool != null)
// releasing tiny chunks may result in releasing current evicted chunk
tinyPool.chunks.removeIf((child, parent) -> Chunk.getParentChunk(child.slab) == parent, evict);
evict.release();
}
}
public void release()
{
if (tinyPool != null)
tinyPool.release();
chunks.release();
reuseObjects.clear();
localPoolReferences.remove(leakRef);
leakRef.clear();
}
@VisibleForTesting
void unsafeRecycle()
{
chunks.unsafeRecycle();
}
@VisibleForTesting
public boolean isTinyPool()
{
return !(parent instanceof GlobalPool);
}
public LocalPool recycleWhenFree(boolean recycleWhenFree)
{
this.recycleWhenFree = recycleWhenFree;
if (tinyPool != null)
tinyPool.recycleWhenFree = recycleWhenFree;
return this;
}
}
private static final class LocalPoolRef extends PhantomReference<LocalPool>
{
private final MicroQueueOfChunks chunks;
public LocalPoolRef(LocalPool localPool, ReferenceQueue<? super LocalPool> q)
{
super(localPool, q);
chunks = localPool.chunks;
}
public void release()
{
chunks.release();
}
}
private void cleanupOneReference() throws InterruptedException
{
Object obj = localPoolRefQueue.remove(100);
if (obj instanceof LocalPoolRef)
{
((LocalPoolRef) obj).release();
localPoolReferences.remove(obj);
}
}
private static ByteBuffer allocateDirectAligned(int capacity)
{
int align = MemoryUtil.pageSize();
if (Integer.bitCount(align) != 1)
throw new IllegalArgumentException("Alignment must be a power of 2");
ByteBuffer buffer = ByteBuffer.allocateDirect(capacity + align);
long address = MemoryUtil.getAddress(buffer);
long offset = address & (align -1); // (address % align)
if (offset == 0)
{ // already aligned
buffer.limit(capacity);
}
else
{ // shift by offset
int pos = (int)(align - offset);
buffer.position(pos);
buffer.limit(pos + capacity);
}
return buffer.slice();
}
/**
* A memory chunk: it takes a buffer (the slab) and slices it
* into smaller buffers when requested.
*
* It divides the slab into 64 units and keeps a long mask, freeSlots,
* indicating if a unit is in use or not. Each bit in freeSlots corresponds
* to a unit, if the bit is set then the unit is free (available for allocation)
* whilst if it is not set then the unit is in use.
*
* When we receive a request of a given size we round up the size to the nearest
* multiple of allocation units required. Then we search for n consecutive free units,
* where n is the number of units required. We also align to page boundaries.
*
* When we reiceve a release request we work out the position by comparing the buffer
* address to our base address and we simply release the units.
*/
final static class Chunk
{
enum Status
{
/** The slab is serving or ready to serve requests */
IN_USE,
/** The slab is not serving requests and ready for partial recycle*/
EVICTED;
}
private final ByteBuffer slab;
final long baseAddress;
private final int shift;
// it may be 0L when all slots are allocated after "get" or when all slots are freed after "free"
private volatile long freeSlots;
private static final AtomicLongFieldUpdater<Chunk> freeSlotsUpdater = AtomicLongFieldUpdater.newUpdater(Chunk.class, "freeSlots");
// the pool that is _currently allocating_ from this Chunk
// if this is set, it means the chunk may not be recycled because we may still allocate from it;
// if it has been unset the local pool has finished with it, and it may be recycled
private volatile LocalPool owner;
private final Recycler recycler;
private static final AtomicReferenceFieldUpdater<Chunk, Status> statusUpdater =
AtomicReferenceFieldUpdater.newUpdater(Chunk.class, Status.class, "status");
private volatile Status status = Status.IN_USE;
@VisibleForTesting
Object debugAttachment;
Chunk(Chunk recycle)
{
assert recycle.freeSlots == 0L;
this.slab = recycle.slab;
this.baseAddress = recycle.baseAddress;
this.shift = recycle.shift;
this.freeSlots = -1L;
this.recycler = recycle.recycler;
}
Chunk(Recycler recycler, ByteBuffer slab)
{
assert MemoryUtil.isExactlyDirect(slab);
this.recycler = recycler;
this.slab = slab;
this.baseAddress = MemoryUtil.getAddress(slab);
// The number of bits by which we need to shift to obtain a unit
// "31 &" is because numberOfTrailingZeros returns 32 when the capacity is zero
this.shift = 31 & (Integer.numberOfTrailingZeros(slab.capacity() / 64));
// -1 means all free whilst 0 means all in use
this.freeSlots = slab.capacity() == 0 ? 0L : -1L;
}
/**
* Acquire the chunk for future allocations: set the owner
*/
void acquire(LocalPool owner)
{
assert this.owner == null;
this.owner = owner;
}
/**
* Set the owner to null and return the chunk to the global pool if the chunk is fully free.
* This method must be called by the LocalPool when it is certain that
* the local pool shall never try to allocate any more buffers from this chunk.
*/
void release()
{
this.owner = null;
boolean statusUpdated = setEvicted();
assert statusUpdated : "Status of chunk " + this + " was not IN_USE.";
tryRecycle();
}
/**
* If the chunk is free, changes the chunk's status to IN_USE and returns the chunk to the pool
* that it was acquired from.
*
* Can recycle the chunk partially if the recycler supports it.
* This method can be called from multiple threads safely.
*
* Calling this method on a chunk that's currently in use (either owned by a LocalPool or already recycled)
* has no effect.
*/
void tryRecycle()
{
// Note that this may race with release(), therefore the order of those checks does matter.
// The EVICTED check may fail if the chunk was already partially recycled.
if (status != Status.EVICTED)
return;
if (owner != null)
return;
// We must use consistently either tryRecycleFully or tryRecycleFullyOrPartially,
// but we must not mix those for a single chunk, because they use a different mechanism for guarding
// that the chunk would be recycled at most once until the next acquire.
//
// If the recycler cannot recycle blocks partially, we have to make sure freeSlots was zeroed properly.
// Only one thread can transition freeSlots from -1 to 0 atomically, so this is a good way
// of ensuring only one thread recycles the block. In this case the chunk's status is
// updated only after freeSlots CAS succeeds.
//
// If the recycler can recycle blocks partially, we use the status field
// to guard at-most-once recycling. We cannot rely on atomically updating freeSlots from -1 to 0, because
// in this case we cannot expect freeSlots to be -1 (if it was, it wouldn't be partial).
if (recycler.canRecyclePartially())
tryRecycleFullyOrPartially();
else
tryRecycleFully();
}
/**
* Returns this chunk to the pool where it was acquired from, if it wasn't returned already.
* The chunk does not have to be totally free, but should have some free bits.
* However, if the chunk is fully free, it is released fully, not partially.
*/
private void tryRecycleFullyOrPartially()
{
assert recycler.canRecyclePartially();
if (free() > 0 && setInUse())
{
assert owner == null;
if (!tryRecycleFully()) // prefer to recycle fully, as fully free chunks are returned to a higher priority queue
recyclePartially();
}
}
private boolean tryRecycleFully()
{
if (!isFree() || !freeSlotsUpdater.compareAndSet(this, -1L, 0L))
return false;
recycleFully();
return true;
}
private void recyclePartially()
{
assert owner == null;
assert status == Status.IN_USE;
recycler.recyclePartially(this);
}
private void recycleFully()
{
assert owner == null;
assert freeSlots == 0L;
Status expectedStatus = recycler.canRecyclePartially() ? Status.IN_USE : Status.EVICTED;
boolean statusUpdated = setStatus(expectedStatus, Status.IN_USE);
// impossible: could only happen if another thread updated the status in the meantime
assert statusUpdated : "Status of chunk " + this + " was not " + expectedStatus;
recycler.recycle(this);
}
/**
* We stash the chunk in the attachment of a buffer
* that was returned by get(), this method simply
* retrives the chunk that sliced a buffer, if any.
*/
static Chunk getParentChunk(ByteBuffer buffer)
{
Object attachment = MemoryUtil.getAttachment(buffer);
if (attachment instanceof Chunk)
return (Chunk) attachment;
if (attachment instanceof Ref)
return ((Ref<Chunk>) attachment).get();
return null;
}
void setAttachment(ByteBuffer buffer)
{
if (Ref.DEBUG_ENABLED)
MemoryUtil.setAttachment(buffer, new Ref<>(this, null));
else
MemoryUtil.setAttachment(buffer, this);
}
boolean releaseAttachment(ByteBuffer buffer)
{
Object attachment = MemoryUtil.getAttachment(buffer);
if (attachment == null)
return false;
if (Ref.DEBUG_ENABLED)
((Ref<Chunk>) attachment).release();
return true;
}
@VisibleForTesting
long setFreeSlots(long val)
{
long ret = freeSlots;
freeSlots = val;
return ret;
}
int capacity()
{
return 64 << shift;
}
final int unit()
{
return 1 << shift;
}
final boolean isFree()
{
return freeSlots == -1L;
}
/** The total free size */
int free()
{
return Long.bitCount(freeSlots) * unit();
}
int freeSlotCount()
{
return Long.bitCount(freeSlots);
}
ByteBuffer get(int size)
{
return get(size, false, null);
}
/**
* Return the next available slice of this size. If
* we have exceeded the capacity we return null.
*/
ByteBuffer get(int size, boolean sizeIsLowerBound, ByteBuffer into)
{
// how many multiples of our units is the size?
// we add (unit - 1), so that when we divide by unit (>>> shift), we effectively round up
int slotCount = (size - 1 + unit()) >>> shift;
if (sizeIsLowerBound)
size = slotCount << shift;
// if we require more than 64 slots, we cannot possibly accommodate the allocation
if (slotCount > 64)
return null;
// convert the slotCount into the bits needed in the bitmap, but at the bottom of the register
long slotBits = -1L >>> (64 - slotCount);
// in order that we always allocate page aligned results, we require that any allocation is "somewhat" aligned
// i.e. any single unit allocation can go anywhere; any 2 unit allocation must begin in one of the first 3 slots
// of a page; a 3 unit must go in the first two slots; and any four unit allocation must be fully page-aligned
// to achieve this, we construct a searchMask that constrains the bits we find to those we permit starting
// a match from. as we find bits, we remove them from the mask to continue our search.
// this has an odd property when it comes to concurrent alloc/free, as we can safely skip backwards if
// a new slot is freed up, but we always make forward progress (i.e. never check the same bits twice),
// so running time is bounded
long searchMask = 0x1111111111111111L;
searchMask *= 15L >>> ((slotCount - 1) & 3);
// i.e. switch (slotCount & 3)
// case 1: searchMask = 0xFFFFFFFFFFFFFFFFL
// case 2: searchMask = 0x7777777777777777L
// case 3: searchMask = 0x3333333333333333L
// case 0: searchMask = 0x1111111111111111L
// truncate the mask, removing bits that have too few slots proceeding them
searchMask &= -1L >>> (slotCount - 1);
// this loop is very unroll friendly, and would achieve high ILP, but not clear if the compiler will exploit this.
// right now, not worth manually exploiting, but worth noting for future
while (true)
{
long cur = freeSlots;
// find the index of the lowest set bit that also occurs in our mask (i.e. is permitted alignment, and not yet searched)
// we take the index, rather than finding the lowest bit, since we must obtain it anyway, and shifting is more efficient
// than multiplication
int index = Long.numberOfTrailingZeros(cur & searchMask);
// if no bit was actually found, we cannot serve this request, so return null.
// due to truncating the searchMask this immediately terminates any search when we run out of indexes
// that could accommodate the allocation, i.e. is equivalent to checking (64 - index) < slotCount
if (index == 64)
return null;
// remove this bit from our searchMask, so we don't return here next round
searchMask ^= 1L << index;
// if our bits occur starting at the index, remove ourselves from the bitmask and return
long candidate = slotBits << index;
if ((candidate & cur) == candidate)
{
// here we are sure we will manage to CAS successfully without changing candidate because
// there is only one thread allocating at the moment, the concurrency is with the release
// operations only
while (true)
{
// clear the candidate bits (freeSlots &= ~candidate)
if (freeSlotsUpdater.compareAndSet(this, cur, cur & ~candidate))
break;
cur = freeSlots;
// make sure no other thread has cleared the candidate bits
assert ((candidate & cur) == candidate);
}
return set(index << shift, size, into);
}
}
}
private ByteBuffer set(int offset, int size, ByteBuffer into)
{
if (into == null)
into = MemoryUtil.getHollowDirectByteBuffer(ByteOrder.BIG_ENDIAN);
MemoryUtil.sliceDirectByteBuffer(slab, into, offset, size);
setAttachment(into);
return into;
}
/**
* Round the size to the next unit multiple.
*/
int roundUp(int v)
{
return BufferPool.roundUp(v, unit());
}
/**
* Release a buffer. Return:
* -1L if it is free (and so we should tryRecycle if owner is now null)
* some other value otherwise
**/
long free(ByteBuffer buffer)
{
if (!releaseAttachment(buffer))
return 1L;
int size = roundUp(buffer.capacity());
long address = MemoryUtil.getAddress(buffer);
assert (address >= baseAddress) & (address + size <= baseAddress + capacity());
int position = ((int)(address - baseAddress)) >> shift;
int slotCount = size >> shift;
long slotBits = 0xffffffffffffffffL >>> (64 - slotCount);
long shiftedSlotBits = (slotBits << position);
long next;
while (true)
{
long cur = freeSlots;
next = cur | shiftedSlotBits;
assert next == (cur ^ shiftedSlotBits); // ensure no double free
if (freeSlotsUpdater.compareAndSet(this, cur, next))
return next;
}
}
void freeUnusedPortion(ByteBuffer buffer)
{
int size = roundUp(buffer.limit());
int capacity = roundUp(buffer.capacity());
if (size == capacity)
return;
long address = MemoryUtil.getAddress(buffer);
assert (address >= baseAddress) & (address + size <= baseAddress + capacity());
// free any spare slots above the size we are using
int position = ((int)(address + size - baseAddress)) >> shift;
int slotCount = (capacity - size) >> shift;
long slotBits = 0xffffffffffffffffL >>> (64 - slotCount);
long shiftedSlotBits = (slotBits << position);
long next;
while (true)
{
long cur = freeSlots;
next = cur | shiftedSlotBits;
assert next == (cur ^ shiftedSlotBits); // ensure no double free
if (freeSlotsUpdater.compareAndSet(this, cur, next))
break;
}
MemoryUtil.setByteBufferCapacity(buffer, size);
}
@Override
public String toString()
{
return String.format("[slab %s, slots bitmap %s, capacity %d, free %d]", slab, Long.toBinaryString(freeSlots), capacity(), free());
}
@VisibleForTesting
public LocalPool owner()
{
return this.owner;
}
@VisibleForTesting
void unsafeFree()
{
Chunk parent = getParentChunk(slab);
if (parent != null)
parent.free(slab);
else
FileUtils.clean(slab);
}
static void unsafeRecycle(Chunk chunk)
{
if (chunk != null)
{
chunk.owner = null;
chunk.freeSlots = 0L;
chunk.recycleFully();
}
}
Status status()
{
return status;
}
private boolean setStatus(Status current, Status update)
{
return statusUpdater.compareAndSet(this, current, update);
}
private boolean setInUse()
{
return setStatus(Status.EVICTED, Status.IN_USE);
}
private boolean setEvicted()
{
return setStatus(Status.IN_USE, Status.EVICTED);
}
}
@VisibleForTesting
public static int roundUp(int size)
{
if (size <= TINY_ALLOCATION_LIMIT)
return roundUp(size, TINY_ALLOCATION_UNIT);
return roundUp(size, NORMAL_ALLOCATION_UNIT);
}
@VisibleForTesting
public static int roundUp(int size, int unit)
{
int mask = unit - 1;
return (size + mask) & ~mask;
}
@VisibleForTesting
public void shutdownLocalCleaner(long timeout, TimeUnit unit) throws InterruptedException, TimeoutException
{
shutdownNow(of(localPoolCleaner));
awaitTermination(timeout, unit, of(localPoolCleaner));
}
@VisibleForTesting
public BufferPoolMetrics metrics()
{
return metrics;
}
/** This is not thread safe and should only be used for unit testing. */
@VisibleForTesting
public void unsafeReset()
{
overflowMemoryUsage.reset();
memoryInUse.reset();
memoryAllocated.set(0);
localPool.get().unsafeRecycle();
globalPool.unsafeFree();
}
@VisibleForTesting
Chunk unsafeCurrentChunk()
{
return localPool.get().chunks.chunk0;
}
@VisibleForTesting
int unsafeNumChunks()
{
LocalPool pool = localPool.get();
return (pool.chunks.chunk0 != null ? 1 : 0)
+ (pool.chunks.chunk1 != null ? 1 : 0)
+ (pool.chunks.chunk2 != null ? 1 : 0);
}
}