StephanEwen commented on a change in pull request #9516: [FLINK-13815][State Backends] Implement the SpaceAllocator URL: https://github.com/apache/flink/pull/9516#discussion_r347254097
########## File path: flink-state-backends/flink-statebackend-heap-spillable/src/main/java/org/apache/flink/runtime/state/heap/space/PowerTwoBucketAllocator.java ########## @@ -0,0 +1,156 @@ +/* + * 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.flink.runtime.state.heap.space; + +import org.apache.flink.annotation.VisibleForTesting; +import org.apache.flink.util.MathUtils; +import org.apache.flink.util.Preconditions; + +import java.util.concurrent.ConcurrentLinkedQueue; + +/** + * This is a simple buddy-like allocator used for small space. The allocator always allocates a block + * of power-of-two size to satisfy a space request. For example, if a space of 54 bytes is requested, + * allocator will allocate a block of 64 bytes to it which leads to a waste of 10 bytes. + * + * <p>A {@link Chunk} will be divided into multiple buckets of the same size. Each bucket is further + * divided into blocks. Blocks in a bucket have the same size, but blocks in different buckets may have + * different size. Size of each block must be a power of two, and the maximum size of block can't exceed + * bucket size. + */ +public class PowerTwoBucketAllocator implements BucketAllocator { + + /** + * Minimum size of a block. + */ + private static final int MIN_BLOCK_SIZE = 32; + + /** + * Number of bits to represent {@link PowerTwoBucketAllocator#MIN_BLOCK_SIZE}. + */ + private static final int MIN_BLOCK_SIZE_BITS = MathUtils.log2strict(MIN_BLOCK_SIZE); + + /** + * Number of bits to represent bucket size. + */ + private final int bucketSizeBits; + + /** + * An array of all buckets. + */ + private Bucket[] allBuckets; + + /** + * An array of block allocator, and each allocator can only allocate blocks with fixed size. + * Size of blocks allocated by a allocator is twice of that allocated by the former allocator + * in the array. For example, size of blocks allocated by allocators in the array can be 32, + * 64, 128. + */ + private BlockAllocator[] blockAllocators; + + /** + * A queue of free buckets. + */ + private final ConcurrentLinkedQueue<Bucket> freeBucketsQueue; + + PowerTwoBucketAllocator(int chunkSize, int bucketSize) { + Preconditions.checkArgument((bucketSize & bucketSize - 1) == 0, + "Bucket size must be a power of 2, but the actual is " + bucketSize); + this.bucketSizeBits = MathUtils.log2strict(bucketSize); + this.freeBucketsQueue = new ConcurrentLinkedQueue<>(); + + int numberBuckets = chunkSize >>> this.bucketSizeBits; + // number of possible values for block size + int numberBlockSize = bucketSizeBits - MIN_BLOCK_SIZE_BITS + 1; + Preconditions.checkArgument(numberBuckets >= numberBlockSize, + "Number of possible values for block size is more than the number of buckets, " + + "so allocator can't satisfy requests for different block size at the same time. " + + "Try to use a larger chunk."); + this.allBuckets = new Bucket[numberBuckets]; + for (int i = 0; i < allBuckets.length; ++i) { + allBuckets[i] = new Bucket(i << this.bucketSizeBits, bucketSize); + this.freeBucketsQueue.offer(allBuckets[i]); + } + + this.blockAllocators = new BlockAllocator[this.bucketSizeBits - MIN_BLOCK_SIZE_BITS + 1]; + for (int i = 0; i < blockAllocators.length; i++) { + blockAllocators[i] = new BlockAllocator(i, this.freeBucketsQueue); + } + } + + @Override + public int allocate(int len) { + Preconditions.checkArgument(len > 0, Review comment: Avoid string concatenation in checking statements. It is very expensive. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services
