io.grpc.internal.ShardedAtomicLongCounter Maven / Gradle / Ivy
/*
* Copyright 2017, gRPC Authors All rights reserved.
*
* 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.
*/
package io.grpc.internal;
import com.google.common.annotations.VisibleForTesting;
import java.util.concurrent.atomic.AtomicLongArray;
/**
* An implementation of {@link LongCounter} that works by sharded across an array of
* {@link AtomicLong} objects. Do not instantiate directly, instead use {@link LongCounterFactory}.
*/
final class ShardedAtomicLongCounter implements LongCounter {
private final AtomicLongArray counters;
private final int mask;
/**
* Accepts a hint on how many shards should be created. The actual number of shards may differ.
*/
ShardedAtomicLongCounter(int numShardsHint) {
int numShards = forcePower2(numShardsHint);
counters = new AtomicLongArray(numShards);
mask = numShards - 1;
}
/**
* Force the shard size to a power of 2, with a reasonable ceiling value.
* Let's avoid clever bit twiddling and keep it simple.
*/
static int forcePower2(int numShardsHint) {
if (numShardsHint >= 64) {
return 64;
} else if (numShardsHint >= 32) {
return 32;
} else if (numShardsHint >= 16) {
return 16;
} else {
return 8;
}
}
@VisibleForTesting
int getCounterIdx(int hashCode) {
return hashCode & mask;
}
@Override
public void add(long delta) {
// TODO(zpencer): replace fixed hashcode with a lightweight RNG. See guava's Striped64.
counters.addAndGet(getCounterIdx(Thread.currentThread().hashCode()), delta);
}
@Override
public long value() {
long val = 0;
for (int i = 0; i < counters.length(); i++) {
val += counters.get(i);
}
return val;
}
}