| /* |
| * Copyright (C) 2016 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. |
| */ |
| |
| package com.android.internal.util; |
| |
| import android.os.SystemClock; |
| |
| import static com.android.internal.util.Preconditions.checkArgumentNonnegative; |
| import static com.android.internal.util.Preconditions.checkArgumentPositive; |
| |
| /** |
| * A class useful for rate-limiting or throttling that stores and distributes tokens. |
| * |
| * A TokenBucket starts with a fixed capacity of tokens, an initial amount of tokens, and |
| * a fixed filling period (in milliseconds). |
| * |
| * For every filling period, the bucket gains one token, up to its maximum capacity from |
| * which point tokens simply overflow and are lost. Tokens can be obtained one by one or n by n. |
| * |
| * The available amount of tokens is computed lazily when the bucket state is inspected. |
| * Therefore it is purely synchronous and does not involve any asynchronous activity. |
| * It is not synchronized in any way and not a thread-safe object. |
| * |
| * {@hide} |
| */ |
| public class TokenBucket { |
| |
| private final int mFillDelta; // Time in ms it takes to generate one token. |
| private final int mCapacity; // Maximum number of tokens that can be stored. |
| private long mLastFill; // Last time in ms the bucket generated tokens. |
| private int mAvailable; // Current number of available tokens. |
| |
| /** |
| * Create a new TokenBucket. |
| * @param deltaMs the time in milliseconds it takes to generate a new token. |
| * Must be strictly positive. |
| * @param capacity the maximum token capacity. Must be strictly positive. |
| * @param tokens the starting amount of token. Must be positive or zero. |
| */ |
| public TokenBucket(int deltaMs, int capacity, int tokens) { |
| mFillDelta = checkArgumentPositive(deltaMs, "deltaMs must be strictly positive"); |
| mCapacity = checkArgumentPositive(capacity, "capacity must be strictly positive"); |
| mAvailable = Math.min(checkArgumentNonnegative(tokens), mCapacity); |
| mLastFill = scaledTime(); |
| } |
| |
| /** |
| * Create a new TokenBucket that starts completely filled. |
| * @param deltaMs the time in milliseconds it takes to generate a new token. |
| * Must be strictly positive. |
| * @param capacity the maximum token capacity. Must be strictly positive. |
| */ |
| public TokenBucket(int deltaMs, int capacity) { |
| this(deltaMs, capacity, capacity); |
| } |
| |
| /** Reset this TokenBucket and set its number of available tokens. */ |
| public void reset(int tokens) { |
| checkArgumentNonnegative(tokens); |
| mAvailable = Math.min(tokens, mCapacity); |
| mLastFill = scaledTime(); |
| } |
| |
| /** Returns this TokenBucket maximum token capacity. */ |
| public int capacity() { |
| return mCapacity; |
| } |
| |
| /** Returns this TokenBucket currently number of available tokens. */ |
| public int available() { |
| fill(); |
| return mAvailable; |
| } |
| |
| /** Returns true if this TokenBucket as one or more tokens available. */ |
| public boolean has() { |
| fill(); |
| return mAvailable > 0; |
| } |
| |
| /** Consumes a token from this TokenBucket and returns true if a token is available. */ |
| public boolean get() { |
| return (get(1) == 1); |
| } |
| |
| /** |
| * Try to consume many tokens from this TokenBucket. |
| * @param n the number of tokens to consume. |
| * @return the number of tokens that were actually consumed. |
| */ |
| public int get(int n) { |
| fill(); |
| if (n <= 0) { |
| return 0; |
| } |
| if (n > mAvailable) { |
| int got = mAvailable; |
| mAvailable = 0; |
| return got; |
| } |
| mAvailable -= n; |
| return n; |
| } |
| |
| private void fill() { |
| final long now = scaledTime(); |
| final int diff = (int) (now - mLastFill); |
| mAvailable = Math.min(mCapacity, mAvailable + diff); |
| mLastFill = now; |
| } |
| |
| private long scaledTime() { |
| return SystemClock.elapsedRealtime() / mFillDelta; |
| } |
| } |