dubbo的均衡策略

RoundRobinLoadBalance

public class RoundRobinLoadBalance extends AbstractLoadBalance {    public static final String NAME = "roundrobin";    private final ConcurrentMap<String, AtomicPositiveInteger> sequences = new ConcurrentHashMap<String, AtomicPositiveInteger>();    private static final class IntegerWrapper {        public IntegerWrapper(int value) {            this.value = value;        }        private int value;        public int getValue() {            return value;        }        public void setValue(int value) {            this.value = value;        }        public void decrement() {            this.value--;        }    }    protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {        String key = invokers.get(0).getUrl().getServiceKey() + "." + invocation.getMethodName();        int length = invokers.size(); // 总个数        int maxWeight = 0; // 最大权重        int minWeight = Integer.MAX_VALUE; // 最小权重        final LinkedHashMap<Invoker<T>, IntegerWrapper> invokerToWeightMap = new LinkedHashMap<Invoker<T>, IntegerWrapper>();        int weightSum = 0;        // 1.计算最大权重/最小权重/总权重        for (int i = 0; i < length; i++) {            int weight = getWeight(invokers.get(i), invocation);            maxWeight = Math.max(maxWeight, weight);            minWeight = Math.min(minWeight, weight);            if (weight > 0) {                invokerToWeightMap.put(invokers.get(i), new IntegerWrapper(weight));                weightSum += weight;            }        }        // 2.获取当前服务的调用次数，并加一返回        AtomicPositiveInteger sequence = sequences.get(key);        if (sequence == null) {            sequences.putIfAbsent(key, new AtomicPositiveInteger());            sequence = sequences.get(key);        }        int currentSequence = sequence.getAndIncrement();        // 3.取调用次数和总权重之模作为插点，轮询服务提供方        if (maxWeight > 0 && minWeight < maxWeight) { // 权重不一样            int mod = currentSequence % weightSum;// 取模            for (int i = 0; i < maxWeight; i++) {                for (Map.Entry<Invoker<T>, IntegerWrapper> each : invokerToWeightMap.entrySet()) {                    final Invoker<T> k = each.getKey();                    final IntegerWrapper v = each.getValue();                    if (mod == 0 && v.getValue() > 0) {                        // 如果轮询到该服务方且其权重没衰减完                        return k;                    }                    if (v.getValue() > 0) {                        // 减模，减少权重，确保权重低优先被跳过                        v.decrement();                        mod--;                    }                }            }        }        return invokers.get(currentSequence % length);    }}

ConsistentHashLoadBalance

public class ConsistentHashLoadBalance extends AbstractLoadBalance {    private final ConcurrentMap<String, ConsistentHashSelector<?>> selectors = new ConcurrentHashMap<String, ConsistentHashSelector<?>>();    @SuppressWarnings("unchecked")    @Override    protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {        String key = invokers.get(0).getUrl().getServiceKey() + "." + invocation.getMethodName();        int identityHashCode = System.identityHashCode(invokers);        ConsistentHashSelector<T> selector = (ConsistentHashSelector<T>) selectors.get(key);        if (selector == null || selector.getIdentityHashCode() != identityHashCode) {            selectors.put(key, new ConsistentHashSelector<T>(invokers, invocation.getMethodName(), identityHashCode));            selector = (ConsistentHashSelector<T>) selectors.get(key);        }        return selector.select(invocation);    }    private static final class ConsistentHashSelector<T> {        private final TreeMap<Long, Invoker<T>> virtualInvokers;        private final int replicaNumber;        private final int identityHashCode;        private final int[] argumentIndex;        // 构建红黑树，存储虚拟节点，key为指定的参数的hash值，value为服务提供方        public ConsistentHashSelector(List<Invoker<T>> invokers, String methodName, int identityHashCode) {            this.virtualInvokers = new TreeMap<Long, Invoker<T>>();            this.identityHashCode = System.identityHashCode(invokers);            URL url = invokers.get(0).getUrl();            this.replicaNumber = url.getMethodParameter(methodName, "hash.nodes", 160);// 虚拟节点参数            String[] index = Constants.COMMA_SPLIT_PATTERN.split(url.getMethodParameter(methodName, "hash.arguments", "0"));// 需要hash的参数            argumentIndex = new int[index.length];// 记录需要进行hash的参数位置            for (int i = 0; i < index.length; i++) {                argumentIndex[i] = Integer.parseInt(index[i]);            }            // 添加虚拟节点            for (Invoker<T> invoker : invokers) {                for (int i = 0; i < replicaNumber / 4; i++) {                    byte[] digest = md5(invoker.getUrl().toFullString() + i);// 对每个提供方进行加标志位后md5                    for (int h = 0; h < 4; h++) {                        long m = hash(digest, h);// 再计算hash                        virtualInvokers.put(m, invoker);// 添加虚拟节点                    }                }            }        }        public int getIdentityHashCode() {            return identityHashCode;        }        // 组装入参进行hash，找到最接近入参的最小的hash值对应的服务        public Invoker<T> select(Invocation invocation) {            String key = toKey(invocation.getArguments());// 组织参数            byte[] digest = md5(key);            Invoker<T> invoker = sekectForKey(hash(digest, 0));            return invoker;        }        private String toKey(Object[] args) {            StringBuilder buf = new StringBuilder();            for (int i : argumentIndex) {                if (i >= 0 && i < args.length) {                    buf.append(args[i]);                }            }            return buf.toString();        }        private Invoker<T> sekectForKey(long hash) {            Invoker<T> invoker;            Long key = hash;            if (!virtualInvokers.containsKey(key)) {                // 查找最近的节点                SortedMap<Long, Invoker<T>> tailMap = virtualInvokers.tailMap(key);//找到当前虚拟节点之后的而所有节点                if (tailMap.isEmpty()) {                    key = virtualInvokers.firstKey();// 之后没有节点，从头结点                } else {                    key = tailMap.firstKey();//找到最近的                }            }            invoker = virtualInvokers.get(key);// 正好命中            return invoker;        }        //不清楚，需要看        private long hash(byte[] digest, int number) {            return (((long) (digest[3 + number * 4] & 0xFF) << 24) | ((long) (digest[2 + number * 4] & 0xFF) << 16)                    | ((long) (digest[1 + number * 4] & 0xFF) << 8) | (digest[0 + number * 4] & 0xFF)) & 0xFFFFFFFFL;        }        private byte[] md5(String value) {            MessageDigest md5;            try {                md5 = MessageDigest.getInstance("MD5");            } catch (NoSuchAlgorithmException e) {                throw new IllegalStateException(e.getMessage(), e);            }            md5.reset();            byte[] bytes = null;            try {                bytes = value.getBytes("UTF-8");            } catch (UnsupportedEncodingException e) {                throw new IllegalStateException(e.getMessage(), e);            }            md5.update(bytes);            return md5.digest();        }    }}