Flow 、SubmissionPubliser类是 java9中新增的类，都被放在JUC包中
Flow
定义了一种生产者和消费者(订阅者)模型的接口，可以用于流式控制中
Publisher
//流式接口
//定义生产者
@FunctionalInterface
public static interface Publisher<T> {
/**
* 增加订阅者
*
* @param subscriber 订阅者
* @throws NullPointerException if subscriber is null
*/
public void subscribe(Subscriber<? super T> subscriber);
}
Subscriber
//订阅者
public static interface Subscriber<T> {
/**
* 在Publisher接收一个新的订阅者时，会调用该方法
*
* @param subscription 订阅包，提供了获取下一个元素和取消获取操作的方法
*/
public void onSubscribe(Subscription subscription);
/**
* 获取一个新元素，每次有新元素的时候会被调用
*
* @param item the item
*/
public void onNext(T item);
/**
* 发送异常时会被调用
*
* @param throwable the exception
*/
public void onError(Throwable throwable);
/**
* 当数据接收完成后调用
*/
public void onComplete();
}
Subscription
//订阅包
public static interface Subscription {
/**
* 发起请求，获取元素
*
* @param n 获取的增量，Long.MAX_VALUE表示无限的
*/
public void request(long n);
/**
* 取消消息接收
*/
public void cancel();
}
Processor
//既可以充当生产者，也可以充当订阅者
public static interface Processor<T,R> extends Subscriber<T>, Publisher<R> {
}
static final int DEFAULT_BUFFER_SIZE = 256;
/**
* 定义的默认缓存区，256
*
* @return the buffer size value
*/
public static int defaultBufferSize() {
return DEFAULT_BUFFER_SIZE;
}
SubmissionPublisher
FLow 类的一种实现，可以在并发环境下使用
JDK中的说明：
SubmissionPublisher提供了使用Executor的构造函数，如果生产者是在独立线程中运行，并且能估计消费者数量，就使用Executors.newFixedThreadPool(int)固定线程数量的线程池，否则使用默认，ForkJoinPool.commonPool()
SubmissionPublisher提供缓冲功能，能够使生产者和消费者以不同的速率运行，每个消费者独立使用一个缓冲区，缓冲区在首次使用的时候创建，提供了一个默认值256，并会根据需要扩大到最大值，容量通常扩大到最近的2的次幂或者支持的最大值
SubmissionPublisher可以在多个线程之间共享，会在发布项目之前执行操作或者会发出一个happen-before信号给每个对应的消费者
发布方法支持设置在缓冲区满时如何处理的不同策略，submit(Object)方法会阻塞直到有可用资源，这种用法最简单，但速度慢；offer方法虽然会丢弃项目，但提供了插入动作重试的机会
如果任何Subscriber方法抛出异常，在其订阅将被取消
方法consume(Consumer)简化了对常见情况的支持，其中订阅者的唯一操作是使用supplied的函数请求和处理所有项目
此类还可以作为生成元素的子类的基类，并使用此类中的方法发布。例如，下面是一个周期性发布supplier生成元素的类。 （实际上，您可以添加独立启动和停止生成的方法，在发布者之间共享Executor等，或者使用SubmissionPublisher作为组件而不是超类。）
class PeriodicPublisher<T> extends SubmissionPublisher<T> {
final ScheduledFuture<?> periodicTask;
final ScheduledExecutorService scheduler;
PeriodicPublisher(Executor executor, int maxBufferCapacity,
Supplier<? extends T> supplier,
long period, TimeUnit unit) {
super(executor, maxBufferCapacity);
scheduler = new ScheduledThreadPoolExecutor(1);
periodicTask = scheduler.scheduleAtFixedRate(
() -> submit(supplier.get()), 0, period, unit);
}
public void close() {
periodicTask.cancel(false);
scheduler.shutdown();
super.close();
}
}
以下是Flow.Processor实现的示例，为了简化说明，使用单步向publisher发起请求，更合适的版本可以使用submit方法或者其他实用方法来监控流量
class TransformProcessor<S,T> extends SubmissionPublisher<T>
implements Flow.Processor<S,T> {
final Function<? super S, ? extends T> function;
Flow.Subscription subscription;
TransformProcessor(Executor executor, int maxBufferCapacity,
Function<? super S, ? extends T> function) {
super(executor, maxBufferCapacity);
this.function = function;
}
public void onSubscribe(Flow.Subscription subscription) {
(this.subscription = subscription).request(1);
}
public void onNext(S item) {
subscription.request(1);
submit(function.apply(item));
}
public void onError(Throwable ex) {
closeExceptionally(ex); }
public void onComplete() {
close(); }
}
使用示例
@Test
public void test1() throws Exception {
SubmissionPublisher<Integer> submissionPublisher = new SubmissionPublisher<>();
submissionPublisher.consume(System.out::println);
submissionPublisher.submit(1);
submissionPublisher.submit(2);
submissionPublisher.offer(3, (x, y) -> {
System.out.println("xxx");
return false;
});
}
使用二进制来表示状态码可以参考：https://blog.csdn.net/qq_36631014/article/details/79675924
基本属性
//缓存区最大值，1073741824
static final int BUFFER_CAPACITY_LIMIT = 1 << 30;
//初始的最大缓存区，缓存区大小必须是2的幂次
static final int INITIAL_CAPACITY = 32;
/**
* BufferedSubscription通过next字段维护了一个链表，这种结构对循环发布非常有用
* 需要遍历O(n)次来检查重复的消费者，但是预计消费比发布少的多
* 取消订阅只发生在遍历循环期间，如果BufferedSubscription方法返回负值表示他们已经关闭
* 为了减少head-of-line阻塞，submit和offer方法首先调用BufferedSubscription的offer方法
* 在满的时候提供了重试
*/
BufferedSubscription<T> clients;
/** 运行状态，只在锁内更新*/
volatile boolean closed;
/** 在第一次调用subscribe的时候，设置为true，初始化消费的所有者线程*/
boolean subscribed;
/** 第一次调用subscribe的线程，如果线程曾经改变过，则为null */
Thread owner;
/** 如果不为null，说明在closeExceptionally中生成了异常 */
volatile Throwable closedException;
// 用于构造BufferedSubscriptions的参数
final Executor executor;
//onNext中发生异常时的处理函数
final BiConsumer<? super Subscriber<? super T>, ? super Throwable> onNextHandler;
//表示缓冲区最大容量
final int maxBufferCapacity;
构造函数
//默认构造函数，默认使用ForkJoinPool的公共线程池异步运行subscriber，除非并发级别不支持，则使用普通的线程池
//ThreadPerTaskExecutor
//subscriber的最大缓冲区为256
//Subscriber的异常处理器为null
public SubmissionPublisher() {
this(ASYNC_POOL, Flow.defaultBufferSize(), null);
}
//使用指定的线程池，指定的缓冲区容量创建
public SubmissionPublisher(Executor executor, int maxBufferCapacity) {
this(executor, maxBufferCapacity, null);
}
public SubmissionPublisher(Executor executor, int maxBufferCapacity,
BiConsumer<? super Subscriber<? super T>, ? super Throwable> handler) {
if (executor == null)
throw new NullPointerException();
if (maxBufferCapacity <= 0)
throw new IllegalArgumentException("capacity must be positive");
this.executor = executor;
this.onNextHandler = handler;
//最大容量为离2的幂次最近的值，跟hashMap的计算最大容量算法一样
this.maxBufferCapacity = roundCapacity(maxBufferCapacity);
}
内部类
ConsumerSubscriber
/** 订阅者,供内部使用*/
static final class ConsumerSubscriber<T> implements Subscriber<T> {
final CompletableFuture<Void> status;
final Consumer<? super T> consumer;
Subscription subscription;
ConsumerSubscriber(CompletableFuture<Void> status,
Consumer<? super T> consumer) {
this.status = status; this.consumer = consumer;
}
public final void onSubscribe(Subscription subscription) {
this.subscription = subscription;
//如果元素已经消费完成，那么取消订阅
status.whenComplete((v, e) -> subscription.cancel());
//没有完成继续请求
if (!status.isDone())
subscription.request(Long.MAX_VALUE);
}
//发送错误时候的处理
public final void onError(Throwable ex) {
status.completeExceptionally(ex);
}
//元素消费完成时候的处理
public final void onComplete() {
status.complete(null);
}
//有新元素的时候会被调用
public final void onNext(T item) {
try {
//执行Consumer函数
consumer.accept(item);
} catch (Throwable ex) {
subscription.cancel();
status.completeExceptionally(ex);
}
}
}
ConsumerTask
//订阅者的消费任务
static final class ConsumerTask<T> extends ForkJoinTask<Void>
implements Runnable, CompletableFuture.AsynchronousCompletionTask {
final BufferedSubscription<T> consumer;
ConsumerTask(BufferedSubscription<T> consumer) {
this.consumer = consumer;
}
public final Void getRawResult() {
return null; }
public final void setRawResult(Void v) {
}
public final boolean exec() {
consumer.consume(); return false; }
public final void run() {
consumer.consume(); }
}
BufferedSubscription
//基于数组的可扩展的环形缓冲区，通过CAS原子操作来实现插入和获取元素
//在任何时间内最多只有一个活动的消费者任务
//publisher通过锁来保证单个生产者
//生成者和消费者之间的同步依赖于volatile修饰的ctl、demand、waiting变量
//使用ctl管理状态
//缓存区开始很小，只在需要的时候扩容
//使用了Contended类避免CPU伪共享问题
//当生成者和消费者以不同的速度运行时，会出现失衡，通过人为细分一些消费者方法，包括隔离所有subscriber回调
@jdk.internal.vm.annotation.Contended
static final class BufferedSubscription<T>
implements Subscription, ForkJoinPool.ManagedBlocker {
long timeout; // Long.MAX_VALUE 表示一直等待
int head; // 下一个获取的位置
int tail; // 下一个插入的位置
final int maxCapacity; // 最大缓冲大小
volatile int ctl; // 以volatile方式运行状态标志
Object[] array; // 缓冲数组
final Subscriber<? super T> subscriber; //消费者
final BiConsumer<? super Subscriber<? super T>, ? super Throwable> onNextHandler; //用于处理异常
Executor executor; // 线程池，发生错误为null
Thread waiter; // 生成者线程被阻塞
Throwable pendingError; // onError发生时会赋值该变量
BufferedSubscription<T> next; // publisher使用
BufferedSubscription<T> nextRetry; // publisher使用
@jdk.internal.vm.annotation.Contended("c") // 隔离CPU缓存行
volatile long demand; // 未获取的请求
@jdk.internal.vm.annotation.Contended("c")
volatile int waiting; // 如果生产者被阻塞，则不为零
// ctl 16进制值
static final int CLOSED = 0x01; // 设置了，忽略其他位
static final int ACTIVE = 0x02; // 保存消费者任务一直存活
static final int REQS = 0x04; // 非零请求
static final int ERROR = 0x08; // 发生错误时，调用onError
static final int COMPLETE = 0x10; // 当完成时，调用onComplete
static final int RUN = 0x20; // 任务正在跑或刚开始跑
static final int OPEN = 0x40; // 订阅后位true
static final long INTERRUPTED = -1L; // 超时或者中断标志
BufferedSubscription(Subscriber<? super T> subscriber,
Executor executor,
BiConsumer<? super Subscriber<? super T>,
? super Throwable> onNextHandler,
Object[] array,
int maxBufferCapacity) {
this.subscriber = subscriber;
this.executor = executor;
this.onNextHandler = onNextHandler;
this.array = array;
this.maxCapacity = maxBufferCapacity;
}
// Wrappers for some VarHandle methods
//cas更新ctl变量
final boolean weakCasCtl(int cmp, int val) {
return CTL.weakCompareAndSet(this, cmp, val);
}
//进行或计算
final int getAndBitwiseOrCtl(int bits) {
return (int)CTL.getAndBitwiseOr(this, bits);
}
//这段代码会将demand的值减去指定的k
final long subtractDemand(int k) {
long n = (long)(-k);
//为什么还要再加n呢？
return n + (long)DEMAND.getAndAdd(this, n);
}
//cas设置demand值
final boolean casDemand(long cmp, long val) {
return DEMAND.compareAndSet(this, cmp, val);
}
// SubmissionPublisher实用方法
/**
* 如果关闭了返回true (消费任务可能还在运行中).
*/
final boolean isClosed() {
return (ctl & CLOSED) != 0;
}
/**
* 返回估计的元素数量，如果关闭了返回-1
*/
final int estimateLag() {
int c = ctl, n = tail - head;
return ((c & CLOSED) != 0) ? -1 : (n < 0) ? 0 : n;
}
// 提交元素的方法
/**
* 尝试插入元素，并启动消费任务
* @return 如果关闭返回-1，0表示满了
*/
final int offer(T item, boolean unowned) {
//存放元素的数组
Object[] a;
//cap 表示数组的容量
int stat = 0, cap = ((a = array) == null) ? 0 : a.length;
//i 表示要插入的索引位置；n表示已有的元素
int t = tail, i = t & (cap - 1), n = t + 1 - head;
if (cap > 0) {
boolean added;
if (n >= cap && cap < maxCapacity) // 发生扩容
added = growAndOffer(item, a, t);
else if (n >= cap || unowned) // 如果不是自身的线程，就说明有竞争，需要使用CAS来更新
added = QA.compareAndSet(a, i, null, item);
else {
// 使用release 模式插入元素到数组中
QA.setRelease(a, i, item);
added = true;
}
//插入成功，tail后移一位
if (added) {
tail = t + 1;
stat = n;
}
}
return startOnOffer(stat); //尝试唤醒消费线程
}
/**
* 尝试扩展缓冲区，并插入元素，成功返回true。如果内存溢出就会失败
*/
final boolean growAndOffer(T item, Object[] a, int t) {
int cap = 0, newCap = 0;
Object[] newArray = null;
if (a != null && (cap = a.length) > 0 && (newCap = cap << 1) > 0) {
//进行两倍扩容
try {
newArray = new Object[newCap];
} catch (OutOfMemoryError ex) {
}
}
if (newArray == null)
return false;
else {
//从原数组中取值，并插入新数组中
int newMask = newCap - 1;
newArray[t-- & newMask] = item;
for (int mask = cap - 1, k = mask; k >= 0; --k) {
Object x = QA.getAndSet(a, t & mask, null);
if (x == null) //x为null说明已经获取
break;
else
newArray[t-- & newMask] = x;
}
array = newArray;
VarHandle.releaseFence(); //释放空数组
return true;
}
}
/**
* 重试版本，没有扩容或者偏置
*/
final int retryOffer(T item) {
Object[] a;
int stat = 0, t = tail, h = head, cap;
if ((a = array) != null && (cap = a.length) > 0 &&
QA.compareAndSet(a, (cap - 1) & t, null, item))
//将tail后移1位
stat = (tail = t + 1) - h;
return startOnOffer(stat);
}
/**
* 唤醒消费者任务
* @return 如果是关闭的返回负数
*/
final int startOnOffer(int stat) {
int c; // 如果存在请求且未激活，则启动或保持活动状态
if (((c = ctl) & (REQS | ACTIVE)) == REQS &&
((c = getAndBitwiseOrCtl(RUN | ACTIVE)) & (RUN | CLOSED)) == 0)
//启动消费者线程
tryStart();
else if ((c & CLOSED) != 0)
stat = -1;
return stat;
}
/**
* 启动消费的任务。 失败设置错误状态。
*/
final void tryStart() {
try {
Executor e;
//消费者任务
ConsumerTask<T> task = new ConsumerTask<T>(this);
if ((e = executor) != null) // 发生错误就跳过
e.execute(task);
} catch (RuntimeException | Error ex) {
//设置ctl状态
getAndBitwiseOrCtl(ERROR | CLOSED);
throw ex;
}
}
// 向消费者任务发信号
/**
* 设置给定的控制位，启动任务，如果任务没有运行或者没有关闭
* @param 运行状态位
*/
final void startOnSignal(int bits) {
if ((ctl & bits) != bits &&
(getAndBitwiseOrCtl(bits) & (RUN | CLOSED)) == 0)
tryStart();
}
//订阅中
final void onSubscribe() {
startOnSignal(RUN | ACTIVE);
}
//已完成
final void onComplete() {
startOnSignal(RUN | ACTIVE | COMPLETE);
}
//发生错误
final void onError(Throwable ex) {
int c; Object[] a; //发生异步错误了清空缓冲区
if (ex != null)
pendingError = ex;
if (((c = getAndBitwiseOrCtl(ERROR | RUN | ACTIVE)) & CLOSED) == 0) {
//还没有关闭
if ((c & RUN) == 0) //没有运行，尝试重试
tryStart();
else if ((a = array) != null) //清空缓冲区
Arrays.fill(a, null);
}
}
//取消
public final void cancel() {
onError(null);
}
//请求为获取的数据
public final void request(long n) {
if (n > 0L) {
for (;;) {
long p = demand, d = p + n; // saturate
if (casDemand(p, d < p ? Long.MAX_VALUE : d))
break;
}
startOnSignal(RUN | ACTIVE | REQS);
}
else
onError(new IllegalArgumentException(
"non-positive subscription request"));
}
// 消费者的方法
/**
* ConsumerTask调用，循环消费元素，或者在提交元素的时候，间接触发
*/
final void consume() {
Subscriber<? super T> s;
if ((s = subscriber) != null) {
// hoist checks
//触发消费者，请求更多的数据
subscribeOnOpen(s);
long d = demand;
//从数组头到尾进行循环
for (int h = head, t = tail;;) {
int c, taken; boolean empty;
//如果发生了错误，中断消费
if (((c = ctl) & ERROR) != 0) {
closeOnError(s, null);
break;
}
//一直获取元素，直到消费完或者发生错误
else if ((taken = takeItems(s, d, h)) > 0) {
//头指针后移
head = h += taken;
//修改未获取数据的局部变量demand
d = subtractDemand(taken);
}
else if ((d = demand) == 0L && (c & REQS) != 0)
weakCasCtl(c, c & ~REQS); // 已经消费完，删除ctl中的请求标志位
else if (d != 0L && (c & REQS) == 0)
weakCasCtl(c, c | REQS); // 有新元素需要消费，增加ctl中的请求标志位
else if (t == (t = tail)) {
// 稳定性检查
if ((empty = (t == h)) && (c & COMPLETE) != 0) {
//已经消费完了，但缓存区还没关闭
closeOnComplete(s); //关闭缓存区
break;
}
else if (empty || d == 0L) {
//判断ctl运行标志是否有ACTIVE标志，有bit=ACTIVE
//没有bit=RUN
int bit = ((c & ACTIVE) != 0) ? ACTIVE : RUN;
//删除相应的标志位，并更新ctl值，如果是RUN状态，需要退出消费任务
if (weakCasCtl(c, c & ~bit) && bit == RUN)
break; // 取消激活或者退出
}
}
}
}
}
/**
* 一直消费元素直到 不可用 或者 达到边界 或者 发生错误
*
* @param s subscriber 消费者
* @param d demand 当前需要获取的数量
* @param h current head 当前的头指针位置
* @return number taken 获取的数量
*/
final int takeItems(Subscriber<? super T> s, long d, int h) {
Object[] a;
int k = 0, cap;
if ((a = array) != null && (cap = a.length) > 0) {
int m = cap - 1, b = (m >>> 3) + 1; // min(1, cap/8)
int n = (d < (long)b) ? (int)d : b;
for (; k < n; ++h, ++k) {
//获取元素，并置为null
Object x = QA.getAndSet(a, h & m, null);
if (waiting != 0)
//唤醒被阻塞的生成者
signalWaiter();
if (x == null)
break;
else if (!consumeNext(s, x)) //调用消费者的onNext方法，来处理元素
break;
}
}
return k;
}
//调用消费者的onNext方法，来处理元素
final boolean consumeNext(Subscriber<? super T> s, Object x) {
try {
@SuppressWarnings("unchecked") T y = (T) x;
if (s != null)
s.onNext(y);
return true;
} catch (Throwable ex) {
//处理异常
handleOnNext(s, ex);
return false;
}
}
/**
* 处理 Subscriber.onNext中的异常
*/
final void handleOnNext(Subscriber<? super T> s, Throwable ex) {
BiConsumer<? super Subscriber<? super T>, ? super Throwable> h;
try {
if ((h = onNextHandler) != null)
//调用自定义的BiConsumer函数处理异常
h.accept(s, ex);
} catch (Throwable ignore) {
}
//关闭缓冲并调用消费者的onError方法
closeOnError(s, ex);
}
/**
* 如果是第一次执行，那么执行subscriber.onSubscribe，用于请求更多数据
*/
final void subscribeOnOpen(Subscriber<? super T> s) {
if ((ctl & OPEN) == 0 && (getAndBitwiseOrCtl(OPEN) & OPEN) == 0)
consumeSubscribe(s);
}
//执行subscriber.onSubscribe，用于请求更多数据
final void consumeSubscribe(Subscriber<? super T> s) {
try {
if (s != null) // ignore if disabled
s.onSubscribe(this);
} catch (Throwable ex) {
closeOnError(s, ex);
}
}
/**
* 缓冲区还没关闭，就执行subscriber.onComplete
*/
final void closeOnComplete(Subscriber<? super T> s) {
if ((getAndBitwiseOrCtl(CLOSED) & CLOSED) == 0)
consumeComplete(s);
}
//执行subscriber.onComplete
final void consumeComplete(Subscriber<? super T> s) {
try {
if (s != null)
s.onComplete();
} catch (Throwable ignore) {
}
}
/**
* 发生错误，执行subscriber.onError,并且唤醒阻塞的生产者
*/
final void closeOnError(Subscriber<? super T> s, Throwable ex) {
if ((getAndBitwiseOrCtl(ERROR | CLOSED) & CLOSED) == 0) {
if (ex == null)
ex = pendingError;
pendingError = null; // detach
executor = null; // suppress racing start calls
signalWaiter();
consumeError(s, ex);
}
}
//执行subscriber.onError
final void consumeError(Subscriber<? super T> s, Throwable ex) {
try {
if (ex != null && s != null)
s.onError(ex);
} catch (Throwable ignore) {
}
}
// 阻塞支持
/**
* 唤醒等待的生产者
*/
final void signalWaiter() {
Thread w;
waiting = 0;
if ((w = waiter) != null)
LockSupport.unpark(w);
}
/**
* 如果缓冲区关闭了，或者有可用空间，返回true
*/
public final boolean isReleasable() {
Object[] a; int cap;
return ((ctl & CLOSED) != 0 ||
((a = array) != null && (cap = a.length) > 0 &&
QA.getAcquire(a, (cap - 1) & tail) == null));
}
/**
* 一直阻塞知道 timeout, closed,或者有可用空间
*/
final void awaitSpace(long nanos) {
if (!isReleasable()) {
ForkJoinPool.helpAsyncBlocker(executor, this);
if (!isReleasable()) {
timeout = nanos;
try {
ForkJoinPool.managedBlock(this);
} catch (InterruptedException ie) {
timeout = INTERRUPTED;
}
if (timeout == INTERRUPTED)
Thread.currentThread().interrupt();
}
}
}
/**
* 给 ManagedBlocker提供的用于阻塞的方法
*/
public final boolean block() {
long nanos = timeout;
boolean timed = (nanos < Long.MAX_VALUE);
long deadline = timed ? System.nanoTime() + nanos : 0L;
while (!isReleasable()) {
if (Thread.interrupted()) {
timeout = INTERRUPTED;
if (timed)
break;
}
else if (timed && (nanos = deadline - System.nanoTime()) <= 0L)
break;
else if (waiter == null)
waiter = Thread.currentThread();
else if (waiting == 0)
waiting = 1;
else if (timed)
LockSupport.parkNanos(this, nanos);
else
LockSupport.park(this);
}
waiter = null;
waiting = 0;
return true;
}
// VarHandle mechanics 一些变量的封装对象，相当于以前调用UNSAFE的方法
static final VarHandle CTL;
static final VarHandle DEMAND;
static final VarHandle QA;
static {
try {
MethodHandles.Lookup l = MethodHandles.lookup();
CTL = l.findVarHandle(BufferedSubscription.class, "ctl",
int.class);
DEMAND = l.findVarHandle(BufferedSubscription.class, "demand",
long.class);
QA = MethodHandles.arrayElementVarHandle(Object[].class);
} catch (ReflectiveOperationException e) {
throw new ExceptionInInitializerError(e);
}
// 减少首次加载时候的风险
// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
Class<?> ensureLoaded = LockSupport.class;
}
}
ThreadPerTaskExecutor
/** 如果ForkJoinPool.commonPool()不支持并发(公共线程池的并发级别小于1)，将使用该类*/
private static final class ThreadPerTaskExecutor implements Executor {
ThreadPerTaskExecutor() {
} // 禁止使用构造函数创建类
public void execute(Runnable r) {
new Thread(r).start(); }
}
基本方法
subscribe
//给传入的订阅者订阅，如果已经订阅，将调用订阅者的onError方法抛出IllegalStateException异常
//如果订阅成功，则会异步调用订阅者的onSubscribe方法，如果其中抛出异常，订阅将被取消
//如果SubmissionPublisher被异常关闭，那么订阅者的onError方法会被调用
//如果没有异常被关闭了，就会调用订阅者的onComplete方法
//通过调用Subscription的request方法能够接收其他更多数据
//通过调用Subscription的cancel方法取消订阅
public void subscribe(Subscriber<? super T> subscriber) {
if (subscriber == null) throw new NullPointerException();
// 分配初始数组
int max = maxBufferCapacity;
Object[] array = new Object[max < INITIAL_CAPACITY ?
max : INITIAL_CAPACITY];
BufferedSubscription<T> subscription =
new BufferedSubscription<T>(subscriber, executor, onNextHandler,
array, max);
//同步解决了一些变量可见性问题
synchronized (this) {
if (!subscribed) {
subscribed = true;
owner = Thread.currentThread();
}
//循环缓冲区链表，并处理订阅
for (BufferedSubscription<T> b = clients, pred = null;;) {
//新的订阅者，始终会被放到链表的最后,b的变量会在循环末尾被next赋值，最后一个缓冲区的next值为null
if (b == null) {
Throwable ex;
//执行消费者任务
subscription.onSubscribe();
if ((ex = closedException) != null)
//异常处理
subscription.onError(ex);
else if (closed)
//关闭完成处理
subscription.onComplete();
else if (pred == null)
//首次订阅
clients = subscription;
else
//后面的订阅者缓冲区通过next连接成链表
pred.next = subscription;
break;
}
BufferedSubscription<T> next = b.next;
if (b.isClosed()) {
// 缓冲区关闭
b.next = null; // 断开该缓存区的连接
if (pred == null)
clients = next;
else
pred.next = next;
}
else if (subscriber.equals(b.subscriber)) {
//重复的订阅者，抛出异常
b.onError(new IllegalStateException("Duplicate subscribe"));
break;
}
else
pred = b;
b = next;
}
}
}
submit
//将元素发布给每个订阅者，如果缓冲区已满，也会一直等待
public int submit(T item) {
return doOffer(item, Long.MAX_VALUE, null);
}
offer
//提供了自定义BiPredicate用于判断，参数是否满足指定的要求，如果满足将有一次重试的机会
//该方法如果缓存区已满，不会一直等待
public int offer(T item,
BiPredicate<Subscriber<? super T>, ? super T> onDrop) {
return doOffer(item, 0L, onDrop);
}
//跟前者比，多提供了等待超时时间，和时间单位
public int offer(T item, long timeout, TimeUnit unit,
BiPredicate<Subscriber<? super T>, ? super T> onDrop) {
long nanos = unit.toNanos(timeout);
// distinguishes from untimed (only wrt interrupt policy)
if (nanos == Long.MAX_VALUE) --nanos;
return doOffer(item, nanos, onDrop);
}
close
//给当前的订阅者发布onComplete信号
//并禁止后面的发布任务
//该方法无法说明所有的订阅者已经完成
public void close() {
if (!closed) {
BufferedSubscription<T> b;
synchronized (this) {
// no need to re-check closed here
b = clients;
clients = null;
owner = null;
closed = true;
}
//循环处理所有的缓冲区，断开连接，完成消费
while (b != null) {
BufferedSubscription<T> next = b.next;
b.next = null;
b.onComplete();
b = next;
}
}
}
closeExceptionally
//给当前的订阅者发送指定的错误信号，并禁止后续发布
//该方法无法说明订阅者是否已经完成
public void closeExceptionally(Throwable error) {
if (error == null)
throw new NullPointerException();
if (!closed) {
BufferedSubscription<T> b;
synchronized (this) {
b = clients;
if (!closed) {
//再次检查关闭状态，因为有可能其他线程会调用close()
closedException = error;
clients = null;
owner = null;
closed = true;
}
}
while (b != null) {
BufferedSubscription<T> next = b.next;
b.next = null;
b.onError(error);
b = next;
}
}
}
isClosed
//是否关闭
public boolean isClosed() {
return closed;
}
getClosedException
//获取closed异常
public Throwable getClosedException() {
return closedException;
}
hasSubscribers
//判断是否有订阅者，只要有一个订阅者就返回true
//如果有缓冲区已经被关闭，会清理这些缓冲区
public boolean hasSubscribers() {
boolean nonEmpty = false;
synchronized (this) {
for (BufferedSubscription<T> b = clients; b != null;) {
BufferedSubscription<T> next = b.next;
if (b.isClosed()) {
b.next = null;
b = clients = next;
}
else {
nonEmpty = true;
break;
}
}
}
return nonEmpty;
}
getNumberOfSubscribers
//通过缓冲区来计算还订阅的订阅者数量
public int getNumberOfSubscribers() {
synchronized (this) {
return cleanAndCount();
}
}
getExecutor
//获取线程池
public Executor getExecutor() {
return executor;
}
getMaxBufferCapacity
//获取缓冲区最大容量
public int getMaxBufferCapacity() {
return maxBufferCapacity;
}
getSubscribers
//获取还订阅的订阅者列表，并清理缓冲区链表
public List<Subscriber<? super T>> getSubscribers() {
ArrayList<Subscriber<? super T>> subs = new ArrayList<>();
synchronized (this) {
BufferedSubscription<T> pred = null, next;
for (BufferedSubscription<T> b = clients; b != null; b = next) {
next = b.next;
if (b.isClosed()) {
b.next = null;
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
subs.add(b.subscriber);
pred = b;
}
}
}
return subs;
}
isSubscribed
//通过equals判断，指定的订阅者是否还在订阅
public boolean isSubscribed(Subscriber<? super T> subscriber) {
if (subscriber == null) throw new NullPointerException();
if (!closed) {
synchronized (this) {
BufferedSubscription<T> pred = null, next;
for (BufferedSubscription<T> b = clients; b != null; b = next) {
next = b.next;
if (b.isClosed()) {
b.next = null;
if (pred == null)
clients = next;
else
pred.next = next;
}
else if (subscriber.equals(b.subscriber))
return true;
else
pred = b;
}
}
}
return false;
}
estimateMinimumDemand
//返回所有的订阅者中，还没有消费的最少元素数量
public long estimateMinimumDemand() {
long min = Long.MAX_VALUE;
boolean nonEmpty = false;
synchronized (this) {
BufferedSubscription<T> pred = null, next;
for (BufferedSubscription<T> b = clients; b != null; b = next) {
int n; long d;
next = b.next;
if ((n = b.estimateLag()) < 0) {
b.next = null;
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
if ((d = b.demand - n) < min)
min = d;
nonEmpty = true;
pred = b;
}
}
}
return nonEmpty ? min : 0;
}
estimateMaximumLag
//返回所有的订阅者中，还没有消费的最多元素数量
public int estimateMaximumLag() {
int max = 0;
synchronized (this) {
BufferedSubscription<T> pred = null, next;
for (BufferedSubscription<T> b = clients; b != null; b = next) {
int n;
next = b.next;
if ((n = b.estimateLag()) < 0) {
b.next = null;
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
if (n > max)
max = n;
pred = b;
}
}
}
return max;
}
consume
//公开的消费方法
public CompletableFuture<Void> consume(Consumer<? super T> consumer) {
if (consumer == null)
throw new NullPointerException();
CompletableFuture<Void> status = new CompletableFuture<>();
subscribe(new ConsumerSubscriber<T>(status, consumer));
return status;
}
roundCapacity
//计算最大容量的算法
static final int roundCapacity(int cap) {
int n = cap - 1;
n |= n >>> 1;
n |= n >>> 2;
n |= n >>> 4;
n |= n >>> 8;
n |= n >>> 16;
return (n <= 0) ? 1 : // at least 1
(n >= BUFFER_CAPACITY_LIMIT) ? BUFFER_CAPACITY_LIMIT : n + 1;
}
doOffer
//submit 和offer的公共实现
//submit方法nanos == Long.MAX_VALUE
private int doOffer(T item, long nanos,
BiPredicate<Subscriber<? super T>, ? super T> onDrop) {
if (item == null) throw new NullPointerException();
int lag = 0;
boolean complete, unowned;
synchronized (this) {
Thread t = Thread.currentThread(), o;
BufferedSubscription<T> b = clients;
if ((unowned = ((o = owner) != t)) && o != null)
owner = null; // disable bias
if (b == null)
complete = closed;
else {
complete = false;
boolean cleanMe = false;
BufferedSubscription<T> retries = null, rtail = null, next;
do {
next = b.next;
int stat = b.offer(item, unowned);
if (stat == 0) {
// 缓冲区已满，加入重试列表
b.nextRetry = null; // 先重置原来的nextRetry变量
if (rtail == null)
retries = b;
else
rtail.nextRetry = b;
rtail = b;
}
else if (stat < 0) // 缓存区已经关闭
cleanMe = true; // 标记清理，将在后面清理
else if (stat > lag)
lag = stat;
} while ((b = next) != null); //循环处理，直到处理完成
if (retries != null || cleanMe) //重试列表不为空，或者清理标志为true
//重试发布
lag = retryOffer(item, nanos, onDrop, retries, lag, cleanMe);
}
}
//已经关闭抛出异常Closed
if (complete)
throw new IllegalStateException("Closed");
else
return lag;
}
retryOffer
//重试发布元素
private int retryOffer(T item, long nanos,
BiPredicate<Subscriber<? super T>, ? super T> onDrop,
BufferedSubscription<T> retries, int lag,
boolean cleanMe) {
for (BufferedSubscription<T> r = retries; r != null;) {
BufferedSubscription<T> nextRetry = r.nextRetry;
//将缓冲区存入临时变量后，及时断开连接
r.nextRetry = null;
if (nanos > 0L)
//阻塞等待
r.awaitSpace(nanos);
//重试发布
int stat = r.retryOffer(item);
//如果还是发布失败，但自定义了BiPredicate函数，会根据自定义规则进行判断，为true会再重试一次
if (stat == 0 && onDrop != null && onDrop.test(r.subscriber, item))
stat = r.retryOffer(item);
if (stat == 0) //缓冲区满了
lag = (lag >= 0) ? -1 : lag - 1; //这里有点奇怪？
else if (stat < 0) //关闭了，标志为清理
cleanMe = true;
else if (lag >= 0 && stat > lag)
lag = stat;
r = nextRetry;
}
if (cleanMe)
cleanAndCount();
return lag;
}
cleanAndCount
//清理缓存区链表并计算还在订阅的订阅者数量
private int cleanAndCount() {
int count = 0;
BufferedSubscription<T> pred = null, next;
for (BufferedSubscription<T> b = clients; b != null; b = next) {
next = b.next;
if (b.isClosed()) {
b.next = null;
if (pred == null)
clients = next;
else
pred.next = next;
}
else {
pred = b;
++count;
}
}
return count;
}
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