public class InheritableThreadLocal<T> extends ThreadLocal<T> {
    /**
     * Computes the child's initial value for this inheritable thread-local
     * variable as a function of the parent's value at the time the child
     * thread is created.  This method is called from within the parent
     * thread before the child is started.
     * <p>
     * This method merely returns its input argument, and should be overridden
     * if a different behavior is desired.
     *
     * @param parentValue the parent thread's value
     * @return the child thread's initial value
     */
// 這是ThreadLocal的執(zhí)行邏輯，相當(dāng)于一個(gè)模板方法，由子類實(shí)現(xiàn)，ThreadLocal不支持傳遞給子線程
    protected T childValue(T parentValue) {
        return parentValue;
    }
    /**
     * Get the map associated with a ThreadLocal.
     *
     * @param t the current thread
     */
    ThreadLocalMap getMap(Thread t) {
       return t.inheritableThreadLocals;
    }
    /**
     * Create the map associated with a ThreadLocal.
     *
     * @param t the current thread
     * @param firstValue value for the initial entry of the table.
     */
// 顧名思義，只有在線程new出來的時(shí)刻會(huì)調(diào)用當(dāng)前方法，然后調(diào)用childValue
    void createMap(Thread t, T firstValue) {
        t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
    }
}

    // Note about holder:
    // 1. The value of holder is type Map<TransmittableThreadLocal<?>, ?> (WeakHashMap implementation),
    //    but it is used as *set*.
    // 2. WeakHashMap support null value.
// 這是TTL的核心設(shè)計(jì)，組裝為一個(gè) 以TTL對(duì)象為key的map返回,同同時(shí)這個(gè)map對(duì)象還是TTL對(duì)象的一個(gè)內(nèi)部靜態(tài)對(duì)象，一直跟隨客戶端使用的TTL對(duì)象。
    private static InheritableThreadLocal<Map<TransmittableThreadLocal<?>, ?>> holder =
            new InheritableThreadLocal<Map<TransmittableThreadLocal<?>, ?>>() {
// 只有子線程 為new時(shí)調(diào)用
                @Override
                protected Map<TransmittableThreadLocal<?>, ?> initialValue() {
                    return new WeakHashMap<TransmittableThreadLocal<?>, Object>();
                }
// 只有子線程 為new時(shí)調(diào)用,雖然做了拓展，通過一個(gè)跟隨客戶端使用的TTL對(duì)象內(nèi)部構(gòu)造了這個(gè)holder中轉(zhuǎn)站，但是還是使用的引用傳遞，如果主子線程一邊直接修改了引用的對(duì)象，另一邊也會(huì)感知到。并且存在并發(fā)修改問題。因?yàn)槭窃鰪?qiáng)InheritableThreadLocal，并沒有修改這里的引用傳遞邏輯。實(shí)際其它擴(kuò)展有傳遞為不可變對(duì)象的邏輯
                @Override
                protected Map<TransmittableThreadLocal<?>, ?> childValue(Map<TransmittableThreadLocal<?>, ?> parentValue) {
                    return new WeakHashMap<TransmittableThreadLocal<?>, Object>(parentValue);
                }
            };

    private ThreadLocal<StringMap> createThreadLocalMap() {
        return (ThreadLocal)(inheritableMap ? new InheritableThreadLocal<StringMap>() {
            protected StringMap childValue(StringMap parentValue) {
                if (parentValue == null) {
                    return null;
                } else {
// 主要看看這個(gè)接口
                    StringMap stringMap = CopyOnWriteSortedArrayThreadContextMap.this.createStringMap(parentValue);
                    stringMap.freeze();
                    return stringMap;
                }
            }
        } : new ThreadLocal());
    }

// 看名字就知道了，是一個(gè)不可變對(duì)象，也就是不同于InheritableThreadLocal和TTL傳遞的對(duì)象引用，這里做了復(fù)制后變?yōu)椴豢勺儗?duì)象的邏輯，日后小伙伴們也可以借助TTL實(shí)現(xiàn)自己不可變對(duì)象的邏輯
public interface StringMap extends ReadOnlyStringMap {
    void clear();
    boolean equals(Object var1);
    void freeze();
    int hashCode();
    boolean isFrozen();
    void putAll(ReadOnlyStringMap var1);
    void putValue(String var1, Object var2);
    void remove(String var1);
}

    @Override
    public Executor getAsyncExecutor() {
// 這里原本是設(shè)置一個(gè) @Async的默認(rèn)線程池
        ThreadPoolExecutor executor = new ThreadPoolExecutor(4, 8, 30, TimeUnit.SECONDS,
            new LinkedBlockingQueue<>(512), FACTORY);
        executor.setRejectedExecutionHandler(new CustomRejectedHandler());
// 最后我們裝入了TTL的裝飾器返回
        return TtlExecutors.getTtlExecutorService(executor);
    }

public final class TtlCallable<V> implements Callable<V>, TtlEnhanced {
//用于threadLocal中轉(zhuǎn)的對(duì)象，通過Transmitter#capture()在裝飾器初始化時(shí)就創(chuàng)建好，實(shí)際就是獲取當(dāng)前主線程的threadLocal
    private final AtomicReference<Object> capturedRef;
// 被裝飾的目標(biāo)對(duì)象接口
    private final Callable<V> callable;
// 是否釋放TTL對(duì)象傳遞過來的業(yè)務(wù)對(duì)象引用，從代碼看這里只決定了當(dāng)前TtlCallable對(duì)象的引用是否釋放，TtlCallable對(duì)象本身有一定生命周期，再者如果復(fù)用主線程傳遞過來的TTL對(duì)象引用也一直存在于主線程，目前都是false，子線程引用也會(huì)一直隨著主線程傳遞而更新
    private final boolean releaseTtlValueReferenceAfterCall;
    private TtlCallable(@Nonnull Callable<V> callable, boolean releaseTtlValueReferenceAfterCall) {
// 在new這個(gè)對(duì)象時(shí)是在主線程，所以capture()方法拿到的是主線程的TTL對(duì)象最新的引用，包括業(yè)務(wù)對(duì)象也是最新的
        this.capturedRef = new AtomicReference<Object>(capture());
        this.callable = callable;
        this.releaseTtlValueReferenceAfterCall = releaseTtlValueReferenceAfterCall;
    }
    /**
     * wrap method {@link Callable#call()}.
     */
    @Override
    public V call() throws Exception {
// 獲取主線程的 TTL對(duì)象map，就是通過Transmitter#capture()方法從 TTL對(duì)象中上面所說的TTL對(duì)象中的內(nèi)部holder中轉(zhuǎn)map獲取到主線程的所有TTL及業(yè)務(wù)對(duì)象引用
        Object captured = capturedRef.get();
// 如果為空 或者 需要清理TTL對(duì)象引用，則進(jìn)行一次原子操作對(duì)TTL對(duì)象引用置為空
        if (captured == null || releaseTtlValueReferenceAfterCall && !capturedRef.compareAndSet(captured, null)) {
            throw new IllegalStateException("TTL value reference is released after call!");
        }
  // 重放 captured為當(dāng)前裝飾器初始化時(shí)從主線程拿到的，這里對(duì)其進(jìn)行重放替換
// 并返回當(dāng)前子線程的 TTL對(duì)象作為還原
        Object backup = replay(captured);
        try {
//被增項(xiàng)的目標(biāo)方法執(zhí)行
            return callable.call();
        } finally {
// 再將當(dāng)前子線程還原
            restore(backup);
        }
    }
// ----------------省略大部分代碼--------------
}

        @Nonnull
        public static Object capture() {
            Map<TransmittableThreadLocal<?>, Object> captured = new HashMap<TransmittableThreadLocal<?>, Object>();
// 復(fù)制的核心 是從 holder中轉(zhuǎn)對(duì)象中獲取每個(gè)key的threadLocal中的業(yè)務(wù)對(duì)象引用
// 然后再用其TTL對(duì)象作為key 組裝一個(gè) TTL對(duì)象 -> 業(yè)務(wù)對(duì)象的map返回
            for (TransmittableThreadLocal<?> threadLocal : holder.get().keySet()) {
                captured.put(threadLocal, threadLocal.copyValue());
            }
            return captured;
        }
//-----------copyValue 方法----------
   private T copyValue() {
// 復(fù)制就是從當(dāng)前主線程 的threadLocal get
        return copy(get());
    }
//------------copy 方法------
  protected T copy(T parentValue) {
// 復(fù)制的是對(duì)象的引用
        return parentValue;
    }

    @Nonnull
        public static Object replay(@Nonnull Object captured) {
            @SuppressWarnings("unchecked")
// 主線程傳遞過來的引用
            Map<TransmittableThreadLocal<?>, Object> capturedMap = (Map<TransmittableThreadLocal<?>, Object>) captured;
// 當(dāng)前子線程的TTL引用用于返回后 還原
            Map<TransmittableThreadLocal<?>, Object> backup = new HashMap<TransmittableThreadLocal<?>, Object>();
            for (Iterator<? extends Map.Entry<TransmittableThreadLocal<?>, ?>> iterator = holder.get().entrySet().iterator();
                 iterator.hasNext(); ) {
                Map.Entry<TransmittableThreadLocal<?>, ?> next = iterator.next();
                TransmittableThreadLocal<?> threadLocal = next.getKey();
                // backup
                backup.put(threadLocal, threadLocal.get());
                // clear the TTL values that is not in captured
                // avoid the extra TTL values after replay when run task
//清除掉可能失效和舊的子線程的TTL對(duì)象引用，為什么這么做，目前不太清楚
                if (!capturedMap.containsKey(threadLocal)) {
                    iterator.remove();
                    threadLocal.superRemove();
                }
            }
            // set values to captured TTL
// 我們上一篇文章以及當(dāng)前文章上面提到，在thread new的時(shí)候調(diào)用initialValue和childValue 方法時(shí)，會(huì)將主線程的TTL對(duì)象引用傳遞給子線程，但是不同裝飾器增強(qiáng)時(shí)，子線程里的TTL對(duì)象中的業(yè)務(wù)對(duì)象引用是一直不變的，一直是第一次傳遞過來的業(yè)務(wù)對(duì)象的值，而主線程的業(yè)務(wù)對(duì)象變更子線程感知不到，但是TTL對(duì)象也一直是一個(gè)引用這里將其舊的TTL引用
// 放入主線程新得 TTL中的業(yè)務(wù)對(duì)象引用,實(shí)際因?yàn)樽泳€程的TTL對(duì)象引用和主線程的TTL對(duì)象是一樣的，只不過主線程更新了業(yè)務(wù)對(duì)象引用子線程感知不到，因?yàn)閖ava內(nèi)存模型的原因，所以這里直接重新操作一次 子線程的TTL對(duì)象更新 *業(yè)務(wù)對(duì)象引用* 重復(fù)了一次主線程的操作
            setTtlValuesTo(capturedMap);
            // call beforeExecute callback
// 這里其實(shí)是一個(gè)模板方法，包括目標(biāo)對(duì)象執(zhí)行前也就是重放，及目標(biāo)對(duì)象執(zhí)行后，還原的實(shí)際的一個(gè)鉤子
            doExecuteCallback(true);
            return backup;
        }

     private static void setTtlValuesTo(@Nonnull Map<TransmittableThreadLocal<?>, Object> ttlValues) {
            for (Map.Entry<TransmittableThreadLocal<?>, Object> entry : ttlValues.entrySet()) {
                @SuppressWarnings("unchecked")
                TransmittableThreadLocal<Object> threadLocal = (TransmittableThreadLocal<Object>) entry.getKey();
                threadLocal.set(entry.getValue());
            }
        }

    private static void doExecuteCallback(boolean isBefore) {
        for (Map.Entry<TransmittableThreadLocal<?>, ?> entry : holder.get().entrySet()) {
            TransmittableThreadLocal<?> threadLocal = entry.getKey();
            try {
// 兩個(gè)模板方法鉤子
                if (isBefore) threadLocal.beforeExecute();
                else threadLocal.afterExecute();
            } catch (Throwable t) {
                if (logger.isLoggable(Level.WARNING)) {
                    logger.log(Level.WARNING, "TTL exception when " + (isBefore ? "beforeExecute" : "afterExecute") + ", cause: " + t.toString(), t);
                }
            }
        }
    }

// ForkJoinWorkerThreadFactory 的裝飾器
public interface DisableInheritableForkJoinWorkerThreadFactory extends ForkJoinWorkerThreadFactory {
    /**
     * Unwrap {@link DisableInheritableThreadFactory} to the original/underneath one.
     */
    @Nonnull
    ForkJoinWorkerThreadFactory unwrap();
}

  private static ForkJoinPool makeCommonPool() {
        int parallelism = -1;
        ForkJoinWorkerThreadFactory factory = null;
        UncaughtExceptionHandler handler = null;
        try {  // ignore exceptions in accessing/parsing properties
            String pp = System.getProperty
                ("java.util.concurrent.ForkJoinPool.common.parallelism");
// ForkJoin會(huì)有一個(gè)擴(kuò)展邏輯，這里如果獲取到指定的線程工廠類則不會(huì)使用默認(rèn)的。但是當(dāng)前makeCommonPool 方法在 static {} 代碼塊中執(zhí)行，經(jīng)過測(cè)試直接System.setProperty無法掌控好加載順序，可能獲取不到自定義的系統(tǒng)變量，索性直接通過jvm啟動(dòng)參數(shù)指定
            String fp = System.getProperty
                ("java.util.concurrent.ForkJoinPool.common.threadFactory");
            String hp = System.getProperty
                ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
            if (pp != null)
                parallelism = Integer.parseInt(pp);
            if (fp != null)
// 如果有自定義的線程工廠會(huì)初始化
                factory = ((ForkJoinWorkerThreadFactory)ClassLoader.
                           getSystemClassLoader().loadClass(fp).newInstance());
            if (hp != null)
                handler = ((UncaughtExceptionHandler)ClassLoader.
                           getSystemClassLoader().loadClass(hp).newInstance());
        } catch (Exception ignore) {
        }
        if (factory == null) {
            if (System.getSecurityManager() == null)
                factory = defaultForkJoinWorkerThreadFactory;
            else // use security-managed default
                factory = new InnocuousForkJoinWorkerThreadFactory();
        }
        if (parallelism < 0 && // default 1 less than #cores
            (parallelism = Runtime.getRuntime().availableProcessors() - 1) <= 0)
            parallelism = 1;
        if (parallelism > MAX_CAP)
            parallelism = MAX_CAP;
        return new ForkJoinPool(parallelism, factory, handler, LIFO_QUEUE,
                                "ForkJoinPool.commonPool-worker-");
    }

class DisableInheritableForkJoinWorkerThreadFactoryWrapper implements DisableInheritableForkJoinWorkerThreadFactory {
    final ForkJoinWorkerThreadFactory threadFactory;
    public DisableInheritableForkJoinWorkerThreadFactoryWrapper(@Nonnull ForkJoinWorkerThreadFactory threadFactory) {
        this.threadFactory = threadFactory;
    }
    @Override
    public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
// 看到這里在new thread時(shí)進(jìn)行了 TTL對(duì)象的清理
//這個(gè)執(zhí)行時(shí)機(jī)其實(shí)還是在主線程中，如果正常不執(zhí)行這個(gè)代碼子線程會(huì)拿到一個(gè)舊的主線程的TTL對(duì)象引用，但是這里清除了，就不會(huì)拿到了，方便開發(fā)測(cè)試階段發(fā)現(xiàn)問題
        final Object backup = TransmittableThreadLocal.Transmitter.clear();
        try {
            return threadFactory.newThread(pool);
        } finally {
// 執(zhí)行完后進(jìn)行還原
            TransmittableThreadLocal.Transmitter.restore(backup);
        }
    }
    @Nonnull
    @Override
    public ForkJoinWorkerThreadFactory unwrap() {
        return threadFactory;
    }
}

public  class CustomForkJoinThreadFactory implements DisableInheritableForkJoinWorkerThreadFactory {
// 被增強(qiáng)的默認(rèn)的線程工廠
    final ForkJoinWorkerThreadFactory threadFactory = ForkJoinPool.defaultForkJoinWorkerThreadFactory;
// 有無參構(gòu)造才可以 加載成功噢
    public CustomForkJoinThreadFactory() {
    }
    @Override
    public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
        final Object backup = TransmittableThreadLocal.Transmitter.clear();
        try {
            return threadFactory.newThread(pool);
        } finally {
            TransmittableThreadLocal.Transmitter.restore(backup);
        }
    }
    @Nonnull
    @Override
    public ForkJoinWorkerThreadFactory unwrap() {
        return threadFactory;
    }
}

-Djava.util.concurrent.ForkJoinPool.common.threadFactory=xxx.xxx.xxx.CustomForkJoinThreadFactory