TransmittableThreadLocal

TransmittableThreadLocal<String> parent = new TransmittableThreadLocal<String>();
parent.set("value-set-in-parent");

Runnable task = new Task("1");
// 额外的处理，生成修饰了的对象ttlRunnable
Runnable ttlRunnable = TtlRunnable.get(task); 
executorService.submit(ttlRunnable);

// Task中可以读取, 值是"value-set-in-parent"
String value = parent.get();

public final class TtlRunnable implements Runnable {
    private final AtomicReference<Map<TransmittableThreadLocal<?>, Object>> copiedRef;
    private final Runnable runnable;
    private final boolean releaseTtlValueReferenceAfterRun;

    private TtlRunnable(Runnable runnable, boolean releaseTtlValueReferenceAfterRun) {
    //从父类copy值到本类当中
        this.copiedRef = new AtomicReference<Map<TransmittableThreadLocal<?>, Object>>(TransmittableThreadLocal.copy());
        this.runnable = runnable;//提交的runable,被修饰对象
        this.releaseTtlValueReferenceAfterRun = releaseTtlValueReferenceAfterRun;
    }
    /**
     * wrap method {@link Runnable#run()}.
     */
    @Override
    public void run() {
        Map<TransmittableThreadLocal<?>, Object> copied = copiedRef.get();
        if (copied == null || releaseTtlValueReferenceAfterRun && !copiedRef.compareAndSet(copied, null)) {
            throw new IllegalStateException("TTL value reference is released after run!");
        }
        //装载到当前线程
        Map<TransmittableThreadLocal<?>, Object> backup = TransmittableThreadLocal.backupAndSetToCopied(copied);
        try {
            runnable.run();//执行提交的task
        } finally {
        //clear
            TransmittableThreadLocal.restoreBackup(backup);
        }
    }
}