[Sybase] ThreadLocal及其扩展

static class Entry extends WeakReference<java.lang.ThreadLocal<?>> {
// 往ThreadLocal里实际塞入的值
Object value;
Entry(java.lang.ThreadLocal<?> k, Object v) {
super(k);
value = v;
   }
}

public T get() {
Thread t = Thread.currentThread(); //获取当前线程
ThreadLocalMap map = getMap(t); // 获取当前线程对象的实例变量threadLocals
if (map != null) {
ThreadLocalMap.Entry e = map.getEntry(this);
if (e != null) {
@SuppressWarnings("unchecked")
T result = (T)e.value;
return result;
    }
  }
return setInitialValue();
}

public void set(T value) {
  Thread t = Thread.currentThread();
  ThreadLocalMap map = getMap(t);
  if (map != null)
    map.set(this, value);
  else
    createMap(t, value);
}

public class InheritableThreadLocal<T> extends ThreadLocal<T> {
protected T childValue(T parentValue) {
return parentValue;
  }

ThreadLocalMap getMap(Thread t) {
return t.inheritableThreadLocals;
  }

void createMap(Thread t, T firstValue) {
t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
  }
}

if (parent.inheritableThreadLocals != null)
      this.inheritableThreadLocals =
        ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);

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• ​​capture​​方法：抓取线程（线程A）的所有​​TTL​​值。
  
• ​​replay​​方法：在另一个线程（线程B）中，回放在​​capture​​方法中抓取的​​TTL​​值(回放的过程也就是把第一步抓取的线程实例本地变量设置到当前线程的实例本地变量中)，并返回 回放前​​TTL​​值的备份
  
• ​​restore​​方法：恢复线程B执行​​replay​​方法之前的​​TTL​​值（即备份，把第二步返回的回放前​​TTL​​值重新设置回池化中线程的实例本地变量）
  
  
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private final AtomicReference<Object> capturedRef; //用户存放线程本地变量的map引用

public static Object capture() {
  Map<TransmittableThreadLocal<?>, Object> captured = new HashMap<TransmittableThreadLocal<?>, Object>();
//holder是TransmittableThreadLocal类的静态对象，类型为InheritableThreadLocal<Map<TransmittableThreadLocal<?>, ?>>，用于存储线程的本地变量，这一份本地变量被TransmittableThreadLocal用于CRR操作
  for (TransmittableThreadLocal<?> threadLocal : holder.get().keySet()) {
captured.put(threadLocal, threadLocal.copyValue());
  }
return captured;
}

public static Object replay(Object captured) {
@SuppressWarnings("unchecked")
Map<TransmittableThreadLocal<?>, Object> capturedMap = (Map<TransmittableThreadLocal<?>, Object>) captured;
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 value only in captured
if (!capturedMap.containsKey(threadLocal)) {
iterator.remove();
threadLocal.superRemove();
    }
  }
// 把capture抓取的线程本地变量设置到当前线程的本地变量中
for (Map.Entry<TransmittableThreadLocal<?>, Object> entry : capturedMap.entrySet()) {
@SuppressWarnings("unchecked")
TransmittableThreadLocal<Object> threadLocal = (TransmittableThreadLocal<Object>) entry.getKey();
threadLocal.set(entry.getValue());
  }
// call beforeExecute callback
doExecuteCallback(true);
return backup;
}

public static void restore(Object backup) {
@SuppressWarnings("unchecked")
Map<TransmittableThreadLocal<?>, Object> backupMap = (Map<TransmittableThreadLocal<?>, Object>) backup;
// call afterExecute callback
doExecuteCallback(false);

for (Iterator<? extends Map.Entry<TransmittableThreadLocal<?>, ?>> iterator = holder.get().entrySet().iterator();
iterator.hasNext(); ) {
Map.Entry<TransmittableThreadLocal<?>, ?> next = iterator.next();
TransmittableThreadLocal<?> threadLocal = next.getKey();

// clear the TTL value only in backup
// avoid the extra value of backup after restore
if (!backupMap.containsKey(threadLocal)) {
iterator.remove();
threadLocal.superRemove();
    }
  }

// 把replay步骤备份前`TTL`值重新设置回池化中线程的本地变量
for (Map.Entry<TransmittableThreadLocal<?>, Object> entry : backupMap.entrySet()) {
@SuppressWarnings("unchecked")
TransmittableThreadLocal<Object> threadLocal = (TransmittableThreadLocal<Object>) entry.getKey();
threadLocal.set(entry.getValue());
  }
}