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熟悉ThreadPoolExcutor源码
下载/上传的工具模块，支持断点续传，分片下载，内存文件映射。 应用四大组件、数据库。··1·· 编写demo，单元测试，和设计文档 应用设计模式
加密解密
借鉴DownloadManager，其基本实现思路如下图
开始下载至下载完成的时序图
状态图
定时器查看 map==空
同步 队列
异步 线程池队列
线程池：核心线程可以回收 ， 拒绝策略
暴露 eqeue(call). execute(call) cancel()
ThreadPoolExecutor:有些线程不想在用了Looper，无法知道线程池是否空闲，futureTask cancel()不掉
任务队列 worker 对线程的封装
ReentrantLock 基于其内部类Sync实现。Sync继承AQS
无任务 destory
Worker workQueue任务队列
HashSet<Worker> workers 》worker的 Runnable firstTask;
BlockingQueue<Runnable> workQueue;
firstTask=null
任务执行
执行完去队列再拿
AbstractQueuedSynchronizer
state作为锁，几个线程去访问它
线程由链表保存，表头可以运行。其他用LockSupport阻塞
表头运行完了，下一个结点运行
class AbstractQueuedSynchronizer{// 阻塞使用LockSupport
void acquire(int arg) // 获得锁，lock()的底层实现。status的值加1
boolean release(int arg) // 释放锁，unlock()的底层实现。status的值减1。调用tryRelease
// 返回true，那么就是获取锁成功；如果返回false，那么就是未获得锁，需要加入阻塞等待队列。
boolean tryAcquire(int arg) // 空实现，需子类重载。可参考ReentrantLock#FairSync公平锁
Node addWaiter(Node mode)// 存当前线程信息的节点加入到等待队列中
boolean acquireQueued(final Node node, int arg)
boolean tryRelease(int releases) // 空实现由子类重载，释放独占性
// 值就代表锁的有无。当state=0时，表示锁未被占有，否在表示当前锁已经被占有。
volatile int state; // 线程独占的变量，代表抽象概念的锁.（compareAndSet+volatile）保证独占性
// 双向链表，保存竞争锁的thread信息。队首结点可获得state（锁），其他线程阻塞。waitStatus
// 1 CANCELLED：当前线程被取消；
// -1 SIGNAL：当前节点的后继节点需要运行；
// -2 CONDITION：当前节点在等待condition；
// -3 PROPAGATE：当前场景下后续的acquireShared可以执行；
// 0 默认值，当前节点在sync队列中等待获取锁。
static final class Node;
}LockSupport
LockSupport.park();
LockSupport.unpark(mThread);public interface Lock {
/** 锁上，让其他线程阻塞，等锁 */
void lock();
/**
* Acquires the lock unless the current thread is
* {@linkplain Thread#interrupt interrupted}.
*
* <p>Acquires the lock if it is available and returns immediately.
*
* <p>If the lock is not available then the current thread becomes
* disabled for thread scheduling purposes and lies dormant until
* one of two things happens:
*
* <ul>
* <li>The lock is acquired by the current thread; or
* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
* current thread, and interruption of lock acquisition is supported.
* </ul>
*
* <p>If the current thread:
* <ul>
* <li>has its interrupted status set on entry to this method; or
* <li>is {@linkplain Thread#interrupt interrupted} while acquiring the
* lock, and interruption of lock acquisition is supported,
* </ul>
* then {@link InterruptedException} is thrown and the current thread's
* interrupted status is cleared.
*
* <p><b>Implementation Considerations</b>
*
* <p>The ability to interrupt a lock acquisition in some
* implementations may not be possible, and if possible may be an
* expensive operation. The programmer should be aware that this
* may be the case. An implementation should document when this is
* the case.
*
* <p>An implementation can favor responding to an interrupt over
* normal method return.
*
* <p>A {@code Lock} implementation may be able to detect
* erroneous use of the lock, such as an invocation that would
* cause deadlock, and may throw an (unchecked) exception in such
* circumstances. The circumstances and the exception type must
* be documented by that {@code Lock} implementation.
*
* @throws InterruptedException if the current thread is
* interrupted while acquiring the lock (and interruption
* of lock acquisition is supported)
*/
void lockInterruptibly() throws InterruptedException;
/**
* Acquires the lock only if it is free at the time of invocation.
*
* <p>Acquires the lock if it is available and returns immediately
* with the value {@code true}.
* If the lock is not available then this method will return
* immediately with the value {@code false}.
*
* <p>A typical usage idiom for this method would be:
* <pre> {@code
* Lock lock = ...;
* if (lock.tryLock()) {
* try {
* // manipulate protected state
* } finally {
* lock.unlock();
* }
* } else {
* // perform alternative actions
* }}</pre>
*
* This usage ensures that the lock is unlocked if it was acquired, and
* doesn't try to unlock if the lock was not acquired.
*
* @return {@code true} if the lock was acquired and
* {@code false} otherwise
*/
boolean tryLock();
/**
* Acquires the lock if it is free within the given waiting time and the
* current thread has not been {@linkplain Thread#interrupt interrupted}.
*
* <p>If the lock is available this method returns immediately
* with the value {@code true}.
* If the lock is not available then
* the current thread becomes disabled for thread scheduling
* purposes and lies dormant until one of three things happens:
* <ul>
* <li>The lock is acquired by the current thread; or
* <li>Some other thread {@linkplain Thread#interrupt interrupts} the
* current thread, and interruption of lock acquisition is supported; or
* <li>The specified waiting time elapses
* </ul>
*
* <p>If the lock is acquired then the value {@code true} is returned.
*
* <p>If the current thread:
* <ul>
* <li>has its interrupted status set on entry to this method; or
* <li>is {@linkplain Thread#interrupt interrupted} while acquiring
* the lock, and interruption of lock acquisition is supported,
* </ul>
* then {@link InterruptedException} is thrown and the current thread's
* interrupted status is cleared.
*
* <p>If the specified waiting time elapses then the value {@code false}
* is returned.
* If the time is
* less than or equal to zero, the method will not wait at all.
*
* <p><b>Implementation Considerations</b>
*
* <p>The ability to interrupt a lock acquisition in some implementations
* may not be possible, and if possible may
* be an expensive operation.
* The programmer should be aware that this may be the case. An
* implementation should document when this is the case.
*
* <p>An implementation can favor responding to an interrupt over normal
* method return, or reporting a timeout.
*
* <p>A {@code Lock} implementation may be able to detect
* erroneous use of the lock, such as an invocation that would cause
* deadlock, and may throw an (unchecked) exception in such circumstances.
* The circumstances and the exception type must be documented by that
* {@code Lock} implementation.
*
* @param time the maximum time to wait for the lock
* @param unit the time unit of the {@code time} argument
* @return {@code true} if the lock was acquired and {@code false}
* if the waiting time elapsed before the lock was acquired
*
* @throws InterruptedException if the current thread is interrupted
* while acquiring the lock (and interruption of lock
* acquisition is supported)
*/
boolean tryLock(long time, TimeUnit unit) throws InterruptedException;
/**
* Releases the lock.
*
* <p><b>Implementation Considerations</b>
*
* <p>A {@code Lock} implementation will usually impose
* restrictions on which thread can release a lock (typically only the
* holder of the lock can release it) and may throw
* an (unchecked) exception if the restriction is violated.
* Any restrictions and the exception
* type must be documented by that {@code Lock} implementation.
*/
void unlock();
/**
* Returns a new {@link Condition} instance that is bound to this
* {@code Lock} instance.
*
* <p>Before waiting on the condition the lock must be held by the
* current thread.
* A call to {@link Condition#await()} will atomically release the lock
* before waiting and re-acquire the lock before the wait returns.
*
* <p><b>Implementation Considerations</b>
*
* <p>The exact operation of the {@link Condition} instance depends on
* the {@code Lock} implementation and must be documented by that
* implementation.
*
* @return A new {@link Condition} instance for this {@code Lock} instance
* @throws UnsupportedOperationException if this {@code Lock}
* implementation does not support conditions
*/
Condition newCondition();
} 双亲代理 图片加载框架
case:只有running状态能stop，暂放在pauseDownload(Context context, Request info)
Case:完善删除状态图
case：同一个下载对象，使用不同下载方式下载。