一、线程
在Android开发中，你不可能都在主线程中开发，毕竟要联网，下载数据，保存数据等操作，当然这就离不开线程。
（当然你可以在Android4.0以前的手机里在主线程请求网络，我最早开发的时候，用的手机比较古老。。。）
在Android中你可以随意创建线程，于是就会造成线程不可控，内存泄漏，创建线程消耗资源，线程太多了消耗资源等问题。
具体线程怎么创建我就不在文章里描述了，毕竟这主要将并发编程。。。。
大家知道线程不可控就好了。。。于是就需要对线程进行控制，防止一系列问题出现，这就用到了如下要讲的东西。
二、线程池
线程池：顾名思义，就是放线程的大池子。
如何创建一个线程池？
先说说几个系统的线程池：
FixedThreadPool 创建定长线程的线程池
CachedThreadPool 需要的时候建立新的线程，超时线程销毁
SingleThreadPool 单个线程的线程池
ScheduledThreadPool 可以定时的线程池，创建周期性的任务
这几个线程池不做多余阐述，因为这些线程池的原理都与我下面要讲的有关。。。。
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如何自定义线程池（先来了解几个必须知道的参数）：
corePoolSize：
核心线程池大小，线程池中主要工作的线程的多少。
maximumPoolSize：
线程池最大线程数。
keepAliveTime：
空闲线程可保持的时间是多久，如果你启用了allowCoreThreadTimeOut方法，你的线程池里的空闲线程在这个时间段后会自动销毁，如果没启用，则只要不超过corePoolSize，空闲线程也不会销毁。
Unit：
keepAliveTime的时间单位
workQueue：
阻塞队列，当任务达到corePoolSize，就会被放入这个队列
常见几种BlockingQueue实现
ArrayBlockingQueue : 有界的数组队列
LinkedBlockingQueue : 可支持有界/无界的队列，使用链表实现
PriorityBlockingQueue : 优先队列，可以针对任务排序
SynchronousQueue : 队列长度为1的队列，和Array有点区别就是：client thread提交到block queue会是一个阻塞过程，直到有一个worker thread连接上来poll task。
threadFactory：
线程工厂，主要用来创建线程；
handler：
表示当拒绝处理任务时的策略，也就是参数maximumPoolSize达到后丢弃处理的方法。有以下四种取值：
ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。
ThreadPoolExecutor.DiscardPolicy：也是丢弃任务，但是不抛出异常。
ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面的任务，然后重新尝试执行任务（重复此过程）
ThreadPoolExecutor.CallerRunsPolicy：由调用线程处理该任务
用户也可以实现接口RejectedExecutionHandler定制自己的策略。
代码展示：
//线程工厂
public class TaskThreadFactory implements ThreadFactory {
private final AtomicInteger mThreadNumber = new AtomicInteger(1);
private final String mNamePrefix;
TaskThreadFactory(String name) {
mNamePrefix = name + "#";
}
public Thread newThread(Runnable r) {
Thread t = new Thread(r,mNamePrefix + mThreadNumber.getAndIncrement());
// if (t.isDaemon())
// t.setDaemon(false);
//
// if (t.getPriority() != Thread.NORM_PRIORITY)
// t.setPriority(Thread.NORM_PRIORITY);
return t;
}
}
//重写runnable
public class PRunnable implements Runnable {
public static final int HIGH = 1;//优先级高
public static final int NORMAL = 2;//优先级中等
public static final int LOW = 3;//优先级低
@IntDef({HIGH,NORMAL,LOW})
@Retention(RetentionPolicy.SOURCE)
public @interface Priority{}
public final int priority;
private final Runnable runnable;
public int serial;
public PRunnable(Runnable runnable){
this(NORMAL,runnable);
}
public PRunnable(@Priority int priority,Runnable runnable){
this.priority = priority;
this.runnable = runnable;
}
@Override
public void run() {
if (runnable != null) {
runnable.run();
}
}
/**
* 线程队列方式 先进先出
* @param r1
* @param r2
* @return
*/
public static final int compareFIFO(PRunnable r1, PRunnable r2) {
int result = r1.priority-r2.priority;
return result==0?r1.serial-r2.serial:result;
}
/**
* 线程队列方式 后进先出
* @param r1
* @param r2
* @return
*/
public static final int compareLIFO(PRunnable r1, PRunnable r2) {
int result = r1.priority-r2.priority;
return result==0?r2.serial-r1.serial:result;
}
}
//线程池实现
public class TaskExecutor implements Executor {
private final static int QUEUE_INIT_CAPACITY = 20;
private static final int CORE = 3;
private static final int MAX = 5;
private static final int TIMEOUT = 30 * 1000;
private AtomicInteger SERIAL = new AtomicInteger(0);//主要获取添加任务
public static class Config {
public int core;
public int max;
public int timeout;
public boolean allowCoreTimeOut;
public boolean fifo;
public Config(int core, int max, int timeout, boolean allowCoreTimeOut,boolean fifo) {
this.core = core;
this.max = max;
this.timeout = timeout;
this.allowCoreTimeOut = allowCoreTimeOut;
this.fifo = fifo;
}
}
public static Config defaultConfig = new Config(CORE, MAX, TIMEOUT, true,true);
private final String name;
private final Config config;
private ExecutorService service;
public TaskExecutor(String name) {
this(name, defaultConfig);
}
public TaskExecutor(String name, Config config) {
this(name, config, true);
}
public TaskExecutor(String name, Config config, boolean startup) {
this.name = name;
this.config = config;
if (startup) {
startup();
}
}
public void startup() {
synchronized (this) {
if (service != null && !service.isShutdown()) {
return;
}
service = createExecutor(config);
}
}
public void shutdown() {
ExecutorService executor = null;
synchronized (this) {
// 交换变量
if (service != null) {
executor = service;
service = null;
}
}
if (executor != null) {
// 停止线程
if (!executor.isShutdown()) {
executor.shutdown();
}
// 回收变量
executor = null;
}
}
private void executeRunnable(PRunnable runnable) {
synchronized (this) {
if (service == null || service.isShutdown()) {
return;
}
runnable.serial = SERIAL.getAndIncrement();
service.execute(runnable);
}
}
@Override
public void execute(Runnable runnable) {
if (runnable instanceof PRunnable) {
executeRunnable((PRunnable) runnable);
}else{
executeRunnable(new PRunnable(runnable));
}
}
public Future<?> submit(Runnable runnable) {
synchronized (this) {
if (service == null || service.isShutdown()) {
return null;
}
if (runnable instanceof PRunnable) {
((PRunnable) runnable).serial = SERIAL.getAndIncrement();
return service.submit(runnable);
}else{
PRunnable pRunnable = new PRunnable(runnable);
pRunnable.serial = SERIAL.getAndIncrement();
return service.submit(pRunnable);
}
}
}
public void execute(Runnable runnable, @PRunnable.Priority int priority) {
executeRunnable(new PRunnable(priority,runnable));
}
private ExecutorService createExecutor(Config config) {
ThreadPoolExecutor service = new ThreadPoolExecutor(config.core, config.max, config.timeout,
TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>(QUEUE_INIT_CAPACITY, config.fifo ? mQueueFIFOComparator : mQueueLIFOComparator),
new TaskThreadFactory(name), new ThreadPoolExecutor.DiscardPolicy());
allowCoreThreadTimeOut(service, config.allowCoreTimeOut);
return service;
}
public boolean isBusy() {
synchronized (this) {
if (service == null || service.isShutdown()) {
return false;
}
if(service instanceof ThreadPoolExecutor){
ThreadPoolExecutor tService = (ThreadPoolExecutor) service;
return tService.getActiveCount() >= tService.getCorePoolSize();
}
return false;
}
}
private static final void allowCoreThreadTimeOut(ThreadPoolExecutor service, boolean value) {
if (Build.VERSION.SDK_INT >= 9) {
allowCoreThreadTimeOut9(service, value);
}
}
@TargetApi(9)
private static final void allowCoreThreadTimeOut9(ThreadPoolExecutor service, boolean value) {
service.allowCoreThreadTimeOut(value);
}
Comparator<Runnable> mQueueFIFOComparator = new Comparator<Runnable>() {
@Override
public int compare(Runnable lhs, Runnable rhs) {
PRunnable r1 = (PRunnable) lhs;
PRunnable r2 = (PRunnable) rhs;
return PRunnable.compareFIFO(r1, r2);
}
};
Comparator<Runnable> mQueueLIFOComparator = new Comparator<Runnable>() {
@Override
public int compare(Runnable lhs, Runnable rhs) {
PRunnable r1 = (PRunnable) lhs;
PRunnable r2 = (PRunnable) rhs;
return PRunnable.compareLIFO(r1, r2);
}
};
}
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