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。。。。

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runnablepublic 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); } };}

以上所述是小编给大家介绍的Android开发经验谈：并发编程（线程与线程池）详解整合，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对网站的支持！