Android开发经验谈：并发编程（线程与线程池）（推荐）

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：

1. fixedthreadpool 创建定长线程的线程池
2. cachedthreadpool 需要的时候建立新的线程，超时线程销毁
3. singlethreadpool 单个线程的线程池
4. 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

1. arrayblockingqueue :  有界的数组队列
2. linkedblockingqueue : 可支持有界/*的队列，使用链表实现
3. priorityblockingqueue : 优先队列，可以针对任务排序
4. 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：

1. threadpoolexecutor.abortpolicy:丢弃任务并抛出rejectedexecutionexception异常。
2. threadpoolexecutor.discardpolicy：也是丢弃任务，但是不抛出异常。
3. 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）
4. 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);
  }
 };

}

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