android线程池简书,Android - 线程池

水深无声 2022-10-05 00:58 196阅读 0赞

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老婆保佑，代码无BUG

前言

2018 准备换工作，也得好好准备面试，PS，小伙伴需要招人不，求推荐

面试题： 说说你对JAVA 线程池的理解

一：线程池的优点

二：线程种类

三：使用介绍

FixedThreadPool (定长线程池)

CacheThreadPool (可缓存线程池)

SingleThreadExecutor (单线程化线程池)

ScheduledThreadPool (定时线程池)

四：源码分析

五：ThreadPoolExecutor参数

参考

一：线程池的优点

减少在创建和销毁线程上所花的时间以及系统资源的开销。

有效控制线程并发，避免大量线程之间因抢占资源导致阻塞现象

二：线程种类

FixedThreadPool (定长线程池)

SingleThreadExecutor (单线程化线程池)

CachedThreadPool (可缓存线程池)

ScheduledThreadPool (定时线程池)

三：使用介绍

1. FixedThreadPool

ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);

特点：

这是一种数量固定的线程池,当线程处于空闲的时候,并不会被回收,除非线程池被关闭.

当所有的线程都处于活动状态时,新任务都会处于等待状态,直到有线程空闲出来.

由于FixedThreadPool中只有核心线程并且这些核心线程不会被回收,这意味着它能够更加快速地响应外界的请求.

eg:

private void init\_TestThread() \{

ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);

for (int i = 0; i < 10; i++) \{

final int finalI = i;

Runnable runnable = new Runnable() \{

@Override

public void run() \{

SystemClock.sleep(3000);

Log.d("TAG", "run: " + finalI + " thread: "+Thread.currentThread().getName());

\};

fixedThreadPool.execute(runnable);

log:

02-11 02:52:42.609 4305-4464/com.cpsc.rxjavademo D/TAG: run: 1 thread: pool-3-thread-2

02-11 02:52:42.622 4305-4463/com.cpsc.rxjavademo D/TAG: run: 0 thread: pool-3-thread-1

02-11 02:52:42.631 4305-4465/com.cpsc.rxjavademo D/TAG: run: 2 thread: pool-3-thread-3

02-11 02:52:45.612 4305-4464/com.cpsc.rxjavademo D/TAG: run: 3 thread: pool-3-thread-2

02-11 02:52:45.625 4305-4463/com.cpsc.rxjavademo D/TAG: run: 4 thread: pool-3-thread-1

02-11 02:52:45.634 4305-4465/com.cpsc.rxjavademo D/TAG: run: 5 thread: pool-3-thread-3

02-11 02:52:48.614 4305-4464/com.cpsc.rxjavademo D/TAG: run: 6 thread: pool-3-thread-2

02-11 02:52:48.628 4305-4463/com.cpsc.rxjavademo D/TAG: run: 7 thread: pool-3-thread-1

02-11 02:52:48.636 4305-4465/com.cpsc.rxjavademo D/TAG: run: 8 thread: pool-3-thread-3

02-11 02:52:51.617 4305-4464/com.cpsc.rxjavademo D/TAG: run: 9 thread: pool-3-thread-2

2. CacheThreadPool

ExecutorService cachedThreadPool = Executors.newCachedThreadPool();

特点：

它是一种线程数量不定的线程池,它只有非核心线程,并且其最大线程数为Integer.MAX\_VALUE(也就相当于线程池的线程数量可以无限大).

当线程池中所有线程都处于活动的状态时,线程池会创建新的线程来处理新任务,否则就会复用空闲线程来处理.

eg:

private void init\_TestThread() \{

ExecutorService fixedThreadPool = Executors.newCachedThreadPool();

for (int i = 0; i < 10; i++) \{

final int finalI = i;

Runnable runnable = new Runnable() \{

@Override

public void run() \{

SystemClock.sleep(3000);

Log.d("TAG", "run: " + finalI + " thread: "+Thread.currentThread().getName());

\};

fixedThreadPool.execute(runnable);

log:

02-11 02:54:16.162 4305-4510/com.cpsc.rxjavademo D/TAG: run: 0 thread: pool-4-thread-1

02-11 02:54:16.164 4305-4511/com.cpsc.rxjavademo D/TAG: run: 1 thread: pool-4-thread-2

02-11 02:54:16.169 4305-4512/com.cpsc.rxjavademo D/TAG: run: 2 thread: pool-4-thread-3

02-11 02:54:16.170 4305-4513/com.cpsc.rxjavademo D/TAG: run: 3 thread: pool-4-thread-4

02-11 02:54:16.172 4305-4514/com.cpsc.rxjavademo D/TAG: run: 4 thread: pool-4-thread-5

02-11 02:54:16.173 4305-4515/com.cpsc.rxjavademo D/TAG: run: 5 thread: pool-4-thread-6

02-11 02:54:16.176 4305-4516/com.cpsc.rxjavademo D/TAG: run: 6 thread: pool-4-thread-7

02-11 02:54:16.180 4305-4517/com.cpsc.rxjavademo D/TAG: run: 7 thread: pool-4-thread-8

02-11 02:54:16.182 4305-4518/com.cpsc.rxjavademo D/TAG: run: 8 thread: pool-4-thread-9

02-11 02:54:16.184 4305-4520/com.cpsc.rxjavademo D/TAG: run: 9 thread: pool-4-thread-10

3. SingleThreadExecutor

ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();

特点

这类线程池内部只有一个核心线程,它确保所有的任务都在同一个线程中按顺序执行.

eg:

private void init\_TestThread() \{

ExecutorService fixedThreadPool = Executors.newSingleThreadExecutor();

for (int i = 0; i < 10; i++) \{

final int finalI = i;

Runnable runnable = new Runnable() \{

@Override

public void run() \{

SystemClock.sleep(3000);

Log.d("TAG", "run: " + finalI + " thread: "+Thread.currentThread().getName());

\};

fixedThreadPool.execute(runnable);

log:

02-11 02:55:26.466 4305-4557/com.cpsc.rxjavademo D/TAG: run: 0 thread: pool-5-thread-1

02-11 02:55:29.466 4305-4557/com.cpsc.rxjavademo D/TAG: run: 1 thread: pool-5-thread-1

02-11 02:55:32.472 4305-4557/com.cpsc.rxjavademo D/TAG: run: 2 thread: pool-5-thread-1

02-11 02:55:35.473 4305-4557/com.cpsc.rxjavademo D/TAG: run: 3 thread: pool-5-thread-1

02-11 02:55:38.475 4305-4557/com.cpsc.rxjavademo D/TAG: run: 4 thread: pool-5-thread-1

02-11 02:55:41.476 4305-4557/com.cpsc.rxjavademo D/TAG: run: 5 thread: pool-5-thread-1

02-11 02:55:44.478 4305-4557/com.cpsc.rxjavademo D/TAG: run: 6 thread: pool-5-thread-1

02-11 02:55:47.479 4305-4557/com.cpsc.rxjavademo D/TAG: run: 7 thread: pool-5-thread-1

02-11 02:55:50.480 4305-4557/com.cpsc.rxjavademo D/TAG: run: 8 thread: pool-5-thread-1

02-11 02:55:53.481 4305-4557/com.cpsc.rxjavademo D/TAG: run: 9 thread: pool-5-thread-1

4. ScheduledThreadPool

ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3);

特点

它的核心线程数量是固定的,而非核心线程数是没有限制的,并且当非核心线程闲置时会被立即回收.

eg:

private void init\_TestThread() \{

ExecutorService fixedThreadPool = Executors.newScheduledThreadPool(3);

for (int i = 0; i < 10; i++) \{

final int finalI = i;

Runnable runnable = new Runnable() \{

@Override

public void run() \{

SystemClock.sleep(3000);

Log.d("TAG", "run: " + finalI + " thread: "+Thread.currentThread().getName());

\};

fixedThreadPool.execute(runnable);

log:

02-11 03:41:32.230 6981-7045/com.cpsc.rxjavademo D/TAG: run: 0 thread: pool-1-thread-1

02-11 03:41:32.236 6981-7046/com.cpsc.rxjavademo D/TAG: run: 1 thread: pool-1-thread-2

02-11 03:41:32.239 6981-7047/com.cpsc.rxjavademo D/TAG: run: 2 thread: pool-1-thread-3

02-11 03:41:35.233 6981-7045/com.cpsc.rxjavademo D/TAG: run: 3 thread: pool-1-thread-1

02-11 03:41:35.238 6981-7046/com.cpsc.rxjavademo D/TAG: run: 4 thread: pool-1-thread-2

02-11 03:41:35.240 6981-7047/com.cpsc.rxjavademo D/TAG: run: 5 thread: pool-1-thread-3

02-11 03:41:38.234 6981-7045/com.cpsc.rxjavademo D/TAG: run: 6 thread: pool-1-thread-1

02-11 03:41:38.240 6981-7046/com.cpsc.rxjavademo D/TAG: run: 7 thread: pool-1-thread-2

02-11 03:41:38.242 6981-7047/com.cpsc.rxjavademo D/TAG: run: 8 thread: pool-1-thread-3

02-11 03:41:41.237 6981-7045/com.cpsc.rxjavademo D/TAG: run: 9 thread: pool-1-thread-1

四：源码分析

FixedThreadPool

public static ExecutorService newFixedThreadPool(int nThreads) \{

return new ThreadPoolExecutor(nThreads, nThreads,

0L, TimeUnit.MILLISECONDS,

new LinkedBlockingQueue());

CacheThreadPool

public static ExecutorService newCachedThreadPool() \{

return new ThreadPoolExecutor(0, Integer.MAX\_VALUE,

60L, TimeUnit.SECONDS,

new SynchronousQueue());

SingleThreadExecutor

public static ExecutorService newSingleThreadExecutor() \{

return new FinalizableDelegatedExecutorService

(new ThreadPoolExecutor(1, 1,

0L, TimeUnit.MILLISECONDS,

new LinkedBlockingQueue()));

ScheduledThreadPool

public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) \{

return new ScheduledThreadPoolExecutor(corePoolSize);

public ScheduledThreadPoolExecutor(int corePoolSize) \{

super(corePoolSize, Integer.MAX\_VALUE,

DEFAULT\_KEEPALIVE\_MILLIS, MILLISECONDS,

new DelayedWorkQueue());

五：ThreadPoolExecutor参数

public ThreadPoolExecutor(int corePoolSize,

int maximumPoolSize,

long keepAliveTime,

TimeUnit unit,

BlockingQueue workQueue) \{\}

参数说明

参数

说明

corePoolSize

线程池中核心线程的数量

maximumPoolSize

线程池中最大线程数量

keepAliveTime

非核心线程的超时时长，当系统中非核心线程闲置时间超过keepAliveTime之后，则会被回收。如果ThreadPoolExecutor的allowCoreThreadTimeOut属性设置为true，则该参数也表示核心线程的超时时长

unit

用于指定keepAliveTime参数单位，有纳秒、微秒、毫秒、秒、分、时、天等

workQueue

线程池中的任务队列，该队列主要用来存储已经被提交但是尚未执行的任务。存储在这里的任务是由ThreadPoolExecutor的execute方法提交来的。

参考

[88f6f4ff04c8]: /images/20221005/232dc4bdc39f41918e6b6ab24079566a.png

android线程池简书,Android - 线程池

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