Java并發(fā)編程中使用Executors類創(chuàng)建和管理線程的用法
1. 類 Executors
Executors類可以看做一個(gè)“工具類”。援引JDK1.6 API中的介紹：
此包中所定義的 Executor、ExecutorService、ScheduledExecutorService、ThreadFactory 和 Callable 類的工廠和實(shí)用方法。此類支持以下各種方法：
（1）創(chuàng)建并返回設(shè)置有常用配置字符串的 ExecutorService 的方法。
（2）創(chuàng)建并返回設(shè)置有常用配置字符串的 ScheduledExecutorService 的方法。
（3）創(chuàng)建并返回“包裝的”ExecutorService 方法，它通過(guò)使特定于實(shí)現(xiàn)的方法不可訪問(wèn)來(lái)禁用重新配置。
（4）創(chuàng)建并返回 ThreadFactory 的方法，它可將新創(chuàng)建的線程設(shè)置為已知的狀態(tài)。
（5）創(chuàng)建并返回非閉包形式的 Callable 的方法，這樣可將其用于需要 Callable 的執(zhí)行方法中。
通過(guò)這個(gè)類能夠獲得多種線程池的實(shí)例，例如可以調(diào)用newSingleThreadExecutor()獲得單線程的ExecutorService，調(diào) 用newFixedThreadPool()獲得固定大小線程池的ExecutorService，等等。拿到ExecutorService可以做的事情就比 較多了，最簡(jiǎn)單的是用它來(lái)執(zhí)行Runnable對(duì)象，也可以執(zhí)行一些實(shí)現(xiàn)了Callable<T>的對(duì)象。用Thread的start()方 法沒有返回值，如果該線程執(zhí)行的方法有返回值那用ExecutorService就再好不過(guò)了，可以選擇submit()、invokeAll()或者 invokeAny()，根據(jù)具體情況選擇合適的方法即可。
此類中提供的一些方法有：
1.1 public static ExecutorService newCachedThreadPool()
創(chuàng)建一個(gè)可根據(jù)需要?jiǎng)?chuàng)建新線程的線程池，但是在以前構(gòu)造的線程可用時(shí)將重用它們。對(duì)于執(zhí)行很多短期異步任務(wù)的程序而言，這些線程池通?？商岣叱绦蛐阅?。
1.2 public static ExecutorService newFixedThreadPool(int nThreads)
創(chuàng)建一個(gè)可重用固定線程數(shù)的線程池，以共享的無(wú)界隊(duì)列方式來(lái)運(yùn)行這些線程。
1.3 public static ExecutorService newSingleThreadExecutor()
創(chuàng)建一個(gè)使用單個(gè) worker 線程的 Executor，以無(wú)界隊(duì)列方式來(lái)運(yùn)行該線程。
這三個(gè)方法都可以配合接口ThreadFactory的實(shí)例一起使用。并且返回一個(gè)ExecutorService接口的實(shí)例。
2. 接口 ThreadFactory
根據(jù)需要?jiǎng)?chuàng)建新線程的對(duì)象。使用線程工廠就無(wú)需再手工編寫對(duì) new Thread 的調(diào)用了，從而允許應(yīng)用程序使用特殊的線程子類、屬性等等。
此接口最簡(jiǎn)單的實(shí)現(xiàn)就是：
class SimpleThreadFactory implements ThreadFactory {
public Thread newThread(Runnable r) {
return new Thread(r);
}
}
3. 接口ExecutorService
該接口提供了管理終止的方法。
4.創(chuàng)建標(biāo)準(zhǔn)線程池啟動(dòng)線程
4.1 提供一個(gè)簡(jiǎn)單的實(shí)現(xiàn)Runnable接口的線程
MyThread.java
package com.zj.concurrency.executors;
public class MyThread implements Runnable {
private int count = 1, number;
public MyThread(int num) {
number = num;
System.out.println("Create Thread-" + number);
}
public void run() {
while (true) {
System.out.println("Thread-" + number + " run " + count+" time(s)");
if (++count == 3)
return;
}
}
}
這個(gè)線程會(huì)打印出相應(yīng)的創(chuàng)建和執(zhí)行信息。
4.2使用CachedThreadPool啟動(dòng)線程
CachedThreadPool.java
package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CachedThreadPool {
public static void main(String[] args) {
ExecutorService exec = Executors.newCachedThreadPool();
for (int i = 0; i < 5; i++)
exec.execute(new MyThread(i));
exec.shutdown();
}
}
結(jié)果：
Create Thread-0 Create Thread-1 Create Thread-2 Create Thread-3 Thread-0 run 1 time(s) Thread-0 run 2 time(s) Thread-1 run 1 time(s) Thread-1 run 2 time(s) Thread-2 run 1 time(s) Thread-2 run 2 time(s) Create Thread-4 Thread-4 run 1 time(s) Thread-4 run 2 time(s) Thread-3 run 1 time(s) Thread-3 run 2 time(s)
4.3 使用FixedThreadPool啟動(dòng)線程
FixedThreadPool.java
package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class FixedThreadPool {
public static void main(String[] args) {
ExecutorService exec = Executors.newFixedThreadPool(2);
for (int i = 0; i < 5; i++)
exec.execute(new MyThread(i));
exec.shutdown();
}
}
結(jié)果：
Create Thread-0 Create Thread-1 Create Thread-2 Create Thread-3 Create Thread-4 Thread-0 run 1 time(s) Thread-0 run 2 time(s) Thread-2 run 1 time(s) Thread-2 run 2 time(s) Thread-3 run 1 time(s) Thread-3 run 2 time(s) Thread-4 run 1 time(s) Thread-4 run 2 time(s) Thread-1 run 1 time(s) Thread-1 run 2 time(s)
4.4 使用SingleThreadExecutor啟動(dòng)線程
SingleThreadExecutor.java
package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class SingleThreadExecutor {
public static void main(String[] args) {
ExecutorService exec = Executors.newSingleThreadExecutor();
for (int i = 0; i < 5; i++)
exec.execute(new MyThread(i));
exec.shutdown();
}
}
結(jié)果：
Create Thread-0 Create Thread-1 Create Thread-2 Create Thread-3 Create Thread-4 Thread-0 run 1 time(s) Thread-0 run 2 time(s) Thread-1 run 1 time(s) Thread-1 run 2 time(s) Thread-2 run 1 time(s) Thread-2 run 2 time(s) Thread-3 run 1 time(s) Thread-3 run 2 time(s) Thread-4 run 1 time(s) Thread-4 run 2 time(s)
5.配合ThreadFactory接口的使用
我們?cè)噲D給線程加入daemon和priority的屬性設(shè)置。
5.1設(shè)置后臺(tái)線程屬性
DaemonThreadFactory.java
package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;
public class DaemonThreadFactory implements ThreadFactory {
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setDaemon(true);
return t;
}
}
5.2 設(shè)置優(yōu)先級(jí)屬性
最高優(yōu)先級(jí)MaxPriorityThreadFactory.java
package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;
public class MaxPriorityThreadFactory implements ThreadFactory {
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setPriority(Thread.MAX_PRIORITY);
return t;
}
}
最低優(yōu)先級(jí)MinPriorityThreadFactory.java
package com.zj.concurrency.executors.factory;
import java.util.concurrent.ThreadFactory;
public class MinPriorityThreadFactory implements ThreadFactory {
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setPriority(Thread.MIN_PRIORITY);
return t;
}
}
5.3啟動(dòng)帶有屬性設(shè)置的線程
ExecFromFactory.java
package com.zj.concurrency.executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import com.zj.concurrency.executors.factory.DaemonThreadFactory;
import com.zj.concurrency.executors.factory.MaxPriorityThreadFactory;
import com.zj.concurrency.executors.factory.MinPriorityThreadFactory;
public class ExecFromFactory {
public static void main(String[] args) throws Exception {
ExecutorService defaultExec = Executors.newCachedThreadPool();
ExecutorService daemonExec = Executors
.newCachedThreadPool(new DaemonThreadFactory());
ExecutorService maxPriorityExec = Executors
.newCachedThreadPool(new MaxPriorityThreadFactory());
ExecutorService minPriorityExec = Executors
.newCachedThreadPool(new MinPriorityThreadFactory());
for (int i = 0; i < 10; i++)
daemonExec.execute(new MyThread(i));
for (int i = 10; i < 20; i++)
if (i == 10)
maxPriorityExec.execute(new MyThread(i));
else if (i == 11)
minPriorityExec.execute(new MyThread(i));
else
defaultExec.execute(new MyThread(i));
}
}
結(jié)果：
Create Thread-0 Create Thread-1 Create Thread-2 Create Thread-3 Thread-0 run 1 time(s) Thread-0 run 2 time(s) Thread-1 run 1 time(s) Thread-1 run 2 time(s) Thread-2 run 1 time(s) Thread-2 run 2 time(s) Create Thread-4 Thread-4 run 1 time(s) Thread-4 run 2 time(s) Create Thread-5 Thread-5 run 1 time(s) Thread-5 run 2 time(s) Create Thread-6 Create Thread-7 Thread-7 run 1 time(s) Thread-7 run 2 time(s) Create Thread-8 Thread-8 run 1 time(s) Thread-8 run 2 time(s) Create Thread-9 Create Thread-10 Thread-10 run 1 time(s) Thread-10 run 2 time(s) Create Thread-11 Thread-9 run 1 time(s) Thread-9 run 2 time(s) Thread-6 run 1 time(s) Thread-6 run 2 time(s) Thread-3 run 1 time(s) Thread-3 run 2 time(s) Create Thread-12 Create Thread-13 Create Thread-14 Thread-12 run 1 time(s) Thread-12 run 2 time(s) Thread-13 run 1 time(s) Thread-13 run 2 time(s) Create Thread-15 Thread-15 run 1 time(s) Thread-15 run 2 time(s) Create Thread-16 Thread-16 run 1 time(s) Thread-16 run 2 time(s) Create Thread-17 Create Thread-18 Create Thread-19 Thread-14 run 1 time(s) Thread-14 run 2 time(s) Thread-17 run 1 time(s) Thread-17 run 2 time(s) Thread-18 run 1 time(s) Thread-18 run 2 time(s) Thread-19 run 1 time(s) Thread-19 run 2 time(s) Thread-11 run 1 time(s) Thread-11 run 2 time(s)
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