四種常見執行緒池使用舉例
阿新 • • 發佈:2019-01-05
執行緒池:Executor 管理多個非同步任務的執行,而無需程式設計師顯式地管理執行緒的生命週期。這裡的非同步是指多個任務的執行互不干擾,不需要進行同步操作。
主要有四種執行緒池:
快取池
newCachedThreadPool建立一個可緩存執行緒池,如果執行緒池長度超過處理需要,可靈活回收空閒執行緒,若無可回收,則新建執行緒。
下面是它的使用方法:
package com.xzj; import java.util.Date; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;// @ author :zjxu time:2019/1/5 public class Main { public static void main(String[] args) { ExecutorService cachedThreadPool = Executors.newCachedThreadPool(); for (int i = 0; i < 10; i++) { cachedThreadPool.execute(new MyRunnable()); } cachedThreadPool.shutdown(); } }class MyRunnable implements Runnable { @Override public void run() { System.out.println(new Date().toString()); try { Thread.sleep(2000); } catch (InterruptedException ie) { ie.printStackTrace(); } } }
newFixedThreadPool可以建立一個定長的執行緒池。定長執行緒池最多隻能同時執行一定個數的執行緒,這個容量在new的時候設定。
下面是一個示例:
package com.xzj; import java.util.Date; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; // @ author :zjxu time:2019/1/5 public class Main { public static void main(String[] args) { ExecutorService cachedThreadPool = Executors.newFixedThreadPool(3); for (int i = 0; i < 10; i++) { cachedThreadPool.execute(new MyRunnable()); } cachedThreadPool.shutdown(); } } class MyRunnable implements Runnable { @Override public void run() { System.out.println(new Date().toString()); try { Thread.sleep(2000); } catch (InterruptedException ie) { ie.printStackTrace(); } } }
執行結果:
Sat Jan 05 11:59:13 CST 2019 Sat Jan 05 11:59:13 CST 2019 Sat Jan 05 11:59:13 CST 2019 Sat Jan 05 11:59:15 CST 2019 Sat Jan 05 11:59:15 CST 2019 Sat Jan 05 11:59:15 CST 2019 Sat Jan 05 11:59:17 CST 2019 Sat Jan 05 11:59:17 CST 2019 Sat Jan 05 11:59:17 CST 2019 Sat Jan 05 11:59:19 CST 2019
定時池
newScheduledThreadPool建立一個定長執行緒池,支援延遲執行和週期性任務執行。後一種執行方式類似於微控制器的定時器中斷。
1、延遲執行
package com.xzj; import java.util.Date; import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; // @ author :zjxu time:2019/1/5 public class Main { public static void main(String[] args) { ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5); System.out.println(new Date().toString()); scheduledThreadPool.schedule(new MyRunnable(), 3, TimeUnit.SECONDS); } } class MyRunnable implements Runnable { @Override public void run() { System.out.println(new Date().toString()); } }
結果:
SatJan0512:15:35CST2019
SatJan0512:15:38CST2019
1、週期執行
scheduleAtFixedRate(x,x,x,x)的第二個引數的意義是初始化延遲,第三個引數的意義是定時間隔延遲。
package com.xzj; import java.util.Date; import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; // @ author :zjxu time:2019/1/5 public class Main { public static void main(String[] args) { ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5); System.out.println(new Date().toString()); scheduledThreadPool.scheduleAtFixedRate(new MyRunnable(), 1, 3, TimeUnit.SECONDS); try { Thread.sleep(15 * 1000); } catch (InterruptedException ie) { ie.printStackTrace(); } scheduledThreadPool.shutdown(); } } class MyRunnable implements Runnable { @Override public void run() { System.out.println(new Date().toString()); } }
執行的結果
1 Sat Jan 05 12:21:07 CST 2019 2 Sat Jan 05 12:21:08 CST 2019 3 Sat Jan 05 12:21:11 CST 2019 4 Sat Jan 05 12:21:14 CST 2019 5 Sat Jan 05 12:21:17 CST 2019 6 Sat Jan 05 12:21:20 CST 2019
結果中第一二行的原因就是初始化延遲引數形成的。
newSingleThreadExecutor建立一個單執行緒化的執行緒池,這個執行緒池當前池中的執行緒死後(或發生異常時),才能重新啟動新的一個執行緒來替代原來的執行緒繼續執行下去。也就是說按照單執行緒的模式,會按照執行緒新增的順序,一個一個的執行這些執行緒的工作。
package com.xzj; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; // @ author :zjxu time:2019/1/5 public class Main { public static void main(String[] args) { ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor(); for (int i = 0; i < 10; i++) { final int index = i; singleThreadExecutor.execute(new MyRunnable(index)); } } } class MyRunnable implements Runnable { int i = 0; public MyRunnable(int i) { this.i = i; } @Override public void run() { try { System.out.print(i+" "); Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } } }
執行的結果
0 1 2 3 4 5 6 7 8 9
按照順序,一個一個一次執行。