Executors建立執行緒的例項
Java通過Executors提供四種執行緒池,分別為:
newCachedThreadPool建立一個可快取執行緒池,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。
newFixedThreadPool 建立一個定長執行緒池,可控制執行緒最大併發數,超出的執行緒會在佇列中等待。
newScheduledThreadPool 建立一個定長執行緒池,支援定時及週期性任務執行。
newSingleThreadExecutor 建立一個單執行緒化的執行緒池,它只會用唯一的工作執行緒來執行任務,保證所有任務按照指定順序(FIFO, LIFO, 優先順序)執行。
(1) newCachedThreadPool
建立一個可快取執行緒池,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。示例程式碼如下:
- package test;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- public class ThreadPoolExecutorTest {
- public static void main(String[] args) {
- ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
- for (int i = 0; i < 10; i++) {
- final int index = i;
- try {
- Thread.sleep(index * 1000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- cachedThreadPool.execute(new Runnable() {
- public void run() {
- System.out.println(index);
- }
- });
- }
- }
- }
執行緒池為無限大,當執行第二個任務時第一個任務已經完成,會複用執行第一個任務的執行緒,而不用每次新建執行緒。
(2) newFixedThreadPool(專案用過)
建立一個定長執行緒池,可控制執行緒最大併發數,超出的執行緒會在佇列中等待。示例程式碼如下:
- package test;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- public class ThreadPoolExecutorTest {
- public static void main(String[] args) {
- ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);
- for (int i = 0; i < 10; i++) {
- final int index = i;
- fixedThreadPool.execute(new Runnable() {
- public void run() {
- try {
- System.out.println(index);
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- });
- }
- }
- }
因為執行緒池大小為3,每個任務輸出index後sleep 2秒,所以每兩秒列印3個數字。
定長執行緒池的大小最好根據系統資源進行設定。如Runtime.getRuntime().availableProcessors()
(3) newScheduledThreadPool
建立一個定長執行緒池,支援定時及週期性任務執行。延遲執行示例程式碼如下:
- package test;
- import java.util.concurrent.Executors;
- import java.util.concurrent.ScheduledExecutorService;
- import java.util.concurrent.TimeUnit;
- public class ThreadPoolExecutorTest {
- public static void main(String[] args) {
- ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
- scheduledThreadPool.schedule(new Runnable() {
- public void run() {
- System.out.println("delay 3 seconds");
- }
- }, 3, TimeUnit.SECONDS);
- }
- }
表示延遲3秒執行。
定期執行示例程式碼如下:
Java程式碼- package test;
- import java.util.concurrent.Executors;
- import java.util.concurrent.ScheduledExecutorService;
- import java.util.concurrent.TimeUnit;
- public class ThreadPoolExecutorTest {
- public static void main(String[] args) {
- ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
- scheduledThreadPool.scheduleAtFixedRate(new Runnable() {
- public void run() {
- System.out.println("delay 1 seconds, and excute every 3 seconds");
- }
- }, 1, 3, TimeUnit.SECONDS);
- }
- }
表示延遲1秒後每3秒執行一次。
(4) newSingleThreadExecutor
建立一個單執行緒化的執行緒池,它只會用唯一的工作執行緒來執行任務,保證所有任務按照指定順序(FIFO, LIFO, 優先順序)執行。示例程式碼如下:
- package test;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- public class ThreadPoolExecutorTest {
- public static void main(String[] args) {
- ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
- for (int i = 0; i < 10; i++) {
- final int index = i;
- singleThreadExecutor.execute(new Runnable() {
- public void run() {
- try {
- System.out.println(index);
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- });
- }
- }
- }
結果依次輸出,相當於順序執行各個任務。
你可以使用JDK自帶的監控工具來監控我們建立的執行緒數量,執行一個不終止的執行緒,建立指定量的執行緒,來觀察:
工具目錄:C:\Program Files\Java\jdk1.6.0_06\bin\jconsole.exe
執行程式做稍微修改:
- package test;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- public class ThreadPoolExecutorTest {
- public static void main(String[] args) {
- ExecutorService singleThreadExecutor = Executors.newCachedThreadPool();
- for (int i = 0; i < 100; i++) {
- final int index = i;
- singleThreadExecutor.execute(new Runnable() {
- public void run() {
- try {
- while(true) {
- System.out.println(index);
- Thread.sleep(10 * 1000);
- }
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- });
- try {
- Thread.sleep(500);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- }
- }
轉載自:https://blog.csdn.net/mack415858775/article/details/51508831