使用線程池的好處有很多,比如節(jié)省系統(tǒng)資源的開銷,節(jié)省創(chuàng)建和銷毀線程的時間等,當我們需要處理的任務較多時,就可以使用線程池,可能還有很多用戶不知道Java線程池如何使用?下面小編給大家分享Java四種線程池的使用方法。
線程池介紹:
線程池是一種多線程處理形式,處理過程中將任務添加到隊列,然后在創(chuàng)建線程后自動啟動這些任務。線程池線程都是后臺線程。每個線程都使用默認的堆棧大小,以默認的優(yōu)先級運行,并處于多線程單元中。如果某個線程在托管代碼中空閑(如正在等待某個事件),則線程池將插入另一個輔助線程來使所有處理器保持繁忙。如果所有線程池線程都始終保持繁忙,但隊列中包含掛起的工作,則線程池將在一段時間后創(chuàng)建另一個輔助線程但線程的數(shù)目永遠不會超過最大值。超過最大值的線程可以排隊,但他們要等到其他線程完成后才啟動。
Java四種線程池的使用:
Java通過Executors提供四種線程池,分別為:
newCachedThreadPool創(chuàng)建一個可緩存線程池,如果線程池長度超過處理需要,可靈活回收空閑線程,若無可回收,則新建線程。
newFixedThreadPool 創(chuàng)建一個定長線程池,可控制線程最大并發(fā)數(shù),超出的線程會在隊列中等待。
newScheduledThreadPool 創(chuàng)建一個定長線程池,支持定時及周期性任務執(zhí)行。
newSingleThreadExecutor 創(chuàng)建一個單線程化的線程池,它只會用唯一的工作線程來執(zhí)行任務,保證所有任務按照指定順序(FIFO, LIFO, 優(yōu)先級)執(zhí)行。
。1) newCachedThreadPool
創(chuàng)建一個可緩存線程池,如果線程池長度超過處理需要,可靈活回收空閑線程,若無可回收,則新建線程。示例代碼如下:
- 01package test;
- 02import java.util.concurrent.ExecutorService;
- 03import java.util.concurrent.Executors;
- 04public class ThreadPoolExecutorTest {
- 05public static void main(String[] args) {
- 06ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
- 07for (int i = 0; i < 10; i++) {
- 08final int index = i;
- 09try {
- 10Thread.sleep(index * 1000);
- 11} catch (InterruptedException e) {
- 12e.printStackTrace();
- 13}
- 14cachedThreadPool.execute(new Runnable() {
- 15public void run() {
- 16System.out.println(index);
- 17}
- 18});
- 19}
- 20}
- 21}
復制代碼
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);
}
});
}
}
}
線程池為無限大,當執(zhí)行第二個任務時第一個任務已經完成,會復用執(zhí)行第一個任務的線程,而不用每次新建線程。
(2) newFixedThreadPool
創(chuàng)建一個定長線程池,可控制線程最大并發(fā)數(shù),超出的線程會在隊列中等待。示例代碼如下:
- 01package test;
- 02import java.util.concurrent.ExecutorService;
- 03import java.util.concurrent.Executors;
- 04public class ThreadPoolExecutorTest {
- 05public static void main(String[] args) {
- 06ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);
- 07for (int i = 0; i < 10; i++) {
- 08final int index = i;
- 09fixedThreadPool.execute(new Runnable() {
- 10public void run() {
- 11try {
- 12System.out.println(index);
- 13Thread.sleep(2000);
- 14} catch (InterruptedException e) {
- 15e.printStackTrace();
- 16}
- 17}
- 18});
- 19}
- 20}
- 21}
復制代碼
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();
}
}
});
}
}
}
因為線程池大小為3,每個任務輸出index后sleep 2秒,所以每兩秒打印3個數(shù)字。
定長線程池的大小最好根據系統(tǒng)資源進行設置。如Runtime.getRuntime().availableProcessors()
。3) newScheduledThreadPool
創(chuàng)建一個定長線程池,支持定時及周期性任務執(zhí)行。延遲執(zhí)行示例代碼如下:
- 01package test;
- 02import java.util.concurrent.Executors;
- 03import java.util.concurrent.ScheduledExecutorService;
- 04import java.util.concurrent.TimeUnit;
- 05public class ThreadPoolExecutorTest {
- 06public static void main(String[] args) {
- 07ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
- 08scheduledThreadPool.schedule(new Runnable() {
- 09public void run() {
- 10System.out.println("delay 3 seconds");
- 11}
- 12}, 3, TimeUnit.SECONDS);
- 13}
- 14}
復制代碼
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.schedule(new Runnable() {
public void run() {
System.out.println("delay 3 seconds");
}
}, 3, TimeUnit.SECONDS);
}
}
表示延遲3秒執(zhí)行。
定期執(zhí)行示例代碼如下:
- 01package test;
- 02import java.util.concurrent.Executors;
- 03import java.util.concurrent.ScheduledExecutorService;
- 04import java.util.concurrent.TimeUnit;
- 05public class ThreadPoolExecutorTest {
- 06public static void main(String[] args) {
- 07ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
- 08scheduledThreadPool.scheduleAtFixedRate(new Runnable() {
- 09public void run() {
- 10System.out.println("delay 1 seconds, and excute every 3 seconds");
- 11}
- 12}, 1, 3, TimeUnit.SECONDS);
- 13}
- 14}
復制代碼
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秒后每3秒執(zhí)行一次。
。4) newSingleThreadExecutor
創(chuàng)建一個單線程化的線程池,它只會用唯一的工作線程來執(zhí)行任務,保證所有任務按照指定順序(FIFO, LIFO, 優(yōu)先級)執(zhí)行。示例代碼如下:
- 01package test;
- 02import java.util.concurrent.ExecutorService;
- 03import java.util.concurrent.Executors;
- 04public class ThreadPoolExecutorTest {
- 05public static void main(String[] args) {
- 06ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
- 07for (int i = 0; i < 10; i++) {
- 08final int index = i;
- 09singleThreadExecutor.execute(new Runnable() {
- 10public void run() {
- 11try {
- 12System.out.println(index);
- 13Thread.sleep(2000);
- 14} catch (InterruptedException e) {
- 15e.printStackTrace();
- 16}
- 17}
- 18});
- 19}
- 20}
- 21}
復制代碼
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,相當于順序執(zhí)行各個任務。
你可以使用JDK自帶的監(jiān)控工具來監(jiān)控我們創(chuàng)建的線程數(shù)量,運行一個不終止的線程,創(chuàng)建指定量的線程,來觀察:
工具目錄:C:\Program Files\Java\jdk1.6.0_06\bin\jconsole.exe
運行程序做稍微修改:
- 01package test;
- 02import java.util.concurrent.ExecutorService;
- 03import java.util.concurrent.Executors;
- 04public class ThreadPoolExecutorTest {
- 05public static void main(String[] args) {
- 06ExecutorService singleThreadExecutor = Executors.newCachedThreadPool();
- 07for (int i = 0; i < 100; i++) {
- 08final int index = i;
- 09singleThreadExecutor.execute(new Runnable() {
- 10public void run() {
- 11try {
- 12while(true) {
- 13System.out.println(index);
- 14Thread.sleep(10 * 1000);
- 15}
- 16} catch (InterruptedException e) {
- 17e.printStackTrace();
- 18}
- 19}
- 20});
- 21try {
- 22Thread.sleep(500);
- 23} catch (InterruptedException e) {
- 24e.printStackTrace();
- 25}
- 26}
- 27}
- 28}
復制代碼
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();
}
}
}
}
效果如下:
選擇我們運行的程序:
監(jiān)控運行狀態(tài)
關于Java四種線程池的使用技巧就給大家分享到這里了,正所謂工欲善其事,必先利其器,我們掌握了訣竅,處理事情才能事倍功半,希望可以幫助到大家。
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