如何使用synchronized實現一個Lock
這篇文章主要為大家展示了“如何使用synchronized實現一個Lock”，內容簡而易懂，條理清晰，希望能夠幫助大家解決疑惑，下面讓小編帶領大家一起研究并學習一下“如何使用synchronized實現一個Lock”這篇文章吧。
網站建設哪家好，找成都創新互聯公司！專注于網頁設計、網站建設、微信開發、小程序定制開發、集團企業網站建設等服務項目。為回饋新老客戶創新互聯還提供了豐臺免費建站歡迎大家使用！
方式一：
public synchronized void a(){
//TODO
}方式二：
public void b(){
synchronized(this){
//TODO
}
}從這兩種方式來看，鎖都是加在｛｝之間的，我們再來看看Lock是如何做的呢:
public void c() {
lock.lock();
try {
// TODO
} finally {
lock.unlock();
}
}這種方式的鎖是加在lock()和unlock()之間的，所以要想實現一個lock功能，就要想怎么實現這樣兩個方法，lock()和unlock()方法，先定義一個框架如下所示：
public void lock(){
}
public void unlock(){
}然后要想怎么用synchronized去實現這兩個方法。
現在其實只是稍微清楚了一點思路，但是還不知道怎么去填充這兩個方法，這是后再來分析一下Lock的加鎖有什么特點，再來看看這段代碼：
public void c() {
lock.lock();
//When current thread get the lock, other thread has to wait
try {
//current thread get in the lock, other thread can not get in
// TODO
}
finally {
lock.unlock();
//current thread release the lock
}
}這段代碼我只是加了一點注釋，別的什么都沒有做，是不是幫助理解這段代碼，看看出現頻率最高的詞是什么，是currentthread，那么我們去填充lock()和unlock()方法的時候是不是注意要抓住currentthread這個關鍵字就可以找到解決方案呢？答案是肯定的。
接著分析，使用synchronized的時候如何讓線程等待呢？是用wait()方法。怎么讓線程喚醒呢，是用notify()方法。那么就要在lock()方法中使用wait()方法，在unlock()方法中使用notify()方法。那么我們在使用wait()和notify()的時候是有一個條件的，想想我們應該使用什么作為條件呢？
我們應該使用當前鎖是否被占用作為判斷條件，如果鎖被占用，currentthread等待，想想我們在使用synchronized的時候是不是一直使用的這個條件，答案也是肯定的。
再來分析一下什么時候釋放鎖，使用什么作為條件，想想如果線程A拿到了鎖，線程B能釋放嗎？當然不能，如果B能釋放就違反了原則，當然不能。肯定是A線程的鎖只能A來釋放。所以判斷條件就是判斷持有鎖的線程是不是currentthread，如果是的話，可以釋放，不是的話當然不能。
現在來看看完整的代碼：
package test.lock;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
public class NaiveLock {
private static final long NONE = -1;
private long owner = NONE;
private Boolean isLooked() {
return owner != NONE;
}
public synchronized void lock() {
long currentThreadId = Thread.currentThread().getId();
if (owner == currentThreadId) {
throw new IllegalStateException("Lock has been acquired by current thread");
}
while (this.isLooked()) {
System.out.println(String.format("thread %s is waitting lock", currentThreadId));
try {
wait();
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
owner = currentThreadId;
System.out.println(String.format("Lock is acquired by thread %s", owner));
}
public synchronized void unlock() {
if (!this.isLooked() || owner != Thread.currentThread().getId()) {
throw new IllegalStateException("Only Lock owner can unlock the lock");
}
System.out.println(String.format("thread %s is unlocking", owner));
System.out.println();
owner = NONE;
notify();
}
public static void main(String[] args) {
final NaiveLock lock = new NaiveLock();
ExecutorService executor = Executors.newFixedThreadPool(20, new ThreadFactory() {
private ThreadGroup group = new ThreadGroup("test thread group");
{
group.setDaemon(true);
}
@Override
public Thread newThread(Runnable r) {
return new Thread(group, r);
}
}
);
for (int i = 0; i < 20; i++) {
executor.submit(new Runnable() {
@Override
public void run() {
lock.lock();
System.out.println(String.format("thread %s is running...", Thread.currentThread().getId()));
try {
Thread.sleep(new Random().nextint(1000));
}
catch (InterruptedException e) {
e.printStackTrace();
}
lock.unlock();
}
}
);
}
}
}運行一下看看結果：
Lock is acquired by thread 8 thread 8 is running... thread 27 is waitting lock thread 26 is waitting lock thread 25 is waitting lock thread 24 is waitting lock thread 23 is waitting lock thread 22 is waitting lock thread 21 is waitting lock thread 20 is waitting lock thread 19 is waitting lock thread 18 is waitting lock thread 17 is waitting lock thread 16 is waitting lock thread 15 is waitting lock thread 14 is waitting lock thread 13 is waitting lock thread 12 is waitting lock thread 11 is waitting lock thread 10 is waitting lock thread 9 is waitting lock thread 8 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 27 is unlocking Lock is acquired by thread 26 thread 26 is running... thread 26 is unlocking Lock is acquired by thread 25 thread 25 is running... thread 25 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 23 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 22 is unlocking Lock is acquired by thread 21 thread 21 is running... thread 21 is unlocking Lock is acquired by thread 20 thread 20 is running... thread 20 is unlocking Lock is acquired by thread 19 thread 19 is running... thread 19 is unlocking Lock is acquired by thread 18 thread 18 is running... thread 18 is unlocking Lock is acquired by thread 17 thread 17 is running... thread 17 is unlocking Lock is acquired by thread 16 thread 16 is running... thread 16 is unlocking Lock is acquired by thread 15 thread 15 is running... thread 15 is unlocking Lock is acquired by thread 14 thread 14 is running... thread 14 is unlocking Lock is acquired by thread 13 thread 13 is running... thread 13 is unlocking Lock is acquired by thread 12 thread 12 is running... thread 12 is unlocking Lock is acquired by thread 11 thread 11 is running... thread 11 is unlocking Lock is acquired by thread 10 thread 10 is running... thread 10 is unlocking Lock is acquired by thread 9 thread 9 is running... thread 9 is unlocking
如果把for循環改成30次，再看一下結果：
Lock is acquired by thread 8 thread 8 is running... thread 27 is waitting lock thread 26 is waitting lock thread 25 is waitting lock thread 24 is waitting lock thread 23 is waitting lock thread 22 is waitting lock thread 21 is waitting lock thread 20 is waitting lock thread 19 is waitting lock thread 18 is waitting lock thread 17 is waitting lock thread 16 is waitting lock thread 15 is waitting lock thread 14 is waitting lock thread 13 is waitting lock thread 12 is waitting lock thread 11 is waitting lock thread 10 is waitting lock thread 9 is waitting lock thread 8 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 8 is waitting lock thread 27 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 26 is waitting lock thread 27 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 25 is waitting lock thread 27 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 27 is waitting lock thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 24 is waitting lock thread 23 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 23 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 21 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 20 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 19 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 18 is waitting lock thread 22 is unlocking Lock is acquired by thread 17 thread 17 is running... thread 17 is unlocking Lock is acquired by thread 16 thread 16 is running... thread 16 is unlocking Lock is acquired by thread 15 thread 15 is running... thread 15 is unlocking Lock is acquired by thread 14 thread 14 is running... thread 14 is unlocking Lock is acquired by thread 13 thread 13 is running... thread 13 is unlocking Lock is acquired by thread 12 thread 12 is running... thread 12 is unlocking Lock is acquired by thread 11 thread 11 is running... thread 11 is unlocking Lock is acquired by thread 10 thread 10 is running... thread 10 is unlocking Lock is acquired by thread 9 thread 9 is running... thread 9 is unlocking Lock is acquired by thread 8 thread 8 is running... thread 8 is unlocking Lock is acquired by thread 26 thread 26 is running... thread 26 is unlocking Lock is acquired by thread 25 thread 25 is running... thread 25 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 27 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 23 is unlocking Lock is acquired by thread 21 thread 21 is running... thread 21 is unlocking Lock is acquired by thread 20 thread 20 is running... thread 20 is unlocking Lock is acquired by thread 19 thread 19 is running... thread 19 is unlocking Lock is acquired by thread 18 thread 18 is running... thread 18 is unlocking
以上是“如何使用synchronized實現一個Lock”這篇文章的所有內容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內容對大家有所幫助，如果還想學習更多知識，歡迎關注創新互聯行業資訊頻道！
新聞標題：如何使用synchronized實現一個Lock
鏈接URL：http://www.2m8n56k.cn/article4/ihgpie.html
成都網站建設公司_創新互聯，為您提供手機網站建設、關鍵詞優化、動態網站、靜態網站、建站公司、網站收錄
聲明：本網站發布的內容（圖片、視頻和文字）以用戶投稿、用戶轉載內容為主，如果涉及侵權請盡快告知，我們將會在第一時間刪除。文章觀點不代表本網站立場，如需處理請聯系客服。電話：028-86922220；郵箱：[email protected]。內容未經允許不得轉載，或轉載時需注明來源： 創新互聯
- 羅湖網站建設：自適應網站有哪些優點？ 2016-08-09
- 響應式網站建設與自適應網站建設的區別 2016-11-12
- 自適應網站設計就像水一樣 2022-01-24
- 響應時和自適應網站設計布局如何選擇 2022-06-02
- 自適應網站建設應該注意哪些方面呢? 2017-02-19
- 自適應網站建設要注意哪些問題？自適應網站建設要注意哪幾點 2016-09-01
- 自適應網站建設一般要注意哪些細節 2016-10-26
- 自適應網站有和特點和優勢呢？ 2016-11-12
- 自適應網站優勢詳解! 2020-08-12
- 自適應網站的優勢及缺點解析，建站失敗的原因解析 2022-10-24
- 手機網站與自適應網站的區別？ 2016-11-10
- 成都網站建設對你說自適應網站的設計構思 2016-09-15