一手遮天 Android - 锁和并发处理: Lock 演示 ReentrantLock 的使用
一手遮天 Android - 锁和并发处理: Lock 演示 ReentrantLock 的使用
示例如下:
/concurrent/ReentrantLockDemo1.java
/**
* ReentrantLock 实现了 Lock 接口，关于 Lock 的相关知识点请参见“concurrent.LockDemo1”, “concurrent.LockDemo2”, “concurrent.LockDemo3”
* 顾名思义，ReentrantLock 是可重入锁，也就是说 ReentrantLock 可以递归调用，即支持嵌套
*
* ReentrantLock
* new ReentrantLock(boolean fair) - 实例化 ReentrantLock 并指定其是否为公平锁，默认是非公平锁
* 公平锁 - 按照请求锁的顺序来获取锁
* 非公平锁 - 是否能获取到锁与请求锁的顺序无关
* isFair() - 是否是公平锁
* isLocked() - 是否持有锁
* hasQueuedThreads() - 锁等待队列中是否有线程在等待锁
* hasQueuedThread(Thread thread) - 指定的线程是否存在于锁等待队列中
* getQueueLength() - 锁等待队列中的等待线程数
* isHeldByCurrentThread() - 当前线程是否持有此锁
* getHoldCount() - 当前线程持有此锁的数量（是数量，而不是次数。比如嵌套锁时，当前线程持有此锁的数量就可能会大于 1）
* // 举个例子如下：
* try {
* _reentrantLock.lock();
* _reentrantLock.getHoldCount(); // 当前线程持有此锁的数量为 1
* try {
* _reentrantLock.lock();
* _reentrantLock.getHoldCount(); // 当前线程持有此锁的数量为 2
* } finally {
* _reentrantLock.unlock();
* }
* } finally {
* _reentrantLock.unlock();
* }
* hasWaiters(Condition condition) - 是否有线程在等待指定的 condition
* getWaitQueueLength(Condition condition) - 返回等待指定的 condition 的线程数
*/
package com.webabcd.androiddemo.concurrent;
import android.os.SystemClock;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
import com.webabcd.androiddemo.R;
import java.util.concurrent.locks.ReentrantLock;
public class ReentrantLockDemo1 extends AppCompatActivity {
private TextView _textView1;
private ReentrantLock _reentrantLock = new ReentrantLock(false);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_concurrent_lockdemo1);
_textView1 = (TextView) findViewById(R.id.textView1);
sample();
}
private void sample() {
for (int i = 0; i < 5; i++) {
Thread thread = new MyThread("thread" + i);
thread.setDaemon(true);
thread.start();
}
}
private class MyThread extends Thread {
public MyThread(String name){
super(name);
}
@Override
public void run() {
for (int i = 0; i < 5; i++) {
SystemClock.sleep(10);
_reentrantLock.lock();
try {
SystemClock.sleep(10);
writeMessage(String.format("%b, %b, %b, %d, %b, %d",
_reentrantLock.isFair(),
_reentrantLock.isLocked(),
_reentrantLock.hasQueuedThreads(),
_reentrantLock.getQueueLength(),
_reentrantLock.isHeldByCurrentThread(),
_reentrantLock.getHoldCount()));
} catch (Exception ex) {
} finally {
_reentrantLock.unlock();
}
}
}
}
private void writeMessage(final String message) {
final String threadName = Thread.currentThread().getName();
runOnUiThread(new Runnable() {
@Override
public void run() {
_textView1.append(String.format("%s（%s）\n", message, threadName));
}
});
}
}
/layout/activity_concurrent_lockdemo1.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
