Android之实现具有优先级的线程池

      在Android开发中为了复用线程以及节约线程开销，线程池是使用较多的一种方法，有时也会有这样的需求，不同的线程执行任务的紧急度是不一样的，后加入线程池队列的任务可能需要优先处理，在ThreadPoolExecutor的构造函数中需要传递一个继承BlockQueue的子类。

     在SDK中已经提供了一个PriorityBlockingQueue这样的优先级阻塞队列，我们要做的就是扩展Runnable，添加一个优先级的属性

public abstract class RunWithPriority implements Runnable{

public int priority;

public RunWithPriority(int priority){
this.priority = priority;
}

public int getPriority() {
return priority;
}
}

然后就是为PriorityBlockingQueue构造函数的第二个参数，继承Comparator实现一个比较优先级的类
public class ComparePriority<T extends RunWithPriority> implements Comparator<T> {

@Override
public int compare(T lhs, T rhs) {
return rhs.getPriority() - lhs.getPriority();
}
}

完成了这个类之后我们就能实际使用了，写一个test类

public class Test {

public static void main(String[] args){
//在PriorityBlockingQueue传入比较优先级的规则
PriorityBlockingQueue<Runnable> queue = new PriorityBlockingQueue<>(20,new ComparePriority());
Executor exe = new ThreadPoolExecutor(2,6,10, TimeUnit.SECONDS,queue);
//RunWithPriority的构造函数中的数字就是优先级大小
exe.execute(new RunWithPriority(2) {
@Override
public void run() {
System.out.println(this.getPriority() + " started");
try {
Thread.sleep(3000);
} catch (InterruptedException ex) {
}
System.out.println(this.getPriority() + " finished");
}
});
exe.execute(new RunWithPriority(10) {
@Override
public void run() {
System.out.println(this.getPriority() + " started");
try {
Thread.sleep(3000);
} catch (InterruptedException ex) {

}
System.out.println(this.getPriority() + " finished");
}
});
exe.execute(new RunWithPriority(5) {
@Override
public void run() {
System.out.println(this.getPriority() + " started");
try {
Thread.sleep(3000);
} catch (InterruptedException ex) {

}
System.out.println(this.getPriority() + " finished");
}
});
exe.execute(new RunWithPriority(3) {
@Override
public void run() {
System.out.println(this.getPriority() + " started");
try {
Thread.sleep(3000);
} catch (InterruptedException ex) {

}
System.out.println(this.getPriority() + " finished");
}
});
exe.execute(new RunWithPriority(4) {
@Override
public void run() {
System.out.println(this.getPriority() + " started");
try {
Thread.sleep(3000);
} catch (InterruptedException ex) {

}
System.out.println(this.getPriority() + " finished");
}
});
}

}

我们通过输出log来看
10 started
2 started
10 finished
5 started
2 finished
4 started
5 finished
3 started
4 finished
3 finished

可以看出核心线程是2个 也就是刚开始进入的10 和 2 ， 后面的调用顺序是5、3、4，在队列中经过优先级排列变成了5、4、3
，真正的按照优先级的大小进行排列调用顺序