Timer定时器实现源码分析

Timer实现使用：入口1:private Timer mTimer ＝ new Timer();入口2:mTimer.schedule(new TimerTask() {// schedule(TimerTask task, long delay, long period)            @Override            public void run() {                //System.out.println("timer running...");                updateWidgetTime();            }1000, 1000}; 源码分析：入口1:// 1.public Timer() {    impl = new TimerImpl("java.util.Timer", false); }// 2.启动线程查询是否有任务    TimerImpl(String name, boolean isDaemon) {// TimerImpl继承自Thread            this.setName(name);            this.setDaemon(isDaemon);            this.start();// 开启线程        }入口2:// 3.插入一个任务队列public void schedule(TimerTask task, long delay, long period) {    scheduleImpl(task, delay, period, false);// schedule:时刻表}    private void scheduleImpl(TimerTask task, long delay, long period,            boolean fixed) {                      long when = delay + System.currentTimeMillis();// 下一次schedule的时间        task.when = when;        task.period = period;        task.fixedRate = fixed;          // insert the newTask into queue        impl.insertTask(task);// 将TimerTask插入到TimerTree中        /* private void insertTask(TimerTask newTask) {            // callers are synchronized            tasks.insert(new TimerNode(newTask));            this.notify();        }        }        */    }// 4.线程执行，不断查询任务并执行TimerImpl.run // 线程中执行各个任务@Overridepublic void run() {    while (true) {        TimerTask task;            // 5.查找是否有任务需要执行        // need to check cancelled inside the synchronized block        if (cancelled) {            return;        }        if (tasks.isEmpty()) {            if (finished) {                return;            }            // no tasks scheduled -- sleep until any task appear                  this.wait();// 如果任务队列中没有任务，则休眠                       continue;// wait方法经常和while＋continue何用        }        // 6.计算距任务执行还需要的时间，并且sleep消耗掉剩余时间        long currentTime = System.currentTimeMillis();        TimerNode taskNode = tasks.minimum(); // 取出任务队列中离任务执行剩余时间最少的任务        task = taskNode.task;        long timeToSleep;             if (task.cancelled) {            tasks.delete(taskNode);            continue;        }        // check the time to sleep for the first task scheduled        timeToSleep = task.when - currentTime;            if (timeToSleep > 0) {            // sleep!                       this.wait(timeToSleep);// 把任务执行还剩余时间消耗掉                       continue; // continue用法同上        }        // 7.执行到点的任务，并删除该任务，如果该任务是repeat，则重新设置定点时间，并把任务重新添加到队列        // no sleep is necessary before launching the task        if (task.cancelled) {            tasks.delete(taskNode);            continue;        }        // set time to schedule        task.setScheduledTime(task.when); // 内部实现：scheduledTime = time;（将when赋值给schedule）        // remove task from queue        tasks.delete(taskNode); // 将未来要执行的任务删除队列。 删除即将执行的任务节点        // 循环定时器，而非只定时一次        // set when the next task should be launched        if (task.period >= 0) {            // this is a repeating task,                       // task is scheduled at fixed delay            task.when = System.currentTimeMillis()                    + task.period;                       // insert this task into queue            insertTask(task); // 将当前任务重新插入到队列        } else {            task.when = 0;        }             task.run();// 真正的业务执行代码    }}小结：1.Timer中对象的关系：－Timer－TimerImpl 定时器的控制对象，内部维护TimerTree。本质是线程类——TimerTree 定时器队列，内部维护TimerNode链表－TimerNode 定时器节点，内部维护一个定时任务－TimerTask 定时任务，内部是具体定是任务执行代码（内部实现Runnable接口）2.大概执行过程：如步骤1-7创建定时器（本质是线程类），并执行线程方法，线程方法查询当前任务队列中是否有任务队列，如果有任务直接执行任务，并将任务移除队列，重新添加任务到任务队列中。补充：各个类核心成员数据private static final class TimerImpl extends Thread {    /**     * True if the method cancel() of the Timer was called or the !!!stop()     * method was invoked     */    private boolean cancelled;    /**     * True if the Timer has become garbage     */    private boolean finished;    /**     * Vector consists of scheduled events, sorted according to     * {@code when} field of TaskScheduled object.     */    private TimerTree tasks = new TimerTree();// TimerTree维护着TimerTree｝private static final class TimerTree {    int deletedCancelledNumber;    TimerNode root;｝private static final class TimerNode {            TimerNode parent, left, right;            TimerTask task;            public TimerNode(TimerTask value) {                this.task = value;            }            public void deleteIfCancelled(TimerTree tasks) {// 删除TimeTree上的TiemNode节点                /*                 * All changes in the tree structure during deleting this node                 * affect only the structure of the subtree having this node as                 * its root                 */                if (left != null) {                    left.deleteIfCancelled(tasks);                }                if (right != null) {                    right.deleteIfCancelled(tasks);                }                if (task.cancelled) {                    tasks.delete(this);                    tasks.deletedCancelledNumber++;                }            }        }｝public abstract class TimerTask implements Runnable {    /* Lock object for synchronization. It's also used by Timer class. */    final Object lock = new Object();    /* If timer was cancelled */    boolean cancelled;    /* Slots used by Timer */    long when;    long period;    boolean fixedRate;    /*     * The time when task will be executed, or the time when task was launched     * if this is task in progress.     */    private long scheduledTime;｝