Timer底层原理
今天，扒拉了一下ribbon负载均很策略，其中有一个策略是RetryRule,顾名思义就是客户端rpc调用失败时，它会不断地重新请求服务方进行尝试获取数据。
思想：在指定时间内不断的重新请求，直到超时。
上代码：
public Server choose(ILoadBalancer lb, Object key) {
long requestTime = System.currentTimeMillis();
long deadline = requestTime + maxRetryMillis;
Server answer = null;
answer = subRule.choose(key);
if (((answer == null) || (!answer.isAlive()))
&& (System.currentTimeMillis() < deadline)) {
InterruptTask task = new InterruptTask(deadline
- System.currentTimeMillis());
while (!Thread.interrupted()) {
answer = subRule.choose(key);
if (((answer == null) || (!answer.isAlive()))
&& (System.currentTimeMillis() < deadline)) {
Thread.yield();
} else {
break;
}
}
task.cancel();
}
if ((answer == null) || (!answer.isAlive())) {
return null;
} else {
return answer;
}
}
public class Timer {
private final TaskQueue queue = new TaskQueue();
private final TimerThread thread = new TimerThread(queue);
private final Object threadReaper = new Object() {
protected void finalize() throws Throwable {
synchronized(queue) {
thread.newTasksMayBeScheduled = false;
queue.notify();
}
}
};
private final static AtomicInteger nextSerialNumber = new AtomicInteger(0);
private static int serialNumber() {
return nextSerialNumber.getAndIncrement();
}
public Timer() {
this("Timer-" + serialNumber());
}
public Timer(boolean isDaemon) {
this("Timer-" + serialNumber(), isDaemon);
}
public Timer(String name) {
thread.setName(name);
thread.start();
}
public Timer(String name, boolean isDaemon) {
thread.setName(name);
thread.setDaemon(isDaemon);
thread.start();
}
public void schedule(TimerTask task, long delay) {
if (delay < 0)
throw new IllegalArgumentException("Negative delay.");
sched(task, System.currentTimeMillis()+delay, 0);
}
public void schedule(TimerTask task, Date time) {
sched(task, time.getTime(), 0);
}
public void schedule(TimerTask task, long delay, long period) {
if (delay < 0)
throw new IllegalArgumentException("Negative delay.");
if (period <= 0)
throw new IllegalArgumentException("Non-positive period.");
sched(task, System.currentTimeMillis()+delay, -period);
}
public void schedule(TimerTask task, Date firstTime, long period) {
if (period <= 0)
throw new IllegalArgumentException("Non-positive period.");
sched(task, firstTime.getTime(), -period);
}
public void scheduleAtFixedRate(TimerTask task, long delay, long period) {
if (delay < 0)
throw new IllegalArgumentException("Negative delay.");
if (period <= 0)
throw new IllegalArgumentException("Non-positive period.");
sched(task, System.currentTimeMillis()+delay, period);
}
public void scheduleAtFixedRate(TimerTask task, Date firstTime,
long period) {
if (period <= 0)
throw new IllegalArgumentException("Non-positive period.");
sched(task, firstTime.getTime(), period);
}
private void sched(TimerTask task, long time, long period) {
if (time < 0)
throw new IllegalArgumentException("Illegal execution time.");
if (Math.abs(period) > (Long.MAX_VALUE >> 1))
period >>= 1;
synchronized(queue) {
if (!thread.newTasksMayBeScheduled)
throw new IllegalStateException("Timer already cancelled.");
synchronized(task.lock) {
if (task.state != TimerTask.VIRGIN)
throw new IllegalStateException(
"Task already scheduled or cancelled");
task.nextExecutionTime = time;
task.period = period;
task.state = TimerTask.SCHEDULED;
}
queue.add(task);
if (queue.getMin() == task)
queue.notify();
}
}
public void cancel() {
synchronized(queue) {
thread.newTasksMayBeScheduled = false;
queue.clear();
queue.notify();
}
}
public int purge() {
int result = 0;
synchronized(queue) {
for (int i = queue.size(); i > 0; i--) {
if (queue.get(i).state == TimerTask.CANCELLED) {
queue.quickRemove(i);
result++;
}
}
if (result != 0)
queue.heapify();
}
return result;
}
}
class TimerThread extends Thread {
boolean newTasksMayBeScheduled = true;
private TaskQueue queue;
TimerThread(TaskQueue queue) {
this.queue = queue;
}
public void run() {
try {
mainLoop();
} finally {
synchronized(queue) {
newTasksMayBeScheduled = false;
queue.clear();
}
}
}
private void mainLoop() {
while (true) {
try {
TimerTask task;
boolean taskFired;
synchronized(queue) {
while (queue.isEmpty() && newTasksMayBeScheduled)
queue.wait();
if (queue.isEmpty())
break;
long currentTime, executionTime;
task = queue.getMin();
synchronized(task.lock) {
if (task.state == TimerTask.CANCELLED) {
queue.removeMin();
continue;
}
currentTime = System.currentTimeMillis();
executionTime = task.nextExecutionTime;
if (taskFired = (executionTime<=currentTime)) {
if (task.period == 0) {
queue.removeMin();
task.state = TimerTask.EXECUTED;
} else {
queue.rescheduleMin(
task.period<0 ? currentTime - task.period
: executionTime + task.period);
}
}
}
if (!taskFired)
queue.wait(executionTime - currentTime);
}
if (taskFired)
task.run();
} catch(InterruptedException e) {
}
}
}
}
class TaskQueue {
private TimerTask[] queue = new TimerTask[128];
private int size = 0;
int size() {
return size;
}
void add(TimerTask task) {
if (size + 1 == queue.length)
queue = Arrays.copyOf(queue, 2*queue.length);
queue[++size] = task;
fixUp(size);
}
TimerTask getMin() {
return queue[1];
}
TimerTask get(int i) {
return queue[i];
}
void removeMin() {
queue[1] = queue[size];
queue[size--] = null;
fixDown(1);
}
void quickRemove(int i) {
assert i <= size;
queue[i] = queue[size];
queue[size--] = null;
}
void rescheduleMin(long newTime) {
queue[1].nextExecutionTime = newTime;
fixDown(1);
}
boolean isEmpty() {
return size==0;
}
void clear() {
for (int i=1; i<=size; i++)
queue[i] = null;
size = 0;
}
private void fixUp(int k) {
while (k > 1) {
int j = k >> 1;
if (queue[j].nextExecutionTime <= queue[k].nextExecutionTime)
break;
TimerTask tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
private void fixDown(int k) {
int j;
while ((j = k << 1) <= size && j > 0) {
if (j < size &&
queue[j].nextExecutionTime > queue[j+1].nextExecutionTime)
j++;
if (queue[k].nextExecutionTime <= queue[j].nextExecutionTime)
break;
TimerTask tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
k = j;
}
}
void heapify() {
for (int i = size/2; i >= 1; i--)
fixDown(i);
}
}
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