【发布时间】：2017-02-19 02:25:05
【问题描述】：
我正在做一个项目，我需要做以下事情：
- 将特定套接字上的某些数据发送到另一个系统。我必须在给定的套接字上发送一个特定的字节数组。每个字节数组都有一个唯一的长地址。
- 然后使用下面实现的
RetryStrategy之一继续重试发送相同的数据。 - 启动后台轮询线程，告诉您发送的数据是否已在其他系统中收到。如果收到了，我们会将其从
pending队列中删除，这样它就不会被重试，如果由于某种原因没有收到，我们将使用我们使用的 RetryStrategy 再次重试发送相同的数据。李>
例如：如果我们发送了byteArrayA，它的唯一长地址为addressA，并且如果它在另一个系统中被接收，那么我的轮询线程将把这个addressA作为确认返回，这意味着它已被接收所以现在我们可以从待处理队列中删除这个地址，这样它就不会再被重试了。
我有两个RetryStrategy 实现了ConstantBackoff 和ExponentialBackoff。所以我想出了下面的模拟器来模拟上述流程。
public class Experimental {
/** Return the desired backoff delay in millis for the given retry number, which is 1-based. */
interface RetryStrategy {
long getDelayMs(int retry);
}
public enum ConstantBackoff implements RetryStrategy {
INSTANCE;
@Override
public long getDelayMs(int retry) {
return 1000L;
}
}
public enum ExponentialBackoff implements RetryStrategy {
INSTANCE;
@Override
public long getDelayMs(int retry) {
return 100 + (1L << retry);
}
}
/** A container that sends messages with retries. */
private static class Sender {
private final ScheduledExecutorService executorService = Executors.newScheduledThreadPool(20);
private final ConcurrentMap<Long, Retrier> pending = new ConcurrentHashMap<>();
/** Send the given (simulated) data with given address on the given socket. */
void sendTo(long addr, byte[] data, int socket) {
System.err.println("Sending " + Arrays.toString(data) + "@" + addr + " on " + socket);
}
/** The state of a message that's being retried. */
private class Retrier implements Runnable {
private final RetryStrategy retryStrategy;
private final long addr;
private final byte[] data;
private final int socket;
private int retry;
private Future<?> future;
Retrier(RetryStrategy retryStrategy, long addr, byte[] data, int socket) {
this.retryStrategy = retryStrategy;
this.addr = addr;
this.data = data;
this.socket = socket;
this.retry = 0;
}
private synchronized void start() {
if (future == null) {
future = executorService.submit(this);
pending.put(addr, this);
}
}
private synchronized void cancel() {
if (future != null) {
future.cancel(true);
future = null;
}
}
private synchronized void reschedule() {
if (future != null) {
future = executorService.schedule(this, retryStrategy.getDelayMs(++retry), MILLISECONDS);
}
}
@Override
synchronized public void run() {
sendTo(addr, data, socket);
reschedule();
}
}
/**
* Get a (simulated) verified message address. Just picks a pending
* one. Returns zero if none left.
*/
long getVerifiedAddr() {
System.err.println("Pending messages: " + pending.size());
Iterator<Long> i = pending.keySet().iterator();
long addr = i.hasNext() ? i.next() : 0;
return addr;
}
/** A polling loop that cancels retries of (simulated) verified messages. */
class CancellationPoller implements Runnable {
@Override
public void run() {
while (!Thread.currentThread().isInterrupted()) {
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
long addr = getVerifiedAddr();
if (addr == 0) {
continue;
}
System.err.println("Verified message (to be cancelled) " + addr);
Retrier retrier = pending.remove(addr);
if (retrier != null) {
retrier.cancel();
}
}
}
}
private Sender initialize() {
executorService.submit(new CancellationPoller());
return this;
}
private void sendWithRetriesTo(RetryStrategy retryStrategy, long addr, byte[] data, int socket) {
new Retrier(retryStrategy, addr, data, socket).start();
}
}
public static void main(String[] args) {
Sender sender = new Sender().initialize();
for (long i = 1; i <= 10; i++) {
sender.sendWithRetriesTo(ConstantBackoff.INSTANCE, i, null, 42);
}
for (long i = -1; i >= -10; i--) {
sender.sendWithRetriesTo(ExponentialBackoff.INSTANCE, i, null, 37);
}
}
}
我想看看上面的代码中是否有任何竞争条件或任何线程安全问题？因为在多线程中正确处理内容很困难。
如果有更好或更有效的方法来做同样的事情，请告诉我。
【问题讨论】：
-
我的建议是不要使用线程，除非你真的有......你可以使用事件循环在一个线程中执行所有事情，但仍然有异步执行
标签： java multithreading design-patterns thread-safety guava