如果未收到数据,java是否发送并重试数据?
我正在从事一个项目,我需要做以下事情:
- 将特定socket上的特定数据发送到另一个系统。我必须在给定的socket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李>
- 然后使用下面实现的
RetryStrategy
之一继续尝试发送相同的数据李> - 启动一个后台轮询线程,告诉您发送的数据是否在其他系统中收到。如果它被接收到,那么我们将从
pending
队列中删除它,这样它就不会被重试。如果出于任何原因它没有被接收到,那么我们将使用我们使用的RetryStrategy再次尝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
,并且如果它是在另一个系统中接收到的,那么我的轮询器线程将把这个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挂起队列中删除这个地址,这样它就不会再次被重试
我有两个{
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存在任何争用条件或线程安全问题?因为在多线程中正确处理内容是很困难的
让我知道是否有更好或有效的方法来做同样的事情
# 1 楼答案
如果您的代码中没有针对第三方库的内容,那么您可以看看这个https://github.com/nurkiewicz/async-retry。假设我正确理解了您的问题,此库允许您在不重新发明轮子的情况下处理此类问题。它写得很清楚,而且有很好的文档记录,所以我希望你能找到自己的路。:)