我对多线程在 Java 中如何在低级别上工作的知识很少。我知道当您有两个线程运行时，Java 会为每个线程分配“时间块”以供执行。
例如：
public void test()
{
Thread testThread = new Thread(new TestThread());
testThread.start();
for (int i = 0; i < Integer.MAX_VALUE; ++i)
System.out.print("a");
}
private class TestThread extends Thread
{
public void run()
{
for (int i = 0; i < Integer.MAX_VALUE; ++i)
System.out.print("b");
}
}
会打印出类似：
aaaaaaaaaabbbbbbbbbbbbbbaaaaaaaaaaabbbbbbbbbbbbbaaaaaaa...
而不是：
abababababababababababababababab.....
我的问题是：是否有可能减少“时间块”，所以我们更接近：
aabbaaabbaabbaaabbaabbbaabbaabbbaabbaaaa...
为什么？我正在尝试编写一个苹果推送通知服务器（只是为了好玩）。当您向苹果推送通知服务写入请求时，可能会发生一两件事：
1. 如果请求有效，则不会返回任何内容。
2. 如果请求无效，将返回错误码并关闭连接，并且在无效请求之后和连接关闭之前发送的所有请求都将被丢弃。
因为读取套接字会阻塞，直到有数据可供读取（如果我不写任何无效请求，这可能永远不会发生），我不能简单地在每次写入后读取以查看是否有错误而不设置 200-500 毫秒的超时. 如果我们有 100 万个写入请求（很有可能），这个超时会增加 55 - 138 小时，并且我们可能会因为短暂的超时而错过返回的错误，这将导致请求永远不会被发送。
所以我有两个线程，就像我上面的例子一样，一个正在写入服务器，一个正在读取等待查看是否返回错误。这就是问题所在：如果请求 #4 是错误的，但我们在读取错误并且连接关闭之前写入了 #5-#10，则请求 #5-10 会被 Apple 服务丢弃。因此，一旦我们知道 #4 是错误的并且我们知道我们写的最后一个请求是 #10，我们需要重新排队 #5-10 以再次发送。
我现在遇到的问题是因为“时间卡盘”很大，我可以在读取线程读取之前写入请求 #1-#400再次。然后读取线程读取 #21 存在错误，因此 #22-#400 被重新排队并再次发送......等等。理想情况下，读取线程能够从套接字读取每写入 5-10 个请求。
资源：
private Object readWriteLock = new Object();
private volatile int lastWrittenIndex;
private volatile boolean doneWriting;
private List<PushNotificationRequest> pushNotificationRequestsResnedList = new ArrayList<PushNotificationRequest>();
public boolean write()
{
// get the requests read list
List<PushNotificationRequest> requests = getPushNotificationRequests(false);
// as long as there are more notifications to write...
while (requests.size() > 0)
{
lastWrittenIndex = -1;
doneWriting = false;
// create and start the read thread
Thread readThread = new Thread(new ReadThread(), "APNS Reader");
readThread.start();
for (int i = 0; i < requests.size(); ++i)
{
PushNotificationRequest request = requests.get(i);
// write
boolean success = false;
// attempt to send the notification a number of times
for (int j = 0; j < MAX_NUM_PN_WRITE_ATTEMPTS; ++j)
{
synchronized (readWriteLock)
{
try
{
// get the socket connection
SSLSocket socket = getAppleServiceSSLSockett();
OutputStream socketOutputStream = socket.getOutputStream();
socketOutputStream.write(request.binary);
socketOutputStream.flush();
success = true;
lastWrittenIndex = i;
break;
}
catch (IOException e)
{
e.printStackTrace();
}
catch (AppleServiceConnectionException e)
{
e.printStackTrace();
}
}
}
if (!success)
System.err.println("APNS Unable to send push notification:\n" + request);
}
// wait for some time so we can make sure the read thread can read everything
try
{
Thread.sleep(Config.APNS_READ_TIME_AFTER_DONE_WRITING_MILLISECONDS);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
// let the read thread know we are done writing and close the connection so it unblocks
doneWriting = true;
closeAppleServiceSSLSockett();
// wait for the read thread to return
try
{
readThread.join();
}
catch (InterruptedException e)
{
e.printStackTrace();
}
// clear the reading list
requests.clear();
// add the requests from the re-send to the list
if (pushNotificationRequestsResnedList.size() > 0)
{
requests.addAll(pushNotificationRequestsResnedList);
// clear the re-send list
pushNotificationRequestsResnedList.clear();
}
}
}
private class ReadThread extends Thread
{
public void run()
{
byte[] readBuffer = new byte[1024];
int numBytesRead;
int totalNumBytesRead;
while (!doneWriting)
{
try
{
// get the socket connection
SSLSocket socket = getAppleServiceSSLSockett();
socket.setSoTimeout(Config.APNS_READ_TIMEOUT_MILLISECONDS);
InputStream socketInputStream = socket.getInputStream();
// read (blocking)
totalNumBytesRead = 0;
while ((numBytesRead = socketInputStream.read(readBuffer)) != -1)
totalNumBytesRead += numBytesRead;
// check for an error
if (totalNumBytesRead > 0)
{
synchronized (readWriteLock)
{
try
{
PushNotificationResponse response = new PushNotificationResponse(readBuffer, 0);
System.err.println("APNS Read got response with id: " + response.identifier);
// find the request with the given identifier
int i;
for (i = lastWrittenIndex; i > -1; --i)
{
if (pushNotificationRequestsReadingList.get(i).identifier == response.identifier)
break;
}
if (i == -1)
{
// something went wrong, we didn't find the identifier
System.err.println("APNS Read unable to find request with id: " + response.identifier);
}
else
{
System.err.println("APNS Read " + response.getErrorMessage(pushNotificationRequestsReadingList.get(i)));
// add the requests between the bad request and the last written (included)
for (++i; i <= lastWrittenIndex; ++i)
pushNotificationRequestsResnedList.add(pushNotificationRequestsReadingList.get(i));
}
}
catch (InvalidPushNotificationResponseException g)
{
g.printStackTrace();
}
}
// the socket will be closed, reopen it
try
{
reopenAppleServiceSSLSockett();
}
catch (AppleServiceConnectionException e)
{
e.printStackTrace();
}
}
}
catch (SocketException e)
{
// ignore a close, it is expected
if (!e.getMessage().equals("Socket closed"))
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
catch (AppleServiceConnectionException e)
{
e.printStackTrace();
}
}
}
}