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Multiple Socket Servers in single netty server

I am trying to develop a socket server supporting TCP sockets and WebSockets. I created two ServerBootsraps with their channels and handlers. I started them with different ports with (skipping unnecessary code parts because they are working ok)
...
ChannelFuture channelFuture = serverBootstrap.bind(port);
...
...
ChannelFuture channelFutureWebsocket = serverBootstrapWebSocket.bind(webSocketPort);
In the tutorials I've seen, they were all ending with serverBootstrap.bind(port).sync(); But If I end with sync, the server stops and waits for packets and I cannot start the other server (as expected). If I don't end with sync, the server runs ok but I am doubtful if it will cause an error in the future.
If my method, skipping sync(), is wrong, how can I run 2 different servers simultaneously?

The javadoc on the Future.sync says: "Waits for this future until it is done, and rethrows the cause of the failure if this future failed."
So what you want to do is get both futures and wait on them both instead of waiting on the 1st future before you've even had a chance to bind the 2nd server.
A simple way to wait on 2 futures is to use a while loop and check both futures using non-blocking methods
ChannelFuture bindFuture1 = bootstrap1.bind(port);
ChannelFuture bindFuture2 = bootstrap2.bind(port);
while (!bindFuture1.isDone() && !bindFuture2.isDone()) Thread.Sleep(INTERVAL);
//Evaluate both futures to see if there were any errors, wait for the other future to be done or do whatever else you need to based on your requirements.
I suggest you read up on futures to understand what the sync method does and why it's necessary. Also have a look here: Waiting on a list of Future

Why adding socket read timeout doesn't help for socketread0 [duplicate]

Performing millions of HTTP requests with different Java libraries gives me threads hanged on:
java.net.SocketInputStream.socketRead0()
Which is native function.
I tried to set up Apche Http Client and RequestConfig to have timeouts on (I hope) everythig that is possible but still, I have (probably infinite) hangs on socketRead0. How to get rid of them?
Hung ratio is about ~1 per 10000 requests (to 10000 different hosts) and it can last probably forever (I've confirmed thread hung as still valid after 10 hours).
JDK 1.8 on Windows 7.
My HttpClient factory:
SocketConfig socketConfig = SocketConfig.custom()
.setSoKeepAlive(false)
.setSoLinger(1)
.setSoReuseAddress(true)
.setSoTimeout(5000)
.setTcpNoDelay(true).build();
HttpClientBuilder builder = HttpClientBuilder.create();
builder.disableAutomaticRetries();
builder.disableContentCompression();
builder.disableCookieManagement();
builder.disableRedirectHandling();
builder.setConnectionReuseStrategy(new NoConnectionReuseStrategy());
builder.setDefaultSocketConfig(socketConfig);
return HttpClientBuilder.create().build();
My RequestConfig factory:
HttpGet request = new HttpGet(url);
RequestConfig config = RequestConfig.custom()
.setCircularRedirectsAllowed(false)
.setConnectionRequestTimeout(8000)
.setConnectTimeout(4000)
.setMaxRedirects(1)
.setRedirectsEnabled(true)
.setSocketTimeout(5000)
.setStaleConnectionCheckEnabled(true).build();
request.setConfig(config);
return new HttpGet(url);
OpenJDK socketRead0 source
Note: Actually I have some "trick" - I can schedule .getConnectionManager().shutdown() in other Thread with cancellation of Future if request finished properly, but it is depracated and also it kills whole HttpClient, not only that single request.

Though this question mentions Windows, I have the same problem on Linux. It appears there is a flaw in the way the JVM implements blocking socket timeouts:
https://bugs.openjdk.java.net/browse/JDK-8049846
https://bugs.openjdk.java.net/browse/JDK-8075484
To summarize, timeout for blocking sockets is implemented by calling poll on Linux (and select on Windows) to determine that data is available before calling recv. However, at least on Linux, both methods can spuriously indicate that data is available when it is not, leading to recv blocking indefinitely.
From poll(2) man page BUGS section:
See the discussion of spurious readiness notifications under the BUGS section of select(2).
From select(2) man page BUGS section:
Under Linux, select() may report a socket file descriptor as "ready
for reading", while nevertheless a subsequent read blocks. This could
for example happen when data has arrived but upon examination has
wrong checksum and is discarded. There may be other circumstances
in which a file descriptor is spuriously reported as ready. Thus it
may be safer to use O_NONBLOCK on sockets that should not block.
The Apache HTTP Client code is a bit hard to follow, but it appears that connection expiration is only set for HTTP keep-alive connections (which you've disabled) and is indefinite unless the server specifies otherwise. Therefore, as pointed out by oleg, the Connection eviction policy approach won't work in your case and can't be relied upon in general.

As Clint said, you should consider a Non-blocking HTTP client, or (seeing that you are using the Apache Httpclient) implement a Multithreaded request execution to prevent possible hangs of the main application thread (this not solve the problem but is better than restart your app because is freezed). Anyway, you set the setStaleConnectionCheckEnabled property but the stale connection check is not 100% reliable, from the Apache Httpclient tutorial:
One of the major shortcomings of the classic blocking I/O model is
that the network socket can react to I/O events only when blocked in
an I/O operation. When a connection is released back to the manager,
it can be kept alive however it is unable to monitor the status of the
socket and react to any I/O events. If the connection gets closed on
the server side, the client side connection is unable to detect the
change in the connection state (and react appropriately by closing the
socket on its end).
HttpClient tries to mitigate the problem by testing whether the
connection is 'stale', that is no longer valid because it was closed
on the server side, prior to using the connection for executing an
HTTP request. The stale connection check is not 100% reliable and adds
10 to 30 ms overhead to each request execution.
The Apache HttpComponents crew recommends the implementation of a Connection eviction policy
The only feasible solution that does not involve a one thread per
socket model for idle connections is a dedicated monitor thread used
to evict connections that are considered expired due to a long period
of inactivity. The monitor thread can periodically call
ClientConnectionManager#closeExpiredConnections() method to close all
expired connections and evict closed connections from the pool. It can
also optionally call ClientConnectionManager#closeIdleConnections()
method to close all connections that have been idle over a given
period of time.
Take a look at the sample code of the Connection eviction policy section and try to implement it in your application along with the Multithread request execution, I think the implementation of both mechanisms will prevent your undesired hangs.

You should consider a Non-blocking HTTP client like Grizzly or Netty which do not have blocking operations to hang a thread.

I have more than 50 machines that make about 200k requests/day/machine. They are running Amazon Linux AMI 2017.03. I previously had jdk1.8.0_102, now I have jdk1.8.0_131. I am using both apacheHttpClient and OKHttp as scraping libraries.
Each machine was running 50 threads, and sometimes, the threads get lost. After profiling with Youkit java profiler I got
ScraperThread42 State: RUNNABLE CPU usage on sample: 0ms
java.net.SocketInputStream.socketRead0(FileDescriptor, byte[], int, int, int) SocketInputStream.java (native)
java.net.SocketInputStream.socketRead(FileDescriptor, byte[], int, int, int) SocketInputStream.java:116
java.net.SocketInputStream.read(byte[], int, int, int) SocketInputStream.java:171
java.net.SocketInputStream.read(byte[], int, int) SocketInputStream.java:141
okio.Okio$2.read(Buffer, long) Okio.java:139
okio.AsyncTimeout$2.read(Buffer, long) AsyncTimeout.java:211
okio.RealBufferedSource.indexOf(byte, long) RealBufferedSource.java:306
okio.RealBufferedSource.indexOf(byte) RealBufferedSource.java:300
okio.RealBufferedSource.readUtf8LineStrict() RealBufferedSource.java:196
okhttp3.internal.http1.Http1Codec.readResponse() Http1Codec.java:191
okhttp3.internal.connection.RealConnection.createTunnel(int, int, Request, HttpUrl) RealConnection.java:303
okhttp3.internal.connection.RealConnection.buildTunneledConnection(int, int, int, ConnectionSpecSelector) RealConnection.java:156
okhttp3.internal.connection.RealConnection.connect(int, int, int, List, boolean) RealConnection.java:112
okhttp3.internal.connection.StreamAllocation.findConnection(int, int, int, boolean) StreamAllocation.java:193
okhttp3.internal.connection.StreamAllocation.findHealthyConnection(int, int, int, boolean, boolean) StreamAllocation.java:129
okhttp3.internal.connection.StreamAllocation.newStream(OkHttpClient, boolean) StreamAllocation.java:98
okhttp3.internal.connection.ConnectInterceptor.intercept(Interceptor$Chain) ConnectInterceptor.java:42
okhttp3.internal.http.RealInterceptorChain.proceed(Request, StreamAllocation, HttpCodec, Connection) RealInterceptorChain.java:92
okhttp3.internal.http.RealInterceptorChain.proceed(Request) RealInterceptorChain.java:67
okhttp3.internal.http.BridgeInterceptor.intercept(Interceptor$Chain) BridgeInterceptor.java:93
okhttp3.internal.http.RealInterceptorChain.proceed(Request, StreamAllocation, HttpCodec, Connection) RealInterceptorChain.java:92
okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(Interceptor$Chain) RetryAndFollowUpInterceptor.java:124
okhttp3.internal.http.RealInterceptorChain.proceed(Request, StreamAllocation, HttpCodec, Connection) RealInterceptorChain.java:92
okhttp3.internal.http.RealInterceptorChain.proceed(Request) RealInterceptorChain.java:67
okhttp3.RealCall.getResponseWithInterceptorChain() RealCall.java:198
okhttp3.RealCall.execute() RealCall.java:83
I found out that they have a fix for this
https://bugs.openjdk.java.net/browse/JDK-8172578
in JDK 8u152 (early access). I have installed it on one of our machines. Now I am waiting to see some good results.

Given no one else responded so far, here is my take
Your timeout setting looks perfectly OK to me. The reason why certain requests appear to be constantly blocked in a java.net.SocketInputStream#socketRead0() call is likely to be due to a combination of misbehaving servers and your local configuration. Socket timeout defines a maximum period of inactivity between two consecutive i/o read operations (or in other words two consecutive incoming packets). Your socket timeout setting is 5,000 milliseconds. As long as the opposite endpoint keeps on sending a packet every 4,999 milliseconds for a chunk encoded message the request will never time out and will end up sending most of its time blocked in java.net.SocketInputStream#socketRead0(). You can find out whether or not this is the case by running HttpClient with wire logging turned on.

For Apache HTTP Client (blocking) I found best solution is to getConnectionManager(). and shutdown it.
So in high-reliability solution I just schedule shutdown in other thread and in case request does not complete I'm shutting in down from other thread

I bumped into the same issue using apache common http client.
There's a pretty simple workaround (which doesn't require shutting the connection manager down):
In order to reproduce it, one needs to execute the request from the question in a new thread paying attention to details:
run request in separate thread, close request and release it's connection in a different thread, interrupt hanging thread
don't run EntityUtils.consumeQuietly(response.getEntity()) in finally block (because it hangs on 'dead' connection)
First, add the interface
interface RequestDisposer {
void dispose();
}
Execute an HTTP request in a new thread
final AtomicReference<RequestDisposer> requestDisposer = new AtomicReference<>(null);
final Thread thread = new Thread(() -> {
final HttpGet request = new HttpGet("http://my.url");
final RequestDisposer disposer = () -> {
request.abort();
request.releaseConnection();
};
requestDiposer.set(disposer);
try (final CloseableHttpResponse response = httpClient.execute(request))) {
...
} finally {
disposer.dispose();
}
};)
thread.start()
Call dispose() in the main thread to close hanging connection
requestDisposer.get().dispose(); // better check if it's not null first
thread.interrupt();
thread.join();
That fixed the issue for me.
My stacktrace looked like this:
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:139)
at org.apache.http.impl.io.SessionInputBufferImpl.fillBuffer(SessionInputBufferImpl.java:155)
at org.apache.http.impl.io.SessionInputBufferImpl.readLine(SessionInputBufferImpl.java:284)
at org.apache.http.impl.io.ChunkedInputStream.getChunkSize(ChunkedInputStream.java:253)
at org.apache.http.impl.io.ChunkedInputStream.nextChunk(ChunkedInputStream.java:227)
at org.apache.http.impl.io.ChunkedInputStream.read(ChunkedInputStream.java:186)
at org.apache.http.conn.EofSensorInputStream.read(EofSensorInputStream.java:137)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
To whom it might be interesting, it easily reproducable, interrupt the thread without aborting request and releasing connection (ratio is about 1/100).
Windows 10, version 10.0.
jdk8.151-x64.

I feel that all these answers are way too specific.
We have to note that this is probably a real JVM bug. It should be possible to get the file descriptor and close it. All this timeout-talk is too high level. You do not want a timeout to the extent that the connection fails, what you want is an ability to hard break this stuck thread and stop or interrupt it.
The way the JVM should implemented the SocketInputStream.socketRead function is to set some internal default timeout, which should be even as low as 1 second. Then when the timeout comes, immediately looping back to the socketRead0. While that is happening, the Thread.interrupt and Thread.stop commands can take effect.
The even better way of doing this of course is not to do any blocking wait at all, but instead use a the select(2) system call with a list of file descriptors and when any one has data available, let it perform the read operation.
Just look all over the internet all these people having trouble with threads stuck in java.net.SocketInputStream#socketRead0, it's the most popular topic about java.net.SocketInputStream hands down!
So, while the bug is not fixed, I wonder about the most dirty trick I can come up with to break up this situation. Something like connecting with the debugger interface to get to the stack frame of the socketRead call and grab the FileDescriptor and then break into that to get the int fd number and then make a native close(2) call on that fd.
Do we have a chance to do that? (Don't tell me "it's not good practice") -- if so, let's do it!

I faced the same issue today. Based on #Sergei Voitovich I've tried to make it work still using Apache Http Client.
Since I am using Java 8 its simpler to make a timeout to abort the connection.
Here's is a draft of the implementation:
private HttpResponse executeRequest(Request request){
InterruptibleRequestExecution requestExecution = new InterruptibleRequestExecution(request, executor);
ExecutorService executorService = Executors.newSingleThreadExecutor();
try {
return executorService.submit(requestExecution).get(<your timeout in milliseconds>, TimeUnit.MILLISECONDS);
} catch (TimeoutException | ExecutionException e) {
// Your request timed out, you can throw an exception here if you want
throw new UsefulExceptionForYourApplication(e);
} catch (InterruptedException e) {
// Always remember to call interrupt after catching InterruptedException
Thread.currentThread().interrupt();
throw new UsefulExceptionForYourApplication(e);
} finally {
// This method forces to stop the Thread Pool (with single thread) created by Executors.newSingleThreadExecutor() and makes the pending request to abort inside the thread. So if the request is hanging in socketRead0 it will stop and also the thread will be terminated
forceStopIdleThreadsAndRequests(requestExecution, executorService);
}
}
private void forceStopIdleThreadsAndRequests(InterruptibleRequestExecution execution,
ExecutorService executorService) {
execution.abortRequest();
executorService.shutdownNow();
}
The code above will create a new Thread to execute the request using org.apache.http.client.fluent.Executor. Timeout can be easily configured.
The execution of the thread is defined in InterruptibleRequestExecution which you can see below.
private static class InterruptibleRequestExecution implements Callable<HttpResponse> {
private final Request request;
private final Executor executor;
private final RequestDisposer disposer;
public InterruptibleRequestExecution(Request request, Executor executor) {
this.request = request;
this.executor = executor;
this.disposer = request::abort;
}
#Override
public HttpResponse call() {
try {
return executor.execute(request).returnResponse();
} catch (IOException e) {
throw new UsefulExceptionForYourApplication(e);
} finally {
disposer.dispose();
}
}
public void abortRequest() {
disposer.dispose();
}
#FunctionalInterface
interface RequestDisposer {
void dispose();
}
}
The results are really good. We've had times where some connections where hanging in sockedRead0 for 7 hours! Now, it never passes the defined timeout and its working in production with millions of requests per day without having any problems.

How to set Java NIO AsynchronousSocketChannel connect timeout

Looking at JDK 1.7 API. I cannot seem to be able to set a connection timeout on an AsynchonousSocketChannel. Is there anyway I can setup a connection timeout on such a channel?
Thanks.

The answer is: you can't.
The first thing to understand is how a TCP connect works. The kernel is sending SYN packets, backing off the time between each retry. This can be tuned via kernel parameters. An article covering this in detail (for linux) can be found here
To give you an idea of what's involved to implement your own shorter timeout for a socket connect is to put the socket in nonblocking mode, throw it in a select() with a timeout, then use getsockopt() to see what happened. This StackOverflow answer shows how this works.
With NIO.2, the connection process is handled for you using threads that you don't have access to. Unfortunately there's no way to tell it you want a shorter timeout on connects; it just calls your completion handler / notifies the Future when the connection either succeeds of fails (including timing out).
You do have the option of calling get(timeout, unit) on the returned Future, then cancelling the Futureif it times out ... but that means if you want the connect to be async you have to add another layer of threading / callbacks and may as well just implement your own async thing with nio.
One last thing worth mentioning since you're looking at async network stuff is that Netty does give this to you (using Nio):
Bootstrap bootstrap = new Bootstrap()
.group(new NioEventLoopGroup())
.channel(NioSocketChannel.class)
.remoteAddress(new InetSocketAddress(remoteAddress, port))
.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, connectionTimeout);
ChannelFuture f = bootstrap.connect();
And you can register a listener with that ChannelFuture for a callback.

Apache HttpClient Interim Error: NoHttpResponseException

I have a webservice which is accepting a POST method with XML. It is working fine then at some random occasion, it fails to communicate to the server throwing IOException with message The target server failed to respond. The subsequent calls work fine.
It happens mostly, when i make some calls and then leave my application idle for like 10-15 min. the first call which I make after that returns this error.
I tried couple of things ...
I setup the retry handler like
HttpRequestRetryHandler retryHandler = new HttpRequestRetryHandler() {
public boolean retryRequest(IOException e, int retryCount, HttpContext httpCtx) {
if (retryCount >= 3){
Logger.warn(CALLER, "Maximum tries reached, exception would be thrown to outer block");
return false;
}
if (e instanceof org.apache.http.NoHttpResponseException){
Logger.warn(CALLER, "No response from server on "+retryCount+" call");
return true;
}
return false;
}
};
httpPost.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, retryHandler);
but this retry never got called. (yes I am using right instanceof clause). While debugging this class never being called.
I even tried setting up HttpProtocolParams.setUseExpectContinue(httpClient.getParams(), false); but no use. Can someone suggest what I can do now?
IMPORTANT
Besides figuring out why I am getting the exception, one of the important concerns I have is why isn't the retryhandler working here?

Most likely persistent connections that are kept alive by the connection manager become stale. That is, the target server shuts down the connection on its end without HttpClient being able to react to that event, while the connection is being idle, thus rendering the connection half-closed or 'stale'. Usually this is not a problem. HttpClient employs several techniques to verify connection validity upon its lease from the pool. Even if the stale connection check is disabled and a stale connection is used to transmit a request message the request execution usually fails in the write operation with SocketException and gets automatically retried. However under some circumstances the write operation can terminate without an exception and the subsequent read operation returns -1 (end of stream). In this case HttpClient has no other choice but to assume the request succeeded but the server failed to respond most likely due to an unexpected error on the server side.
The simplest way to remedy the situation is to evict expired connections and connections that have been idle longer than, say, 1 minute from the pool after a period of inactivity. For details please see the 2.5. Connection eviction policy of the HttpClient 4.5 tutorial.

Accepted answer is right but lacks solution. To avoid this error, you can add setHttpRequestRetryHandler (or setRetryHandler for apache components 4.4) for your HTTP client like in this answer.

HttpClient 4.4 suffered from a bug in this area relating to validating possibly stale connections before returning to the requestor. It didn't validate whether a connection was stale, and this then results in an immediate NoHttpResponseException.
This issue was resolved in HttpClient 4.4.1. See this JIRA and the release notes

Solution: change the ReuseStrategy to never
Since this problem is very complex and there are so many different factors which can fail I was happy to find this solution in another post: How to solve org.apache.http.NoHttpResponseException
Never reuse connections:
configure in org.apache.http.impl.client.AbstractHttpClient:
httpClient.setReuseStrategy(new NoConnectionReuseStrategy());
The same can be configured on a org.apache.http.impl.client.HttpClientBuilder builder:
builder.setConnectionReuseStrategy(new NoConnectionReuseStrategy());

Although accepted answer is right, but IMHO is just a workaround.
To be clear: it's a perfectly normal situation that a persistent connection may become stale. But unfortunately it's very bad when the HTTP client library cannot handle it properly.
Since this faulty behavior in Apache HttpClient was not fixed for many years, I definitely would prefer to switch to a library that can easily recover from a stale connection problem, e.g. OkHttp.
Why?
OkHttp pools http connections by default.
It gracefully recovers from situations when http connection becomes stale and request cannot be retried due to being not idempotent (e.g. POST). I cannot say it about Apache HttpClient (mentioned NoHttpResponseException).
Supports HTTP/2.0 from early drafts and beta versions.
When I switched to OkHttp, my problems with NoHttpResponseException disappeared forever.

Nowadays, most HTTP connections are considered persistent unless declared otherwise. However, to save server ressources the connection is rarely kept open forever, the default connection timeout for many servers is rather short, for example 5 seconds for the Apache httpd 2.2 and above.
The org.apache.http.NoHttpResponseException error comes most likely from one persistent connection that was closed by the server.
It's possible to set the maximum time to keep unused connections open in the Apache Http client pool, in milliseconds.
With Spring Boot, one way to achieve this:
public class RestTemplateCustomizers {
static public class MaxConnectionTimeCustomizer implements RestTemplateCustomizer {
#Override
public void customize(RestTemplate restTemplate) {
HttpClient httpClient = HttpClientBuilder
.create()
.setConnectionTimeToLive(1000, TimeUnit.MILLISECONDS)
.build();
restTemplate.setRequestFactory(
new HttpComponentsClientHttpRequestFactory(httpClient));
}
}
}
// In your service that uses a RestTemplate
public MyRestService(RestTemplateBuilder builder ) {
restTemplate = builder
.customizers(new RestTemplateCustomizers.MaxConnectionTimeCustomizer())
.build();
}

This can happen if disableContentCompression() is set on a pooling manager assigned to your HttpClient, and the target server is trying to use gzip compression.

Same problem for me on apache http client 4.5.5
adding default header
Connection: close
resolve the problem

Use PoolingHttpClientConnectionManager instead of BasicHttpClientConnectionManager
BasicHttpClientConnectionManager will make an effort to reuse the connection for subsequent requests with the same route. It will, however, close the existing connection and re-open it for the given route.

I have faced same issue, I resolved by adding "connection: close" as extention,
Step 1: create a new class ConnectionCloseExtension
import com.github.tomakehurst.wiremock.common.FileSource;
import com.github.tomakehurst.wiremock.extension.Parameters;
import com.github.tomakehurst.wiremock.extension.ResponseTransformer;
import com.github.tomakehurst.wiremock.http.HttpHeader;
import com.github.tomakehurst.wiremock.http.HttpHeaders;
import com.github.tomakehurst.wiremock.http.Request;
import com.github.tomakehurst.wiremock.http.Response;
public class ConnectionCloseExtension extends ResponseTransformer {
#Override
public Response transform(Request request, Response response, FileSource files, Parameters parameters) {
return Response.Builder
.like(response)
.headers(HttpHeaders.copyOf(response.getHeaders())
.plus(new HttpHeader("Connection", "Close")))
.build();
}
#Override
public String getName() {
return "ConnectionCloseExtension";
}
}
Step 2: set extension class in wireMockServer like below,
final WireMockServer wireMockServer = new WireMockServer(options()
.extensions(ConnectionCloseExtension.class)
.port(httpPort));

How do you prevent a denial of service from exhausting a thread pool on a socket server in Java?

For work I have written a specialized HTTP server which only performs 301/302/Frame redirections for web sites. Recently, some nefarious clients have been intentionally opening sockets and writing one character every 500 milliseconds in order to defeat my TCP socket timeout. Then they keep the socket open indefinitely and have multiple clients doing the same thing in a distributed denial of service. This eventually exhausts the thread pool which handles the TCP connections. How would you write your code to make it less susceptible to this sort of bad behavior? Here's my socket accept code:
while (true) {
// Blocks while waiting for a new connection
log.debug("Blocking while waiting for a new connection.") ;
try {
Socket server = httpServer.accept() ;
// After receiving a new connection, set the SO_LINGER and SO_TIMEOUT options
server.setReuseAddress(true) ;
server.setSoTimeout(timeout) ;
server.setSoLinger(true, socketTimeout) ;
// Hand off the new socket connection to a worker thread
threadPool.execute(new Worker(cache, server, requests, geoIp)) ;
} catch (IOException e) {
log.error("Unable to accept socket connection.", e) ;
continue ;
}
}
timeout and socketTimeout are currently set to 500 milliseconds.

Start closing sockets after a certain time has passed. If a socket has stayed open too long just close it down. You could do this in two ways:
You could also put a time limit on how long the client takes to send you a request. If they don't sustain a certain level of throughput close em. That can be pretty easy to do in your read loop when your thread is reading the request by adding a System.currentTimeInMillis() at the start and compare to where you are as you loop. If it drifts past a certain limit they are shutdown and dropped.
An alternative idea to this idea is possibly not reject them but let your thread return to the pool, but put the socket on a stack to watch. Let the bytes pile up and after they reached a certain size you can them pass them to a thread in the pool to process. This the hybrid approach to cut em off vs. maybe they aren't bad but slow.
Another way to handle that is watch how long a thread has been working on a request, and if it's not finished within a time limit close the underlying socket. Then the thread will get a SocketException and it can shutdown and clean up.
Here are some other ideas that mostly involve using outside hardware like firewalls, load balancers, etc.
https://security.stackexchange.com/questions/114/what-techniques-do-advanced-firewalls-use-to-protect-againt-dos-ddos/792#792