How to implement shutdown hook handler in google appengine . Im not understanding their doc here https://developers.google.com/appengine/docs/java/backends/overview#Shutdown. what i need is, i need to be notified in the code when backend is stopped due to any to reason.
this is my code
try{
while (haveMoreWork() &&
!LifecycleManager.getInstance().isShuttingDown()) {
process(); // this is my function to read all the data.if it fails because of termination.i need to be notified.
}catch(Exception e){
log.log(Level.SEVERE, e.getMessage(), e);
log.severe("error occured"+e);
log.info("failed ");
}
You need to use the hook instead of the status report:
LifecycleManager.getInstance().setShutdownHook(new ShutdownHook() {
public void shutdown() {
// code
}
});
Related
I have a Server that can receive multiple request at the same time.
In my Server, I have to make some traitement and wait for response. This traitmenet is done by externe library so I don't how much should I wait.
So the Server looks like :
public class MyServer{
#Override
//method from the library
public void workonRequest(){
//---
response=[...]
}
public void listenRequest() {
new Thread(() -> {
while (true) {
try {
socket = server.accept();
ObjectInputStream input = new ObjectInputStream(socket.getInputStream());
ObjectOutputStream output = new ObjectOutputStream(socket.getOutputStream());
socket.setTcpNoDelay(true); //TODO : Not sure !
new Thread(() -> {
try {
handleRequest(input, output);
} catch (IOException e) {
throw new RuntimeException(e);
}
}).start();
} catch (IOException ex) {
System.out.println(ex.getMessage());
}
}
}).start();
}
And the handle request method is :
public void handleRequest(ObjectInputStream input, ObjectOutputStream output) throws IOException {
try {
while (true) {
//forward the request to the library
//work on it [means using the library and waiting]
// return response
}
}
}
The response object is the result that I want return to the client
How to deal with the problem of waiting for the answer?
How can I make sure that there will be no problems when more than 2 clients send requests at the same time.
Thanks in advance
How to deal with the problem of waiting for the answer ?###
Using while(true) can create issues because you are blocking the thread and opening sub thread and multi streams will make it more complex. There is easy way called reactive programming which handles this kind of multi-threaded issues easily, quarkus async solution and spring, if you still want to manage your sockets from java code you can use akka
How can I make sure that there will be no problems when more than 2 clients send requests at the same time.
That can be done by not blocking the main thread and If you manage to use reactive and/or async approach you will not have that problem.
Reference
https://quarkus.io/guides/getting-started-reactive
https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html
My current Lambda function is calling a 3rd party web service Synchronously.This function occasionally times out (current timeout set to 25s and cannot be increased further)
My code is something like:
handleRequest(InputStream input, OutputStream output, Context context) throws IOException {
try{
response = calling 3rd party REST service
}catch(Exception e){
//handle exceptions
}
}
1)I want to custom handle the timeout (tracking the time and handling few milli seconds before actual timeout) within my Lambda function by sending a custom error message back to the client.
How can I effectively use the
context.getRemainingTimeInMillis()
method to track the time remaining while my synchronous call is running? Planning to call the context.getRemainingTimeInMillis() asynchronously.Is that the right approach?
2)What is a good way to test the timeout custom functionality ?
I solved my problem by increasing the Lambda timeout and invoking my process in a new thread and timing out the Thread after n seconds.
ExecutorService service = Executors.newSingleThreadExecutor();
try {
Runnable r = () ->{
try {
myFunction();
} catch (Exception e) {
e.printStackTrace();
}
};
f = service.submit(r);
f.get(n, TimeUnit.MILLISECONDS);// attempt the task for n milliseconds
}catch(TimeoutException toe){
//custom logic
}
Another option is to use the
readTimeOut
property of the RestClient(in my case Jersey) to set the timeout.But I see that this property is not working consistently within the Lambda code.Not sure if it's and issue with the Jersey client or the Lambda.
You can try with cancellation token to return custom exceptions with lambda before timeout.
try
{
var tokenSource = new CancellationTokenSource(TimeSpan.FromMinutes(1)); // set timeout value
var taskResult = ApiCall(); // call web service method
while (!taskResult.IsCompleted)
{
if (tokenSource.IsCancellationRequested)
{
throw new OperationCanceledException("time out for lambda"); // throw custom exceptions eg : OperationCanceledException
}
}
return taskResult.Result;
}
catch (OperationCanceledException ex)
{
// handle exception
}
I have connected telnet server using socket, I am passing various command using this connection, now as per my requirement after getting output I have to pass command like "Ctrl+]" over socket using java.
can you anyone explain me how I pass the same command using java.
below are the method for reference:
public void logout(){
System.out.println("TelnetHelper : Inside logout()");
try {
telnetWrapper.send("\u001d");
telnetWrapper.send("quit");
} catch (IOException e) {
System.out.println("logout() : IOExcepton - "+e.getMessage());
} catch (Exception e) {
System.out.println("logout() : General Excepton - "+e.getMessage());
}
System.out.println("TelnetHelper : logout() Finished");
}
But this is not working in my case
Just close the connection, I suppose that would be telnetWrapper.close();
I think you may want to send \u001b ...
http://wiki.bash-hackers.org/scripting/terminalcodes
In my servlet, I am executing the following code:
RequestConfig requestConfig = RequestConfig.custom().setSocketTimeout(3000).setConnectTimeout(3000).build();
CloseableHttpAsyncClient client = HttpAsyncClients.custom().setDefaultRequestConfig(requestConfig).build();
try
{
client.start();
for (String request : preparedURLs)
{
client.execute(new HttpGet(request), new FutureCallback<HttpResponse>()
{
public void failed(Exception ex)
{
System.out.println("\n\nRequest Failed Due to : " + ex.getMessage());
}
public void completed(HttpResponse response)
{
System.out.println("\n\nRequest COMPLETED");
}
public void cancelled()
{
System.out.println("\n\nRequest CANCELLED");
}
});
System.out.println("\n\n" + request);
}
}
finally
{
System.out.println("\n*** Finally called ***\n\n");
client.close();
}
But I don't get any response at all. Following is printed in my catalina.out:
http://localhost:8080/servlet/?ps=true
http://localhost:8080/servlet/?ps=true
http://localhost:8080/servlet/?ps=false
*** Finally called ***
I have wrote this code, taking this as example from apache's official site.
I have only omitted the latch part. Is this some thing to do with latch?
If possible please explain the reason of failure too.
This latch that you have removed is actually the synchronization part of the example.
The idea of async client is to make some requests and wait for the responses on other thread. By removing the synchronization the execution directly passes to the finally block instead of waiting the responses and closes the HttpAsyncClient.
In order to get it back working add the latch code from the example.
This is the correct behaviour. You are creating a socket with a conditional Future, and then you proceed to close it without waiting for it.
The example code you linked use a "latch" variable to do so.
You may move the close code inside future callback, but probably this will confuse your waring.
Or you can use the same system of the example, with a shared synchronised counter (maybe just a final AtomicBoolean triggered by an aswer) and wait for it before continuing with your program flow, but that destroy the idea of using async call
I'm using a variation of the example at http://svn.apache.org/repos/asf/activemq/trunk/assembly/src/release/example/src/StompExample.java to receive message from a queue. What I'm trying to do is to keep listening to a queue and perform some action upon reception of a new message. The problem is that I couldn't find a way to register a listener to any of the related objects. I've tried something like:
public static void main(String args[]) throws Exception {
StompConnection connection = null;
try {
connection = new StompConnection();
connection.open("localhost", 61613);
connection.connect("admin", "activemq");
connection.subscribe("/queue/worker", Subscribe.AckModeValues.AUTO);
while (true) {
StompFrame message = connection.receive();
System.out.println(message.getBody());
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
}
}
but this doesn't work as a time out occurs after a few seconds (java.net.SocketTimeoutException: Read timed out). Is there anything I can do to indefinitely listen to this queue?
ActiveMQ's StompConnection class is a relatively primitive STOMP client. Its not capable of async callbacks on Message or for indefinite waits. You can pass a timeout to receive but depending on whether you are using STOMP v1.1 it could still timeout early if a heart-beat isn't received in time. You can of course always catch the timeout exception and try again.
For STOMP via Java you're better off using StompJMS or the like which behaves like a real JMS client and allows for async Message receipt.
#Tim Bish: I tried StompJMS, but couldn't find any example that I could use (maybe you can provide a link). I 'fixed' the problem by setting the timeout to 0 which seems to be blocking.
even i was facing the same issue.. you can fix this by adding time out to your receive() method.
Declare a long type variable.
long waitTimeOut = 5000; //this is 5 seconds
now modify your receive function like below.
StompFrame message = connection.receive(waitTimeOut);
This will definitely work.