I am implementing Circuit breaker using Hystrix in my Spring boot application, my code is something like below:
#service
public class MyServiceHandler {
#HystrixCommand(fallbackMethod="fallback")
public String callService() {
// if(remote service is not reachable
// throw ServiceException
}
public String fallback() {
// return default response
}
}
// In application.properties, I have below properties defined:
hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds=10000
hystrix.command.default.circuitBreaker.requestVolumeThreshold=3
hystrix.command.default.circuitBreaker.sleepWindowInMilliseconds=30000
hystrix.threadpool.default.coreSize=4
hystrix.threadpool.default.metrics.rollingStats.timeInMilliseconds=200000
I see that the fallback() is getting called with each failure of callService(). However, the circuit is not opening after 3 failures. After 3 failures, I was expecting that it will directly call fallback() and skip callService(). But this is not happening. Can someone advise what I am doing wrong here?
Thanks,
B Jagan
Edited on 26th July to add more details below:
Below is the actual code. I played a bit further with this. I see that the Circuit opens as expected on repeated failured when I call the remote service directly in the RegistrationHystrix.registerSeller() method. But, when I wrap the remote service call within Spring retry template, it keeps going into fallback method, but circuit never opens.
#Service
public class RegistrationHystrix {
Logger logger = LoggerFactory.getLogger(RegistrationHystrix.class);
private RestTemplate restTemplate;
private RetryTemplate retryTemplate;
public RegistrationHystrix(RestTemplate restTemplate) {
this.restTemplate = restTemplate;
retryTemplate = new RetryTemplate();
FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy();
fixedBackOffPolicy.setBackOffPeriod(1000l);
retryTemplate.setBackOffPolicy(fixedBackOffPolicy);
SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();
retryPolicy.setMaxAttempts(3);
retryTemplate.setRetryPolicy(retryPolicy);
}
#HystrixCommand(fallbackMethod = "fallbackForRegisterSeller", commandKey = "ordermanagement")
public String registerSeller(SellerDto sellerDto) throws Exception {
String response = retryTemplate.execute(new RetryCallback<String, Exception>() {
#Override
public String doWithRetry(RetryContext context) {
logger.info(String.format("Retry count %d", context.getRetryCount()));
return restTemplate.postForObject("/addSeller", sellerDto, String.class);
}
});
return response;
}
public List<SellerDto> getSellersList() {
return restTemplate.getForObject("/sellersList", List.class);
}
public String fallbackForRegisterSeller(SellerDto sellerDto, Throwable t) {
logger.error("Inside fall back, cause - {}", t.toString());
return "Inside fallback method. Some error occured while calling service for seller registration";
}
}
Below is the service class which in turn calls the above Hystrix wrapped service. This class in turn is invoked by a controller.
#Service
public class RegistrationServiceImpl implements RegistrationService {
Logger logger = LoggerFactory.getLogger(RegistrationServiceImpl.class);
private RegistrationHystrix registrationHystrix;
public RegistrationServiceImpl(RegistrationHystrix registrationHystrix) {
this.registrationHystrix = registrationHystrix;
}
#Override
public String registerSeller(SellerDto sellerDto) throws Exception {
long start = System.currentTimeMillis();
String registerSeller = registrationHystrix.registerSeller(sellerDto);
logger.info("add seller call returned in - {}", System.currentTimeMillis() - start);
return registerSeller;
}
So, I am trying to understand why the Circuit breaker is not working as expected when using it along with Spring RetryTemplate.
You should be using metrics.healthSnapshot.intervalInMilliseconds while testing. I guess you are executing all 3 request within default 500 ms and hence the circuit isn't getting open. You can either decrease this interval or you may put a sleep between the 3 requests.
Related
Earlier I asked about a simple hello world example for Flink. This gave me some good examples!
However I would like to ask for a more ‘streaming’ example where we generate an input value every second. This would ideally be random, but even just the same value each time would be fine.
The objective is to get a stream that ‘moves’ with no/minimal external touch.
Hence my question:
How to show Flink actually streaming data without external dependencies?
I found how to show this with generating data externally and writing to Kafka, or listening to a public source, however I am trying to solve it with minimal dependence (like starting with GenerateFlowFile in Nifi).
Here's an example. This was constructed as an example of how to make your sources and sinks pluggable. The idea being that in development you might use a random source and print the results, for tests you might use a hardwired list of input events and collect the results in a list, and in production you'd use the real sources and sinks.
Here's the job:
/*
* Example showing how to make sources and sinks pluggable in your application code so
* you can inject special test sources and test sinks in your tests.
*/
public class TestableStreamingJob {
private SourceFunction<Long> source;
private SinkFunction<Long> sink;
public TestableStreamingJob(SourceFunction<Long> source, SinkFunction<Long> sink) {
this.source = source;
this.sink = sink;
}
public void execute() throws Exception {
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Long> LongStream =
env.addSource(source)
.returns(TypeInformation.of(Long.class));
LongStream
.map(new IncrementMapFunction())
.addSink(sink);
env.execute();
}
public static void main(String[] args) throws Exception {
TestableStreamingJob job = new TestableStreamingJob(new RandomLongSource(), new PrintSinkFunction<>());
job.execute();
}
// While it's tempting for something this simple, avoid using anonymous classes or lambdas
// for any business logic you might want to unit test.
public class IncrementMapFunction implements MapFunction<Long, Long> {
#Override
public Long map(Long record) throws Exception {
return record + 1 ;
}
}
}
Here's the RandomLongSource:
public class RandomLongSource extends RichParallelSourceFunction<Long> {
private volatile boolean cancelled = false;
private Random random;
#Override
public void open(Configuration parameters) throws Exception {
super.open(parameters);
random = new Random();
}
#Override
public void run(SourceContext<Long> ctx) throws Exception {
while (!cancelled) {
Long nextLong = random.nextLong();
synchronized (ctx.getCheckpointLock()) {
ctx.collect(nextLong);
}
}
}
#Override
public void cancel() {
cancelled = true;
}
}
I am trying to implement a javax.mail.event.MessageCountListener in Tomcat. When I start the application the contextInitialized method seems to run and the mailbox is read. However, I see the log message "Idling" only once. I would expect that it would idle constantly and invoke the AnalyzerService() when an email is received or deleted.
Update: Found that the idle() method is not returning. It runs untill com.sun.mail.iap.ResponseInputStream.readResponse(ByteArray ba) method where it runs into a while loop where it never gets out.
Am I misusing the idle() method for something I should not do? Is this a bug in com.sun.mail.iap package?
The AnalyzerContextListener.java:
import com.sun.mail.imap.IMAPStore;
import java.util.Properties;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import javax.mail.Folder;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.event.MessageCountListener;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class AnalyzerContextListener implements ServletContextListener {
private ExecutorService executorService;
private final String username = "myemail#gmail.com";
private final String password = "mypassword";
private final String mailhost = "imap.gmail.com";
private final String foldername = "INBOX";
#Override
public void contextInitialized(ServletContextEvent sce) {
final ServletContext servletContext = sce.getServletContext();
executorService = Executors.newFixedThreadPool(3);
Session session = Session.getInstance(new Properties());
try {
final IMAPStore store = (IMAPStore) session.getStore("imaps");
store.connect(mailhost, username, password);
final Folder folder = store.getFolder(foldername);
if (folder == null) {
servletContext.log("Folder in mailbox bestaat niet.");
return;
}
folder.open(Folder.READ_ONLY);
MessageCountListener countListener = new AnalyzerService();
folder.addMessageCountListener(countListener);
Runnable runnable = new Runnable() {
#Override
public void run() {
while (true) {
try {
servletContext.log("Aantal berichten in folder: " + folder.getMessageCount());
servletContext.log("Idling");
store.idle();
} catch (MessagingException ex) {
servletContext.log(ex.getMessage());
return;
}
}
}
};
executorService.execute(runnable);
servletContext.log("Executorservice gestart");
} catch (MessagingException ex) {
servletContext.log(ex.getMessage());
}
}
#Override
public void contextDestroyed(ServletContextEvent sce) {
sce.getServletContext().log("Context wordt vernietigd");
executorService.shutdown();
sce.getServletContext().log("Executorservice gestopt");
}
}
The AnalyzerService.java:
import javax.mail.Message;
import javax.mail.MessagingException;
import javax.mail.event.MessageCountEvent;
import javax.mail.event.MessageCountListener;
class AnalyzerService implements MessageCountListener {
public AnalyzerService() {
}
#Override
public void messagesAdded(MessageCountEvent event) {
Message[] addedMessages = event.getMessages();
for (Message message : addedMessages) {
try {
System.out.println(message.getSubject());
} catch (MessagingException ex) {
System.out.println(ex.getMessage());
}
}
}
#Override
public void messagesRemoved(MessageCountEvent event) {
Message[] removedMessages = event.getMessages();
for (Message message : removedMessages) {
try {
System.out.println(message.getSubject());
} catch (MessagingException ex) {
System.out.println(ex.getMessage());
}
}
}
}
while (true) {
try {
servletContext.log("Aantal berichten in folder: " + folder.getMessageCount());
servletContext.log("Idling");
store.idle();
} catch (MessagingException ex) {
servletContext.log(ex.getMessage());
return;
}
}
has exactly 2 3 possibilities to end earlier than never run only once.
The loop actually ends either:
Through the explicit return in case of a MessagingException. Look at your logs, there either a message or something strange like "null". Consider using a proper stacktrace log (.log(String message, Throwable throwable)) since Exception#getMessage() is often empty or not telling you much.
Through any unchecked exception. You should notice that in some log though since uncaught exceptions via executorService.execute should invoke the nearest uncaught exeption handler which is generally bad. See Choose between ExecutorService's submit and ExecutorService's execute
The loop stops executing after it logs "Idling"
store.idle() never returns. (every other line of code could do that theoretically as well, e.g. the folder.getMessageCount() call in a 2nd iteration but that's very unlikely)
Regarding No 3 - the documentation
Use the IMAP IDLE command (see RFC 2177), if supported by the server, to enter idle mode so that the server can send unsolicited notifications without the need for the client to constantly poll the server. Use a ConnectionListener to be notified of events. When another thread (e.g., the listener thread) needs to issue an IMAP comand for this Store, the idle mode will be terminated and this method will return. Typically the caller will invoke this method in a loop.
If the mail.imap.enableimapevents property is set, notifications received while the IDLE command is active will be delivered to ConnectionListeners as events with a type of IMAPStore.RESPONSE. The event's message will be the raw IMAP response string. Note that most IMAP servers will not deliver any events when using the IDLE command on a connection with no mailbox selected (i.e., this method). In most cases you'll want to use the idle method on IMAPFolder.
That sounds like this method is not designed to return any time soon. In your case never since you don't issue any commands towards the server after you enter idle. Besides that
folder.idle() could be what you should actually do
I guess the documentation is wrong, however ConnectionListener and MessageCountListener are two different things.
I read where someone was able to do this, but I'm having a hard time getting it to work.
Basically, I'm scheduling an HTTP callout to a page that has a controller that builds a CSV and emails it to a recipient.
The Scheduled class:
global class ReportExporter implements System.Schedulable {
global void execute(SchedulableContext sc) {
getmailReportOutput ex = new getmailReportOutput();
ex.exportCSV();
}
}
The getEmailReportOutput class:
public class getmailReportOutput{
public Static String strSessionID;
public getmailReportOutput() {
}
public void exportCSV() {
makeReportRequest();
}
#future (callout=true)
public Static void makeReportRequest() {
strHost ='c.cs4.visual.force.com';
strSessionID = UserInfo.getSessionId();
String requestUrl = 'https://' + strHost + '/apex/TestSendReport#';
HttpRequest req = new HttpRequest();
req.setEndpoint(requestUrl);
req.setMethod('GET');
req.setHeader('Cookie','sid=' + strSessionID );
String output = new Http().send(req).getBody();
System.debug('HTTP RESPONSE RETURNED: ' + output);
}
}
The getEmailReportOutput class does an HTTP Callout to a VF page: I make sure to send the sessionID with the request:
And the "TestSendReport" is just a simple callout to a controller:
<apex:page controller="Exporter" action="{!runrpt}">
</apex:page>
...And the controller is calling the report content:
public class Exporter {
public static Boolean isTest;
public static String strEmailAddr;
public void runrpt() {
executeRpt();
}
#future
public static void executeRpt() {
System.debug('CALLING REPORT EXPORTER...');
String ReportName__c = '00OP0000000Jp3N';
String strEmailAddr = 'myname#email.com';
ApexPages.PageReference report = new ApexPages.PageReference( '/' + RptName__c + '?csv=1');
Messaging.EmailFileAttachment attachment = new Messaging.EmailFileAttachment();
attachment.setFileName('report.csv');
attachment.setBody(report.getContent());
attachment.setContentType('text/csv');
Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage();
message.setFileAttachments(new Messaging.EmailFileAttachment[] { attachment } );
message.setSubject('Report');
message.setPlainTextBody('The report is attached.');
message.setToAddresses( new String[] { strEmailAddr } );
Messaging.sendEmail( new Messaging.SingleEmailMessage[] { message } );
}
}
...Any ideas? The debug logs show all is well, but nothing is received. I know this is a wall of code, but it seems to be what people recommend to accomplish the task - I just can't see anything wrong.
I don't see anything obviously missing here :/
Just to be safe - getEmailReportOutput & getmailReportOutput are the same class (typo error in the post, not in your actual code)?
This looks like jumping a lot of hops, do I read it correctly that it's scheduled class -> REST callout -> VF page with action -> #future -> send an email? Geez, a lot can go wrong here ;) I've read somewhere that SF will keep some kind of reference counter and calling out to same instance might block you from using page.getContent...
Can you see the report body System.debug(report.getContent().toString());? Can you try saving this email as task for your own user or under a sample Account for example (setSaveAsActivity())?
As blatant plug as it is - I've used different path to solve similar requirement. Check out https://salesforce.stackexchange.com/questions/4303/scheduled-reports-as-attachment and see if you can get it to work?
In a WPF application, I have a 3rd party library that is publishing messages.
The messages are like :
public class DialectMessage
{
public string PathAndQuery { get; private set; }
public byte[] Body { get; private set; }
public DialectMessage(string pathAndQuery, byte[] body)
{
this.PathAndQuery = pathAndQuery;
this.Body = body;
}
}
And I setup the external message source from my app.cs file :
public partial class App : Application
{
static App()
{
MyComponent.MessageReceived += MessageReceived;
MyComponent.Start();
}
private static void MessageReceived(Message message)
{
//handle message
}
}
These messages can be publishing from multiple thread at a time, making possible to call the event handler multiple times at once.
I have a service object that have to parse the incoming messages. This service implements the following interface :
internal interface IDialectService
{
void Parse(Message message);
}
And I have a default static instance in my app.cs file :
private readonly static IDialectService g_DialectService = new DialectService();
In order to simplify the code of the parser, I would like to ensure only one message at a time is parsed.
I also want to avoid locking in my event handler, as I don't want to block the 3rd party object.
Because of this requirements, I cannot directly call g_DialectService.Parse from my message event handler
What is the correct way to ensure this single threaded execution?
My first though is to wrap my parsing operations in a Produce/Consumer pattern. In order to reach this goal, I've try the following :
Declare a BlockingCollection in my app.cs :
private readonly static BlockingCollection<Message> g_ParseOperations = new BlockingCollection<Message>();
Change the body of my event handler to add an operation :
private static void MessageReceived(Message message)
{
g_ParseOperations.Add(message);
}
Create a new thread that pump the collection from my app constructor :
static App()
{
MyComponent.MessageReceived += MessageReceived;
MyComponent.Start();
Task.Factory.StartNew(() =>
{
Message message;
while (g_ParseOperations.TryTake(out message))
{
g_DialectService.Parse(message);
}
});
}
However, this code does not seems to work. The service Parse method is never called.
Moreover, I'm not sure if this pattern will allow me to properly shutdown the application.
What have I to change in my code to ensure everything is working?
PS: I'm targeting .Net 4.5
[Edit] After some search, and the answer of ken2k, i can see that I was wrongly calling trytake in place of take.
My updated code is now :
private readonly static CancellationTokenSource g_ShutdownToken = new CancellationTokenSource();
private static void MessageReceived(Message message)
{
g_ParseOperations.Add(message, g_ShutdownToken.Token);
}
static App()
{
MyComponent.MessageReceived += MessageReceived;
MyComponent.Start();
Task.Factory.StartNew(() =>
{
while (!g_ShutdownToken.IsCancellationRequested)
{
var message = g_ParseOperations.Take(g_ShutdownToken.Token);
g_DialectService.Parse(message);
}
});
}
protected override void OnExit(ExitEventArgs e)
{
g_ShutdownToken.Cancel();
base.OnExit(e);
}
This code acts as expected. Messages are processed in the correct order. However, as soon I exit the application, I get a "CancelledException" on the Take method, even if I just test the IsCancellationRequested right before.
The documentation says about BlockingCollection.TryTake(out T item):
If the collection is empty, this method immediately returns false.
So basically your loop exits immediately. What you may want is to call the TryTake method with a timeout parameter instead, and exit your loop when a mustStop variable becomes true:
bool mustStop = false; // Must be set to true on somewhere else when you exit your program
...
while (!mustStop)
{
Message yourMessage;
// Waits 500ms if there's nothing in the collection. Avoid to consume 100% CPU
// for nothing in the while loop when the collection is empty.
if (yourCollection.TryTake(out yourMessage, 500))
{
// Parses yourMessage here
}
}
For your edited question: if you mean you received a OperationCanceledException, that's OK, it's exactly how methods that take a CancellationToken object as parameter must behave :) Just catch the exception and exit gracefully.
Just getting my head around WCF, so forgive me for the inelegant coding.
The issue I'm having is I seem to be submitting data twice to my service (see screenshot), even though (I think) I'm only doing it once.
Could someone please let me know what I might be doing wrong? Or even just suggest a better way to do it if I'm doing it inefficiently.
Code follows:
public void EndOfLevel()
{
GlobalVariable.TotalQuestionsAsked = 10;
GlobalVariable.CorrectDecimal = GlobalVariable.Correct / GlobalVariable.TotalQuestionsAsked;
//Show loading screen
UploadingScreen.Visibility = Visibility.Visible;
//Submit this levels results.
Service1Client client = null;
client = new Service1Client();
//Gather the results and details
Result thislevel = new Result();
thislevel.Datetime = DateTime.Now;
thislevel.result = GlobalVariable.CorrectDecimal;
thislevel.TimesTable = GlobalVariable.NeedsHelpWith;
//submit them
try
{
client.SubmitResultAsync(thislevel);
}
catch
{
MessageBox.Show("Error uploading data");
}
finally
{
client.Close();
Results r3 = new Results();
this.NavigationService.Navigate(r3);
}
}
WCF Test Client:
Cheers,
Nick
If I may, here's a pattern for managing our asynchronous calls between our WPF applications and our WCF Services.
In this section we have a public accessor to our service client that ensures that the connection to the client is open prior to calling a service method:
public static MyServiceClient Client
{
get
{
return GetMyServiceClient();
}
}
private static MyServiceClient client;
private static MyService.MyServiceClient GetMyServiceClient()
{
VerifyClientConnection();
return client;
}
private static void VerifyClientConnection()
{
if (client == null || client.State == System.ServiceModel.CommunicationState.Closed)
{
client = new MyService.MyServiceClient();
}
}
And in this section is an example of our asynchronous call and callback pattern (this example shows the delegate and callback we're using for passing exception data to our service):
public delegate void LogExceptionCompletedEvent();
public static LogExceptionCompletedEvent LogExceptionCompleted;
public static void LogExceptionAsync(SilverlightException exception)
{
string json = JsonConvert.SerializeObject(exception);
Client.LogExceptionCompleted -= client_LogExceptionCompleted;
Client.LogExceptionCompleted += client_LogExceptionCompleted;
Client.LogExceptionAsync(json);
}
private static void client_LogExceptionCompleted(object sender, AsyncCompletedEventArgs e)
{
if (LogExceptionCompleted != null)
{
LogExceptionCompleted();
}
}
In this example, a view model could attach an event handler to the LogExceptionCompleted delegate and in turn receive the result of the callback when it returns from the service.
We basically repeat this pattern for the asynchronous WCF service calls we need to make from our application and it keeps them very organized as well as unit testable.