Problem statement
I have a JMS listener running as a thread listening to a topic. As soon a message comes in, I spawn a new Thread to process the in-bounded message. So for each incoming message I spawn a new Thread.
I have a scenario where duplicate message is also being processed when it is injected immediately in a sequential order. I need to prevent this from being processed. I tried using a ConcurrentHashMap to hold the process times where I add in the entry as soon as Thread is spawn and remove it from the map as soon Thread completes its execution. But it did not help when I tried with the scenario where I passed in same one after the another in concurrent fashion.
General Outline of my issue before you plunge into the actual code base
onMessage(){
processIncomingMessage(){
ExecutorService executorService = Executors.newFixedThreadPool(1000);
//Map is used to make an entry before i spawn a new thread to process incoming message
//Map contains "Key as the incoming message" and "value as boolean"
//check map for duplicate check
//The below check is failing and allowing duplicate messages to be processed in parallel
if(entryisPresentInMap){
//return doing nothing
}else{
//spawn a new thread for each incoming message
//also ensure a duplicate message being processed when it in process by an active thread
executorService.execute(new Runnable() {
@Override
public void run() {
try {
//actuall business logic
}finally{
//remove entry from the map so after processing is done with the message
}
}
}
}
Standalone example to mimic the scenario
public class DuplicateCheck {
private static Map<String,Boolean> duplicateCheckMap =
new ConcurrentHashMap<String,Boolean>(1000);
private static String name=null;
private static String[] nameArray = new String[20];
public static void processMessage(String message){
System.out.println("Processed message =" +message);
}
public static void main(String args[]){
nameArray[0] = "Peter";
nameArray[1] = "Peter";
nameArray[2] = "Adam";
for(int i=0;i<=nameArray.length;i++){
name=nameArray[i];
if(duplicateCheckMap.get(name)!=null && duplicateCheckMap.get(name)){
System.out.println("Thread detected for processing your name ="+name);
return;
}
addNameIntoMap(name);
new Thread(new Runnable() {
@Override
public void run() {
try {
processMessage(name);
} catch (Exception e) {
System.out.println(e.getMessage());
} finally {
freeNameFromMap(name);
}
}
}).start();
}
}
private static synchronized void addNameIntoMap(String name) {
if (name != null) {
duplicateCheckMap.put(name, true);
System.out.println("Thread processing the "+name+" is added to the status map");
}
}
private static synchronized void freeNameFromMap(String name) {
if (name != null) {
duplicateCheckMap.remove(name);
System.out.println("Thread processing the "+name+" is released from the status map");
}
}
Snippet of the code is below
public void processControlMessage(final Message message) {
RDPWorkflowControlMessage rdpWorkflowControlMessage= unmarshallControlMessage(message);
final String workflowName = rdpWorkflowControlMessage.getWorkflowName();
final String controlMessageEvent=rdpWorkflowControlMessage.getControlMessage().value();
if(controlMessageStateMap.get(workflowName)!=null && controlMessageStateMap.get(workflowName)){
log.info("Cache cleanup for the workflow :"+workflowName+" is already in progress");
return;
}else {
log.info("doing nothing");
}
Semaphore controlMessageLock = new Semaphore(1);
try{
controlMessageLock.acquire();
synchronized(this){
new Thread(new Runnable(){
@Override
public void run() {
try {
lock.lock();
log.info("Processing Workflow Control Message for the workflow :"+workflowName);
if (message instanceof TextMessage) {
if ("REFRESH".equalsIgnoreCase(controlMessageEvent)) {
clearControlMessageBuffer();
enableControlMessageStatus(workflowName);
List<String> matchingValues=new ArrayList<String>();
matchingValues.add(workflowName);
ConcreteSetDAO tasksSetDAO=taskEventListener.getConcreteSetDAO();
ConcreteSetDAO workflowSetDAO=workflowEventListener.getConcreteSetDAO();
tasksSetDAO.deleteMatchingRecords(matchingValues);
workflowSetDAO.deleteMatchingRecords(matchingValues);
fetchNewWorkflowItems();
addShutdownHook(workflowName);
}
}
} catch (Exception e) {
log.error("Error extracting item of type RDPWorkflowControlMessage from message "
+ message);
} finally {
disableControlMessageStatus(workflowName);
lock.unlock();
}
}
}).start();
}
} catch (InterruptedException ie) {
log.info("Interrupted Exception during control message lock acquisition"+ie);
}finally{
controlMessageLock.release();
}
}
private void addShutdownHook(final String workflowName) {
Runtime.getRuntime().addShutdownHook(new Thread() {
public void run() {
disableControlMessageStatus(workflowName);
}
});
log.info("Shut Down Hook Attached for the thread processing the workflow :"+workflowName);
}
private RDPWorkflowControlMessage unmarshallControlMessage(Message message) {
RDPWorkflowControlMessage rdpWorkflowControlMessage = null;
try {
TextMessage textMessage = (TextMessage) message;
rdpWorkflowControlMessage = marshaller.unmarshalItem(textMessage.getText(), RDPWorkflowControlMessage.class);
} catch (Exception e) {
log.error("Error extracting item of type RDPWorkflowTask from message "
+ message);
}
return rdpWorkflowControlMessage;
}
private void fetchNewWorkflowItems() {
initSSL();
List<RDPWorkflowTask> allTasks=initAllTasks();
taskEventListener.addRDPWorkflowTasks(allTasks);
workflowEventListener.updateWorkflowStatus(allTasks);
}
private void clearControlMessageBuffer() {
taskEventListener.getRecordsForUpdate().clear();
workflowEventListener.getRecordsForUpdate().clear();
}
private synchronized void enableControlMessageStatus(String workflowName) {
if (workflowName != null) {
controlMessageStateMap.put(workflowName, true);
log.info("Thread processing the "+workflowName+" is added to the status map");
}
}
private synchronized void disableControlMessageStatus(String workflowName) {
if (workflowName != null) {
controlMessageStateMap.remove(workflowName);
log.info("Thread processing the "+workflowName+" is released from the status map");
}
}
I have modified my code to incorporate suggestions provided below but still it is not working
public void processControlMessage(final Message message) {
ExecutorService executorService = Executors.newFixedThreadPool(1000);
try{
lock.lock();
RDPWorkflowControlMessage rdpWorkflowControlMessage= unmarshallControlMessage(message);
final String workflowName = rdpWorkflowControlMessage.getWorkflowName();
final String controlMessageEvent=rdpWorkflowControlMessage.getControlMessage().value();
if(controlMessageStateMap.get(workflowName)!=null && controlMessageStateMap.get(workflowName)){
log.info("Cache cleanup for the workflow :"+workflowName+" is already in progress");
return;
}else {
log.info("doing nothing");
}
enableControlMessageStatus(workflowName);
executorService.execute(new Runnable() {
@Override
public void run() {
try {
//actual code
fetchNewWorkflowItems();
addShutdownHook(workflowName);
}
}
} catch (Exception e) {
log.error("Error extracting item of type RDPWorkflowControlMessage from message "
+ message);
} finally {
disableControlMessageStatus(workflowName);
}
}
});
} finally {
executorService.shutdown();
lock.unlock();
}
}
private void addShutdownHook(final String workflowName) {
Runtime.getRuntime().addShutdownHook(new Thread() {
public void run() {
disableControlMessageStatus(workflowName);
}
});
log.info("Shut Down Hook Attached for the thread processing the workflow :"+workflowName);
}
private synchronized void enableControlMessageStatus(String workflowName) {
if (workflowName != null) {
controlMessageStateMap.put(workflowName, true);
log.info("Thread processing the "+workflowName+" is added to the status map");
}
}
private synchronized void disableControlMessageStatus(String workflowName) {
if (workflowName != null) {
controlMessageStateMap.remove(workflowName);
log.info("Thread processing the "+workflowName+" is released from the status map");
}
}
This is how you should add a value to a map. This double checking makes sure that only one thread adds a value to a map at any particular moment of time and you can control the access afterwards. Remove all the locking logic afterwards. It is as simple as that
public void processControlMessage(final String workflowName) {
if(!tryAddingMessageInProcessingMap(workflowName)){
Thread.sleep(1000); // sleep 1 sec and try again
processControlMessage(workflowName);
return ;
}
System.out.println(workflowName);
try{
// your code goes here
} finally{
controlMessageStateMap.remove(workflowName);
}
}
private boolean tryAddingMessageInProcessingMap(final String workflowName) {
if(controlMessageStateMap .get(workflowName)==null){
synchronized (this) {
if(controlMessageStateMap .get(workflowName)==null){
controlMessageStateMap.put(workflowName, true);
return true;
}
}
}
return false;
}
Read here more for https://en.wikipedia.org/wiki/Double-checked_locking
The issue is fixed now. Many thanks to @awsome for the approach. It is avoiding the duplicates when a thread is already processing the incoming duplicate message. If no thread is processing then it gets picked up
public void processControlMessage(final Message message) {
try {
lock.lock();
RDPWorkflowControlMessage rdpWorkflowControlMessage = unmarshallControlMessage(message);
final String workflowName = rdpWorkflowControlMessage.getWorkflowName();
final String controlMessageEvent = rdpWorkflowControlMessage.getControlMessage().value();
new Thread(new Runnable() {
@Override
public void run() {
try {
if (message instanceof TextMessage) {
if ("REFRESH".equalsIgnoreCase(controlMessageEvent)) {
if (tryAddingWorkflowNameInStatusMap(workflowName)) {
log.info("Processing Workflow Control Message for the workflow :"+ workflowName);
addShutdownHook(workflowName);
clearControlMessageBuffer();
List<String> matchingValues = new ArrayList<String>();
matchingValues.add(workflowName);
ConcreteSetDAO tasksSetDAO = taskEventListener.getConcreteSetDAO();
ConcreteSetDAO workflowSetDAO = workflowEventListener.getConcreteSetDAO();
tasksSetDAO.deleteMatchingRecords(matchingValues);
workflowSetDAO.deleteMatchingRecords(matchingValues);
List<RDPWorkflowTask> allTasks=fetchNewWorkflowItems(workflowName);
updateTasksAndWorkflowSet(allTasks);
removeWorkflowNameFromProcessingMap(workflowName);
} else {
log.info("Cache clean up is already in progress for the workflow ="+ workflowName);
return;
}
}
}
} catch (Exception e) {
log.error("Error extracting item of type RDPWorkflowControlMessage from message "
+ message);
}
}
}).start();
} finally {
lock.unlock();
}
}
private boolean tryAddingWorkflowNameInStatusMap(final String workflowName) {
if(controlMessageStateMap.get(workflowName)==null){
synchronized (this) {
if(controlMessageStateMap.get(workflowName)==null){
log.info("Adding an entry in to the map for the workflow ="+workflowName);
controlMessageStateMap.put(workflowName, true);
return true;
}
}
}
return false;
}
private synchronized void removeWorkflowNameFromProcessingMap(String workflowName) {
if (workflowName != null
&& (controlMessageStateMap.get(workflowName) != null && controlMessageStateMap
.get(workflowName))) {
controlMessageStateMap.remove(workflowName);
log.info("Thread processing the " + workflowName+ " is released from the status map");
}
}
来源：https://stackoverflow.com/questions/34356093/preventing-thread-from-duplicate-processing-in-java