Q:
How to stop multiple threads for same class for example web service
I've been given a task to write a class which will send 3 asynchronous messages to server (web service) and wait for the response for those 3 messages to come.
What I want is to stop any of the 3 threads for e.g if a client asks for a new message, the first thread which is still working will finish executing, the second one will start executing again and so on.
I've tried to do that by this but it's not working, my program is still working as if it's not stopped and there are multiple threads being executed simultaneously.
private class CommunicationThread extends Thread{
public CommunicationThread(){
super();
}
@Override
public void run(){
System.out.println("Thread is executing");
while(true){
System.out.println("Creating client");
try {
HttpClient httpclient = new DefaultHttpClient();
String host="http://www.google.com";
HttpGet request = new HttpGet();
request.setURI(new URI("http://www.google.com/search?q=test"));
HttpResponse response = httpclient.execute(request);
HttpEntity entity = response.getEntity();
System.out.println("Response Code: "+response.getStatusLine().getStatusCode());
if (entity != null) {
// do something useful with the response body
// Print the response entity body
try {
System.out.println("Read content...");
BufferedReader rd = new BufferedReader(new InputStreamReader(
entity.getContent()));
while ((line = rd.readLine()) != null) {
System.out.println("Text: "+line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
else{
System.out.println("Entity is null");
}
}
else{
System.out.println("Response is null");
}
}
if (count++<3) {
System.out.println(count);
//System.out.println(i);
synchronized (this) {
try {
this.wait();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
}
I'd appreciate any help.
Thanks a lot.
A:
A busy wait is usually considered a bad idea; if you're going to sleep, you want to do so for as little time as possible.
Here are a couple of possibilities. For brevity, I've omitted some error checking, I'm going to assume you've done that for yourself...
1) Don't use a lock, use a counter:
boolean stop = false;
public void doWork() {
for (int i = 0; i < 3; i++) {
synchronized (this) {
if (stop) return;
// do stuff
}
}
synchronized (this) {
stop = true;
}
}
This has the advantage that you can control exactly how often each thread will attempt to run; it's the same as multiple calls to execute()
2) Use an ExecutorService:
private static final int THREAD_COUNT = 3;
private static final long WORK_DELAY_IN_MS = 1000; // millis
private static final int ITERATIONS_PER_TEST = 5;
private static ExecutorService executor = new Executors.newFixedThreadPool(THREAD_COUNT);
public void doWork() {
List> callables = new ArrayList>();
for (int i = 0; i < ITERATIONS_PER_TEST; i++) {
final int nextRun = i % THREAD_COUNT;
callables.add(new Callable() {
public Integer call() {
Thread.sleep(WORK_DELAY_IN_MS);
return nextRun;
}
});
}
executor.execute(new Runnable() {
public void run() {
for (int i = 0; i < ITERATIONS_PER_TEST; i++) {
int nextRun = callables.get(i).call();
if (nextRun >= THREAD_COUNT) {
callables.remove(i);
}
}
}
});
}
Or, you can use a ReentrantLock if you prefer.
There is one problem with your code as it stands. It's that the synchronization is all around the whole thing; this means that all 3 threads are synchronizing. That can be a problem when one thread is stuck inside the try, and the others are trying to get out.
The easiest fix for that problem is to re-write your code so that it doesn't need all that synchronization. But then, you'll need to rethink your algorithm.
A:
Instead of using your count-variable you could directly start your loop with 0 as argument.
private class CommunicationThread extends Thread {
public CommunicationThread() {
super();
}
@Override
public void run() {
System.out.println("Thread is executing");
while (true) {
System.out.println("Creating client");
try {
HttpClient httpclient = new DefaultHttpClient();
String host = "http://www.google.com";
HttpGet request = new HttpGet();
request.setURI(new URI("http://www.google.com/search?q=test"));
HttpResponse response = httpclient.execute(request);
HttpEntity entity = response.getEntity();
System.out.println("Response Code: " + response.getStatusLine().getStatusCode());
if (entity != null) {
// do something useful with the response body
// Print the response entity body
try {
System.out.println("Read content...");
BufferedReader rd = new BufferedReader(new InputStreamReader(
entity.getContent()));
while ((line = rd.readLine()) != null) {
System.out.println("Text: " + line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
else {
System.out.println("Entity is null");
}
}
catch (IOException e) {
e.printStackTrace();
}
}
if (0 < count++ && 0 < count++ && 0 < count++ && 0 < count++) {
System.out.println(count);
System.out.println(count);
