I am attempting to close a stream coming from an http request using Retrofit and rxjava, either because it timedOut, or because I need to change details that went into the request. Both appear to work perfectly, as when I cancel subscription I get the doOnCancel debug message and when doOnNext is completed I get the doOnTerminate message. I also do not receive inputLines from multiple threads. However, my thread count rises every single time either of the above actions happen. It appears that responsebody.close is not releasing their resources and therefore the thread is not dying (I also have gotten error messages along the lines of "OKHTTP leaked. did you close youre responseBody?")
Does anyone have any suggestions?
public boolean closeSubscription() {
flowableAlive = false;
subscription.cancel();
return true;
}
public void subscribeToFlowable() {
streamFlowable.observeOn(Schedulers.newThread()).subscribeOn(Schedulers.newThread())
.doOnTerminate(() -> log.debug("TERMINATED")).doOnCancel(() -> log.debug("FLOWABLE CANCELED"))
.subscribe(new Subscriber<ResponseBody>() {
#Override
public void onSubscribe(Subscription s) {
subscription = s;
subscription.request(Long.MAX_VALUE);
}
#Override
public void onNext(ResponseBody responseBody) {
log.debug("onNext called");
String inputLine;
try (InputStream inputStream = responseBody.byteStream()) {
BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
while (flowableAlive && ((inputLine = br.readLine()) != null)) {
log.debug("stream receive input line for thread " + name);
log.debug(inputLine);
}
} catch (IOException e) {
log.debug("error occurred");
log.debug(e.getMessage());
}
}
#Override
public void onError(Throwable t) {
log.debug("error");
flowableAlive = false;
}
#Override
public void onComplete() {
log.debug("completed");
closeSubscription();
flowableAlive = false;
}
});
}
The result of subscribe() is Disposable object. You should store it as a filed and call Disposable.dispose() on it later as shown here:
https://proandroiddev.com/disposing-on-android-the-right-way-97bd55cbf970
Tour OkHttp call will be interrupted properly because dispose() interrupts thread on which the call runs and OkHttp checks regularly if Thread was interrupted to stop transfer when that happened - it's called cooperative cancelling/interruption.
Related
I am confused with Async feature introduced in Servlet 3.0 spec
From Oracle site (http://docs.oracle.com/javaee/7/tutorial/doc/servlets012.htm):
To create scalable web applications, you must ensure that no threads
associated with a request are sitting idle, so the container can use
them to process new requests.
There are two common scenarios in which a thread associated with a
request can be sitting idle.
1- The thread needs to wait for a resource to become available or process data before building the response. For example, an application
may need to query a database or access data from a remote web service
before generating the response.
2- The thread needs to wait for an event before generating the response. For example, an application may have to wait for a JMS
message, new information from another client, or new data available in
a queue before generating the response.
The first item happens a lot (nearly always, we always query db or call a remote webservice to get some data). And calling an external resource will always consume some time.
Does it mean that we should ALWAYS use servelt async feature for ALL our servelts and filter ?!
I can ask this way too, if I write all my servelts and filters async, will I lose anything (performance)?!
If above is correct the skeleton of ALL our servlets will be:
public class Work implements ServletContextListener {
private static final BlockingQueue queue = new LinkedBlockingQueue();
private volatile Thread thread;
#Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
thread = new Thread(new Runnable() {
#Override
public void run() {
while (true) {
try {
ServiceFecade.doBusiness();
AsyncContext context;
while ((context = queue.poll()) != null) {
try {
ServletResponse response = context.getResponse();
PrintWriter out = response.getWriter();
out.printf("Bussiness done");
out.flush();
} catch (Exception e) {
throw new RuntimeException(e.getMessage(), e);
} finally {
context.complete();
}
}
} catch (InterruptedException e) {
return;
}
}
}
});
thread.start();
}
public static void add(AsyncContext c) {
queue.add(c);
}
#Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
thread.interrupt();
}
}
I got some questions regarding the use of threads, specially when you have to wait for a thread to be finished so you can perform other operations.
In my app, I use threads for operations such as http connections or when I read from or write to a RecordStore.
For example in the following class that I use to initialize my thread, I retrieve some customers from a webservice using the method called HttpQueryCustomers.
public class thrLoadCustomers implements Runnable {
private RMSCustomer mRMSCustomer;
private String mUrl;
public thrLoadCustomers(RMSCustomer rmsCust, String url) {
mRMSCustomer = rmsCust;
mUrl = url;
}
public void run() {
String jsonResultados = "";
try {
jsonResultados = HttpQueryCustomers();
} catch (IOException ex) {
//How to show a message from here??
} catch (SecurityException se) {
//How to show a message here??
} catch (NullPointerException npe) {
//How to show a message from here??
}
if (!jsonResultados.equals("")) {
try {
mRMSCustomer.save(jsonResultados);
} catch (RecordStoreException ex) {
//How to show a message from here???
}
}
}
public String HttpQueryCustomers() throws IOException,SecurityException,NullPointerException {
StringBuffer stringBuffer = new StringBuffer();
HttpConnection hc = null;
InputStream is = null;
System.out.println(mUrl);
try {
hc = (HttpConnection) Connector.open(mUrl);
if (hc.getResponseCode() == HttpConnection.HTTP_OK) {
is = hc.openInputStream();
int ch;
while ((ch = is.read()) != -1) {
stringBuffer.append((char) ch);
}
}
} finally {
is.close();
hc.close();
}
String jsonData = stringBuffer.toString();
return jsonData.toString();
}
}
Notice in the above class that I pass a parameter called rmsCust of the type RMSCustomer
RMSCustomer is a class that I use to handle all the operations related to RMS:
public class RMSCustomer {
private String mRecordStoreName;
private Customer[] mCustomerList;
public RMSCustomer(String recordStoreName) {
mRecordStoreName = recordStoreName;
}
public Customer[] getCustomers() {
return mCustomerList;
}
public Customer get(int index) {
return mCustomerList[index];
}
public void save(String data) throws RecordStoreException,JSONException,NullPointerException {
RecordStore rs = null;
int idNuevoRegistro;
String stringJSON;
try {
rs = RecordStore.openRecordStore(mRecordStoreName, true);
JSONArray js = new JSONArray(data);
//Set the size of the array
mCustomerList = new Customer[js.length()];
for (int i = 0; i < js.length(); i++) {
JSONObject jsObj = js.getJSONObject(i);
stringJSON = jsObj.toString();
idNuevoRegistro = addRecord(stringJSON, rs);
//Add a new Customer to the array
mCustomerList[i] = initializeCustomer(stringJSON, idNuevoRegistro);
}
} finally {
if (rs != null) {
rs.closeRecordStore();
}
}
}
public int addRecord(String stringJSON, RecordStore rs) throws JSONException,RecordStoreException {
byte[] raw = stringJSON.getBytes();
int idNuevoRegistro = rs.addRecord(raw, 0, raw.length);
return idNuevoRegistro;
}
public Customer initializeCustomer(String stringJSON, int idRecord) throws JSONException {
Customer c = new Customer();
JSONObject jsonObj = new JSONObject(stringJSON);
// Set Customer properties
//...
return c;
}
}
This class is used to show a list of customer and ,as you can see, it extends the List class and receives an array of Customers as a parameter.
public class ListCustomers extends List {
private final Customer[] mData;
public static ListCustomers create(Customer[] data) {
int i = 0;
for (; i < data.length; i++) {
if (data[i] == null) {
break;
}
}
String[] names = new String[i];
for (int j = 0; j < i; j++) {
names[j] = data[j].name;
}
return new ListCustomers(names, data);
}
protected ListCustomers(String names[], Customer[] data) {
super("List of Customer", IMPLICIT, names, null);
mData = data;
}
public Customer getSelectedObject() {
return mData[this.getSelectedIndex()];
}
}
Finally this is how I call the thread from the MIDlet (using all the 3 previous classes) when I want to show a List of Customers:
private void showCustomerList(String url) {
showWaitForm();
if (scrCustomerList == null) {
rmsCustomers = new RMSCustomer("rmsCustomers");
thrLoadCustomers load = new thrLoadCustomers(rmsCustomers, url);
Thread t = new Thread(load);
t.start();
try {
t.join();
} catch (InterruptedException ex) {
}
scrCustomerList = ListCustomers.create(rmsCustomers.getCustomers());
scrCustomerList.addCommand(cmdSelect);
scrCustomerList.addCommand(cmdBack);
scrCustomerList.setCommandListener(this);
}
mDisplay.setCurrent(scrCustomerList);
}
Now here's the problems I have :
The showWaitForm() doesn't work (it sets a form with a Gauge as the
Current form)
I don't know how to show all the exceptions that might be thrown from
within the thrLoadCustomers class.
I don't know whether using t.join() is the best choice
The last question is about something the book I'm reading says :
Threads, in particular, can be a scarce commodity. The MSA
specification requires that an application must be allowed to create
ten threads. Just because you can doesn’t mean you should. In general,
try to use the fewest resources possible so that your application will
run as smoothly as possible
This is the first time a use threads, and in my app I might have up to 10 threads (classes). However, I will only execute once thread at the time, will I be going against what the previous quotation says??
I hope I'm not asking too many questions. Thank you very much for your help.
P.D Much of the code I posted here wouldn't have been possible with the help of Gregor Ophey
Question #1 is about a different problem not related to threading, and for which very little code is shown. I'd suggest you to post a new dedicated question with proper explanation of the issue.
Questions #2 and #3: You could define a wrapper class like this:
public class WSResult {
private boolean success; //true if the WS call went ok, false otherwise
private String errorMessage; //Error message to display if the WS call failed.
private Object result; //Result, only if the WS call succeeded.
private boolean completed = false;
//TODO getter and setters methods here
}
In your screen, you can create an instance of result and wait for it:
WSResult result = new WSResult();
//Start thread here
new Thread(new LoadCustomersTask(result)).start();
//This is old school thread sync.
synchronized(result){
while(!result.isCompleted()){
result.wait();
}
}
//Here the thread has returned, and we can diaplay the error message if any
if(result.isSuccess()){
} else {
//Display result.getErrorMessage()
}
Then your runnable would be like this:
class LoadCustomersTask implements Runnable {
private final WSResult result;
public LoadCustomersTask(WSResult res){
result = res;
}
public void run(){
//Do the WS call
//If it went well
result.setSuccess(true);
result.setResult(jsonResultados);
//Else
result.setSuccess(false);
result.setErrorMessage("Your error message");
//In any case, mark as completed
result.setcompleted(true);
//And notify awaiting threads
synchronized(result){
result.notifyAll();
}
}
}
You can also do it with thread.join, but wait/notify is better because you not making the screen depend on the particular thread where the runnable runs. You can wait/notify on the result instance, as shown, or on the runnable if it is intended for a single use.
Question #4: Yes threads must not be abused, specially in JavaME where programs usually run in single core CPUs with a frecuency in the order of MHz. Try not to have more than 1-3 threads running at the same time. If you really need to, consider using a single thread for running all background tasks (a blocking queue).
I have a panel with a JTabbedpane and in every tab you can set parameters to execute a query. When one query is busy retrieving his data from the database, you can already open a new tab to set the new parameters. To avoid overload on the database only one query may be executed at once. But when you click execute the program must remember which queries to execute in the right order. During the execution a loader icon is shown and the GUI may not be frozen, because there is a stop button you can click to stop the execution.
I used a swingworker to avoid the GUI from blocking while executing the query and that works fine. But now I want to prevent the next query to start before the previous has finished. In a model, common for the whole panel, I initialized a semaphore: private final Semaphore semaphore = new Semaphore(1, true);
This is the code which starts the swingworker (I've added println commands to see which is started, stopped or finished)
private void doStoredQuery() {
try {
semaphore.acquire();
System.out.println(queryName + "started");
worker.execute();
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
And this is my swingworker (initializeWorker() is called from the constructor of the main class):
private SwingWorker<StoredQueryDataModel, Integer> initializeWorker() {
worker = new SwingWorker<StoredQueryDataModel, Integer>() {
#Override
protected StoredQueryDataModel doInBackground() throws Exception {
try {
StoredQueryDataModel dataModel = null;
publish(0);
try {
dataModel = new StoredQueryDataModel(queryRunner, ldbName, queryName, params);
} catch (S9SQLException e) {
//
} catch (Throwable e) {
showErrorMessage(e);
}
return dataModel;
}
finally {
semaphore.release();
System.out.println(queryName + "finished");
}
}
#Override
protected void process(List<Integer> chunks) {
//ignore chunks, just reload loader icon
panel.repaint();
}
#Override
protected void done() {
String error;
try {
result = get();
error = null;
} catch (Exception e) {
error = e.getMessage();
}
if(result == null) {
semaphore.release();
System.out.println(queryName + " stopped");
}
if(error == null) {
// process result
}
else {
showErrorMessage(new Throwable(error));
}
}
};
return worker;
}
I've tried putting the acquire and release on other positions in the code, but nothing seems to work. I am bot in Swingworker and sempahores quite new... Can someone help?
I have found the problem: the semaphore had to be a static variable. In my code there were as many semaphores as there are tabs, which caused them to run at the same time instead of sequentially.
I am developping a BlackBerry application which communicates with the server via HTTP requests(javax.microedition.io.HttpConnection). On device, user clicks some UI items, and device sends the requests to server, when the response comes, UI changes. Communication takes place under new thread, while UI thread pushes and pops ProgressDialogScreen.
The problem is sometimes, when response comes and ProgressDialogScreen is popped, UI does not change but after couple seconds UI changes. If you have requested in between when ProgressDialogScreen is popped and when new Screen is pushed, there comes the mess. First oldest new Screen is pushed, and the newest new Screen is pushed. And this situation can be observed like server responsing wrong requests. This problems occur on simulator and device.
The other problem is, sometimes two same response returns for one request. I was able to see these two problems on simulator at the logs, but i have not able to see this issue on device since i can not see the logs.
EDIT:
String utf8Response;
HttpConnection httpConn = null;
try{
httpConn = (HttpConnection) Connector.open(url);
httpConn.setRequestMethod(HttpConnection.GET);
httpConn.setRequestProperty("Content-Type", "text/html; charset=UTF8");
if(sessionIdCookie != null){
//may throw IOException, if the connection is in the connected state.
httpConn.setRequestProperty("Cookie", sessionIdCookie);
}
}catch (Exception e) {
//...
}
try{
httpConn.getResponseCode();
return httpConn;
}catch (IOException e) {
// ...
}
byte[] responseStr = new byte[(int)httpConn.getLength()];
DataInputStream strm = httpConn.openDataInputStream();
strm.readFully(responseStr);
try{
strm.close();
}catch (IOException e) {
// ....
}
utf8Response = new String(responseStr, "UTF-8");
If this code successfully run, this piece of code runs and new screen is pushed:
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
Vector accounts = Parser.parse(utf8Response,Parser.ACCOUNTS);
if (accounts.size() == 0){
DialogBox.inform(Account.NO_DEPOSIT);
return;
}
currentScreen = new AccountListScreen(accounts);
changeScreen(null,currentScreen);
}
});
public void changeScreen(final AbstractScreen currentScreen,final AbstractScreen nextScreen) {
if (currentScreen != null)
UiApplication.getUiApplication().popScreen(currentScreen);
if (nextScreen != null)
UiApplication.getUiApplication().pushScreen(nextScreen);
}
EDITv2:
private static void progress(final Stoppable runThis, String text,boolean cancelable) {
progress = new ProgressBar(runThis, text,cancelable);
Thread threadToRun = new Thread() {
public void run() {
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
try{
UiApplication.getUiApplication().pushScreen(progress);
}catch(Exception e){
Logger.log(e);
}
}
});
try {
runThis.run();
} catch (Throwable t) {
t.printStackTrace();
}
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
try {
UiApplication.getUiApplication().popScreen(progress);
} catch (Exception e) { }
}
});
}
};
threadToRun.start();
}
By the way ProgressBar is extended from net.rim.device.api.ui.container.PopupScreen and Stoppable is extended from Runnable
I preferred to pop progress bar after new Screen is prepared and pushed. This way there will be no new request between request and response.
Why not do:
private static void progress(final Stoppable runThis, String text,boolean cancelable) {
progress = new ProgressBar(runThis, text,cancelable);
UiApplication.getUiApplication().pushScreen(progress);
[...]
Seems like you are parsing on the UI Thread. Please remove Vector accounts = Parser.parse(utf8Response,Parser.ACCOUNTS); from ui thread and do it in a separate thread.
Part of my Silverlight application requires data from three service requests. Up until now I've been chaining the requests so as one completes the other starts... until the end of the chain where I do what I need to do with the data.
Now, I know thats not the best method(!). I've been looking at AutoResetEvent (link to MSDN example) to thread and then synchronize the results but cannot seem to get this to work with async service calls.
Does anyone have any reason to doubt this method or should this work? Code samples gratefully received!
Take a look at this example:
Will fire Completed event and print 'done' to Debug Output once both services returned.
Key thing is that waiting for AutoResetEvents happens in background thread.
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
Completed += (s, a) => { Debug.WriteLine("done"); };
wrk.DoWork += (s, a) =>
{
Start();
};
wrk.RunWorkerAsync();
}
public event EventHandler Completed;
private void Start()
{
auto1.WaitOne();
auto2.WaitOne();
Completed(this, EventArgs.Empty);
}
public AutoResetEvent auto1 = new AutoResetEvent(false);
public AutoResetEvent auto2 = new AutoResetEvent(false);
BackgroundWorker wrk = new BackgroundWorker();
private void Button_Click(object sender, RoutedEventArgs e)
{
ServiceReference1.Service1Client clien = new SilverlightAsyncTest.ServiceReference1.Service1Client();
clien.DoWorkCompleted += new EventHandler<SilverlightAsyncTest.ServiceReference1.DoWorkCompletedEventArgs>(clien_DoWorkCompleted);
clien.DoWork2Completed += new EventHandler<SilverlightAsyncTest.ServiceReference1.DoWork2CompletedEventArgs>(clien_DoWork2Completed);
clien.DoWorkAsync();
clien.DoWork2Async();
}
void clien_DoWork2Completed(object sender, SilverlightAsyncTest.ServiceReference1.DoWork2CompletedEventArgs e)
{
Debug.WriteLine("2");
auto1.Set();
}
void clien_DoWorkCompleted(object sender, SilverlightAsyncTest.ServiceReference1.DoWorkCompletedEventArgs e)
{
Debug.WriteLine("1");
auto2.Set();
}
}
It could be done using the WaitHandle in the IAsyncResult returned by each async method.
The code is simple. In Silverlight I just do 10 service calls that will add an item to a ListBox. I'll wait until all the service calls end to add another message to the list (this has to run in a different thread to avoid blocking the UI). Also note that adding items to the list have to be done through the Dispatcher since they will modify the UI. There're a bunch of lamdas, but it's easy to follow.
public MainPage()
{
InitializeComponent();
var results = new ObservableCollection<string>();
var asyncResults = new List<IAsyncResult>();
resultsList.ItemsSource = results;
var service = new Service1Client() as Service1;
1.To(10).Do(i=>
asyncResults.Add(service.BeginDoWork(ar =>
Dispatcher.BeginInvoke(() => results.Add(String.Format("Call {0} finished: {1}", i, service.EndDoWork(ar)))),
null))
);
new Thread(()=>
{
asyncResults.ForEach(a => a.AsyncWaitHandle.WaitOne());
Dispatcher.BeginInvoke(() => results.Add("Everything finished"));
}).Start();
}
Just to help with the testing, this is the service
public class Service1
{
private const int maxMilliSecs = 500;
private const int minMillisSecs = 100;
[OperationContract]
public int DoWork()
{
int millisSecsToWait = new Random().Next(maxMilliSecs - minMillisSecs) + minMillisSecs;
Thread.Sleep(millisSecsToWait);
return millisSecsToWait;
}
}