I want to write and read from file in the same time without errors.
For example, I will starting new Thread for writing to file from my running service.
In my activity i will starting new Thread for reading from the same file.
I wan't to do this synchronously. Some thing like this :
To wait execution of next thread until previous finished.
Next thread must not start until previous thread stops, irrespective of time consumption.
My code for read and write:
public static final String ROUTE_FILE_NAME = "route.txt";
public static void savePointToFile(Context context, String point) throws IOException {
FileOutputStream fOut = context.openFileOutput(ROUTE_FILE_NAME, Context.MODE_APPEND);
OutputStreamWriter osw = new OutputStreamWriter(fOut);
osw.write(point);
osw.flush();
osw.close();
}
public static String readRouteFromFile(Context context) {
StringBuffer fileContent = new StringBuffer(UIUtils.emptyString());
byte[] buffer = new byte[1024];
try {
FileInputStream fis = context.openFileInput(ROUTE_FILE_NAME);
int length;
while ((length = fis.read(buffer)) != -1) {
fileContent.append(new String(buffer));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return fileContent.toString();
}
Thanks in advance.
If you just want the read method called from a thread to wait for the write method called from another thread to be finished, and vice versa, just synchronize both methods on a common object:
private static final Object fileLock = new Object();
public static String readFile() {
synchronize(fileLock) {
[your current read code here]
}
}
public static void write(String data) {
synchronize(fileLock) {
[your current write code here]
}
}
You can look at a special thread pool executor service.
final ExecutorService threadpool = Executors.newSingleThreadExecutor();
Its fairly easy, just create runnables and put it in the threadpool. It contains a single thread so all your runnables are queued sequentially. Otherwise you could create a normal executorservice and set the threadpool to 1. Effectively its the same. Hope this helps
http://www.concretepage.com/java/newsinglethreadexecutor_java
So its like
WorkerThread.get(context).read()
WorkerThread.get(context).write()
You can even implement future calls instead of defining an explicit callback.
Just a general idea of how it can work. You need to save filepointers so you know where to pause and continue read/write. Other you will always start from the first data position in the file.
class WorkerThread {
interface Callback {
void onCompleteRead(String buffer, int pauseReadPointer);
void onCompleteWrite(int pauseWritePointer);
}
enum Action {
READ,
WRITE
}
private static WorkerThread singleton;
public static synchronized WorkerThread get(final Context context) {
if (instance == null) {
instance = new WorkerThread(context);
}
return instance;
}
private final Context context;
private final ExecutorService threadPool;
private WorkerThread(context) {
threadPool = Executors.newSingleThreadExecutor()
}
// PUBLIC READ CALL
public void read(int resumeReadPointer, Callback callback, "other params") {
queueJob(READ, null, resumeReadPointer, callback);
}
// PUBLIC WRITE CALL
public void write(String in, int resumeWritePointer, Callback callback, "other params") {
queueJob(WRITE, in, resumeWritePointer, callback);
}
private void queueJob(final Action action, String buffer, final int pointer, final Callback callback) {
/* Create handler in UI thread. */
final Handler handler = new Handler() {
#Override
public void handleMessage(Message msg) {
ResultPack pack = (ResultPack) msg.obj;
if (Action.READ == action) {
callback.onCompleteRead(pack.result, pack.pointer);
} else {
callback.onCompleteWrite(pack.pointer);
}
}
};
// single threadpool. everything is FIFO
threadPool.submit(new FileRunnable(action, buffer, handler, pointer));
}
private class ResultPack {
private final String result;
private final int pointer;
private ResultPack(String s, int p) {
this.result = s;
this.pointer = p;
}
}
private class FileRunnable implements Runnable {
private int pointer = 0;
private final Handler handler;
private final buffer = buffer;
FileRunnable(final Action action, String buffer, final Handler handler, final int pointer) {
this.pointer = pointer;
this.handler = handler;
this.buffer = buffer;
}
#Override
public void run() {
if (Action.READ == action) {
ResultPack pack = readRouteFromFile(..., pointer);
} else { // write
ResultPack pack = savePointToFile(..., buffer, pointer);
}
Message message = Message.obtain();
message.obj = pack;
handler.sendMessage(message);
}
}
}
Related
I have a String variable, and I set it's value inside a thread, since it's using a netwok operation.
How can I access the values stored in the Strings?
public class HomeActivity extends AppCompatActivity {
// Initialize AWS DynamoDB Client
public static AmazonDynamoDBClient ddbClient;
public static DynamoDBMapper mapper;
public static Aqua aqua;
// App details
public static String a = "A";
public static String b;
public static Boolean c;
public static String d;
public static String e;
public static String f;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
// Initialize the Amazon Cognito credentials provider
CognitoCachingCredentialsProvider credentialsProvider = new CognitoCachingCredentialsProvider(
getApplicationContext(),
"******", // Identity Pool ID
Regions.**** // Region
);
// Initialize AWS DynamoDB
ddbClient = new AmazonDynamoDBClient(credentialsProvider);
mapper = new DynamoDBMapper(ddbClient);
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
try {
// Get app details
aqua = mapper.load(Aqua.class, a);
b = aqua.getB();
c = aqua.getC();
d = aqua.getD();
e = aqua.getE();
f = aqua.getF();
} catch (Exception e) {
Log.e("error", e.getMessage());
}
}
});
thread.start();
}
}
Use ExecutorService and submit Callable (below assumes you want the data that is stored inside b,c,d,e,f):
ExecutorService exec = Executors.newSingleThreadExecutor();
Future<String[]> future = exec.submit(new Callable<String[]>() {
#Override
public String[] call() {
try {
// Get app details
aqua = mapper.load(Aqua.class, a);
b = aqua.getB();
c = aqua.getC();
d = aqua.getD();
e = aqua.getE();
f = aqua.getF();
} catch (Exception e) {
Log.e("error", e.getMessage());
}
return new String[] {b, c, d, e, f};
}
});
// ... b will be at value[0], c at value[1]
String[] value = future.get();
Declare the string globally in your Activity/Fragment. This way you can acces it from everywhere.
You could also use handler.sendMessage(message); with your String as message to send it whenever your Thread has finished or whenever you want to. You can then retrieve your String int
protected Handler handler = new Handler() {
#Override
public void handleMessage(Message msg) {
String status = (String) msg.obj;
Log.i("Got a new message", "MESSAGE: "+status);
}
};
Hope it helps :)
I am having problems with updating the TextView, I used the Handler method to pass the message to the UI. My application receives data(type integers) true io stream and shows in TextView.
My Activity class looks like this:
public class DeviceView extends Activity {
TextView dataX;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.device_view);
dataX = (TextView) findViewById(R.id.datax);
handler = new Handler() {
#Override
public void handleMessage(Message msg) {
dataX.setText(String.valueOf(msg.arg1));
}
};
}
}
I also have a separate class it extends Thread:
public class IOThread extends Thread {
public void run() {
byte[] buffer = new byte[1024];
int data;
while (true) {
try {
data = in.read(buffer);
Message message= Message.obtain();
message.arg1= data;
DeviceView.handler.sendMessage(message);
} catch (IOException ex) {
break;
}
}
}
}
Do I have to make a separate variable type String and point it to variable data and at last calling the count? Would that be enough to update TextView?
Can you try using an interface. Let the Activity implement it, pass it to the IOThread class. Once you get the result, pass the result to the Activity.
Interface named InterfaceData
public void getData(int data);
public class DeviceView extends Activity implements InterfaceData{
TextView dataX;
Handler handler;
IOThread ioThread;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.device_view);
handler = new Handler();
ioThread = new IOThread(this);
dataX = (TextView) findViewById(R.id.datax);
}
#Override
public void getData(int data){
handler.postDelayed(new Runnable(){
public void run(){
dataX.setText(data);
};
},100);
}
}
> Thread class
public class IOThread extends Thread {
InterfaceData interfaceData;
public IOThread(InterfaceData interfaceData){
this.interfaceData = interfaceData;
}
public void run() {
byte[] buffer = new byte[1024];
int data;
while (true) {
try {
data = in.read(buffer);
interfaceData.getData(data);
} catch (IOException ex) {
break;
}
}
}
}
I have found my problem it was not the Handler issue. THe code i posted at the beginning is coorect. The problem lyis on the way i read the received bytes[] array from the InputStream. I have tested by sending an integer int numbers = (int) 2 and when print this receivd data in terminal in Android app, it receivs only 1, even if i send int 3 or 4, i stil receive 1.
So i preceiated your example code #dcanh121 , but my question is actualy how do i read properly the integers that the server sends?
public void run() {
byte[] buffer = new byte[1024];
int data;
while (true) {
try {
data = in.read(buffer);
Log.d(TAG + data, "test");
Message message = Message.obtain();
message.arg1 = data;
Log.d(TAG + message.arg1, "test");
DeviceView.handler.sendMessageDelayed(message, 100);
} catch (IOException ex) {
Log.e(TAG_IOThread, "disconnected", ex);
break;
}
}
}
I want to add a logging mechanism in my android in which i want to log messages to a file on the sd card.
Since I had to log from different threads and as I do not want these threads to be blocked, I tried to do logging on a different thread.
I've built a class something like this so far -
public class TestLogger {
private static String LOG_FILE_NAME = "/logs.txt";
private static int LOG_FILE_SIZE_LIMIT = 100 * 1024;
private static FileHandler logHandler;
private static Logger logger;
private static ExecutorService executorService;
public synchronized static void init() {
String logFilePathName = Environment.getExternalStorageDirectory() + LOG_FILE_NAME;
try {
logHandler = new FileHandler(logFilePathName, LOG_FILE_SIZE_LIMIT, 1, true);
logHandler.setFormatter(new SimpleFormatter());
logger = Logger.getLogger("com.test.android");
logger.setLevel(Level.ALL);
logger.addHandler(logHandler);
executorService = Executors.newFixedThreadPool(1);
} catch (IOException e) {
e.printStackTrace();
}
}
private synchronized static void writeLog(String msg) {
if(logger == null)
return;
logger.log(Level.FINE, msg);
}
public static void logMessage(String msg) {
executorService.submit(new LogToFile(msg));
}
private static class LogToFile implements Runnable {
String msg;
public LogToFile(String msg) {
this.msg = msg;
}
#Override
public void run() {
TestLogger.writeLog(msg);
}
}
}
When the app is entered, I call TestLogger.init() and from there on I call `TestLogger.logMessage("log message"); whenever I have to log something to the file.
This works fine but instead of creating logs.txt, i also see other files created. Like logs.txt.1 and logs.txt.2 along with their .lck files. By having keyword synchronized, have I not made sure that no two threads write to the same file at the same time?
What am I doing wrong?
I am now using a blocking queue to do the job. it works great now :)
synchronized works with variables not files. You can use the synchronized block to fill a string builder for e.g. and write to the file in a final step.
My Android app should do the following:
The MainActivity launches another thread at the beginning called UdpListener which can receive UDP calls from a remote server. If it receives a packet with a content "UPDATE", the UdpListener should notify the MainActivity to do something.
(In the real app, the use case looks like this that my app listens on the remote server. If there is any new data available on the remote server, it notifies every client (app) by UDP, so the client knows that it can download the new data by using HTTP).
I tried to simulate this in an JUnit test. The test contains an inner class which mocks the MainActivity as well as it sends the UDP call to the UdpListener:
public class UdpListener extends Thread implements Subject {
private DatagramSocket serverSocket;
private DatagramPacket receivedPacket;
private boolean running = false;
private String sentence = "";
private Observer observer;
private static final String TAG = "UdpListener";
public UdpListener(Observer o) throws SocketException {
serverSocket = new DatagramSocket(9800);
setRunning(true);
observer = o;
}
#Override
public void run() {
setName(TAG);
while (isRunning()) {
byte[] receivedData = new byte[1024];
receivedPacket = new DatagramPacket(receivedData, receivedData.length);
try {
serverSocket.receive(receivedPacket);
}
catch (IOException e) {
Log.w(TAG, e.getMessage());
}
try {
sentence = new String(receivedPacket.getData(), 0, receivedPacket.getLength(), "UTF-8");
if ("UPDATE".equals(sentence)) {
notifyObserver();
}
}
catch (UnsupportedEncodingException e) {
Log.w(TAG, e.getMessage());
}
}
}
private boolean isRunning() {
return running;
}
public void setRunning(boolean running) {
this.running = running;
}
#Override
public void notifyObserver() {
observer.update();
}
}
This is the corresponding test:
#RunWith(RobolectricTestRunner.class)
public class UdpListenerTest {
private MainActivityMock mainActivityMock = new MainActivityMock();
#Before
public void setUp() throws Exception {
mainActivityMock.setUpdate(false);
}
#After
public void tearDown() throws Exception {
mainActivityMock.setUpdate(false);
}
#Test
public void canNotifyObserver() throws IOException, InterruptedException {
UdpListener udpListener = new UdpListener(mainActivityMock);
udpListener.setRunning(true);
udpListener.start();
InetAddress ipAddress = InetAddress.getByName("localhost");
DatagramSocket datagramSocket = new DatagramSocket();
DatagramPacket sendPacket = new DatagramPacket("UPDATE".getBytes(), "UPDATE".length(), ipAddress, 9800);
datagramSocket.send(sendPacket);
datagramSocket.close();
assertTrue(mainActivityMock.isUpdate());
udpListener.setRunning(false);
}
private class MainActivityMock implements Observer {
private boolean update = false;
#Override
public void update() {
update = true;
}
public boolean isUpdate() {
return update;
}
public void setUpdate(boolean update) {
this.update = update;
}
}
}
The good thing is that my concept works. But, this test doesn't. That means it only does when I stop with a breakpoint at this line datagramSocket.close(); and wait for about a second. Why this happens is clear. But how can I do that automatically? I thought about using wait() but I have to invoke notify() from the other thread for that. The same problem with CountDownLatch. I'm not sure how to solve that without changing UdpListener.
You could write a simple loop with a specified timeout.
try {
long timeout = 500; // ms
long lastTime = System.currentTimeMillis();
while(timeout > 0 && !mainActivityMock.isUpdate()) {
Thread.sleep(timeout);
timeout -= System.currentTimeMillis() - lastTime;
lastTime = System.currentTimeMillis();
}
} catch(InterruptedException e) {
} finally {
assertTrue(mainActivityMock.isUpdate());
}
By the way - you should declare your running attribute to volatile.
one solution would be to use a blocking queue with size 1 for storing your received results.
The request for isUpdate (which would take an element from the blocking queue) would block until the update package(or any other package) is put into the queue.
is case you want all your calls to be non-blocking you could use a Future for receiving your result. Future.get() would block ontil your result is received.
I have a android application with lots of buttons. If a button is pressed it sends a short cmd to a server via a socket.
Currently, when a button is pressed this adds a cmd to a list.
I have a worker thread that constantly checks the list for cmds and if it finds one opens a socket and sends the cmd.
This is not very efficient as the worker thread is constantly running. What would be the best way to improve this?
public class Arduino implements Runnable{
private static PrintWriter arduinoOutput;
private static Socket ss;
private static Queue<String> cmdsToSend=new LinkedList<String>();
private static String cmd;
public void run(){
while(true){
if(!cmdsToSend.isEmpty()){
cmd = cmdsToSend.poll();
System.out.println("send:"+cmd);
if(connect()){
arduinoOutput.println(cmd);
disconnect();
}
}
}
}
public static void sendCmd(String newcmd){
cmdsToSend.add(newcmd);
}
private static boolean connect(){
try {
ss = new Socket();
InetAddress addr = InetAddress.getByName("192.168.1.8");
int port = 23;
SocketAddress sockaddr = new InetSocketAddress(addr, port);
ss.connect(sockaddr, 2000);
arduinoOutput = new PrintWriter(ss.getOutputStream(),true); //Autoflush
return true;
} catch (UnknownHostException e) {
return false;
} catch (IOException e) {
return false;
}
}
private static void disconnect(){
arduinoOutput.close();
try {
ss.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
The UI activity adds a cmd by calling Arduino.sendCmd("cmdName"); The cmds need to be sent as quickly as possible so a sleep in the loop is no good.
Any ideas or examples would be appreciated.
Use a wait/notify pattern. Put the sender on a thread with the list. Whenever there is something to write to the worker thread, have the writer add the command, and then notify the thread. If the thread is already awake, the notify will do nothing.
Here is a quick example, clearly the mechanism you will use to start the writing thread will be different.
import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.ThreadFactory;
public class Notifier
{
public static void main( String args[] )
{
Writer writingThread = new Writer();
writingThread.addToQueue( "Command 0" );
ThreadFactory.submitInSingleThread( writingThread );
for (int i = 1; i < 1000; i++)
{
writingThread.addToQueue( "Command " + i );
writingThread.notify();
}
}
static class Writer implements Runnable
{
private static Queue<String> cmdsToSend = new LinkedList<String>();
public void addToQueue( String cmd )
{
cmdsToSend.add( cmd );
}
#Override
public void run()
{
while( true )
{
if( !cmdsToSend.isEmpty() )
{
String cmd = cmdsToSend.poll();
System.out.println( "send:" + cmd );
if( connect() )
{
arduinoOutput.println( cmd );
disconnect();
}
}
synchronized( this )
{
wait(); //Can add a timer (100ms, for example)
}
}
}
}
}