Develop Reference

java long term thread

I am currently facing a challenge with executing following thread in my webapplication:
return new Runnable() {
#Override
public void run() {
long lastHeartBeat = -1;
while (true) {
if (isFullAbortRequested()) {
break;
}
if (lastHeartBeat == -1 || lastHeartBeat + 1000 * 60 < new Date().getTime()) {
// once every x minutes send a "i'm still alive!"
DEFAULT_LOGGER.info("still alive!");
lastHeartBeat = new Date().getTime();
}
//DO SOMETHING THAT TAKES 1 MIN
try {
Thread.sleep(1000);
} catch (final InterruptedException e) {
DEFAULT_LOGGER.error("CACHE REFRESH SERVICE DOWN");
}
}
}
};
The problem with this one, is that after some days it just stops (without any known reason). Is this a "expected behaviour" on such "while(true) sleep" threads that they might be closed by OS (?) or anything else?
What would be a durable solution for this "check every second if you have to do something, and if yes, do it (can take 1 min). then wait a second before next check"? The actions in "DO SOMETHING" should never parallize or overlap, so they should be blocking for this thread.
Thank you in advance!

Increasing the performance of a multi-thread Selenium WebDriver based brute force bot

everyone!
I have just created a brute force bot which uses WebDriver and multithreading to brute force a 4-digit code. 4-digit means a range of 0000 - 9999 possible String values. In my case, after clicking the "submit" button, not less than 7 seconds passes before the client gets a response from the server. So, I have decided to use Thread.sleep(7200) to let the page with a response be fully loaded. Then, I found out that I couldn't afford to wait for 9999*7,5 seconds for the task to be accomplished, so I had to use multithreading. I have a Quad-Core AMD machine with 1 virtual core per 1 hardware one, which gives me the opportunity to run 8 threads simultaneously. Ok, I have separated the whole job of 9999 combinations between 8 threads equally, each had got a scope of work of 1249 combinations + remainder thread starting at the very end. Ok, now I'm getting my job done in 1,5 hours (because the right code appears to be in the middle of the scope of work). That is much better, BUT it could be even more better! You know, the Thread.sleep(7500) is a pure waste of time. My machine could be switching to other threads which are wait() because of limited amount of hardware cores. How to do this? Any ideas?
Below are two classes to represent my architecture approach:
public class BruteforceBot extends Thread {
// All the necessary implementation, blah-blah
public void run() {
brutforce();
}
private void brutforce() {
initDriver();
int counter = start;
while (counter <= finish) {
try {
webDriver.get(gatewayURL);
webDriver.findElement(By.name("code")).sendKeys(codes.get(counter));
webDriver.findElement(By.name("code")).submit();
Thread.sleep(7200);
String textFound = "";
try {
do {
textFound = Jsoup.parse(webDriver.getPageSource()).text();
//we need to be sure that the page is fully loaded
} while (textFound.contains("XXXXXXXXXXXXX"));
} catch (org.openqa.selenium.JavascriptException je) {
System.err.println("JavascriptException: TypeError: "
+ "document.documentElement is null");
continue;
}
// Test if the page returns XXXXXXXXXXXXX below
if (textFound.contains("XXXXXXXXXXXXXXXx") && !textFound.contains("YYYYYYY")) {
System.out.println("Not " + codes.get(counter));
counter++;
// Test if the page contains "YYYYYYY" string below
} else if (textFound.contains("YYYYYYY")) {
System.out.println("Correct Code is " + codes.get(counter));
botLogger.writeTheLogToFile("We have found it: " + textFound
+ " ... at the code of " + codes.get(counter));
break;
// Test if any other case of response below
} else {
System.out.println("WTF?");
botLogger.writeTheLogToFile("Strange response for code "
+ codes.get(counter));
continue;
}
} catch (InterruptedException intrrEx) {
System.err.println("Interrupted exception: ");
intrrEx.printStackTrace();
}
}
destroyDriver();
} // end of bruteforce() method
And
public class ThreadMaster {
// All the necessary implementation, blah-blah
public ThreadMaster(int amountOfThreadsArgument,
ArrayList<String> customCodes) {
this();
this.codes = customCodes;
this.amountOfThreads = amountOfThreadsArgument;
this.lastCodeIndex = codes.size() - 1;
this.remainderThread = codes.size() % amountOfThreads;
this.scopeOfWorkForASingleThread
= codes.size()/amountOfThreads;
}
public static void runThreads() {
do {
bots = new BruteforceBot[amountOfThreads];
System.out.println("Bots array is populated");
} while (bots.length != amountOfThreads);
for (int j = 0; j <= amountOfThreads - 1;) {
int finish = start + scopeOfWorkForASingleThread;
try {
bots[j] = new BruteforceBot(start, finish, codes);
} catch (Exception e) {
System.err.println("Putting a bot into a theads array failed");
continue;
}
bots[j].start();
start = finish;
j++;
}
try {
for (int j = 0; j <= amountOfThreads - 1; j++) {
bots[j].join();
}
} catch (InterruptedException ie) {
System.err.println("InterruptedException has occured "
+ "while a Bot was joining a thread ...");
ie.printStackTrace();
}
// if there are any codes that are still remain to be tested -
// this last bot/thread will take care of them
if (remainderThread != 0) {
try {
int remainderStart = lastCodeIndex - remainderThread;
int remainderFinish = lastCodeIndex;
BruteforceBot remainderBot
= new BruteforceBot(remainderStart, remainderFinish, codes);
remainderBot.start();
remainderBot.join();
} catch (InterruptedException ie) {
System.err.println("The remainder Bot has failed to "
+ "create or start or join a thread ...");
}
}
}
I need your advise on how to improve the architecture of this app to make it successfully run with say, 20 threads instead of 8. My problem is - when I simply remove Thread.sleep(7200) and at the same time order to run 20 Thread instances instead of 8, the thread constantly fails to get a response from the server because it doesn't wait for 7 seconds for it to come. Therefore, the performance becomes not just less, it == 0; Which approach would you choose in this case?
P.S.: I order the amount of threads from the main() method:
public static void main(String[] args)
throws InterruptedException, org.openqa.selenium.SessionNotCreatedException {
System.setProperty("webdriver.gecko.driver", "lib/geckodriver.exe");
ThreadMaster tm = new ThreadMaster(8, new CodesGenerator().getListOfCodesFourDigits());
tm.runThreads();

Okay, so everyone can't wait until my question will get a response so I decided to answer it as soon as I can (now!).
If you would like to increase a performance of a Selenium WebDriver-based brute force bot like this one, you need to reject using the Selenium WebDriver. Because the WebDriver is a separate process in the OS, it does not even need a JVM to run. So, every single instance of the Bot was not only a thread managed by my JVM, but a Windows process also! This was the reason why I could hardly use my PC when this app was running with more than 8 threads (each thread was invoking a Windows process geckodriver.exe or chromedriver.exe). Okay, so what you really need to do to increase performance of such a brute force bot is to use HtmlUnit instead of Selenium! HtmlUnit is a pure Java framework, its jar could be found at Maven Central, its dependency could be added to your pom.xml. This way, brute forcing a 4-digit code takes 15 - 20 minutes, taking into account that after each attempt the website responds not faster than 7 seconds after each attempt. To compare, with Selenium WebDriver it took 90 minutes to accomplish the task.
And thanks again to #MartinJames, who has pointed that Thread.sleep() does let the hardware core to switch to other threads!

Text based game with a separate timer loop?

I have started a Java coding short course at a university about 5 months ago. I have learnt quite the amount of things with regards to Java coding, but am still lacking in other things such as threads, handling exceptions, or even making JFrame games. I decided to embark on a text based game to just learn and figure out how a game loop should work (kind of), and how the logic should work (still, very "kind of"). The game I wrote runs with if-else commands, thus you get displayed a screen, type in the command of the option you want to pick, and it bumps you to the next menu, very standard of course. I run these if-else statements within nested for loops.
My nested for loops looks like the following:
// This is just an example, they're actually a lot more cluttered
// in my actual source code.
mainMenu.writeOutput();
reply = keyboardInput.nextLine();
for (int i = 0; i <= 10; i--)
{
for (int ii = 0; i <= 10; i--)
{
if (reply.equalsIgnoreCase("/help")
{
System.out.println("Here I have a separate call to a class
file (excuse me, forgot the exact wording), thus it
call something like help.writeOutput(); to display
the help menu");
reply = keyboardInput.nextLine();
if (reply.equalsIgnoreCase("/makegameeasy")
{
// Just an example.
gamedifficultyEasy.writeOutput();
reply = keyboardInput.nextLine();
if (reply.equalsIgnoreCase("/back")
{
mainMenu.writeOutput();
reply = keyboardInput.nextLine();
break;
}
}
else if (reply.equalsIgnoreCase("/makegamedifficult")
{
// Another example.
gamedifficultHard.writeOutput();
reply = keyboardInput.nextLine();
if (reply.equalsIgnoreCase("/back")
{
mainMenu.writeOutput();
reply = keyboardInput.nextLine();
break;
}
}
else if (reply.equalsIgnoreCase("/back")
{
mainMenu.writeOutput();
reply = keyboardInput.nextLine();
break;
}
}
else
{
System.out.println("Here I print out an error for incorrect
input received, standard fare.");
mainMenu.writeOutput();
reply = keyboard.nextLine();
break;
}
}
}
As mentioned, the above is just an example, it's not very elegant, and I can probably use Exceptions for any incorrect info submitted by the user, however I do not know too much of Exceptions to comfortably add them, so I'll do that at a later time, however my main issue at the moment is a part of my game where "resource mining" has to be done on regular intervals. I have been all over Google, but still can't quite catch how to set a Thread or Timer up for my game so it does the mining automatically, and the player can go on with their game.
The game is essentially one of those games where you build up a base, upgrade your mining tools, and generate more "stuff". I have pasted a few blocks of code from my "mining" class file below that will basically run how much of one thing should be mined. In the game you will be able to buy upgrades of course, so it will get factored into your mining speed.
// I initiate my variables a lot earlier, but just for some
// clarity, I have initiated the variables in the below methods,
// they will not work correctly anyway, I am aware of that, however
// I didn't want to add the other "get, set and initiate"
// variables and methods everywhere, as to not spam this block of code.
// upgradeOS, upgradeHF, and upgradeLM all have their own respective
// set and get methods. They are also all int variables.
public void handleOS()
{
// OS = short for Oxygen Silo
int mineOS = os.getStoredO2() + (1 * upgradeOS);
os.setStoredO2(mineOS);
}
public void handleHF()
{
// HF = short for Hydrogen Fuel
int mineHF = hf.getStoredO2() + (1 * upgradeHF);
hf.setStoredO2(mineHF);
}
public void handleLM()
{
// LM = short for Liquid Minerals
int mineLM = lm.getStoredMinerals() + (1 * upgradeLM);
lm.setStoredMinerals(mineLM);
}
// This is what's going to run the whole time on the set intervals.
public void mine()
{
mineOS = os.getStoredO2() + (1 * upgradeOS);
mineHF = hf.getStoredO2() + (1 * upgradeHF);
mineLM = lm.getStoredMinerals() + (1 * upgradeLM);
os.setStoredO2(mineOS);
hf.setStoredO2(mineHF);
lm.setStoredMinerals(mineLM);
}
// Using 10 seconds here to have it update as quickly as possible so I can
// see any changes. This is just here to write an output.
public void getUpgradeInfo()
{
System.out.println("Oxygen: " + (1 * upgradeOS) + " / per 10 seconds.");
System.out.println("Hydrogen: " + (1 * upgradeHF) + " / per 10 seconds.");
System.out.println("Liquid Mineral: " + (1 * upgradeLM) + " / per 10 seconds.");
}
I'm not the best naming schemes for my materials...
TL;DR: I can't figure out how to implement a thread or timer just for the above mentioned mine() method since I do not have the appropriate amount of knowledge. My if-else rules aren't too elegant, but I'll work on those of course. Basically the if-else rules should run separately from the mine() method, and you can do some AFKing without the game updating the System.out output, thus you can be floating in, for example, the Oxygen Silo upgrade menu, and you won't be bounced back to a different menu due to a thread "waking up", such as being bounced to the main menu, but the mine() method will still generate resources in the background as it should.
Any help on this, or just even a nudge in the right direction will be greatly appreciated.

To answer the question you asked, you can do something like this:
import java.util.*;
TimerTask tt = new TimerTask() {
public void run() {
mine();
}
}
Timer t = new Timer();
t.scheduleAtFixedRate(tt, 0, 1000);
Alternatively, you can use an ActionListener and the swing timer in a similar way. This has the advantage of being Thread-safe in case you build a swing gui on top
Lastly, you should check out the usage of synchronized and volatile to make sure that the variable(s) that are updated in mine() are done so in a thread-safe way

Thanks to #ControlAltDel, definite shove in the right direction. I have taken a bit of code and set it up like this:
import java.util.*;
// extends TimerTask needed
public class TimerTestOne extends TimerTask
{
// Needed
#Override
public void run()
{
TimerTestTwo ttt = new TimerTestTwo();
mine();
}
// Needed, method doesn't need the same name though.
private void completeTask()
{
try
{
//assuming it takes 10 secs to complete the task
Thread.sleep(10000);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
public static void main(String[] args)
{
// You will need to define the following line of code:
TimerTask tt = new TimerTestOne();
Scanner keyboard = new Scanner(System.in);
String reply;
// Following 2 lines of code, yup, need them.
Timer timer = new Timer(true);
timer.scheduleAtFixedRate(tt, 0, 10*1000);
previousMenu();
for (int i = 0; i <= 10000; i++)
{
for (int ii = 0; ii <= 10000; i++)
{
System.out.println("Go to another menu?");
reply = keyboard.nextLine();
if (reply.equalsIgnoreCase("/yes"))
{
yes();
reply = keyboard.nextLine();
}
}
}
}
// I added the following methods, just so I didn't have to work
// off 2 class files.
public void mine()
{
System.out.println("Mined");
}
public static void yes()
{
System.out.println("Next menu");
}
public static void previousMenu()
{
System.out.println("Previous menu");
}
}
So there, if anyone ever needs to have a look at setting a timer up that won't break your text based game.

Executing statement after 10 seconds

I am running my java listener codes.
What happens is that my server will send some command to the client.
Thereafter I want to wait and see in 10s if there is no reply, then keep retrying for 5 times.
Below is what I do.
//Select code from the db with the codeID, codeText.
//send the code to the client.
long t= System.currentTimeMillis();
long end = t+10000;
while(System.currentTimeMillis() < end) {
}
//Select from db to check if codeupdated.
If updated dont do anything else I need to repeat the above pause ?
I having issue to repeat it for 5 times?

There is no guarantee for your construct to last exactly 10 seconds, and it's very costly in terms of performance.
Just use Thread.sleep.
for (int i = 0; i < 5; i++) {
// TODO your request here
boolean success = true; // TODO change to whatever outcome of your
// request
if (success) {
break;
}
else {
try {
Thread.sleep(10000l);
}
catch (InterruptedException ie) {
// TODO handle interruptions if applicable
}
}
}

Use
Thread.sleep(10*1000); //sleep 10 seconds.

You should use Thread.sleep() to pause execution
It's well explained here :
http://docs.oracle.com/javase/tutorial/essential/concurrency/sleep.html

How do I check how many events are happening within 2 seconds? (timer)

I need to check how many events are detected within 2 seconds. I have the timer working and I have everything else working...but I ran into a problem: the loop only checks one time, per second and I can't seem to figure out how to fix that. I need it to check constantly during these two seconds to see how many events there were in total!
Here is what I have:
int seconds = 0;
System.out.println("Seconds: " + seconds);
while(seconds < 2)
{
//Wait 1 second
try {
Thread.sleep(1000);
}
catch(Exception e) {}
seconds++;
System.out.println("Seconds: " + seconds);
//This needs to be looping the whole time.
//But right now, it's being blocked and only checked once
if(eventDetected() && seconds <= 2){
events++;
}
}
So you can see my problem. I can't split them up because then the second timer would run, and THEN eventDetected() would be checked. I need it to check constantly DURING the two second timer...so I basically need both things to happen at once. Is there any way I can do this?
Thanks for any help ahead of time!

I think your design pattern needs work -- I don't know what type event you're looking to detect, but no matter how short your sleep time is, there's a chance you could miss an event using the current pattern. Here's what I suggest:
Have eventDetected() increment your events counter. That way, you won't miss an event.
Then, you just need a way to turn on and off listening (and perhaps resetting the event counter). If you're sure that in you're current pattern you are really in a different thread that won't block your eventDetected() method, you could set a flag to check. For example:
When you want to start listening:
listenForEvents = true;
In eventDetected():
if (listenForEvents) { events++; }
When you want to stop listening (for example, after your Thread.sleep() call):
listenForEvents = false;
With multithreading, make sure to watch out for concurrency issues checking and setting the variables, of course.

I would tell you what kind of event I have to keep track of but then I'd have to kill you :D
Answered my own question. Hopefully this will help anyone else out who has a similar problem at some point! I looked up multithreading a bit...
I created a new class EventTimer which implements Runnable, with a public field for seconds:
public class EventTimer implements Runnable{
int seconds;
static int timerThreadCount = 0;
Thread t;
public EventTimer() {
timerThreadCount++;
this.seconds = 0;
t = new Thread(this, "Event Timer");
t.start(); // Start the thread
}
#Override
public void run() {
// TODO Auto-generated method stub
while(seconds < 2)
{
//Wait 1 second
try {
Thread.sleep(1000);
}
catch(Exception e) {
System.out.println("Waiting interupted.");
}
seconds++;
System.out.println("Seconds: " + seconds);
}
}
}
Then I used an instance of the EventTimer, and used a while loop & if statement to solve my problem.
EventTimer t = new EventTimer();
while(t.seconds < 2){
if(eventDetected()) events++;
}
It was actually quite simple! I realize that each iteration of my loop of operation (since the entire code piece above is inside an infinite loop) will create a new EventTimer thread and I will eventually run into memory problems however. How would I close/end a thread after the timer has reached 2 seconds?