How to share ConcurrentHashMap in threadpool - threadpool

Question

class Task implements Runnable
{
private File file;
private String fileName;
public Task(File file, String fileName)
{
this.file = file;
this.fileName = fileName;
}
public void run()
{
try
{
Scanner scanner = new Scanner(file);
while (scanner.hasNextLine())
{
String line = scanner.nextLine();
for(String feature : StaticClass.STATIC_LIST_FEATURES)
{
if(line.contains(feature))
{
if (result.values().contains(feature))
{
List<String> list = result.get(feature);
list.add(fileName);
result.put(feature, list);
break;
}
else
result.put(feature, new ArrayList<>(List.of(fileName)));
}
}
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
public class MainClass{
// Maximum number of threads in thread pool
static final int MAX_T = 5;
static final Map<String, List<String>> result = new ConcurrentHashMap<>();
public static void main(String[] args)
{
List<Runnable> runnableList = new ArrayList<Runnable>();
File myObj = new File("JsTsresult.txt");
try
{
Scanner myReader = new Scanner(myObj);
while(myReader.hasNextLine())
{
String data = myReader.nextLine().substring(1);
Runnable runnable = new Task(new File("/webdev/NetLedger_NewGitRepo/", data));
runnableList.add(runnable);
}
ExecutorService pool = Executors.newFixedThreadPool(MAX_T);
for(Runnable task : runnableList)
pool.execute(task);
pool.shutdown();
} catch(Exception e)
{
e.printStackTrace();
}
}
}
I am using threadpool to check if features are mentioned in some files that I have inside a file JSTSResult.txt. This txt file has a list of files. I am reading that file one-by-one and want to create a concurrent hash map where key would be that feature and value would be the list of those files. Here I am using a few tasks and I have initialized ConcurrentHashMap. But, not sure on how to share this ConcurrentHashMap to all those Tasks. I have this way, but of course it won't work. Any suggestions?

Answer 1

You can try creating a method to Task and then synchronized it so that only one thread can add in it at a time.
class Task implements Runnable
{
static final Map<String, List<String>> result = new ConcurrentHashMap<>();
public static synchronized void addToResult()
{
result.put();
}
}
If you want to know what synchronized is.
This is a sample explanation based on a book.
class SpeechSynthesizer
{
synchronized void say( String words )
{
// speak
}
}
Because say() is an instance method, a thread must acquire the lock on the SpeechSynthesizer instance it’s using before it can invoke the say() method. When say() has
completed, it gives up the lock, which allows the next waiting thread to acquire the lock
and run the method. It doesn’t matter whether the thread is owned by the SpeechSyn
thesizer itself or some other object; every thread must acquire the same lock, that of
the SpeechSynthesizer instance. If say() were a class (static) method instead of an
instance method, we could still mark it as synchronized. In this case, because no in‐
stance object is involved, the lock is on the class object itself. -Learning Java
Book by Jonathan Knudsen and Patrick