Question

I am having a multi-threaded application that fetches different web pages. For this, I’ve devised a parent child relationship between the threads.
The parent simply takes different urls from its page and spawns new threads. These threads keep on continuously fetching the pages until the page changes. The main thread polls every 2 minutes for the changes at the main page(and creates new threads if there is any change)

Main thread algo

while(true){
    find_new_instances(...);
    if we get any new, then
        Thread.start(...);
    Thread.sleep(120000);
}

The main thread has a String arraylist that stores the url of each new thread that it creates. I’ve heard that threads should only use immutable objects for writes. Is the used of mutable list here causing problems ?
In the child thread, activities such as page fetch and database inserts take place.

However, the application gradually increases its memory requirements and eventually deadlocks/starves into a frozen state or OutOfMemory if the no. of threads are too large.
I am at loss to try out anything. If you have experienced similar problems, kindly suggest.

Answer 1

I faced similar type of issue while I was developing a GUI based application.

Reasons of crashing

• Create a Thread Pool. use the
  available thread in you application.
  You cannot create infinite thread
  that will cause crash in your
  application
• May be you are creating new
  objects(or string) and storing the
  data if possible use the same object
  assign the value. If the data is long
  you can store in file or database.
  rather than holding the data always