Help needed with logging API and threads

**Kristian Bisgaard Lassen** · Jul 17 '05, 09:54 PM

Re: Help needed with logging API and threads

On Thu, 02 Oct 2003 11:21:24 -0700, Huzefa wrote:
[color=blue]
> I am working on a amll project in Java that includes many classes.
> Each of the classes has a Logger object. I have associated a
> FileHandler with
> each of these Logger objects. The file is the same for each of these
> classes "log.xml" Now I want all the classes to log to the same file.
> However, this
> does not happen. Each class creates its own log file. The base class
> uses the file "log.xml". Each subsequent class creates a log file
> "log.xml.1" , "log.xml.2" and so on. Can I get all my classes to log to
> the same file? If so how?[/color]
Declare your OutputStream/FileHandler (the thing you have chosen to write
to files with) static in your Logger class. This means that
their will only be one instance of the OutputStream object in your Logger objects.
Alternatively you could instanciate all you objects with the samme
OutputStream and syncronize acces to the write methods if concurrent
processes are logging at the same time.
Doing the last refactoring can be done using the the
factory pattern for creating you Logger objects, but there are other ways.[color=blue]
>
> The second query is about threads. My project uses the internet to get
> data. Now I want only a specific number of threads to access the net
> at any given time (the exact number will be specified in the
> preferences). The other threads not accessing the net should function
> normally. How can I achieve this sort of behaviour? Please keep in
> mind that this is the first time I am working with threads.[/color]
A simple polling technique would be this:

1. Start as many processes as you want running at the same time.
2. Wait some time.
3. Test if any of them has died.
4. If pending procceses exist or running process exist goto 1, otherwise
you are done.

I have an example you can look at if you need some actual code to
understand the algorithm. The code is not pretty I know (and could be made
more efficient), but I think it is readable:

import java.util.*;

public class test extends Thread {

class Dummy extends Thread {
int count;
public Dummy (int count) {this.count = count;}
public void run () {
try {
sleep (1000);
System.err.prin tln (count+" doing som stuff");
sleep (1000);
System.err.prin tln (count+" ending...");
} catch (Exception e) {e.printStackTr ace (); }
}
}

public static void main (String[] args) throws Exception {
new test (new Integer (args[0]).intValue ());
}

int max_running = 3;
LinkedList processes, running;

public test (int size) throws Exception {
processes = new LinkedList ();
for (int i = 0; i < size; i++) {
processes.add (new Dummy (i));
}
run ();
}

public void run () {
running = new LinkedList ();
while (processes.size () > 0 || running.size () > 0) {
System.err.prin tln ("Start of loop...");
// start threads if possible
int new_threads = max_running - running.size ();
for (int i = 0; i < new_threads && processes.size () >0; i++) {
Thread t = (Thread) processes.getFi rst ();
t.start ();
running.add (t);
processes.remov e (t);
}
// wait some time
try {sleep (50);}
catch (Exception e) {e.printStackTr ace ();}

// remove dead threads
Object[] threads = running.toArray ();
for (int i = 0; i < threads.length; i++) {
Thread t = (Thread) threads[i];
if (! t.isAlive ()) running.remove (t);
}
System.err.prin tln ("End of loop...");
}
}
}

If you want to run this put it in a file test.java and start it with java
<number of processes>. A more effecient implementation would be making the
threads use a callback for when they have died. That is a push algorithm
instead, making the processes tell when they are finished thereby you wont
have to test if a thread has died again and again. But I will leave that
to you to implement that - it is not hard.

Best Regards
Kristian

Help needed with logging API and threads

Help needed with logging API and threads

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