im just experimenting with multithreading where im filling an array with random numbers and comparing how long it takes with two threads and one thread. thing is that the time for the first thread is much longer than the second.
code:
class createList extends Thread
{
int[] array = new int[25000000];
public void run() {
for (int i = 0; i < 25000000; i++)
{
array[i] = randomNumber();
}
}
public static int randomNumber()
{
Random random = new Random();
return random.nextInt(50);
}
}
public class Main {
public static void main(String[] args) {
createList listcreator1 = new createList();
createList listcreator2 = new createList();
listcreator1.start();
listcreator2.start();
Stopwatch sw = new Stopwatch();
listcreator1.run();
System.out.println(sw.elapsedTime());
Stopwatch sw3 = new Stopwatch();
listcreator2.run();
System.out.println(sw3.elapsedTime());
Stopwatch sw2 = new Stopwatch();
int[] array = new int[50000000];
for (int i = 0; i < 50000000; i++)
{
array[i] = randomNumber();
}
System.out.println(sw2.elapsedTime());
}
public static int randomNumber()
{
Random random = new Random();
return random.nextInt(50);
}
}
and the console output is
5.024,
0.945,
1.889
what is the reason for the large difference?
Actually on the first measurement you have calculation run 3 times. You have started 2 threads in the background (by using 'start' method) and 1 on current thread (by method 'run'). Run doesn't create new thread. Just execute operation on current on, it's simple method execution.
Other measurements execute without any jobs in the background so that's way they finish faster.
Related
Today I was trying to learn about memory management in the JVM and I came across the following question: can I mutate a local variable from two threads spawned within the same function?
In Java, if you try something like this the code will not compile, yielding an error with message "local variables referenced from an inner class must be final or effectively final"
public class MyClass {
static void f() throws Exception {
int x = 0;
Thread t1 = new Thread(new Runnable() {
public void run() {
for(int i = 0; i < 1000; i++) {
x = x + 1;
}
}
});
Thread t2 = new Thread(new Runnable() {
public void run() {
for(int i = 0; i < 1000; i++) {
x = x - 1;
}
}
});
t1.start();
t2.start();
t1.join();
t2.join();
System.out.println(x);
}
public static void main(String args[]) throws Exception {
for(int i = 0; i < 20; i++) {
f();
}
}
}
However the equivalent code in Scala does compile and run without problem (despite maybe race conditions):
def f(): Unit = {
var x = 0
val t1 = new Thread(new Runnable {
override def run(): Unit =
(1 to 1000).foreach(_ => {x = x + 1})
})
t1.start()
val t2 = new Thread(new Runnable {
override def run(): Unit =
(1 to 1000).foreach(_ => {x = x - 1})
})
t2.start()
t1.join()
t2.join()
println(x)
}
(1 to 20).foreach(_ => f())
Why is the behavior different in each case?
In Scala lambdas, and by extension anonymous classes, can capture local variables. The scala.runtime package contains some extra classes for that purpose. They effectively lift the local variable into an instance variable of another class whose instances can be shared: https://github.com/scala/scala/blob/v2.13.3/src/library/scala/runtime/ObjectRef.java
Suppose I have a List which have 2000 values, i want to divide the list of values and and passing to the method concurrently, SO I can increase my performance.
I applied bellow multi thread concept but its also taking 10 Minutes
Thread t = new Thread(new Runnable() {
public void run() {
for (int i = 1; i < visitList.size()/2; i = i + 2) {
auditedT1 += accuracyDao.SumOfChartsAudited(visitList.get(i));
}
}
});
Thread t1 = new Thread(new Runnable() {
public void run() {
for (int i = 0; i < visitList.size()/2; i = i + 2) {
auditedT2 += accuracyDao.SumOfChartsAudited(visitList.get(i));
}
}
});
Thread t3 = new Thread(new Runnable() {
public void run() {
for (int i = visitList.size()/2; i < visitList.size(); i = i + 2) {
auditedT3 += accuracyDao.SumOfChartsAudited(visitList.get(i));
}
}
});
Thread t4 = new Thread(new Runnable() {
public void run() {
for (int i = visitList.size()/2+1; i < visitList.size(); i = i + 2) {
auditedT4 += accuracyDao.SumOfChartsAudited(visitList.get(i));
}
}
});
t.start();
t1.start();
t3.start();
t4.start();
t.join();
t1.join();
t3.join();
t4.join();
To answer your main question, check out java parallel streams. It's only one way to do this but it's fairly straightforward. You can use a map operation to perform the database calls, then a collect to sum them all together.
https://docs.oracle.com/javase/tutorial/collections/streams/parallelism.html
There is no guarantee that this will improve performance though. You may have to profile and see where the performance issue really lies. It could be in your database, network, or somewhere else. (assuming you're using a database since there's DAO in your method names)
using System;
namespace rummykhan
{
class Program
{
static void Main(string[] args)
{
for (int i = 0; i < 100; i++)
{
Test t1 = new Test();
}
}
}
class Test
{
public int first;
public int second;
}
}
im trying to make 100 objects but i wish these objects are named automatically using some random string. im unable to figure out.. thanx for help in advance..
EDIT
Looking at my own question after a year, actually i was looking for a way by which i was able to create object by my own chosen name. e.g.
string tmp = "obj1";
var tmp = new Foo();
i was thinking that someway obj1 value may kick in and i could call my variable using obj1, which is totally moronic.
Just store the objects in a List.
example:
List<Test> tests = new List<Test>();
for (int i = 0; i < 100; i++)
{
tests.Add(new Test());
}
Currently your code will destroy t1 after each iteration of the loop. you could do something like this to preserve 100 coppies of test in memory
using System;
namespace rummykhan
{
class Program
{
static void Main(string[] args)
{
List<Test> lstClasses = new List<Test>();
for (int i = 0; i < 100; i++)
{
lstClasses.Add(new Test());
}
}
}
class Test
{
public int first;
public int second;
}
}
write like this.
Test[] dynamic = new Test[100];
for (int i=0; i< 100; i++)
{
dynamic[i] = new Test();
}
I use Task Parallel Library to start some tasks, like so:
public static void Main()
{
for (var i = 0; i < 10; i++)
{
var x = i;
Task.Factory.StartNew(() => new WorkerClass(x).Do());
}
// (*) Here I'd like to wait for all tasks to finish
Task.WaitAll();
Console.WriteLine("Ready.");
Console.ReadLine();
}
The problem is that some tasks can create new tasks themselves. This is how WorkerClass looks like:
public class WorkerClass
{
private static readonly NLog.Logger Log = NLog.LogManager.GetCurrentClassLogger();
private readonly int _i;
public WorkerClass(int i)
{
_i = i;
}
public void Do()
{
if (_i % 3 == 0)
Task.Factory.StartNew(() => new WorkerClass(_i + 101).Do());
Log.Info("Started {0}", _i);
Thread.Sleep(2000);
Log.Info("Done {0}", _i);
}
}
For every value of i that's a multiple of 3, a new Task is started.
I'd like to be able to wait until all tasks (including the ones created by other tasks) are finished.
Is there a clean/built-in way to do this (with or without TPL)?
Keep a reference to all top-level tasks and then just use WaitAll:
var tasks = new Task[10];
for (var i = 0; i < 10; i++)
{
var x = i;
tasks[i] = Task.Factory.StartNew(() => new WorkerClass(x).Do());
}
Task.WaitAll( tasks );
As for the child tasks, just make sure you attach them to the parent task. This means that the parent task will not go into a complete state until all child tasks are also finished.
Task.Factory.StartNew(() => { }, TaskCreationOptions.AttachedToParent);
I have been given the task of running two threads one using extends and one using implements runnable, the output is meant to be similair to this
F(0)
F(1)
F(2)
.........
S(0)
S(1)
S(2)
So far im getting
F(0)
S(1)
F(1)
F(2)
S(2)
public class Fast implements Runnable
{
/** Creates a new instance of Fast */
public void run()
{
for(int i = 0; i <= 9; i++)
{
try
{
System.out.println("F("+ i + ")");
Thread.sleep(200);
}
catch(InterruptedException e)
{
String errMessage = e.getMessage();
System.out.println("Error" + errMessage);
}
}
}
}
and
public class Slow extends Thread
{
/** Creates a new instance of Slow */
public void run()
{
for(int i = 0; i <= 6; i++)
{
try
{
System.out.println("S("+ i + ")");
Thread.sleep(400);
}
catch(InterruptedException e)
{
String errMessage = e.getMessage();
System.out.println("Error" + errMessage);
}
}
}
}
With the main
public class Main
{
public static void main(String args[])
{
Fast f = new Fast();
Slow s = new Slow();
Thread ft = new Thread(f);
ft.start();
s.start();
}
}
It seems like you want to get Slow to run after Fast? Your output is pretty much what i would expect. Eventually F will finish faster (just 2000ms) and S will still be running (2800ms). I'm not what this assignment has got to do with implementing Runnable or extending Thread since they give you the same end-result.
If you want F to finish completely before S you need to join on F first, like this:
Fast f = new Fast();
Slow s = new Slow();
Thread ft = new Thread(f);
ft.start();
ft.join();
s.start();
That will wait for ft to complete before even starting S giving you the desired output F1, F2,... S1,S2,...