Provide to programming example of multithreading that improve performance over a single threaded solutions?

Answer 1

Any kind of sequential program is not a good candidate to be threaded. An example

of this is a program that calculates an individual tax return. (2) Another example is a

"shell" program such as the C-shell or Korn shell. Such a program must closely

monitor its own working space such as open files, environment variables, and

current working directory.

Answer 2

Threading is a facility to allow multiple activities to coexist within a single process. Most modern operating systems support threads, and the concept of threads has been around in various forms for many years. Java is the first mainstream programming language to explicitly include threading within the language itself, rather than treating threading as a facility of the underlying operating system.

Threads are sometimes referred to as light weight processes. Like processes, threads are independent, concurrent paths of execution through a program, and each thread has its own stack, its own program counter, and its own local variables. However, threads within a process are less insulated from each other than separate processes are. They share memory, file handles, and other per-process

state.

A process can support multiple threads, which appear to execute simultaneously and asynchronously to each other. Multiple threads within a process share the same memory address space, which means they have access to the same variables and objects, and they allocate objects from the same heap. While this makes it easy for threads to share information with each other, you must take care to ensure that they do not interfere with other

threads in the same process.

The following example uses two threads, one for timing and one to do actual work. The main thread calculates prime numbers using a very straightforward algorithm. Before it starts, it creates and starts a timer thread, which will sleep for ten seconds, and then set a flag that the main thread will check. After ten seconds, the main thread will stop. Note that the shared flag is declared "volatile".

.

/**

* CalculatePrimes -- calculate as many primes as we can in ten seconds

*/

public class CalculatePrimes extends Thread {

public static final int MAX_PRIMES = 1000000;

public static final int TEN_SECONDS = 10000;

public volatile boolean finished = false;

public void run() {

int[] primes = new int[MAX_PRIMES];

int count = 0;

for (int i=2; count

// Check to see if the timer has expired

if (finished) {

break;

}

boolean prime = true;

for (int j=0; j

if (i % primes[j] == 0) {

prime = false;

break;

}

}

if (prime) {

primes[count++] = i;

System.out.println("Found prime: " + i);

}

}

}

public static void main(String[] args) {

CalculatePrimes calculator = new CalculatePrimes();

calculator.start();

try {

Thread.sleep(TEN_SECONDS);
}

catch (InterruptedException e) {

// fall through

}

calculator.finished = true;
}
}

Answer 3

A typical example would be to copy 2 big files, say 3 minutes each if doing back to back. (total of 6 minutes minimum)

By using 2 threads, those 2 files maybe copied in 3 minutes (plus a little bit overhead, in theory, just a fraction of a second)

(replace "copy 2 big files" by "downloading 2 MP3, or HD movies, or eBooks"...)

Answer 4

Multithreading means that within a program there are different processes (which are called threads) that run simultaneously. As an example, if you use Microsoft Word, there is a foreground process that processes everything you type - that is, while you type letters, the letters appear on the screen. On the other hand, there is a background process that does spell-checking. This is clearly a separate process (thread), and one that has a lower priority; if you type quickly, or paste a lot of text, it can take a while for spelling errors to be marked as such.

Answer 5

* More than one thread doing I/O on the same device (on an I/O bound task)

* More than one thread using the same data that must be locked

-emman