about multi threading

Question

Question 1. You are given a paragraph  which contain n number of words you are given m threads. What you need to do is  each thread should print one word and give the control to next thread ... this way each thread will keep on printing one word  in case last thread come it iwill invoke the first thread ... procedure will repeat until all the words are printed in paragraph. Finally all the thread should exit gracefully. What kind of synchronization will use ? Question 2. How could you make sure that thread A B and C run sequentially without using join method? These question was asked in interview and found this site is too good for c# so hope to get answer as soon as possible. thank you in advance.

Vulpes · Answer

For question 1 the simplest solution is to use a lock with some additional code to make sure that the 'm' threads print the words in order. For example: using System; using System.Threading; class Program { static int m count next; static object padlock = new object(); static string[] words; static void Main() { string paragraph = The quick brown fox jumps over the lazy dog.; words = paragraph.Split(' '); m = 3; // number of threads say count = 0; // word counter next = 0; // thread counter for(int i = 0; i { Thread t = new Thread(Printer); t.Name = i.ToString(); t.Start(); } Console.ReadKey(); } static void Printer() { while(count } static void PrintWord() { // ensure that the threads print each word in order if (Thread.CurrentThread.Name != next.ToString()) return; lock(padlock) { if (count >= words.Length) return; // double check no more words left Console.Write({0}  words[count]); count++; next++; if (next == m) next = 0; // start at beginning again } } } You can check that the threads are printing the words in order by replacing this line: Console.Write({0}  words[count]); with this: Console.Write({0}{1}  words[count] Thread.CurrentThread.Name); The output should then be: The0 quick1 brown2 fox0 jumps1 over2 the0 lazy1 dog.2 The simplest solution for question 2 is to use a flag (isFinished say) which each thread can set to true when it's finished running. The main thread can wait until this flag is set before resetting it to false and starting the next thread. Here's an example: using System; using System.Threading; class Program { static bool isFinished; static void Main() { isFinished = false; Thread A = new Thread(MethodA); A.Start(); while (!isFinished); // wait until thread has finished Console.WriteLine(); isFinished = false; Thread B = new Thread(MethodB); B.Start(); while (!isFinished); Console.WriteLine(); isFinished = false; Thread C = new Thread(MethodC); C.Start(); while (!isFinished); Console.ReadKey(); } static void MethodA() { for (int i = 1; i isFinished = true; // signal main thread } static void MethodB() { for (int i = 1; i isFinished = true; } static void MethodC() { for (int i = 1; i isFinished = true; } } The output is: Iteration 1 in thread A Iteration 2 in thread A Iteration 3 in thread A Iteration 4 in thread A Iteration 5 in thread A Iteration 6 in thread A Iteration 7 in thread A Iteration 8 in thread A Iteration 9 in thread A Iteration 1 in thread B Iteration 2 in thread B Iteration 3 in thread B Iteration 4 in thread B Iteration 5 in thread B Iteration 6 in thread B Iteration 7 in thread B Iteration 8 in thread B Iteration 9 in thread B Iteration 1 in thread C Iteration 2 in thread C Iteration 3 in thread C Iteration 4 in thread C Iteration 5 in thread C Iteration 6 in thread C Iteration 7 in thread C Iteration 8 in thread C Iteration 9 in thread C

Trisha · Answer

thank you vuples your solution is simple and meaningful.