CSS 503 - Lab Work 2: Thread Synchronization

CSS 503
Lab Work 2: Thread Synchronization
Professor: Munehiro Fukuda
Lab work date: See the syllabus

1. Purpose

This laboratory work intends to familiarize you with pthread synchronization. You will code a program that suspends and resumes one after another thread.

2. System Calls

You will use the following pthread functions. Check the specification of each function using man.

pthread_create: creates a child thread that starts from a given function.
pthread_join: suspends the calling thread until one of its childrent gets terminated.
pthread_mutex_lock: enters a critical section.
pthread_cond_wait: waits on a given condition variable.
pthread_cond_signal: signals one of the threads waiting on a given condition variable.
pthread_mutex_unlock: leavs a critical section.

3. Statement of Work

The following code is a template for allocating a given number of condition variables and thereafter launching a given number of child threads, each thread i waiting on the corresponding condition variable cond[i] and signaled by the thread i - 1, which results in suspending and resuming one after another thread 10 times.

   #include <iostream> // cout                                                                         

   using namespace std;

   int nThreads;            // #threads
   int turn;                // turn points which thread should run
   pthread_mutex_t mutex;   // a lock for this critical section
   pthread_cond_t *cond;    // array of condition variable[nThreads]

   void *thread_func( void *arg ) {
     int id = ((int *)arg)[0];                  // this thread's identifier
     delete (int *)arg;

     for ( int loop = 0; loop < 10; loop++ ) {  // repeat 10 times
       // enter the critical section

       while ( turn != id ) {
         // wait until the (id - 1)th thread signals me.
       }
       cout << "thread["<< id << "] got " << loop << "th turn" << endl;
       // singal the next thread
       // leave the critical section
     }
   }

   int main( int argc, char *argv[] ) {
     // validate arguments
     if ( argc != 2 ) {
       cerr << "usage: lab2 #threads" << endl;
       return -1;
     }
     nThreads = atoi( argv[1] );
     if ( nThreads < 1 ) {
       cerr << "usage: lab1 #threads" << endl;
       cerr << "where #threads >= 1" << endl;
       return -1;
     }

     pthread_t *tid = new pthread_t[nThreads];  // an array of thread identifiers
     cond = new pthread_cond_t[nThreads];       // an array of condition variables
     turn = 0;                                  // turn points which thread should run

     for ( int i = 0; i < nThreads; i++ ) {     // start a give number (nThreads) of threads.
       int *id = new int[1];
       id[0] = i;
       pthread_create( &tid[0], NULL, thread_func, (void *)id );
     }

     for ( int i = 0; i < nThreads; i++ )       // wait for all the child threads.
       pthread_join( tid[0], NULL );
   }

The following is an execution output when running the program with 4 child threads.

   [css503@uw1-320-18 lab2]$ ./lab2 4
   thread[0] got 0th turn
   thread[1] got 0th turn
   thread[2] got 0th turn
   thread[3] got 0th turn
   ...
   thread[0] got 8th turn
   thread[1] got 8th turn
   thread[2] got 8th turn
   thread[3] got 8th turn
   thread[0] got 9th turn
   thread[1] got 9th turn
   thread[2] got 9th turn
   thread[3] got 9th turn
   [css503@uw1-320-18 lab2]$

Complete the thread_func() function so that the program runs as specified above. To compile your program, you need to type:

   g++ lab2.cpp -lpthread -o lab2

4. What to Turn in

Turn in the following materials at the end of class:

Your lab2.cpp
Your execution output

If your time runs out, you may submit it together with programming assignment 2.