Lab 3: PThreads Synchronization

1. Purpose




This lab intends to familiarize you with pthread synchronization. Your task is to code a program that suspends and resumes one thread after another.




2. System Calls




You will need to 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.












Statement of Work



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







#include
<stdio.h




#include
<pthread.h




#include
<stdlib.h




#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.




}










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cout << "thread["<< id << "] got " << loop << "th turn" << endl;




signal 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 nThreads number
of threads
int *id =
new int[1];









id[0] = i;




pthread_create( &tid[i], NULL, thread_func, (void *)id );




}



for ( int i = 0; i < nThreads; i++ )




pthread_join( tid[i], NULL );




}




// wait for all the child threads.






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




[css503@uw1-320-18 lab3]$ ./lab3 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 lab3]$













Complete thread_func() so that the program runs as specified above. To compile your program, use the following command:

g++ lab3.cpp -lpthread -o lab3




4. What to Turn in




Turn in the following materials at the end of class:




Source code file lab3.cpp



Your execution output (you can take a screenshot and copy-paste it on a document file)












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