Part 2: Pthread Mutex Observation (5 points) A file named pthread-data-sharing-m
ID: 3750951 • Letter: P
Question
Part 2: Pthread Mutex Observation (5 points)
A file named pthread-data-sharing-mutex-os-call.cpp
has been provided to you in the same project.
Compile the program and execute it several times, at least 10. Make sure to pay close attention to the output that the program produces.
#include <iostream>
#include <pthread.h>
#include <stdlib.h>
#define TOTAL_THREADS 4
int count;
pthread_mutex_t the_mutex; // phread mutex variable
void* myFunction(void* arg)
{
int actual_arg = *((int*) arg);
for(unsigned int i = 0; i < 10; ++i) {
// TODO:
// Use a Pthread mutex to control
// access to the critical region.
// Beginning of the critical region
count++;
std::cout << "Thread #" << actual_arg << " count = " << count << std::endl;
// Random wait - This code is just to ensure that the threads
// show data sharing problems
int max = rand() % 100000;
for (int x = 0; x < max; x++);
// End of random wait code
// End of the critical region
}
pthread_exit(NULL);
}
int main()
{
int rc[TOTAL_THREADS];
pthread_t ids[TOTAL_THREADS];
int args[TOTAL_THREADS];
// TODO: Initialize the pthread mutex here
count = 0;
for(unsigned int i = 0; i < TOTAL_THREADS; ++i) {
args[i] = i;
rc[i] = pthread_create(&ids[i], NULL, myFunction, (void*) &args[i]);
}
for(unsigned int i = 0; i < TOTAL_THREADS; ++i) {
pthread_join(ids[i], NULL);
}
std::cout << "Final count = " << count << std::endl;
pthread_exit(NULL);
}
Create a Word or Google Docs document.
In this document, answer the following questions about the program’s behavior:
What does it do?
What output does it produce?
Examine the program code carefully. Is the program functioning correctly?
If you do not think that the program is working correctly, describe why?
Include one screenshot of the program’s output. Your choice.
Part 3: Pthread Mutex Implementation (10 points)
Modify the pthread-data-sharing-mutex-os-call.cpp program to apply a Pthread mutex solution, i.e., you will use Linux system calls to control access to the critical region.
Refer to the prep materials for background info (section 2.3.6 in the textbook) and also to the Linux manual for the names and parameters of the functions. See https://linux.die.net/man/3/pthread_mutex_init
The necessary changes will be very small, i.e., not a lot of code is needed.
Explanation / Answer
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
pthread_mutex_t count_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t condition_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condition_cond = PTHREAD_COND_INITIALIZER;
void *funcCnt1();
void *funcCnt2();
int count = 0;
#define COUNT_DONE 20
#define COUNT_HALT1 6
#define COUNT_HALT2 12
int main()
{
pthread_t thread1, thread2;
pthread_create( &thread1, NULL, &funcCnt1, NULL);
pthread_create( &thread2, NULL, &funcCnt2, NULL);
pthread_join( thread1, NULL);
pthread_join( thread2, NULL);
exit(0);
}
void *funcCnt1()
{
for(;;)
{
pthread_mutex_lock( &condition_mutex );
while( count >= COUNT_HALT1 && count <= COUNT_HALT2 )
{
pthread_cond_wait( &condition_cond, &condition_mutex );
}
pthread_mutex_unlock( &condition_mutex );
pthread_mutex_lock( &count_mutex );
count++;
printf("Counter value funcCnt1: %d ",count);
pthread_mutex_unlock( &count_mutex );
if(count >= COUNT_DONE) return(NULL);
}
}
void *funcCnt2()
{
for(;;)
{
pthread_mutex_lock( &condition_mutex );
if( count < COUNT_HALT1 || count > COUNT_HALT2 )
{
pthread_cond_signal( &condition_cond );
}
pthread_mutex_unlock( &condition_mutex );
pthread_mutex_lock( &count_mutex );
count++;
printf("Thread count: %d ",count);
pthread_mutex_unlock( &count_mutex );
if(count >= COUNT_DONE) return(NULL);
}
}
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