CS 170 project 3 example code.

buffer.cpp

#include <iostream>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>

#include <queue>


#define BUFFER_SIZE 4
static std::queue<int> buffer; 

static sem_t full;
static sem_t empty;
static sem_t mutex_sem; //using as a mutex

void* producer(void*);
void* consumer(void*);


void print_queue(std::queue<int> q)
{
    while (!q.empty())
        {
            printf("%i ",  q.front());
            q.pop();
        }

    printf("\n");
}


int main(void){
    pthread_t tid1; pthread_t tid2;
    
    sem_init(&mutex_sem, 0, 1);
    sem_init(&full, 0, 0);
    sem_init(&empty, 0, BUFFER_SIZE);

    pthread_create(&tid1, NULL, &consumer, NULL);
    pthread_create(&tid2, NULL, &producer, NULL);


    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    sem_destroy(&mutex_sem);
    sem_destroy(&full);
    sem_destroy(&empty);
}


void* producer(void* arg){

    int produced_item = 0;

    for(int i = 0; i < 10; i++){

        usleep(rand() %300); // produce the item;
        produced_item = rand() %100;
        
        sem_wait(&empty);
        sem_wait(&mutex_sem);

        buffer.push(produced_item);
        printf("pushed new item: buffer is now: ");
        print_queue(buffer);
                
        sem_post(&mutex_sem);
        sem_post(&full);
    }
}


void* consumer(void* arg){

    int consumed_item = 0;
    
    for(int i = 0; i < 10; i++){
        sem_wait(&full);
        sem_wait(&mutex_sem);

        consumed_item = buffer.front();
        buffer.pop();
        printf("popped new item: buffer is now: ");
        print_queue(buffer);
        
        sem_post(&mutex_sem);
        sem_post(&empty);

        usleep(rand() %500); //consume the item
    }
}

join.c

#include <pthread.h>
#include <stdio.h>

void* _thread_join1(void* arg){
    for(int i = 0 ; i < 3; i++){
        printf("In thread 1\n");
    }
    *(int*)arg = 1; 
    return (void*)arg;
}


void* _thread_join2(void* arg){
    for(int i = 0 ; i < 3; i++){
        printf("In thread 2\n");
    }
    *(int*)arg = 2; 
    pthread_exit((void*)arg);
}


int main(void){
    pthread_t tid1 = 0; pthread_t tid2 = 0;
    int a1; int a2;

    int* pa1 = &a1;
    int* pa2 = &a2;
    
    printf("main thread: creating thread 1\n");
    pthread_create(&tid1, NULL,  &_thread_join1, &a1);

    printf("main thread: joining\n");
    pthread_join(tid1, (void**)&pa1);
    printf("main thread: joined with thread 1, return value was %i\n", *pa1);


    printf("main thread: creating thread 2\n");
    pthread_create(&tid2, NULL,  &_thread_join2, &a1);
    
    printf("main thread: joining\n");
    pthread_join(tid2, (void**)&pa2);
    printf("main thread: joined with thread 2, return value was %i\n", *pa2);
}

lock.c

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>

void lock(void);
void unlock(void);

void* _thread_1(void* arg){
    lock();
    for(int i = 0 ; i < 3; i++){
        printf("In thread 1\n");
        sleep(1);
    }
    //unlock();
    while(1);
    return arg;
}
void* _thread_2(void* arg){
    lock();
    for(int i = 0 ; i < 3; i++){
        printf("In thread 2\n");
        sleep(1);
    }
    unlock();
    return arg;
}

int main(void){
    pthread_t tid1 = 0; pthread_t tid2 = 0;

    
    printf("main thread: creating thread 1\n");
    pthread_create(&tid1, NULL,  &_thread_1, NULL);
    pthread_create(&tid2, NULL,  &_thread_2, NULL);
    
    pthread_join(tid2, NULL);
    pthread_join(tid1, NULL);
}

sem.c

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <semaphore.h>

sem_t sem;

void* _thread_1(void* arg){

    printf("thread1 waiting on sem\n");
    sem_wait(&sem);
    
    for(int i = 0 ; i < 3; i++){
        printf("In thread 1\n");
        sleep(1);
    }
    return arg;
}
void* _thread_2(void* arg){

    printf("thread2 waiting on sem\n");
    sem_wait(&sem);
    for(int i = 0 ; i < 3; i++){
        printf("In thread 2\n");
        sleep(1);
    }
    return arg;
}

int main(void){
    pthread_t tid1 = 0; pthread_t tid2 = 0;
        
    sem_init(&sem, 0, 2);
    sem_wait(&sem); // waiting twice her is useless except as a sanity check
    sem_wait(&sem);
    
    printf("main thread: creating threads\n");
    pthread_create(&tid1, NULL,  &_thread_1, NULL);
    pthread_create(&tid2, NULL,  &_thread_2, NULL);
        
    sleep(1);

    printf("main thread: posting sems\n");
    sem_post(&sem);
    sem_post(&sem);
        
    pthread_join(tid2, NULL);
    pthread_join(tid1, NULL);

    sem_destroy(&sem);
}