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semaphore.cpp
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semaphore.cpp
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/*
* Driver program of the semaphore class.
*
* This driver program implements a simple multiple producer/consumer model
*/
#include <iostream>
#include <thread>
#include <random>
#include <chrono>
#include "semaphore.h"
using namespace std;
#define BUF_LEN 16
#define MAX_PRODUCT_COUNT 32
#define NUM_PROD_THREADS 2
#define NUM_CONS_THREADS 4
minstd_rand0 rnd;
int start = 0;
int tail = 0;
int buffer[BUF_LEN] = { 0 };
atomic<int> n_prod(0);
atomic<int> n_cons(0);
atomic<int> prod_count(0);
/*
* Semaphore to ensure consumer will not read if the buffer is empty
*/
semaphore_interface *empty;
/*
* Semaphore to ensure producer will not producing if the buffer is full
*/
semaphore_interface *full;
/*
* Only one consumer can dequeue an item at a time.
*/
semaphore_interface *cs;
/*
* Only one producer can enqueue an item at a time.
*/
semaphore_interface *pd;
/*
* main thread wait to quit.
*/
semaphore_interface *quit;
void producer_func(int pid) {
n_prod++;
while (true) {
this_thread::sleep_for(chrono::seconds(1));
/*
* Only produce if there is empty slot to produce.
*/
empty->wait();
/*
* Only one producer to access the buffer for enqueuing at a time.
*/
pd->wait();
/*
* Reach the production limit, prepare to quit.
*/
if (prod_count >= MAX_PRODUCT_COUNT) {
/*
* Unblock other producer that's waiting.
*/
pd->post();
/*
* Notify the main thread can start quitting.
*/
quit->post();
n_prod--;
break;
}
buffer[tail] = rnd();
cout << "producer:(" << pid << ")" << buffer[tail] << "->" << tail << endl;
tail = (tail + 1) % BUF_LEN;
/*
* Other producer can proceed to access the buffer
*/
pd->post();
/*
* Consumer can start consuming the buffer.
*/
full->post();
}
}
void consumer_func(int cid) {
n_cons++;
while (true) {
int sleep = (rnd() % 3) + 1;
/*
* Sleep for random amount of seconds (1 ~ 3)
*/
this_thread::sleep_for(chrono::seconds(sleep));
/*
* Only consume if there is at least one item in the buffer.
*/
full->wait();
/*
* Only one consumer can access the buffer for dequeuing at a time.
*/
cs->wait();
if (prod_count >= MAX_PRODUCT_COUNT) {
/*
* Reach the production limit, prepare to quit.
*/
cs->post();
/*
* Notify the main thread can start quitting.
*/
quit->post();
n_cons--;
break;
}
cout << "consumer:(" << cid << ")" << start << "<-" << buffer[start] << endl;
start = (start + 1) % BUF_LEN;
/*
* Record the product count
*/
prod_count++;
/*
* Other consumer can proceed to access the buffer.
*/
cs->post();
/*
* Notify the producer that at least one slot is ready for producing.
*/
empty->post();
}
}
int main(int argc, char *argv[]) {
thread producers[NUM_PROD_THREADS];
thread consumers[NUM_CONS_THREADS];
full = new semaphore_lockfree(0);
empty = new semaphore_lockfree(BUF_LEN);
pd = new semaphore_lockfree(1);
cs = new semaphore_lockfree(1);
quit = new semaphore(0);
rnd.seed(chrono::system_clock::now().time_since_epoch().count());
for (int i = 0; i < NUM_PROD_THREADS; i++) {
producers[i] = thread(producer_func, i);
}
for (int i = 0; i < NUM_CONS_THREADS; i++) {
consumers[i] = thread(consumer_func, i);
}
quit->wait();
while (n_prod || n_cons) {
full->post();
empty->post();
}
for (int i = 0; i < NUM_PROD_THREADS; i++) {
producers[i].join();
}
for (int i = 0; i < NUM_CONS_THREADS; i++) {
consumers[i].join();
}
return 0;
}