POSIX Threads (`pthread`) – Advanced

On Unix‑like systems the POSIX thread library (pthread) provides a richer API.

Key components:

• Thread creation – pthread_create(&tid, NULL, func, arg);
• Joining – pthread_join(tid, NULL);
• Mutexes – pthread_mutex_t, init with pthread_mutex_init.
• Condition variables – pthread_cond_t for signalling.
• Read‑write locks – pthread_rwlock_t.
• Thread attributes – stack size, detach state.

---

📚 Example: Producer‑Consumer with Condition Variable

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

#define BUF_SIZE 5
int buffer[BUF_SIZE];
int count = 0; // items in buffer
pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t not_full = PTHREAD_COND_INITIALIZER;
pthread_cond_t not_empty = PTHREAD_COND_INITIALIZER;

void *producer(void *arg) {
    for (int i = 0; i < 20; ++i) {
        pthread_mutex_lock(&mtx);
        while (count == BUF_SIZE) pthread_cond_wait(&not_full, &mtx);
        buffer[count++] = i;
        printf("produced %d (count=%d)\n", i, count);
        pthread_cond_signal(&not_empty);
        pthread_mutex_unlock(&mtx);
        usleep(100000);
    }
    return NULL;
}

void *consumer(void *arg) {
    for (int i = 0; i < 20; ++i) {
        pthread_mutex_lock(&mtx);
        while (count == 0) pthread_cond_wait(&not_empty, &mtx);
        int val = buffer[--count];
        printf("consumed %d (count=%d)\n", val, count);
        pthread_cond_signal(&not_full);
        pthread_mutex_unlock(&mtx);
        usleep(150000);
    }
    return NULL;
}

int main(void) {
    pthread_t prod, cons;
    pthread_create(&prod, NULL, producer, NULL);
    pthread_create(&cons, NULL, consumer, NULL);
    pthread_join(prod, NULL);
    pthread_join(cons, NULL);
    return 0;
}