스레드 프로그래밍

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

void *thread_func(void *arg) {
    int id = *(int *)arg;
    printf("Thread %d running (tid=%lu)\n", id, (unsigned long)pthread_self());
    return NULL;
}

int main() {
    pthread_t threads[3];
    int ids[3] = {1, 2, 3};

    for (int i = 0; i < 3; i++) {
        int ret = pthread_create(&threads[i], NULL, thread_func, &ids[i]);
        if (ret != 0) {
            fprintf(stderr, "pthread_create failed: %d\n", ret);
            exit(1);
        }
    }

    for (int i = 0; i < 3; i++) {
        pthread_join(threads[i], NULL);
    }

    printf("All threads done\n");
    return 0;
}

gcc -o thread_basic pthread_basic.c -pthread

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

void *compute(void *arg) {
    int input = *(int *)arg;
    int *result = malloc(sizeof(int));
    *result = input * input;
    return result;  /* 힙에 할당한 결과를 반환 */
}

int main() {
    pthread_t tid;
    int input = 7;
    void *retval;

    pthread_create(&tid, NULL, compute, &input);
    pthread_join(tid, &retval);

    int *result = (int *)retval;
    printf("7^2 = %d\n", *result);  /* 49 */

    free(result);  /* 스레드가 할당한 메모리를 해제 */
    return 0;
}

/* 이렇게 하면 안 됩니다 */
for (int i = 0; i < 3; i++) {
    pthread_create(&threads[i], NULL, thread_func, &i);
    /* 모든 스레드가 같은 &i를 공유!
       i가 변경되면 스레드가 잘못된 값을 읽을 수 있음 */
}

pthread_t tid;
pthread_create(&tid, NULL, background_task, NULL);
pthread_detach(tid);
/* 이후 join 불가, 스레드 종료 시 자동 자원 회수 */

import threading
import time

def worker(name, delay):
    tid = threading.current_thread().ident
    print(f"Thread {name} starting (tid={tid})")
    time.sleep(delay)
    print(f"Thread {name} done")

threads = []
for i in range(3):
    t = threading.Thread(target=worker, args=(i, 1))
    threads.append(t)
    t.start()

for t in threads:
    t.join()

print("All threads done")

import threading
import time

def cpu_bound(n):
    """CPU 연산 집약적 작업"""
    total = 0
    for i in range(n):
        total += i * i
    return total

def io_bound(seconds):
    """I/O 대기 작업"""
    time.sleep(seconds)

# CPU 바운드: 싱글 스레드
start = time.time()
cpu_bound(10_000_000)
cpu_bound(10_000_000)
print(f"CPU 바운드 순차: {time.time() - start:.2f}s")

# CPU 바운드: 멀티 스레드
start = time.time()
t1 = threading.Thread(target=cpu_bound, args=(10_000_000,))
t2 = threading.Thread(target=cpu_bound, args=(10_000_000,))
t1.start(); t2.start()
t1.join(); t2.join()
print(f"CPU 바운드 2스레드: {time.time() - start:.2f}s")

# I/O 바운드: 싱글 스레드
start = time.time()
io_bound(1); io_bound(1)
print(f"I/O 바운드 순차: {time.time() - start:.2f}s")

# I/O 바운드: 멀티 스레드
start = time.time()
t1 = threading.Thread(target=io_bound, args=(1,))
t2 = threading.Thread(target=io_bound, args=(1,))
t1.start(); t2.start()
t1.join(); t2.join()
print(f"I/O 바운드 2스레드: {time.time() - start:.2f}s")

from multiprocessing import Pool

def cpu_bound(n):
    total = 0
    for i in range(n):
        total += i * i
    return total

with Pool(processes=4) as pool:
    results = pool.map(cpu_bound, [10_000_000] * 4)
    print(sum(results))

import threading
import time

def background_monitor():
    while True:
        print("모니터링 중...")
        time.sleep(2)

t = threading.Thread(target=background_monitor, daemon=True)
t.start()

time.sleep(5)
print("메인 종료")
# 메인이 끝나면 데몬 스레드도 자동 종료

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

#define POOL_SIZE 4
#define QUEUE_SIZE 16

typedef struct {
    void (*function)(void *);
    void *arg;
} task_t;

typedef struct {
    task_t queue[QUEUE_SIZE];
    int head, tail, count;
    pthread_mutex_t lock;
    pthread_cond_t not_empty;
    pthread_cond_t not_full;
    int shutdown;
    pthread_t workers[POOL_SIZE];
} thread_pool_t;

void *worker_thread(void *arg) {
    thread_pool_t *pool = (thread_pool_t *)arg;

    while (1) {
        pthread_mutex_lock(&pool->lock);

        while (pool->count == 0 && !pool->shutdown) {
            pthread_cond_wait(&pool->not_empty, &pool->lock);
        }
        if (pool->shutdown) {
            pthread_mutex_unlock(&pool->lock);
            break;
        }

        task_t task = pool->queue[pool->head];
        pool->head = (pool->head + 1) % QUEUE_SIZE;
        pool->count--;
        pthread_cond_signal(&pool->not_full);
        pthread_mutex_unlock(&pool->lock);

        task.function(task.arg);  /* 작업 실행 */
    }
    return NULL;
}

import threading

counter = 0

def increment():
    global counter
    for _ in range(1_000_000):
        counter += 1  # 이 한 줄이 원자적이지 않음

t1 = threading.Thread(target=increment)
t2 = threading.Thread(target=increment)
t1.start(); t2.start()
t1.join(); t2.join()

print(f"기대값: 2000000, 실제값: {counter}")

import threading

counter = 0
lock = threading.Lock()

def increment():
    global counter
    for _ in range(1_000_000):
        with lock:
            counter += 1

t1 = threading.Thread(target=increment)
t2 = threading.Thread(target=increment)
t1.start(); t2.start()
t1.join(); t2.join()

print(f"기대값: 2000000, 실제값: {counter}")
# 항상 2000000