2024-06-14 21:51:11

Affected files:
src/content/blog/implementing-a-worker-thread-pool-in-c.md

src/content/blog/implementing-a-worker-thread-pool-in-c.md

@@ -188,3 +188,81 @@ void *startThread() {
 그런데, 한 스레드가 critical section(임계 영역)에 들어가 걸어 잠그게 되면, 딴 스레드는 계속 손가락만 빨고 있지만 않습니다.  
 `while(true)`에 의해 계속 mutex lock을 얻고, 본인도 임계 영역에 들어가서 걸어 잠글 수 있는지 수시로 확인합니다.  
 그래서 `htop`으로 각 core를 모니터링했을 때, 모든 코어가 바쁘게 돌아가고 있었던 것입니다.😮
+
+## Condition Variable 도입!
+
+```c
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#define NUM_THREADS 4
+typedef struct task {
+  int a, b;
+} Task;
+
+Task taskQueue[256];
+pthread_mutex_t lockForQueue = PTHREAD_MUTEX_INITIALIZER;
+pthread_cond_t condForQueue = PTHREAD_COND_INITIALIZER;
+int taskCount = 0;
+
+void enqueueTask(Task task);
+void executeTask(Task *task);
+
+void *startThread();
+
+int main() {
+  pthread_t threads[NUM_THREADS];
+  for (int i = 0; i < NUM_THREADS; i++) {
+    if (pthread_create(&threads[i], NULL, startThread, NULL) != 0) {
+      perror("pthread_create");
+    }
+  }
+  srand(time(NULL));
+  for (int i = 0; i < 100; i++) {
+    Task task = {
+        .a = rand() % 100,
+        .b = rand() % 100,
+    };
+    enqueueTask(task);
+  }
+
+  for (int i = 0; i < NUM_THREADS; i++) {
+    if (pthread_join(threads[i], NULL) != 0) {
+      perror("pthread_join");
+    }
+  }
+  pthread_mutex_destroy(&lockForQueue);
+  pthread_cond_destroy(&condForQueue);
+  return 0;
+}
+void enqueueTask(Task task) {
+  pthread_mutex_lock(&lockForQueue);
+  taskQueue[taskCount++] = task;
+  pthread_mutex_unlock(&lockForQueue);
+  pthread_cond_signal(&condForQueue);
+}
+void executeTask(Task *task) {
+  int res = task->a + task->b;
+  printf("the sum of %d and %d is %d\n", task->a, task->b, res);
+}
+
+void *startThread() {
+  while (true) {
+    Task task;
+    pthread_mutex_lock(&lockForQueue);
+    while (taskCount == 0) {
+      pthread_cond_wait(&condForQueue, &lockForQueue);
+    }
+
+    task = taskQueue[0];
+    for (int i = 0; i < taskCount - 1; i++) {
+      taskQueue[i] = taskQueue[i + 1];
+    }
+    taskCount--;
+
+    pthread_mutex_unlock(&lockForQueue);
+    executeTask(&task);
+  }
+}
+```