pthread の例

Makefile

CC=gcc
CFLAGS=-Wall
LIBS=-lpthread
TARGETS=pthread-test

pthread-test: pthread-test.c
	$(CC) $(CFLAGS) -o $@ $< $(LIBS)

all: $(TARGETS)

clean:
	rm -f *.o $(TARGETS)

.PHONY: all clean

pthread-test.c

// マルチスレッドプログラムと mutex の使い方

#include <stdio.h>
#include <sys/timeb.h>
#include <pthread.h>

#define N 50

void* thread1(void* param);
void* thread2(void* param);

int count1 = 0;
int count2 = 0;

unsigned long time_to_print_count1;
unsigned long time_to_print_count2;

int terminating = 0;

pthread_mutex_t mutex;

int main(void) {
  struct timeb now;
  unsigned long now_msec;
  pthread_t tid1, tid2;

  puts("Enter を押すと終了します");

  pthread_mutex_init(&mutex, NULL);

  ftime(&now);
  now_msec = (unsigned long)now.time * 1000 + now.millitm;
  time_to_print_count1 = now_msec + 1000;
  time_to_print_count2 = time_to_print_count1 + 1000;

  pthread_create(&tid1, NULL, thread1, NULL);
  pthread_create(&tid2, NULL, thread2, NULL);

  getchar();
  terminating = 1;

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

  pthread_mutex_destroy(&mutex);

  return 0;
}

void* thread1(void* param) {
  struct timeb now;
  unsigned long now_msec;
  int i;

  while (!terminating) {
    ftime(&now);
    now_msec = (unsigned long)now.time * 1000 + now.millitm;

    if (now_msec >= time_to_print_count1) {
      // mutex 間は他のスレッドから変数を変更できない
      pthread_mutex_lock(&mutex);

      printf("count1: ");
      for (i = 0; i < N; ++i) {
        printf("%2d ", count1++);
      }
      putchar('\n');

      pthread_mutex_unlock(&mutex);

      time_to_print_count1 = now_msec + 2000;
    } else if (now_msec >= time_to_print_count2) {
      // mutex で変数を保護しないと他のスレッドから変数を変更できる
      printf("count2: ");
      for (i = 0; i < N; ++i) {
        printf("%2d ", count2++);
      }
      putchar('\n');

      time_to_print_count2 = now_msec + 2000;
    }
  }

  return NULL;
}

void* thread2(void* param) {
  while (!terminating) {
    // mutex で count1 を保護
    pthread_mutex_lock(&mutex);
    count1 = 0;
    pthread_mutex_unlock(&mutex);

    // count2 は保護せずに変更する
    count2 = 0;
  }

  return NULL;
}