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

/*
条件变量的用途
    按现在的我理解（不一定对），我们可以把条件变量当成一种「信号」（不是那个「信号量」）来使用。
    对于一个「信号」，我们就有两种操作「等待」和「通知」（暂时忽略实现细节）
*/


struct _Condition;
typedef struct _Condition Condition;

Condition *
ConditionNew();

void
ConditionWait(Condition *condition);

void
ConditionNotify(Condition *condition);


struct _Condition {
    bool signaled;
    pthread_mutex_t mutex;
    pthread_cond_t cond;
};

Condition *
ConditionNew() {
    Condition *c = malloc(sizeof(Condition));
    c->signaled = false;
    pthread_mutex_init(&c->mutex, NULL);
    pthread_cond_init(&c->cond, NULL);
    return c;
}

void
ConditionWait(Condition *condition) {
    Condition *c = condition;
    pthread_mutex_lock(&c->mutex);
    while (!c->signaled) {
        pthread_cond_wait(&c->cond, &c->mutex);
    }
    c->signaled = false;
    pthread_mutex_unlock(&c->mutex);
}

void
ConditionNotify(Condition *condition) {
    Condition *c = condition;
    pthread_mutex_lock(&c->mutex);
    c->signaled = true;
    pthread_cond_signal(&c->cond);
    pthread_mutex_unlock(&c->mutex);
}

/*
下面是使用示例
*/

void *
Thread1(void *arg) {
    Condition *cond = arg;
    printf("thread1 waiting....\n");
    ConditionWait(cond);
    printf("thread1 end\n");
    return NULL;
}

void *
Thread2(void *arg) {
    Condition *cond = arg;
    printf("thread2 notify....\n");
    ConditionNotify(cond);
    printf("thread2 end\n");
    return NULL;
}

/*
这里 thread1 会等到 thread2 notify 之后才会结束
*/

int main(void) {
    Condition *cond = ConditionNew();
    pthread_t tid1;
    pthread_create(&tid1, NULL, Thread1, cond);
    pthread_t tid2;
    pthread_create(&tid2, NULL, Thread2, cond);
    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);
}