一个线程同步问题！

[PonyCheng2019]

我想在主线程中读取标准输入，将读取的数据保存在buff中，读完一行再通知writer线程打印buff里的内容，但是
我发现writer似乎没有执行啊，代码如下，希望有高人解答一下！

#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>

struct data
{
        pthread_mutex_t lock;
        pthread_cond_t  cond;
        char buff[BUFSIZ];
};

struct data shared_data;

void *writer(void *arg)
{
        while (1)
        {
                pthread_mutex_lock(&shared_data.lock);
                pthread_cond_wait(&shared_data.cond, &shared_data.lock);
                printf("writer: %s\n", shared_data.buff);
                pthread_mutex_unlock(&shared_data.lock);
        }
        return NULL;
}

int main(int argc, const char *argv[])
{
        pthread_t writer_tid;
        memset(shared_data.buff, 0, sizeof(shared_data.buff));
        pthread_mutex_init(&shared_data.lock, NULL);
        pthread_cond_init(&shared_data.cond, NULL);

        pthread_create(&writer_tid, NULL, writer, NULL);

        while (1)
        {
                pthread_mutex_lock(&shared_data.lock);
                printf("reader: ");
                if (fgets(shared_data.buff, BUFSIZ, stdin))
                {
                        pthread_cond_signal(&shared_data.cond);
                        pthread_mutex_unlock(&shared_data.lock);
                }
        }
        pthread_join(writer_tid, NULL);

        return 0;
}

[ipqtjmqj]

pthread_cond_wait是阻塞的，而且已经用了锁，外面再加个锁是多余的，把四句pthread_mutex_xxxx去掉就可以了