Linux多线程──读者写者问题

// reader_writer.cpp
//////////////////////////////////////////////////////////////////////
// 读者写者问题
// 有一个写者很多读者，多个读者可以同时读文件，但写者在写文件时不允许有读者在读文件，
// 同样有读者读时写者也不能写。
//////////////////////////////////////////////////////////////////////

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

// 定义数据类
class data
{
public:
data(int i, float f):
I(i), F(f)
{}

int I;
float F;
};

// 读者写者读写的内容
data *p_data = NULL;

pthread_rwlock_t lock;

// 写者数目
const int WRITER_NUMBER = 2;

void *reader(void *arg);
void *writer(void *arg);

int main(int argc, char **argv)
{
pthread_t reader_tid;
pthread_t writer_tid[WRITER_NUMBER];

pthread_create(&reader_tid, NULL, reader, NULL);
for (int i = 0; i < WRITER_NUMBER; ++i)
{
pthread_create(&writer_tid[i], NULL, writer, (void *)i);
}

sleep(1);

return 0;
}

void *reader(void *arg)
{
int id = (int)arg;

pthread_detach(pthread_self());

while (true)
{
pthread_rwlock_rdlock(&lock);
printf("reader %d is reading the data; ", id);
if (p_data == NULL)
{
printf("the data is NULL\n");
}
else
{
printf("the data is (%d, %f)\n", p_data->I, p_data->F);
}
pthread_rwlock_unlock(&lock);
}
return (void *)0;
}

void *writer(void *arg)
{
pthread_detach(pthread_self());

while (true)
{
pthread_rwlock_wrlock(&lock);
printf("writer is writing the data; ");
if (p_data == NULL)
{
p_data = new data(1, 1.1f);
printf("writer create the data (%d, %f)\n", p_data->I, p_data->F);
}
else
{
delete p_data;
p_data = NULL;
printf("writer free the data\n");
}
pthread_rwlock_unlock(&lock);
}
return (void *)0;
}