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#include
#include
#include
#include
#include
#define BUFFSIZE 1024 * 1024
#define min(x, y) ((x) < (y) ? (x) : (y))
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
struct cycle_buffer {
unsigned char *buf; /* store data */
unsigned int size; /* cycle buffer size */
unsigned int in; /* next write position in buffer */
unsigned int out; /* next read position in buffer */
pthread_mutex_t lock;
};
static struct cycle_buffer *fifo = NULL;
static int init_cycle_buffer(void)
{
int size = BUFFSIZE, ret;
ret = size & (size - 1); /* size must be power of 2 */
if (ret)
goto err;
fifo = (struct cycle_buffer *) malloc(sizeof(struct cycle_buffer));
if (!fifo)
return -1;
memset(fifo, '\0', sizeof(struct cycle_buffer));
fifo->size = size;
fifo->in = fifo->out = 0;
pthread_mutex_init(&fifo->lock, NULL);
fifo->buf = (unsigned char *) malloc(size);
if (!fifo->buf)
goto malloc_err;
memset(fifo->buf, '\0', size);
return 0;
malloc_err:
free(fifo);
err:
return ret;
}
unsigned int fifo_get(unsigned char *buf, unsigned int len)
{
unsigned int l;
len = min(len, fifo->in - fifo->out);
l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
memcpy(buf, fifo->buf + (fifo->out & (fifo->size - 1)), l);
memcpy(buf + l, fifo->buf, len - l);
fifo->out += len;
return len;
}
unsigned int fifo_put(unsigned char *buf, unsigned int len)
{
unsigned int l;
len = min(len, fifo->size - fifo->in + fifo->out);
l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
memcpy(fifo->buf + (fifo->in & (fifo->size - 1)), buf, l);
memcpy(fifo->buf, buf + l, len - l);
fifo->in += len;
return len;
}
static void * thread_read(void *arg)
{
char buf[1024];
unsigned int n;
pthread_detach(pthread_self());
for (;;) {
memset(buf, '\0', sizeof(buf));
pthread_mutex_lock(&fifo->lock);
n = fifo_get(buf, sizeof(buf));
pthread_mutex_unlock(&fifo->lock);
write(STDOUT_FILENO, buf, n);
}
return NULL;
}
static void * thread_write(void *arg)
{
unsigned char buf[] = "hello world";
pthread_detach(pthread_self());
for (;;) {
pthread_mutex_lock(&fifo->lock);
fifo_put(buf, strlen(buf));
pthread_mutex_unlock(&fifo->lock);
}
return NULL;
}
int main(void)
{
int ret;
pthread_t wtid, rtid;
ret = init_cycle_buffer();
if (ret == -1)
goto err;
pthread_create(&wtid, NULL, thread_write, NULL);
pthread_create(&rtid, NULL, thread_read, NULL);
pthread_exit(NULL);
err:
return ret;
} #include
#include
#include
#include
#define BUFFSIZE 1024 * 1024
#define min(x, y) ((x) < (y) ? (x) : (y))
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
struct cycle_buffer {
unsigned char *buf; /* store data */
unsigned int size; /* cycle buffer size */
unsigned int in; /* next write position in buffer */
unsigned int out; /* next read position in buffer */
pthread_mutex_t lock;
};
static struct cycle_buffer *fifo = NULL;
static int init_cycle_buffer(void)
{
int size = BUFFSIZE, ret;
ret = size & (size - 1); /* size must be power of 2 */
if (ret)
goto err;
fifo = (struct cycle_buffer *) malloc(sizeof(struct cycle_buffer));
if (!fifo)
return -1;
memset(fifo, '\0', sizeof(struct cycle_buffer));
fifo->size = size;
fifo->in = fifo->out = 0;
pthread_mutex_init(&fifo->lock, NULL);
fifo->buf = (unsigned char *) malloc(size);
if (!fifo->buf)
goto malloc_err;
memset(fifo->buf, '\0', size);
return 0;
malloc_err:
free(fifo);
err:
return ret;
}
unsigned int fifo_get(unsigned char *buf, unsigned int len)
{
unsigned int l;
len = min(len, fifo->in - fifo->out);
l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
memcpy(buf, fifo->buf + (fifo->out & (fifo->size - 1)), l);
memcpy(buf + l, fifo->buf, len - l);
fifo->out += len;
return len;
}
unsigned int fifo_put(unsigned char *buf, unsigned int len)
{
unsigned int l;
len = min(len, fifo->size - fifo->in + fifo->out);
l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
memcpy(fifo->buf + (fifo->in & (fifo->size - 1)), buf, l);
memcpy(fifo->buf, buf + l, len - l);
fifo->in += len;
return len;
}
static void * thread_read(void *arg)
{
char buf[1024];
unsigned int n;
pthread_detach(pthread_self());
for (;;) {
memset(buf, '\0', sizeof(buf));
pthread_mutex_lock(&fifo->lock);
n = fifo_get(buf, sizeof(buf));
pthread_mutex_unlock(&fifo->lock);
write(STDOUT_FILENO, buf, n);
}
return NULL;
}
static void * thread_write(void *arg)
{
unsigned char buf[] = "hello world";
pthread_detach(pthread_self());
for (;;) {
pthread_mutex_lock(&fifo->lock);
fifo_put(buf, strlen(buf));
pthread_mutex_unlock(&fifo->lock);
}
return NULL;
}
int main(void)
{
int ret;
pthread_t wtid, rtid;
ret = init_cycle_buffer();
if (ret == -1)
goto err;
pthread_create(&wtid, NULL, thread_write, NULL);
pthread_create(&rtid, NULL, thread_read, NULL);
pthread_exit(NULL);
err:
return ret;
}view plaincopy to clipboardprint?
buffer指向存放数据的缓冲区，size是缓冲区的大小，in是写指针下标，out是读指针下标,在len和(fifo->size - fifo->in + fifo->out)之间取一个较小的值赋给len。注意，当(fifo->in == fifo->out+fifo->size)时，表示缓冲区已满，此时得到的较小值一定是0，后面实际写入的字节数也全为0。另一种边界情况是当len很大时（因为len是无符号的，负数对它来说也是一个很大的正数），这一句也能保证len取到一个较小的值，因为fifo->in总是大于等于fifo->out，所以后面的那个表达式的值不会超过fifo->size的大小把上一步决定的要写入的字节数len“切开”，这里又使用了一个技巧。注意：实际分配给fifo->buffer的字节数fifo->size，必须是2的幂，否则这里就会出错。既然fifo->size是2的幂，那么(fifo->size-1)也就是一个后面几位全为1的数，也就能保证(fifo->in & (fifo->size - 1))总为不超过(fifo->size - 1)的那一部分，和(fifo->in)% (fifo->size - 1)的效果一样。
这样后面的代码就不难理解了，它先向fifo->in到缓冲区末端这一块写数据，如果还没写完，在从缓冲区头开始写入剩下的，从而实现了循环缓冲。最后，把写指针后移len个字节，并返回len。
buffer指向存放数据的缓冲区，size是缓冲区的大小，in是写指针下标，out是读指针下标,在len和(fifo->size - fifo->in + fifo->out)之间取一个较小的值赋给len。注意，当(fifo->in == fifo->out+fifo->size)时，表示缓冲区已满，此时得到的较小值一定是0，后面实际写入的字节数也全为0。另一种边界情况是当len很大时（因为len是无符号的，负数对它来说也是一个很大的正数），这一句也能保证len取到一个较小的值，因为fifo->in总是大于等于fifo->out，所以后面的那个表达式的值不会超过fifo->size的大小把上一步决定的要写入的字节数len“切开”，这里又使用了一个技巧。注意：实际分配给fifo->buffer的字节数fifo->size，必须是2的幂，否则这里就会出错。既然fifo->size是2的幂，那么(fifo->size-1)也就是一个后面几位全为1的数，也就能保证(fifo->in & (fifo->size - 1))总为不超过(fifo->size - 1)的那一部分，和(fifo->in)% (fifo->size - 1)的效果一样。
这样后面的代码就不难理解了，它先向fifo->in到缓冲区末端这一块写数据，如果还没写完，在从缓冲区头开始写入剩下的，从而实现了循环缓冲。最后，把写指针后移len个字节，并返回len。view plaincopy to clipboardprint?
从上面可以看出，fifo->in的值可以从0变化到超过fifo->size的数值，fifo->out也如此，但它们的差不会超过fifo->size
从上面可以看出，fifo->in的值可以从0变化到超过fifo->size的数值，fifo->out也如此，但它们的差不会超过fifo->size
