概述

ring buffer,或者说循环队列，是嵌入式开发中的一个基本模型，常用于命令队列，资源循环分配场合。

示例

ring_buffer.h ring buffer 封装API
testringbuffer.c 测试ring buffer api.

//ring_buffer.h
#include <stdlib.h>

typedef struct s_ring_buffer{
	int tail;
	int head;
	int size;
	int item_size;
	void *buf;
} ring_buffer;

static ring_buffer* ring_buffer_create(int item_size, int size)
{
	size = size + 1;//alloc one more
	void* buf = malloc(item_size * size);
	if (NULL == buf)
		return buf;

	ring_buffer *p_ring_buf = (ring_buffer*)malloc(sizeof(ring_buffer)); 
	if (NULL == p_ring_buf)
		return p_ring_buf;

	p_ring_buf->head = 0; 
	p_ring_buf->tail = 0; 
	p_ring_buf->size = size;
	p_ring_buf->item_size = item_size;
	p_ring_buf->buf = buf;

	return p_ring_buf;
}
static void ring_buffer_free(ring_buffer *p_ring_buf)
{
	if (NULL != p_ring_buf->buf){
		free(p_ring_buf->buf);
		p_ring_buf->buf = NULL;
	
		free(p_ring_buf);
	}
}
static void* ring_buffer_get_tail(ring_buffer *p_ring_buf)
{
	void *item = NULL;
	int tail = p_ring_buf->tail;
	int size = p_ring_buf->size;
	int item_size = p_ring_buf->item_size;
	int n = (tail + 1) % size;
	if (n != p_ring_buf->head){
		item = p_ring_buf->buf + (item_size * tail);
		p_ring_buf->tail = n;
	}
	return item;
}
static void* ring_buffer_get_head(ring_buffer *p_ring_buf)
{
	if (p_ring_buf->head == p_ring_buf->tail)
		return NULL;
	
	int head = p_ring_buf->head;
	int size = p_ring_buf->size;
	int item_size = p_ring_buf->item_size;
	void *item = p_ring_buf->buf + (item_size * head);
	p_ring_buf->head = (head + 1) % size;
	return item;
}
static int ring_buffer_size(ring_buffer *p_ring_buf)
{
	int head = p_ring_buf->head;
	int tail = p_ring_buf->tail;
	int size = p_ring_buf->size;
	return (tail >= head) ? (size - 1 - tail + head) : (size - 1 - head + tail);
}
static int ring_buffer_capacity(ring_buffer *p_ring_buf)
{
	return p_ring_buf->size - 1;
}

//testringbuffer.c
#include "ring_buffer.h"
#include <stdio.h>

void test_get_tail(ring_buffer *ring_buf){
	void *item = ring_buffer_get_tail(ring_buf);
	printf("item %p\n", item);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));
	
	item = ring_buffer_get_tail(ring_buf);
	printf("item %p\n", item);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));

	item = ring_buffer_get_tail(ring_buf);
	printf("item %p\n", item);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));

}
void test_get_head(ring_buffer *ring_buf){
	void *item = ring_buffer_get_head(ring_buf);
	printf("item %p\n", item);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));
	
	item = ring_buffer_get_head(ring_buf);
	printf("item %p\n", item);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));

	item = ring_buffer_get_head(ring_buf);
	printf("item %p\n", item);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));

}

int main(){
	ring_buffer *ring_buf = ring_buffer_create(8, 2);
	printf("buffer size %d, capacity %d\n", ring_buffer_size(ring_buf), ring_buffer_capacity(ring_buf));

	test_get_tail(ring_buf);
	test_get_head(ring_buf);

	return 0;
}

测试结果

$ ./test.exe
buffer size 2, capacity 2
item 0x8000003c0
buffer size 1, capacity 2
item 0x8000003c8
buffer size 0, capacity 2
item 0x0
buffer size 0, capacity 2

item 0x8000003c0
buffer size 1, capacity 2
item 0x8000003c8
buffer size 2, capacity 2
item 0x0
buffer size 2, capacity 2