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

引用

Circular Queue

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ring buffer示例

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