广东微信网站制作报价表,四大门户网站创始人,贵州公司网站建设,优化网站排名公司本期主题#xff1a; 讲解ARRAY_SIZE的作用以及定义#xff0c;还有一个踩坑分析 往期链接#xff1a;
数据结构系列——先进先出队列queue数据结构系列——栈 stackLinux内核链表零长度数组的使用inline的作用嵌入式C基础——ARRAY_SIZE使用以及踩坑分析 目录 1. Ringbuff…本期主题 讲解ARRAY_SIZE的作用以及定义还有一个踩坑分析 往期链接
数据结构系列——先进先出队列queue数据结构系列——栈 stackLinux内核链表零长度数组的使用inline的作用嵌入式C基础——ARRAY_SIZE使用以及踩坑分析 目录 1. Ringbuffer定义及特点2.ringbuffer实例rtos实例2.1 ringbuffer结构体2.2 ringbuffer获取当前长度2.3 ringbuffer put 3.根据rtos代码设计ringbuffer并测试 1. Ringbuffer定义及特点
Ringbuffer的定义 环形缓冲区Ring Buffer也称为循环缓冲区、环形队列Ring Queue或循环队列Circular Queue是一种用于在固定大小的存储区域中存储数据的数据结构。 环形缓冲区通常由一个固定大小的数组和两个指针组成分别用于指示缓冲区的起始位置和结束位置。数据被顺序地存储在数组中当到达数组的末尾时数据会“循环”回到数组的起始位置实现了环形的存储结构。
Ringbuffer的特点 环形缓冲区通常用于实现数据在生产者和消费者之间的高效传输特别是在多线程或多任务环境中。它具有以下特点和优势 高效性 环形缓冲区采用循环结构避免了数据的频繁搬移。这使得对于生产者和消费者来说插入和删除操作的时间复杂度都是 O(1)。固定大小 环形缓冲区有一个固定的大小这使得其占用的内存是可控的。当缓冲区已满时生产者会被阻塞以免过度生产数据同时保护消费者不会因为数据积压而失去响应能力。无需动态内存分配 环形缓冲区一般使用静态数组作为存储空间无需动态内存分配因此可以在嵌入式系统等资源受限的环境中使用。循环利用空间 环形缓冲区的循环结构使得空间可以被循环利用即使数据已经被消费存储空间也可以被后续的数据重新利用。并发安全 当环形缓冲区被多个线程或任务访问时需要通过互斥锁或其他同步机制来保护共享资源以确保线程安全。 使用环形缓冲区时需要注意处理好生产者和消费者之间的同步和竞态条件以及处理好缓冲区空间不足和溢出的情况。同时还需要考虑如何优雅地处理缓冲区已满和已空时的阻塞与唤醒机制。 2.ringbuffer实例rtos实例
ringbuffer比较难处理的一个问题就是 当read_ptr write_ptr 时此时并不是很确定ringbuffer是empty还是fullrtos和Linux中的设计使用的是 镜像法具体的意思是 镜像扩展位是环形缓冲区中的一个额外的标志位或变量用于指示缓冲区的填充状态。它通常有两种取值 未填满Not Full 表示缓冲区还有空闲空间可以继续向缓冲区写入数据。填满Full 表示缓冲区已经填满不能再继续向缓冲区写入数据。此时继续写入数据可能会覆盖已有的数据造成数据丢失。 使用镜像扩展位当缓冲区填满时生产者可以根据镜像扩展位的状态来判断是否继续写入数据。如果缓冲区未填满生产者可以继续写入数据如果缓冲区已经填满则生产者应该等待直到缓冲区有空间可用。 2.1 ringbuffer结构体
看rtos的实例代码
struct rt_ringbuffer
{rt_uint8_t *buffer_ptr;/* use the msb of the {read,write}_index as mirror bit. You can see this as* if the buffer adds a virtual mirror and the pointers point either to the* normal or to the mirrored buffer. If the write_index has the same value* with the read_index, but in a different mirror, the buffer is full.* While if the write_index and the read_index are the same and within the* same mirror, the buffer is empty. The ASCII art of the ringbuffer is:** mirror 0 mirror 1* ---------------------|~~~~~~~~~~~~~~~~~~~~~* | 0 | 1 | 2 | 3 | 4 | 5 | 6 ||| 0 | 1 | 2 | 3 | 4 | 5 | 6 | Full* ---------------------|~~~~~~~~~~~~~~~~~~~~~* read_idx-^ write_idx-^** ---------------------|~~~~~~~~~~~~~~~~~~~~~* | 0 | 1 | 2 | 3 | 4 | 5 | 6 ||| 0 | 1 | 2 | 3 | 4 | 5 | 6 | Empty* ---------------------|~~~~~~~~~~~~~~~~~~~~~* read_idx-^ ^-write_idx*/rt_uint32_t read_mirror : 1;rt_uint32_t read_index : 31;rt_uint32_t write_mirror : 1;rt_uint32_t write_index : 31;/* as we use msb of index as mirror bit, the size should be signed and* could only be positive. */rt_int32_t buffer_size;
};结构体中有一个read_mirror和write_mirror看注释可以知道是表示read/write的指针是否到了mirror区并且
read_index write_index read_mirror和write_mirror不同此时为FULLread_index write_index read_mirror和write_mirror相同此时为EMPTY
2.2 ringbuffer获取当前长度
RTOS中代码
rt_size_t rt_ringbuffer_data_len(struct rt_ringbuffer *rb)
{switch (rt_ringbuffer_status(rb)){case RT_RINGBUFFER_EMPTY:return 0;case RT_RINGBUFFER_FULL:return rb-buffer_size;case RT_RINGBUFFER_HALFFULL:default:{rt_size_t wi rb-write_index, ri rb-read_index;if (wi ri)return wi - ri;elsereturn rb-buffer_size - (ri - wi);}}
}有三种情况
当rt_status为空时len为0当rt_status为满时len为buffer_size当ringbuffer非空/满时如果write_indexread_index那么buffer_size为 wi-ri否则为 rb-buffer_size - (ri - wi)
2.3 ringbuffer put
put代码如下
rt_size_t rt_ringbuffer_put(struct rt_ringbuffer *rb,const rt_uint8_t *ptr,rt_uint32_t length)
{rt_uint32_t size;RT_ASSERT(rb ! RT_NULL);/* whether has enough space */size rt_ringbuffer_space_len(rb);/* no space */if (size 0)return 0;/* drop some data */if (size length)length size;if (rb-buffer_size - rb-write_index length){/* read_index - write_index empty space */rt_memcpy(rb-buffer_ptr[rb-write_index], ptr, length);/* this should not cause overflow because there is enough space for* length of data in current mirror */rb-write_index length;return length;}rt_memcpy(rb-buffer_ptr[rb-write_index],ptr[0],rb-buffer_size - rb-write_index);rt_memcpy(rb-buffer_ptr[0],ptr[rb-buffer_size - rb-write_index],length - (rb-buffer_size - rb-write_index));/* we are going into the other side of the mirror */rb-write_mirror ~rb-write_mirror;rb-write_index length - (rb-buffer_size - rb-write_index);return length;
}
逻辑是
判断剩余空间的size是否足够放下数据如果不够则需要drop一些数据如果可以直接放不需要循环回来那么就直接Memcpy就行如果需要循环回来write_mirror需要取反
3.根据rtos代码设计ringbuffer并测试
代码如下
#include stdio.h
#include stdlib.h
#include unistd.h
#include pthread.h
#include semaphore.h
#include string.h
#include main.hstruct rt_ringbuffer
{rt_uint8_t *buffer_ptr;rt_uint32_t read_mirror : 1;rt_uint32_t read_index : 31;rt_uint32_t write_mirror : 1;rt_uint32_t write_index : 31;rt_int32_t buffer_size;
};enum rt_ringbuffer_state rt_ringbuffer_status(struct rt_ringbuffer *rb)
{if (rb-read_index rb-write_index){if (rb-read_mirror rb-write_mirror)return RT_RINGBUFFER_EMPTY;elsereturn RT_RINGBUFFER_FULL;}return RT_RINGBUFFER_HALFFULL;
}int rt_ringbuffer_data_len(struct rt_ringbuffer *rb)
{switch (rt_ringbuffer_status(rb)){case RT_RINGBUFFER_EMPTY:return 0;case RT_RINGBUFFER_FULL:return rb-buffer_size;case RT_RINGBUFFER_HALFFULL:default:{rt_size_t wi rb-write_index, ri rb-read_index;if (wi ri)return wi - ri;elsereturn rb-buffer_size - (ri - wi);}}
}struct rt_ringbuffer *ringbuffer_init(rt_int32_t size)
{struct rt_ringbuffer *rb;rt_uint8_t *pool;rb (struct rt_ringbuffer *)malloc(sizeof(struct rt_ringbuffer));if (!rb) {printf(rb is null\n);return NULL;}pool (rt_uint8_t *)malloc(size);if (!pool) {printf(pool is null\n);return NULL;}rb-buffer_ptr pool;rb-buffer_size size;rb-read_mirror rb-read_index 0;rb-write_mirror rb-write_index 0;return rb;
} /** return the size of empty space in rb */
#define rt_ringbuffer_space_len(rb) ((rb)-buffer_size - rt_ringbuffer_data_len(rb))int rt_ringbuffer_put(struct rt_ringbuffer *rb,const rt_uint8_t *ptr,rt_uint32_t length)
{rt_uint32_t size;/* whether has enough space */size rt_ringbuffer_space_len(rb);/* no space */if (size 0)return 0;/* drop some data */if (size length)length size;if (rb-buffer_size - rb-write_index length){/* read_index - write_index empty space */memcpy(rb-buffer_ptr[rb-write_index], ptr, length);/* this should not cause overflow because there is enough space for* length of data in current mirror */rb-write_index length;return length;}memcpy(rb-buffer_ptr[rb-write_index],ptr[0],rb-buffer_size - rb-write_index);memcpy(rb-buffer_ptr[0],ptr[rb-buffer_size - rb-write_index],length - (rb-buffer_size - rb-write_index));/* we are going into the other side of the mirror */rb-write_mirror ~rb-write_mirror;rb-write_index length - (rb-buffer_size - rb-write_index);return length;
}int rt_ringbuffer_get(struct rt_ringbuffer *rb,rt_uint8_t *ptr,rt_uint32_t length)
{int size;/* whether has enough data */size rt_ringbuffer_data_len(rb);/* no data */if (size 0)return 0;/* less data */if (size length)length size;if (rb-buffer_size - rb-read_index length){/* copy all of data */memcpy(ptr, rb-buffer_ptr[rb-read_index], length);/* this should not cause overflow because there is enough space for* length of data in current mirror */rb-read_index length;return length;}memcpy(ptr[0],rb-buffer_ptr[rb-read_index],rb-buffer_size - rb-read_index);memcpy(ptr[rb-buffer_size - rb-read_index],rb-buffer_ptr[0],length - (rb-buffer_size - rb-read_index));/* we are going into the other side of the mirror */rb-read_mirror ~rb-read_mirror;rb-read_index length - (rb-buffer_size - rb-read_index);return length;
}int main(void)
{int ret;struct rt_ringbuffer *rb NULL;rb ringbuffer_init(4);if (!rb) {printf(rb init failed\n);return -1;}uint8_t a[4] {0x1, 0x2, 0x3, 0x4};uint8_t read[4] { 0 };ret rt_ringbuffer_put(rb, a, 4);ret rt_ringbuffer_get(rb, read, 1);for (int i 0; i 4; i) {printf(0x%x\n, read[i]);}ret rt_ringbuffer_put(rb, a, 4);ret rt_ringbuffer_get(rb, read, 4);for (int i 0; i 4; i) {printf(0x%x\n, read[i]);}return 0;
}//main.h
#ifndef __MAIN_H__
#define __MAIN_H__#include stdio.h
#include stdint.htypedef uint8_t rt_uint8_t;
typedef uint32_t rt_uint32_t;
typedef int32_t rt_int32_t;
typedef int rt_size_t;enum rt_ringbuffer_state
{RT_RINGBUFFER_EMPTY,RT_RINGBUFFER_FULL,/* half full is neither full nor empty */RT_RINGBUFFER_HALFFULL,
};#endif测试结果
