linux 内核RingBuffer实现

linux 内核RingBuffer实现

实现方式非常巧妙,刚开始看的有点奇怪,当发现实现原理后惊讶了一番…

/**@brief 仿照linux kfifo写的ring buffer
* ring_buffer.h
 * */
 
#ifndef KFIFO_HEADER_H 
#define KFIFO_HEADER_H
 
#include <inttypes.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <assert.h>
 
//判断x是否是2的次方
#define is_power_of_2(x) ((x) != 0 && (((x) & ((x) - 1)) == 0))
//取a和b中最小值
#define min(a, b) (((a) < (b)) ? (a) : (b))
 
struct ring_buffer
{
    void         *buffer;     //缓冲区
    uint32_t     size;       //大小
    uint32_t     in;         //入口位置
    uint32_t       out;        //出口位置
    pthread_mutex_t *f_lock;    //互斥锁
};
//初始化缓冲区
struct ring_buffer* ring_buffer_init(void *buffer, uint32_t size, pthread_mutex_t *f_lock)
{
    assert(buffer);
    struct ring_buffer *ring_buf = NULL;
    if (!is_power_of_2(size))
    {
    fprintf(stderr,"size must be power of 2.\n");
        return ring_buf;
    }
    ring_buf = (struct ring_buffer *)malloc(sizeof(struct ring_buffer));
    if (!ring_buf)
    {
        fprintf(stderr,"Failed to malloc memory,errno:%u,reason:%s",
            errno, strerror(errno));
        return ring_buf;
    }
    memset(ring_buf, 0, sizeof(struct ring_buffer));
    ring_buf->buffer = buffer;
    ring_buf->size = size;
    ring_buf->in = 0;
    ring_buf->out = 0;
        ring_buf->f_lock = f_lock;
    return ring_buf;
}
//释放缓冲区
void ring_buffer_free(struct ring_buffer *ring_buf)
{
    if (ring_buf)
    {
    if (ring_buf->buffer)
    {
        free(ring_buf->buffer);
        ring_buf->buffer = NULL;
    }
    free(ring_buf);
    ring_buf = NULL;
    }
}
 
//缓冲区的长度
uint32_t __ring_buffer_len(const struct ring_buffer *ring_buf)
{
    return (ring_buf->in - ring_buf->out);
}
 
//从缓冲区中取数据
uint32_t __ring_buffer_get(struct ring_buffer *ring_buf, void * buffer, uint32_t size)
{
    assert(ring_buf || buffer);
    uint32_t len = 0;
    size  = min(size, ring_buf->in - ring_buf->out);        
    /* first get the data from fifo->out until the end of the buffer */
    len = min(size, ring_buf->size - (ring_buf->out & (ring_buf->size - 1)));
    memcpy(buffer, ring_buf->buffer + (ring_buf->out & (ring_buf->size - 1)), len);
    /* then get the rest (if any) from the beginning of the buffer */
    memcpy(buffer + len, ring_buf->buffer, size - len);
    ring_buf->out += size;
    return size;
}
//向缓冲区中存放数据
uint32_t __ring_buffer_put(struct ring_buffer *ring_buf, void *buffer, uint32_t size)
{
    assert(ring_buf || buffer);
    uint32_t len = 0;
    size = min(size, ring_buf->size - ring_buf->in + ring_buf->out);
    /* first put the data starting from fifo->in to buffer end */
    len  = min(size, ring_buf->size - (ring_buf->in & (ring_buf->size - 1)));
    memcpy(ring_buf->buffer + (ring_buf->in & (ring_buf->size - 1)), buffer, len);
    /* then put the rest (if any) at the beginning of the buffer */
    memcpy(ring_buf->buffer, buffer + len, size - len);
    ring_buf->in += size;
    return size;
}
 
uint32_t ring_buffer_len(const struct ring_buffer *ring_buf)
{
    uint32_t len = 0;
    pthread_mutex_lock(ring_buf->f_lock);
    len = __ring_buffer_len(ring_buf);
    pthread_mutex_unlock(ring_buf->f_lock);
    return len;
}
 
uint32_t ring_buffer_get(struct ring_buffer *ring_buf, void *buffer, uint32_t size)
{
    uint32_t ret;
    pthread_mutex_lock(ring_buf->f_lock);
    ret = __ring_buffer_get(ring_buf, buffer, size);
    //buffer中没有数据
    if (ring_buf->in == ring_buf->out)
    ring_buf->in = ring_buf->out = 0;
    pthread_mutex_unlock(ring_buf->f_lock);
    return ret;
}
 
uint32_t ring_buffer_put(struct ring_buffer *ring_buf, void *buffer, uint32_t size)
{
    uint32_t ret;
    pthread_mutex_lock(ring_buf->f_lock);
    ret = __ring_buffer_put(ring_buf, buffer, size);
    pthread_mutex_unlock(ring_buf->f_lock);
    return ret;
}
#endif

使用栗子,采用多线程模拟生产者和消费者编写测试程序,如下所示:

/**@brief ring buffer测试程序,创建两个线程,一个生产者,一个消费者。
 * 生产者每隔1秒向buffer中投入数据,消费者每隔2秒去取数据。
 * */
#include "ring_buffer.h"
#include <pthread.h>
#include <time.h>
 
#define BUFFER_SIZE  1024 * 1024
 
typedef struct student_info
{
    uint64_t stu_id;
    uint32_t age;
    uint32_t score;
}student_info;
 
 
void print_student_info(const student_info *stu_info)
{
    assert(stu_info);
    printf("id:%lu\t",stu_info->stu_id);
    printf("age:%u\t",stu_info->age);
    printf("score:%u\n",stu_info->score);
}
 
student_info * get_student_info(time_t timer)
{
    student_info *stu_info = (student_info *)malloc(sizeof(student_info));
    if (!stu_info)
    {
    fprintf(stderr, "Failed to malloc memory.\n");
    return NULL;
    }
    srand(timer);
    stu_info->stu_id = 10000 + rand() % 9999;
    stu_info->age = rand() % 30;
    stu_info->score = rand() % 101;
    print_student_info(stu_info);
    return stu_info;
}
 
void * consumer_proc(void *arg)
{
    struct ring_buffer *ring_buf = (struct ring_buffer *)arg;
    student_info stu_info; 
    while(1)
    {
    sleep(2);
    printf("------------------------------------------\n");
    printf("get a student info from ring buffer.\n");
    ring_buffer_get(ring_buf, (void *)&stu_info, sizeof(student_info));
    printf("ring buffer length: %u\n", ring_buffer_len(ring_buf));
    print_student_info(&stu_info);
    printf("------------------------------------------\n");
    }
    return (void *)ring_buf;
}
 
void * producer_proc(void *arg)
{
    time_t cur_time;
    struct ring_buffer *ring_buf = (struct ring_buffer *)arg;
    while(1)
    {
    time(&cur_time);
    srand(cur_time);
    int seed = rand() % 11111;
    printf("******************************************\n");
    student_info *stu_info = get_student_info(cur_time + seed);
    printf("put a student info to ring buffer.\n");
    ring_buffer_put(ring_buf, (void *)stu_info, sizeof(student_info));
    printf("ring buffer length: %u\n", ring_buffer_len(ring_buf));
    printf("******************************************\n");
    sleep(1);
    }
    return (void *)ring_buf;
}
 
int consumer_thread(void *arg)
{
    int err;
    pthread_t tid;
    err = pthread_create(&tid, NULL, consumer_proc, arg);
    if (err != 0)
    {
    fprintf(stderr, "Failed to create consumer thread.errno:%u, reason:%s\n",
        errno, strerror(errno));
    return -1;
    }
    return tid;
}
int producer_thread(void *arg)
{
    int err;
    pthread_t tid;
    err = pthread_create(&tid, NULL, producer_proc, arg);
    if (err != 0)
    {
    fprintf(stderr, "Failed to create consumer thread.errno:%u, reason:%s\n",
        errno, strerror(errno));
    return -1;
    }
    return tid;
}
 
 
int main()
{
    void * buffer = NULL;
    uint32_t size = 0;
    struct ring_buffer *ring_buf = NULL;
    pthread_t consume_pid, produce_pid;
 
    pthread_mutex_t *f_lock = (pthread_mutex_t *)malloc(sizeof(pthread_mutex_t));
    if (pthread_mutex_init(f_lock, NULL) != 0)
    {
    fprintf(stderr, "Failed init mutex,errno:%u,reason:%s\n",
        errno, strerror(errno));
    return -1;
    }
    buffer = (void *)malloc(BUFFER_SIZE);
    if (!buffer)
    {
    fprintf(stderr, "Failed to malloc memory.\n");
    return -1;
    }
    size = BUFFER_SIZE;
    ring_buf = ring_buffer_init(buffer, size, f_lock);
    if (!ring_buf)
    {
    fprintf(stderr, "Failed to init ring buffer.\n");
    return -1;
    }
#if 0
    student_info *stu_info = get_student_info(638946124);
    ring_buffer_put(ring_buf, (void *)stu_info, sizeof(student_info));
    stu_info = get_student_info(976686464);
    ring_buffer_put(ring_buf, (void *)stu_info, sizeof(student_info));
    ring_buffer_get(ring_buf, (void *)stu_info, sizeof(student_info));
    print_student_info(stu_info);
#endif
    printf("multi thread test.......\n");
    produce_pid  = producer_thread((void*)ring_buf);
    consume_pid  = consumer_thread((void*)ring_buf);
    pthread_join(produce_pid, NULL);
    pthread_join(consume_pid, NULL);
    ring_buffer_free(ring_buf);
    free(f_lock);
    return 0;
}

参考文献

linux内核数据结构之kfifo – Daleshi的技术随笔 – 博客园

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