C语言实现线程安全环形缓冲区详解

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>

#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; 
 unsigned int size; 
 unsigned int in; 
 unsigned int out; 
 pthread_mutex_t lock; 
}; 

static struct cycle_buffer *fifo = NULL; 

// 初始化环形缓冲区
static int init_cycle_buffer(void) 
{
 int size = BUFFSIZE, ret; 
 // 校验 size 是否为 2 的幂
 ret = size & (size - 1); 
 if (ret) 
  return ret;
 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)
  free(fifo);
 else
  memset(fifo->buf, 0, size); 
 return 0; 
}

// 从缓冲区读取数据
unsigned int fifo_get(unsigned char *buf, unsigned int len) 
{ 
 unsigned int l; 
 // 计算可读字节数：剩余总数据与请求长度的较小值
 len = min(len, fifo->in - fifo->out); 
 // 分块复制技巧：第一块写到 buffer 末尾，第二块从头开始
 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; 
}

// 向缓冲区写入数据
unsigned int fifo_put(unsigned char *buf, unsigned int len) 
{ 
 unsigned int l; 
 // 计算可写字节数：剩余空间与请求长度的较小值
 len = min(len, fifo->size - fifo->in + fifo->out); 
 // 分块写入技巧
 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; 
}

// 读取线程函数
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); 
 }
 printf("nnafter thread_read : %snn",buf);
 return NULL; 
}

// 写入线程函数
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) 
  return ret;

 pthread_create(&wtid, NULL, thread_write, NULL); 
 pthread_create(&rtid, NULL, thread_read, NULL); 
 pthread_exit(NULL); 
 return 0;
}