当前位置：首页 > news >正文

termios 线程 poll epoll进化二叉AVL红黑树

news 2025/8/16 11:48:16

struct termios tio 是什么

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>#define SERIAL_PORT "/dev/ttyS0"
#define BUF_SIZE    256int main(void)
{int fd;struct termios tio;/* 1. 打开串口 */fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_SYNC);if (fd < 0) {perror("open");return 1;}/* 2. 配置串口：115200 8N1，无流控 */memset(&tio, 0, sizeof(tio));cfsetospeed(&tio, B115200);cfsetispeed(&tio, B115200);tio.c_cflag &= ~PARENB;        /* 无校验 */tio.c_cflag &= ~CSTOPB;        /* 1 停止位 */tio.c_cflag &= ~CSIZE;tio.c_cflag |= CS8;            /* 8 数据位 */tio.c_cflag |= (CLOCAL | CREAD);tio.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* 原始模式 */tio.c_iflag &= ~(IXON | IXOFF | IXANY);         /* 无软件流控 */tio.c_oflag &= ~OPOST;                          /* 原始输出 */tcflush(fd, TCIOFLUSH);tcsetattr(fd, TCSANOW, &tio);/* 3. 写入数据 */char *tx = "hello world\n";if (write(fd, tx, strlen(tx)) < 0) {perror("write");close(fd);return 1;}/* 4. 循环读取并查找 "flush" */char buf[BUF_SIZE];int len, total = 0;char line[BUF_SIZE * 2] = {0};while (1) {len = read(fd, buf, sizeof(buf));if (len < 0) {perror("read");break;}if (len == 0)continue;/* 把新数据追加到 line 缓冲区 */if (total + len < sizeof(line) - 1) {memcpy(line + total, buf, len);total += len;line[total] = '\0';}/* 判断是否出现 "flush" */if (strstr(line, "flush")) {printf("Received \"flush\", exit.\n");break;}/* 打印刚收到的数据（可选） */printf("Rx[%d]: %.*s", len, len, buf);fflush(stdout); //立即刷新缓冲区//把 C 标准库 为 `stdout`（通常是终端）维护的用户态缓冲区立即刷到内核，确保之前 `printf/puts` 的内容立刻出现在屏幕上}close(fd);return 0;
}

pthread_create

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <pthread.h>#define SERIAL_PORT "/dev/ttyS0"
#define BUF_SIZE    256static int stop = 0;            /* 线程退出标志 */
static pthread_t tid;/* 串口初始化：115200 8N1，阻塞读 */
static int open_serial(void)
{int fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY);if (fd < 0) {perror("open " SERIAL_PORT);return -1;}struct termios tio;tcgetattr(fd, &tio);cfmakeraw(&tio);cfsetispeed(&tio, B115200);cfsetospeed(&tio, B115200);tcflush(fd, TCIOFLUSH);tcsetattr(fd, TCSANOW, &tio);return fd;
}/* 线程函数：一直读串口直到看到 "flush" */
static void *rx_thread(void *arg)
{int fd = (long)arg;char buf[BUF_SIZE];char line[BUF_SIZE * 2] = {0};int total = 0;while (!stop) {int n = read(fd, buf, sizeof(buf));if (n <= 0) continue;/* 追加到行缓冲区并检查子串 */if (total + n < sizeof(line) - 1) {memcpy(line + total, buf, n);total += n;line[total] = '\0';}if (strstr(line, "flush")) {printf("[RX-THREAD] Found \"flush\", exiting.\n");break;}}close(fd);return NULL;
}int main(void)
{int fd = open_serial();if (fd < 0) return 1;/* 创建接收线程 */if (pthread_create(&tid, NULL, rx_thread, (void *)(long)fd) != 0) {perror("pthread_create");close(fd);return 1;}/* 主线程可以干别的事，这里简单等待用户输入 */printf("Press Enter to quit...\n");getchar();/* 通知线程退出并等待结束 */stop = 1;pthread_cancel(tid);    /* 若线程阻塞在 read()，可强制唤醒 */pthread_join(tid, NULL);printf("Main thread exit.\n");return 0;
}

poll

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <poll.h>#define SERIAL_PORT "/dev/ttyS0"
#define BUF_SIZE    256static int open_serial(void)
{int fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NONBLOCK);if (fd < 0) { perror("open"); return -1; }struct termios tio;tcgetattr(fd, &tio);cfmakeraw(&tio);cfsetispeed(&tio, B115200);cfsetospeed(&tio, B115200);tcflush(fd, TCIOFLUSH);tcsetattr(fd, TCSANOW, &tio);return fd;
}int main(void)
{int fd = open_serial();if (fd < 0) return 1;char line[BUF_SIZE * 2] = {0};int total = 0;struct pollfd pfd = { .fd = fd, .events = POLLIN };while (1) {int ret = poll(&pfd, 1, -1);        /* 无限等待可读 */if (ret < 0) { perror("poll"); break; }if (pfd.revents & POLLIN) {char buf[BUF_SIZE];int n = read(fd, buf, sizeof(buf));if (n <= 0) continue;/* 追加到行缓冲并检查 */if (total + n < sizeof(line) - 1) {memcpy(line + total, buf, n);total += n;line[total] = '\0';}if (strstr(line, "flush")) {printf("Got flush, exit.\n");break;}}}close(fd);return 0;
}

epoll

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <sys/epoll.h>#define SERIAL_PORT "/dev/ttyS0"
#define BUF_SIZE    256
#define MAX_EVENTS  1static int open_serial(void)
{int fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NONBLOCK);if (fd < 0) { perror("open"); return -1; }struct termios tio;tcgetattr(fd, &tio);cfmakeraw(&tio);cfsetispeed(&tio, B115200);cfsetospeed(&tio, B115200);tcflush(fd, TCIOFLUSH);tcsetattr(fd, TCSANOW, &tio);return fd;
}int main(void)
{int fd = open_serial();if (fd < 0) return 1;int epfd = epoll_create1(0);if (epfd < 0) { perror("epoll_create1"); return 1; }struct epoll_event ev = { .events = EPOLLIN, .data.fd = fd };if (epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev) < 0) {perror("epoll_ctl"); return 1;}char line[BUF_SIZE * 2] = {0};int total = 0;struct epoll_event events[MAX_EVENTS];while (1) {int nfds = epoll_wait(epfd, events, MAX_EVENTS, -1);if (nfds < 0) { perror("epoll_wait"); break; }for (int i = 0; i < nfds; ++i) {if (events[i].events & EPOLLIN) {char buf[BUF_SIZE];int n = read(fd, buf, sizeof(buf));if (n <= 0) continue;if (total + n < sizeof(line) - 1) {memcpy(line + total, buf, n);total += n;line[total] = '\0';}if (strstr(line, "flush")) {printf("Got flush, exit.\n");goto out;}}}}
out:close(fd);close(epfd);return 0;
}

深入浅出理解select、poll、epoll的实现

select	poll	epoll
性能	随着连接数的增加，性能急剧下降，处理成千上万的并发连接数时，性能很差	随着连接数的增加，性能急剧下降，处理成千上万的并发连接数时，性能很差	随着连接数的增加，性能基本没有变化
连接数	一般1024	无限制	无限制
内存拷贝	每次调用select拷贝	每次调用poll拷贝	fd首次调用epoll_ctl拷贝，每次调用epoll_wait不拷贝
数据结构	bitmap	数组	红黑树
内在处理机制	线性轮询	线性轮询	FD挂在红黑树，通过事件回调callback
时间复杂度	O(n)	O(n)	O(1)

目前支持I/O多路复用的系统调用有select，pselect，poll，epoll

在Linux的缓存IO机制中，操作系统会将IO的数据缓存在文件系统的页缓存（page cache）。也就是说，数据会先被拷贝到操作系统内核的缓冲区中，然后才会从操作系统内核的缓存区拷贝到应用程序的地址空间中

![[Pasted image 20250815160249.png]]

select

select存在三个问题
- 每次调用select，都需要把被监控的fds集合从用户态空间拷贝到内核态空间
- 能监听端口的数量有限，单个进程所能打开的最大连接数由FD_SETSIZE宏定义
- 被监控的fds集合中，只要有一个有数据可读，整个socket集合就会被遍历一次调用sk的poll函数收集可读事件

![[1755245325283-349279b4-9119-11eb-85d0-1278b449b310.gif]]