lua里面写一个程序读取串口数据，用C调用lua，在c中写个线程读取同一个串口数据，要求两个读取互斥

以下是一个基本的示例程序，演示如何在 C 中创建线程读取串口数据，并使用 Lua 与该线程进行互斥。

#include <stdio.h>
#include <string.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
#include <pthread.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>

#define SERIAL_PORT "/dev/ttyUSB0"
#define BAUD_RATE B9600

int running = 1;
pthread_mutex_t mutex;
int serial_fd = -1;

void *read_serial(void *arg) {
    char buffer[1024];
    int bytes_read;

    while (running) {
        pthread_mutex_lock(&mutex);
        if (serial_fd >= 0) {
            bytes_read = read(serial_fd, buffer, sizeof(buffer));
            if (bytes_read > 0) {
                lua_State *L = (lua_State *) arg;
                lua_getglobal(L, "on_serial_data");
                lua_pushlstring(L, buffer, bytes_read);
                lua_call(L, 1, 0);
            }
        }
        pthread_mutex_unlock(&mutex);
        usleep(1000);
    }

    return NULL;
}

int open_serial_port() {
    int fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd < 0) {
        fprintf(stderr, "Error opening serial port %s\n", SERIAL_PORT);
        return -1;
    }

    struct termios options;
    tcgetattr(fd, &options);

    cfsetispeed(&options, BAUD_RATE);
    cfsetospeed(&options, BAUD_RATE);

    options.c_cflag |= (CLOCAL | CREAD);
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;
    options.c_cflag &= ~PARENB;
    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CRTSCTS;

    tcsetattr(fd, TCSANOW, &options);
    fcntl(fd, F_SETFL, 0);

    return fd;
}

int lua_open_serial_port(lua_State *L) {
    serial_fd = open_serial_port();
    if (serial_fd < 0) {
        lua_pushboolean(L, 0);
    } else {
        lua_pushboolean(L, 1);
    }
    return 1;
}

int lua_close_serial_port(lua_State *L) {
    if (serial_fd >= 0) {
        close(serial_fd);
        serial_fd = -1;
    }
    return 0;
}

int lua_is_serial_port_open(lua_State *L) {
    if (serial_fd >= 0) {
        lua_pushboolean(L, 1);
    } else {
        lua_pushboolean(L, 0);
    }
    return 1;
}

int lua_start_serial_read_thread(lua_State *L) {
    pthread_t thread_id;
    pthread_mutex_init(&mutex, NULL);
    pthread_create(&thread_id, NULL, read_serial, L);
    pthread_detach(thread_id);
    return 0;
}

int main(int argc, char **argv) {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);

    lua_pushcfunction(L, lua_open_serial_port);
    lua_setglobal(L, "open_serial_port");

    lua_pushcfunction(L, lua_close_serial_port);
    lua_setglobal(L, "close_serial_port");

    lua_pushcfunction(L, lua_is_serial_port_open);
    lua_setglobal(L, "is_serial_port_open");

    lua_pushcfunction(L, lua_start_serial_read_thread);
    lua_setglobal(L, "start_serial_read_thread");

    luaL_dofile(L, "main.lua");

    running = 0;

    pthread_mutex_destroy(&mutex);
    lua_close(L);

    return 0;
}

在 `main.lua` 文件中，我们可以编写 Lua 代码来调用 C 函数，并在 `on_serial_data` 函数中处理串口数据。

function on_serial_data(data)
    print("Received data: " .. data)
end

-- 打开串口
if not open_serial_port() then
    print("Failed to open serial port")
    return
end

-- 开启读取线程
start_serial_read_thread()

-- 等待用户输入退出命令
while true do
    local line = io.read()
    if line == "exit" then
        break
    end
end

-- 关闭串口
close_serial_port()

注意，在 `read_serial` 函数中，我们使用了一个互斥锁来保证在串口被读取时，C 和 Lua 两个线程不会同时读取串口。我们还使用了 `usleep` 函数来避免过多的 CPU 开销。