Simple timer

This article implements a simple time wheel timer based on a loop array.

The timer can be triggered single-shot or cyclically. The timer goes down a grid every second and scans the array nodes for events to be triggered. There may be multiple nodes in a grid, and the node with a level of 0 is triggered. This example is relatively simple. It is implemented through the alarm system call. The alarm will send the SIGALRM signal to trigger the execution of the tick function.

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

#define TIME_WHEEL_SIZE 8          // 轮子大小
typedef void (*func_t)(int data);  // 回调函数类型

// 时间轮节点
struct timer_node {
    int rotation;             //轮数，有多少轮
    func_t func;              // 回调函数
    int data;                 // 回调函数的参数
    struct timer_node *next;  // 下一个节点
};

// 时间轮
struct timer_wheel {
    struct timer_node *slot[TIME_WHEEL_SIZE];  //节点数组
    int current;                               // 当前节点
};

// 初始化时间轮
struct timer_wheel timer = {
   
   {0}, 0};

// 时间轮最小单元，每一秒检查一下时间轮
void tick(int signo) {
    struct timer_node **cur = &timer.slot[timer.current];  //当前slot
    while (*cur) {
        struct timer_node *curr = *cur;
        if (curr->rotation > 0) {
            curr->rotation--;
            cur = &curr->next;
        } else {
            curr->func(curr->data);
            *cur = curr->next;
            free(curr);
        }
    }
    timer.current = (timer.current + 1) % TIME_WHEEL_SIZE;
    alarm(1);  // 如果要多次触发，通常的做法是在这行加入alarm
}

// 添加节点
void add_timer(int len, func_t func) {
    int pos = (len + timer.current) % TIME_WHEEL_SIZE;  // 新增节点的位置
    struct timer_node *node = malloc(sizeof(struct timer_node));

    node->next = timer.slot[pos];
    timer.slot[pos] = node;
    node->rotation = len / TIME_WHEEL_SIZE;  // 新增节点处于第几轮
    node->data = 0;
    node->func = func;
}
int g_sec = 0;

void do_time1(int data) {
    printf("timer %s, %d\n", __FUNCTION__, g_sec++);
    add_timer(1, do_time1);  // 循环添加
}

// 只打印一次
void do_time2(int data) { printf("timer %s, %d\n", __FUNCTION__, g_sec++); }

int main(int argc, char const *argv[]) {
    signal(SIGALRM, tick);
    alarm(1);
    add_timer(1, do_time1);
    add_timer(3, do_time2);
    add_timer(15, do_time2);
    // alarm(1);// signal只生效一次，之后恢复默认，多次调用alarm不会回调
    while (1) pause();
    return 0;
}

reference:

[1] The realization principle and usage method of Linux C/C++ timer

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