simple-query.c

/* -*- mode: c; coding: utf-8 -*-

   https://bugs.mysql.com/bug.php?id=92394
   How to reproduce

   gcc  simple-query.c $(mysql_config --cflags) $(mysql_config --libs) -o simple-query
   MYSQL_USER=scott MYSQL_PWD=tiger ./simple-query

   mysql client version: 50724
   > while true; do kill -USR1 5922 || break; sleep 15; done
   > do_query
   < 1
   > safe_sleep: 110
   caught signal: 10
   caught signal: 10
   caught signal: 10
   caught signal: 10
   caught signal: 10
   caught signal: 10
   caught signal: 10
   caught signal: 10
   > do_query
   caught signal: 10
   ^C
 */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <time.h>

#include <mysql.h>

void signal_handler(int signum) {
    fprintf(stderr, "caught signal: %d\n", signum);
}

void do_query(MYSQL mysql) {
    int r;
    MYSQL_RES *result;
    MYSQL_ROW row;

    fprintf(stderr, "> do_query\n");

    char *stmt = "select 1";
    unsigned int stmt_len = strlen(stmt);


    r = mysql_real_query(&mysql, stmt, stmt_len);
    if (r != 0) {
        fprintf(stderr, "query: %s\n", mysql_error(&mysql));
        exit(1);
    }

    result = mysql_store_result(&mysql);
    while ((row = mysql_fetch_row(result))) {
        printf("< %s\n", row[0]);
    }
    mysql_free_result(result);
}

void safe_sleep(time_t sec) {
    int r;
    struct timespec req, rem;

    fprintf(stderr, "> safe_sleep: %ld\n", sec);

    req.tv_sec = sec;
    req.tv_nsec = 0;

    for (;;) {
        r = nanosleep(&req, &rem);
        if (r == 0) {
            break;
        } else {
            req.tv_sec = rem.tv_sec;
            req.tv_nsec = rem.tv_nsec;
        }
    }
}

int main(int argc, char** argv) {
    int r;
    char *host = getenv("MYSQL_HOST");
    char *user = getenv("MYSQL_USER");
    char *password = getenv("MYSQL_PWD");
    MYSQL mysql;
    struct sigaction sa;

    if (host == NULL)
        host = "127.0.0.1";
    if (user == NULL)
        user = "root";

    if (fork() == 0) {
        pid_t p_pid = getppid();
        char cmd[255];
        // char *signal = "TERM";
        // char *signal = "ALRM";
        char *signal = "USR1";

        sprintf(cmd, "while true; do kill -%s %d || break; sleep 15; done",
                signal,
                p_pid);
        fprintf(stderr, "> %s\n", cmd);
        sleep(3);
        execl("/bin/sh", "/bin/sh", "-c", cmd, (char *)NULL);

        perror("failed to exec");
        exit(1);
    }

    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = signal_handler;

    if (sigaction(SIGTERM, &sa, NULL) != 0) {
        perror("sigaction");
        exit(1);
    }
    if (sigaction(SIGALRM, &sa, NULL) != 0) {
        perror("sigaction");
        exit(1);
    }
    if (sigaction(SIGUSR1, &sa, NULL) != 0) {
        perror("sigaction");
        exit(1);
    }

    fprintf(stderr, "mysql client version: %ld\n", mysql_get_client_version());
    mysql_init(&mysql);
    if (!mysql_real_connect(&mysql, host, user, password, "", 3306, NULL, 0)) {
        fprintf(stderr, "connect: %s\n", mysql_error(&mysql));
        exit(1);
    }

    int sleep_second = 110;
    for (;;) {
        do_query(mysql);
        safe_sleep(sleep_second);
        sleep_second += 10;
    }

    mysql_close(&mysql);
    return 0;
}