(i) Redis source reading

Directory

• 1. Srand () and Rand () functions and random number seeds
• 2. Daemon and PID files
• 3. Signal processing when initializing the server
• 4. Log stack information when the program Coredump StackTrace

1. Srand () and Rand () functions and random number seeds

srand(time(NULL)^getpid());struct timeval tv;gettimeofday(&tv,NULL);dictSetHashFunctionSeed(tv.tv_sec^tv.tv_usec^getpid());

2. Daemon and PID files

In the main () function, the configuration file determines whether to run in daemon mode.

if (server.daemonize) daemonize();     // 守护进程if (server.daemonize) createPidFile();  // 记录pid的文件

// 将程序以守护进程方式运行void daemonize(void) {    int fd;    if (fork() != 0) exit(0); /* parent exits */    setsid(); /* create a new session */    /* Every output goes to /dev/null. If Redis is daemonized but     * the ‘logfile‘ is set to ‘stdout‘ in the configuration file     * it will not log at all. */    if ((fd = open("/dev/null", O_RDWR, 0)) != -1) {        dup2(fd, STDIN_FILENO);        dup2(fd, STDOUT_FILENO);        dup2(fd, STDERR_FILENO);        if (fd > STDERR_FILENO) close(fd);    }}// 保存进程ID到文件void createPidFile(void) {    /* Try to write the pid file in a best-effort way. */    FILE *fp = fopen(server.pidfile,"w");    if (fp) {        fprintf(fp,"%d\n",(int)getpid());        fclose(fp);    }}

3. Signal processing when initializing the server

// 初始化服务器函数void initServer(void) {    // 忽视信号: SIGHUP, SIGPIPE     signal(SIGHUP, SIG_IGN);    signal(SIGPIPE, SIG_IGN);    // 设置SIGTERM, SIGINT 信号处理函数    setupSignalHandlers();

 //Set signal processing function, when Sigtern, SIGINT, exit program void Setupsignalhandlers (void) {struct Sigaction act;     /* When the SA_SIGINFO flag are set in Sa_flags then Sa_sigaction is used. * Otherwise, Sa_handler is used.    */Sigemptyset (&act.sa_mask);    act.sa_flags = 0;    Act.sa_handler = Sigshutdownhandler;    Sigaction (SIGTERM, &act, NULL);    Sigaction (SIGINT, &act, NULL); #ifdef have_backtrace Sigemptyset (&act.sa_mask); Act.sa_flags = Sa_nodefer | Sa_resethand |    Sa_siginfo;    Act.sa_sigaction = Sigsegvhandler;    Sigaction (SIGSEGV, &act, NULL);    Sigaction (Sigbus, &act, NULL);    Sigaction (SIGFPE, &act, NULL); Sigaction (Sigill, &act, NULL); #endif return;}  

Signal processing function, CTRL + C will produce SIGINT signal, two consecutive times, will exit the program.    static void Sigshutdownhandler (int sig) {char *msg;        Switch (SIG) {Case sigint:msg = "Received SIGINT scheduling shutdown ...";    Break        Case sigterm:msg = "Received SIGTERM scheduling shutdown ...";    Break    default:msg = "Received shutdown signal, scheduling shutdown ...";    };     /* SIGINT is often delivered via CTRL + C in an interactive session. * IF we receive the signal the second time, we interpret this as * the user really wanting to quit ASAP without waitin G to persist * on disk. */if (Server.shutdown_asap && sig = = SIGINT) {Redislogfromhandler (redis_warning, "you insist ... Exitin        G now. ");        Rdbremovetempfile (Getpid ()); Exit (1); /* Exit with the error since this is not a clean shutdown.    */} else if (server.loading) {exit (0);    } redislogfromhandler (redis_warning, msg);  After receiving the sigterm/sigint signal, the SERVER.SHUTDOWN_ASAP is set to 1 in the signal processing function;  The next time you run the Servercron function, the value is checked and the program exits safely. SERVER.SHUTDOWN_ASAP = 1;}

4. Log stack information when the program Coredump StackTrace

/* Logs the stack trace using the backtrace() call. This function is designed * to be called from signal handlers safely. */void logStackTrace(ucontext_t *uc) {    void *trace[100];    int trace_size = 0, fd;    int log_to_stdout = server.logfile[0] == ‘\0‘;    /* Open the log file in append mode. */    fd = log_to_stdout ?        STDOUT_FILENO :        open(server.logfile, O_APPEND|O_CREAT|O_WRONLY, 0644);    if (fd == -1) return;    /* Generate the stack trace */    trace_size = backtrace(trace, 100);    /* overwrite sigaction with caller‘s address */    if (getMcontextEip(uc) != NULL)        trace[1] = getMcontextEip(uc);    /* Write symbols to log file */    backtrace_symbols_fd(trace, trace_size, fd);    /* Cleanup */    if (!log_to_stdout) close(fd);}

(i) Redis source reading