（一）redis源碼閱讀

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目錄

• 1. srand()和rand()函數以及隨機數種子
• 2. 守護進程及pid檔案
• 3. 初始化伺服器時的訊號處理
• 4. 在程式coredump時記錄堆棧資訊StackTrace

1. srand()和rand()函數以及隨機數種子

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

2. 守護進程及pid檔案

在main()函數中，通過設定檔判斷是否以守護進程模式運行。

if (server.daemonize) daemonize();     // 守護進程if (server.daemonize) createPidFile();  // 記錄pid的檔案

// 將程式以守護進程方式運行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);    }}// 儲存進程ID到檔案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. 初始化伺服器時的訊號處理

// 初始化伺服器函數void initServer(void) {    // 忽視訊號: SIGHUP, SIGPIPE     signal(SIGHUP, SIG_IGN);    signal(SIGPIPE, SIG_IGN);    // 設定SIGTERM, SIGINT 訊號處理函數    setupSignalHandlers();

// 設定訊號處理函數，當SIGTERN, SIGINT時，退出程式void setupSignalHandlers(void) {    struct sigaction act;    /* When the SA_SIGINFO flag is 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;}

// 訊號處理函數，ctrl+c 會產生 SIGINT訊號，連續兩次，會退出程式。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 waiting to persist     * on disk. */    if (server.shutdown_asap && sig == SIGINT) {        redisLogFromHandler(REDIS_WARNING, "You insist... exiting now.");        rdbRemoveTempFile(getpid());        exit(1); /* Exit with an error since this was not a clean shutdown. */    } else if (server.loading) {        exit(0);    }    redisLogFromHandler(REDIS_WARNING, msg);    // 在接收到SIGTERM/SIGINT訊號後，在訊號處理函數中將server.shutdown_asap置為1；    // 當下次運行serverCron函數時，會檢查該值，然後安全退出程式。    server.shutdown_asap = 1;}

4. 在程式coredump時記錄堆棧資訊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);}

（一）redis源碼閱讀