libev loop_init分析

尼玛 C语言学不好真是桑心呐！

看了libev的代码有一种想死的感觉，但是还是要硬着头皮看下去，一定看完！

/* initialise a loop structure, must be zero-initialised */
static void loop_init ( unsigned int flags)
{
  if (!loop->backend)
    {
      origflags = flags;

#if EV_USE_REALTIME
      if (!have_realtime)
        {
          struct timespec ts;

          if (!clock_gettime (CLOCK_REALTIME, &ts))
            have_realtime = 1;
        }
#endif

#if EV_USE_MONOTONIC
      if (!have_monotonic)
        {
          struct timespec ts;

          if (!clock_gettime (CLOCK_MONOTONIC, &ts))
            have_monotonic = 1;
        }
#endif

      /* pid check not overridable via env */
#ifndef _WIN32
      if (flags & EVFLAG_FORKCHECK)
        curpid = getpid ();
#endif

      if (!(flags & EVFLAG_NOENV)
          && !enable_secure ()
          && getenv ("LIBEV_FLAGS"))
        flags = atoi (getenv ("LIBEV_FLAGS"));

      ev_rt_now          = ev_time ();
      mn_now             = get_clock ();
      now_floor          = mn_now;
      rtmn_diff          = ev_rt_now - mn_now;
#if EV_FEATURE_API
      invoke_cb          = ev_invoke_pending;
#endif

      io_blocktime       = 0.;
      timeout_blocktime  = 0.;
      backend            = 0;
      backend_fd         = -1;
      sig_pending        = 0;
#if EV_ASYNC_ENABLE
      async_pending      = 0;
#endif
      pipe_write_skipped = 0;
      pipe_write_wanted  = 0;
      evpipe [0]         = -1;
      evpipe [1]         = -1;
#if EV_USE_INOTIFY
      fs_fd              = flags & EVFLAG_NOINOTIFY ? -1 : -2;
#endif
#if EV_USE_SIGNALFD
      sigfd              = flags & EVFLAG_SIGNALFD  ? -2 : -1;
#endif

      if (!(flags & EVBACKEND_MASK))
        flags |= ev_recommended_backends ();

#if EV_USE_IOCP
      if (!backend && (flags & EVBACKEND_IOCP  )) backend = iocp_init   (EV_A_ flags);
#endif
#if EV_USE_PORT
      if (!backend && (flags & EVBACKEND_PORT  )) backend = port_init   (EV_A_ flags);
#endif
#if EV_USE_KQUEUE
      if (!backend && (flags & EVBACKEND_KQUEUE)) backend = kqueue_init (EV_A_ flags);
#endif
#if EV_USE_EPOLL
      if (!backend && (flags & EVBACKEND_EPOLL )) backend = epoll_init  (EV_A_ flags);
#endif
#if EV_USE_POLL
      if (!backend && (flags & EVBACKEND_POLL  )) backend = poll_init   (EV_A_ flags);
#endif
#if EV_USE_SELECT
      if (!backend && (flags & EVBACKEND_SELECT)) backend = select_init (EV_A_ flags);
#endif

      ev_prepare_init (&pending_w, pendingcb);

#if EV_SIGNAL_ENABLE || EV_ASYNC_ENABLE
      ev_init (&pipe_w, pipecb);
      ev_set_priority (&pipe_w, EV_MAXPRI);
#endif
    }
}

主要就是初始化loop中的数据成员，其中最重要的是backend的初始化，比如win32选择IOCP，Select等，获取当前时间等。

void *event_init (void)
{
#if EV_MULTIPLICITY //定义多线程，就是可以有多个loop
  if (ev_x_cur)
    ev_x_cur = (struct event_base *)ev_loop_new (EVFLAG_AUTO);
  else
    ev_x_cur = (struct event_base *)ev_default_loop (EVFLAG_AUTO);
#else
  assert (("libev: multiple event bases not supported when not compiled with EV_MULTIPLICITY", !ev_x_cur));

  ev_x_cur = (struct event_base *)(long)ev_default_loop (EVFLAG_AUTO);
#endif

  return ev_x_cur;
}

其中ev_default_loop就是把一个全局的static loop赋给ev_default_loop_ptr，然后返回。这样就可以全局用define的东东调来调去，好不羞涩。

ev_loop_new就new出来一个loop并对loop进行初始化。

ok，第一步完成！