message: added trace log.
diff: @@ -795,6 +795,8 @@ int swServer_shutdown(swServer *serv)
  int swServer_free(swServer *serv)
  {
  + swTraceLog(SW_TRACE_SERVER, "release service.");
  +
  /**
  * shutdown workers
  */
  @@ -807,6 +809,7 @@ int swServer_free(swServer *serv)
  */
  if (SwooleG.heartbeat_pidt)
  {
  + swTraceLog(SW_TRACE_SERVER, "terminate heartbeat thread.");
  if (pthread_cancel(SwooleG.heartbeat_pidt) < 0)
  {
  swSysError("pthread_cancel(%ld) failed.", (ulong_t )SwooleG.heartbeat_pidt);
  @@ -819,6 +822,7 @@ int swServer_free(swServer *serv)
  }
  if (serv->factory_mode == SW_MODE_SINGLE)
  {
  + swTraceLog(SW_TRACE_SERVER, "terminate task workers.");
  if (SwooleG.task_worker_num > 0)
  {
  swProcessPool_shutdown(&SwooleGS->task_workers);
  @@ -826,6 +830,7 @@ int swServer_free(swServer *serv)
  }
  else
  {
  + swTraceLog(SW_TRACE_SERVER, "terminate reactor threads.");
  /**
  * Wait until all the end of the thread
  */
  @@ -1380,6 +1385,8 @@ int swServer_get_socket(swServer *serv, int port)
  static void swServer_signal_hanlder(int sig)
  {
  + swTraceLog(SW_TRACE_SERVER, "signal[%d] triggered.", sig);
  +
  int status;
  pid_t pid;
  switch (sig)
  