pqinitmask();
  PG_SETMASK(&BlockSig);
  pqsignal_pm(SIGHUP, SIGHUP_handler);  /* reread config file and have children do same */
  pqsignal_pm(SIGINT, pmdie); /* send SIGTERM and shut down */
  pqsignal_pm(SIGQUIT, pmdie);  /* send SIGQUIT and die */
  pqsignal_pm(SIGTERM, pmdie);  /* wait for children and shut down */
  pqsignal_pm(SIGALRM, SIG_IGN);  /* ignored */
  pqsignal_pm(SIGPIPE, SIG_IGN);  /* ignored */
  pqsignal_pm(SIGUSR1, sigusr1_handler);  /* message from child process */
  pqsignal_pm(SIGUSR2, dummy_handler);  /* unused, reserve for children */
  pqsignal_pm(SIGCHLD, reaper);  /* handle child termination */

posmaster主进程与后端进程信号通信机制

后端进程向posmaster主进程发信号机制
postmaster主进程处理后端进程信号 sigusr1_handler

postmaster主进程向后端进程发信号机制
后端进程处理postmaster主进程信号

判活机制

进程退出注册回调函数机制