Kill Processes Back

• call exit() to kill processes
  • if the process is the group leader of a processes group, then send SIGHUP to all processes in this group
  • close all socket opened by this process
  • if there are children process, then set their parent as init process
  • send SIGCHLD to its parent
• Zombie(僵屍) Process will be created when SIGCHLD is not handled by its parent
  • Zombies will occupy a Process Table Entry(進程表項) in the system
• ways to kill Zomebie Process
  • ignore SIGCHLD using SIG_IGN, and system will clear their Process Table Entries.
  • use wait() or waitpid() to wait for killing child processes.
  • use waitpid() to handler more than one killing child process by setting WNOHANG, prevented to be blocked, rather than wait().
  • fork() twice so that child process will be controled by init process.

method

pid_t waitpid(pid_t pid, int* status, int option)

parameters

• pid: 進程id
  • >0: 只等待進程號為pid的子進程退出
  • -1: 等待任何子進程退出
• option: 選項
  • WHONANG: 無子進程退出時不阻塞
• status: 存儲狀態信息

return values

• 退出的子進程id
• 0: 設置WHONANG且無子進程退出
• -1: failure
• errno: error code

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