Share information between processes

  1. 透過硬碟上的文件溝通
    • 超慢
  2. 透過 kernel buffer
    • 滿快的，但這樣要一直在 user mode 和 kernel mode 來回切換，因為kernel buffer 在 kernel space
  3. 透過 shared memory region
    • shared memory region 在 user space

Mechanisms

  1. Signals

  2. Communication

    1. Data transfer
      • Byte Stream
        • Pipes
        • FIFOs(Named Pipes)
        • stream sockets
      • Message Passing
        • SystemV MsgQ
        • POSIX MsgQ
        • datagram sockets
    2. Shared Memory
      • SystemV S.M
      • POSIX S.M
      • Memory Mapping
        • anonymous memory mapping
        • memory mapped file

  3. Synchronization

Pipes

  • Related processes
    • parent-child
    • sibling
  • Executing on same machine
  • 用法
    • cmd1 | cmd2
      • cmd1 不是輸出到 stdout，而是由 kernel 維護的 buffer，也就是 pipe
      • cmd 不是從 stdin 獲取輸入，而是從 pipe 獲取
    • cmd1 | cmd2 | … | cmdn

Named Pipes / FIFOs

  • Related / Unrelated processes

  • Executing on same machine

  • creat a FIFO

    • commands
      • mkfifo
      • mknod

嘗試寫入或讀取 FIFO 時，會被 redirect 到 pipe

Signal Handling

Signal

  • Used by OS to notify running process some event has occured without the process needing to pull for that event
  • process 收到 signal 後會先停止執行並執行 signal handler
  1. A process did something
    • SIGSEGV(11), SIGFPE(8), SIGILL(4), SIGPIPE(13)…
  2. A process wants to tell another process something
    • SIGCHILD(17)
      • child process terminated
  3. User sends sig to foreground processes
    • Ctrl + C SIGINT(2)
    • Ctrl + \ SIGQUIT(3)
    • Ctrl + Z SIGTSTP(20)

disposition

決定 process 遇到 signal 時該怎麼處理

  • Term
    • teminate process
  • Ign
    • ignore
  • Core
    • terminate the process and dump core
  • Stop
    • stop the process
  • Cont
    • continue the process if it is stopped

Signal can’t not be caught

  • SIGKILL(9)
  • SIGSTOP(19)

Commands

  • trap

    可以 handle signal

kill

kill - L 可以看到 standard signal 和 real-time signal

standard signal 開頭是 SIG，realt-time signal 是 SIGRT