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Operating System

Operating System. Inter-Process Communication. IPC. How does one process communicate with another process? semaphores -- signal notifies waiting process software interrupts -- process notified asynchronously pipes -- unidirectional stream communication

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Operating System

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  1. Operating System Inter-Process Communication

  2. IPC • How does one process communicate with another process? • semaphores -- signal notifies waiting process • software interrupts -- process notified asynchronously • pipes -- unidirectional stream communication • message passing -- processes send and receive messages.

  3. Software Interrupts • Similar to hardware interrupt. • Processes interrupt each other (often for system call) • Asynchronous! Stops execution then restarts • cntl-C • child process completes • alarm scheduled by the process expires • Unix: SIGALRM from alarm() or setitimer() • resource limit exceeded (disk quota, CPU time...) • programming errors: invalid data, divide by zero

  4. Software Interrupts • SendInterrupt(pid, num) • type num to process pid, • kill() in Unix • HandleInterrupt(num, handler) • type num, use function handler • signal() in Unix • Typical handlers: • ignore • terminate (maybe w/core dump) • user-defined • (Hey, show demos!)

  5. Unreliable Signals • Before POSIX.1 standard: signal(SIGINT, sig_int); ... sig_int() { /* re-establish handler */ signal(SIGINT, sig_int); } • Another signal could come before handler re-established!

  6. more ls Pipes • One process writes, 2nd process reads % ls | more 1 Shell 2 3 stdout stdin • shell: • create a pipe • create a process for ls command, setting stdout to write side of pipe • create a process for more command, setting stdin to read side of pipe

  7. The Pipe • Bounded Buffer • shared buffer (Unix 4096K) • block writes to full pipe • block reads to empty pipe \0 b l a h . c write fd read fd

  8. The Pipe • Process inherits file descriptors from parent • file descriptor 0 stdin, 1 stdout, 2 stderr • Process doesn't know (or care!) when reading from keyboard, file, or process or writing to terminal, file, or process • System calls: • read(fd, buffer, nbytes) (scanf() built on top) • write(fd, buffer, nbytes) (printf() built on top) • pipe(rgfd) creates a pipe • rgfd array of 2 fd. Read from rgfd[0], write to rgfd[1] • (Hey, show sample code!)

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