Inter-Process Communications

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• Processes within a host may be independent or cooperating.
• Reasons for cooperating processes:
  • Information sharing
  • Computation speedup
  • Modularity
  • Convenience
• Means of communication for cooperating processes is called Inter-Process Communication

IPC Communication Models

Process is designed for isolation, so IPC is not easy!!

• Message-passing
  • useful for exchanding small amounts of data
  • simple to implement in the OS
  • somtimes cumbersome for the user as code is sprinkled with send/recv operations
  • high-overhead: one syscall per communication operation
• Shared Memory
  • low-overhead: a few syscalls initially, and then none.
  • more difficult to implement in the OS.

Shared Memory

• Processes need to establish a shared memory region
  • One process creates a shared memory segement
  • Processes can then attach it to their address spaces. (Note that this is really contrary to the memory protection idea central to multi-programming!)

存在的问题就是不安全，我们可以拿到 share_id, 就可以把共享内存 attach 到自己的进程上，可以观察到其它进程的数据。

We are breaking one of the fundamental abstractions provided by the OS: memory isolation.

Sharing memory among multiple running contet is done using threads.

Message Passing

• Two fundamental operations
  • send: to send a message
  • recv: to receive a message
• If processes P and Q wish to communicate they
  • establish a communication link between them
  • place calls to sned() and recv()
  • optionally shutdown the communication link
• Message passing is key for distributed computing.

Implementing Message-Passing

• Implementation of commmunication link
  • Physical: shared memory, hardware bus, network
  • Logical: Direct or indirect, synchronous or asynchronous, automatic or explicit buffering
• Direct Communication
  • Processes must name each other explicitly.
  • link 太多了
• Indirect Communication
  • Messages are directed and received from mailboxes(also referred to as ports)

Synchronization

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最后更新: 2024年10月20日 11:25:08
创建日期: 2024年10月20日 11:25:08