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# Optional Operating System Services

The modules described in this chapter provide interfaces to operating system features that are available on selected operating systems only. The interfaces are generally modeled after the Unix or C interfaces but they are available on some other systems as well (e.g. Windows or NT). Here’s an overview:

- `select` — Waiting for I/O completion
  - Edge and Level Trigger Polling (epoll) Objects
  - Polling Objects
  - Kqueue Objects
  - Kevent Objects
- `threading` — Higher-level threading interface
  - Thread Objects
  - Lock Objects
  - RLock Objects
  - Condition Objects
  - Semaphore Objects
    - `Semaphore` Example
  - Event Objects
  - Timer Objects
  - Using locks, conditions, and semaphores in the `with` statement
  - Importing in threaded code
- `dummy_threading` — Drop-in replacement for the `threading` module
- `_thread` — Low-level threading API
- `_dummy_thread` — Drop-in replacement for the `_thread` module
- `multiprocessing` — Process-based “threading” interface
  - Introduction
    - The `Process` class
    - Exchanging objects between processes
    - Synchronization between processes
    - Sharing state between processes
    - Using a pool of workers
  - Reference
    - `Process` and exceptions
    - Pipes and Queues
    - Miscellaneous
    - Connection Objects
    - Synchronization primitives
    - Shared `ctypes` Objects
      - The `multiprocessing.sharedctypes` module
    - Managers
      - Namespace objects
      - Customized managers
      - Using a remote manager
    - Proxy Objects
      - Cleanup
    - Process Pools
    - Listeners and Clients
      - Address Formats
    - Authentication keys
    - Logging
    - The `multiprocessing.dummy` module
  - Programming guidelines
    - All platforms
    - Windows
  - Examples
- `mmap` — Memory-mapped file support
- `readline` — GNU readline interface
  - Example
- `rlcompleter` — Completion function for GNU readline
  - Completer Objects

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