Concurrent Execution

The modules described in this chapter provide support for concurrent execution of code. The appropriate choice of tool will depend on the task to be executed (CPU bound vs IO bound) and preferred style of development (event driven cooperative multitasking vs preemptive multitasking). See the Concurrency HOWTO.

Here’s an overview of the modules:

• threading — Thread-based parallelism
  • Thread-Local Data
  • Thread Objects
  • Lock Objects
  • RLock Objects
  • Condition Objects
  • Semaphore Objects
    • Semaphore Example
  • Event Objects
  • Timer Objects
  • Barrier Objects
  • Using locks, conditions, and semaphores in the with statement
• multiprocessing — Process-based parallelism
  • Introduction
    • The Process class
    • Contexts and start methods
    • 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
      • 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 start methods
    • The spawn and forkserver start methods
  • Examples
• multiprocessing.shared_memory — Shared memory for direct access across processes
• The concurrent package
• concurrent.futures — Launching parallel tasks
  • Executor Objects
  • ThreadPoolExecutor
    • ThreadPoolExecutor Example
  • InterpreterPoolExecutor
  • ProcessPoolExecutor
    • ProcessPoolExecutor Example
  • Future Objects
  • Module Functions
  • Exception classes
• subprocess — Subprocess management
  • Using the subprocess Module
    • Frequently Used Arguments
    • Popen Constructor
    • Exceptions
  • Security Considerations
  • Popen Objects
  • Windows Popen Helpers
    • Windows Constants
  • Older high-level API
  • Replacing Older Functions with the subprocess Module
    • Replacing /bin/sh shell command substitution
    • Replacing shell pipeline
    • Replacing os.system()
    • Replacing the os.spawn family
    • Replacing os.popen()
  • Legacy Shell Invocation Functions
  • Notes
    • Converting an argument sequence to a string on Windows
    • Disable use of posix_spawn()
• sched — Event scheduler
  • Scheduler Objects
• queue — A synchronized queue class
  • Queue Objects
    • Terminating queues
  • SimpleQueue Objects
• contextvars — Context Variables
  • Context Variables
  • Manual Context Management
  • asyncio support

The following are support modules for some of the above services:

• _thread — Low-level threading API