Thread Safety

There is a concept of an app-root, and thread-root XContext. The app-root stores dependecies that can be shared between threads, whule the thread-root context stores dependence for a specific thread.

By default, each Dependency subclass can be shared between different threads, ie: it's assumed to be thread-safe.

You can indicate a Dependency subclass should not be shared between threads by inheriting from xinject.dependency.DependencyPerThread instead, or by setting the class attribute (on your subclass of Dependency) thread_sharable to False; ie:

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from xinject import Dependency, DependencyPerThread

class MyThreadUnsafeDependencyOpt1(DependencyPerThread):
    ...

class MyThreadUnsafeDependencyOpt2(Dependency, thread_sharable=False):
    ...

Things that are probably not thread-safe in general are resources that contain network/remote type connections/sessions/clients.

Example for which you would want a separate dependency instance/object per-thread:

  • requests library session
  • Requests libraries session object is not thread-safe, there is issue that's been around for 7 years to make it thread safe that's still open. For now, you need a seperate requests Session per-thread.
  • requests-mock also needs the session created after it's setup, so after unit test runs.
  • boto client/dependency
  • Library says it's not thread-safe, you need to use a different object per-thread.
  • Moto mocking library for AWS services needs you to allocate a client after it's setup, (so lazily allocate client/dependency from boto).
Last update: 2023-04-15