OpenCensus Runtime Context

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The OpenCensus Runtime Context provides in-process context propagation. By default, thread local storage is used for Python 2.7, 3.4 and 3.5; contextvars is used for Python >= 3.6, which provides asyncio support.

Installation

This library is installed by default with opencensus, there is no need to install it explicitly.

Usage

In most cases context propagation happens automatically within a process, following the control flow of threads and asynchronous coroutines. The runtime context is a dictionary stored in a context variable <https://docs.python.org/3/library/contextvars.html>_ when available, and in thread local storage <https://docs.python.org/2/library/threading.html#threading.local>_ otherwise.

There are cases where you may want to propagate the context explicitly:

Explicit Thread Creation

.. code:: python

    from threading import Thread
    from opencensus.common.runtime_context import RuntimeContext

    def work(name):
        # here you will get the context from the parent thread
        print(RuntimeContext)

    thread = Thread(
        # propagate context explicitly
        target=RuntimeContext.with_current_context(work),
        args=('foobar',),
    )
    thread.start()
    thread.join()

Thread Pool
~~~~~~~~~~~

.. code:: python

    from multiprocessing.dummy import Pool as ThreadPool
    from opencensus.common.runtime_context import RuntimeContext

    def work(name):
        # here you will get the context from the parent thread
        print(RuntimeContext)

    pool = ThreadPool(2)
    # propagate context explicitly
    pool.map(RuntimeContext.with_current_context(work), [
        'bear',
        'cat',
        'dog',
        'horse',
        'rabbit',
    ])
    pool.close()
    pool.join()

References
----------

* `Examples <https://github.com/census-instrumentation/opencensus-python/tree/master/context/opencensus-context/examples>`_
* `OpenCensus Project <https://opencensus.io/>`_