GitHub user BryanCutler opened a pull request:
https://github.com/apache/spark/pull/18825
[SPARK-12717][PYTHON] Adding thread-safe broadcast pickle registry
## What changes were proposed in this pull request?
When using PySpark broadcast variables in a multi-threaded environment,
`SparkContext._pickled_broadcast_vars` becomes a shared resource. A race
condition can occur when broadcast variables that are pickled from one thread
get added to the shared ` _pickled_broadcast_vars` and become part of the
python command from another thread. This PR introduces a thread-safe pickled
registry using thread local storage so that when python command is pickled
(causing the broadcast variable to be pickled and added to the registry) each
thread will have their own view of the pickle registry to retrieve and clear
the broadcast variables used.
## How was this patch tested?
Added a unit test that causes this race condition using another thread.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/BryanCutler/spark
pyspark-bcast-threadsafe-SPARK-12717-2_1
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/18825.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #18825
----
commit cc239a401d9d38bb0d85c34ee0a720038d9cb943
Author: Bryan Cutler <[email protected]>
Date: 2017-07-20T21:36:09Z
Added thread-safe broadcast pickle registry, using thread local storage
added regression test for multithreaded broadcast pickle
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