Josh Rosen created HADOOP-11209:
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Summary: Configuration is not thread-safe
Key: HADOOP-11209
URL: https://issues.apache.org/jira/browse/HADOOP-11209
Project: Hadoop Common
Issue Type: Bug
Components: conf
Reporter: Josh Rosen
{{Configuration}} objects are not fully thread-safe, which causes problems in
multi-threaded frameworks like Spark that use these configurations to interact
with existing Hadoop APIs (such as InputFormats).
SPARK-2546 is an example of a problem caused by this lack of thread-safety. In
that bug, multiple concurrent modifications of the same Configuration (in
third-party code) caused an infinite loop because Configuration's internal
{{java.util.HashMap}} is not thread-safe.
One workaround is for our code to clone Configuration objects; unfortunately,
this also suffers from thread-safety issues on older Hadoop versions because
Configuration's constructor wasn't thread-safe (HADOOP-10456).
[Looking at a recent version of
Configuration.java|https://github.com/apache/hadoop/blob/d989ac04449dc33da5e2c32a7f24d59cc92de536/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java#L666],
it seems that the private {{updatingResource}} HashMap and {{finalParameters}}
HashSet fields the only non-thread-safe collections in Configuration (Java's
{{Properties}} class is thread-safe), so I don't think that it would be hard to
make Configuration fully thread-safe.
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