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From "Josh Rosen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-11209) Configuration is not thread-safe
Date Fri, 17 Oct 2014 21:39:33 GMT
Josh Rosen created HADOOP-11209:

             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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