[C++] Threadsafety in arrow/io/hdfs.h

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Some parts of this module may be threadsafe while others not. We should investigate libhdfs threadsafety and either add appropriate locks to permit concurrent use or add comments to provide guidance about otherwise concurrent use.

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-424. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
TensorFlow's HDFS interface may provide some guidance about best practices here with libhdfs threadsafety: https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/platform/hadoop/hadoop_file_system.cc

[asfimport]

Wes McKinney / @wesm:
PR: #712

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 712
#712