Sahil Takiar created HDFS-14348:
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Summary: Fix JNI exception handling issues in libhdfs
Key: HDFS-14348
URL: https://issues.apache.org/jira/browse/HDFS-14348
Project: Hadoop HDFS
Issue Type: Bug
Components: hdfs-client, libhdfs, native
Reporter: Sahil Takiar
Assignee: Sahil Takiar
During some manual digging through the libhdfs code, we found several places
where we are not handling exceptions properly.
Specifically, there seem to be some violation of the following snippet from the
JNI Oracle docs
(https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/design.html#exceptions_and_error_codes):
{quote}
*Exceptions and Error Codes*
Certain JNI functions use the Java exception mechanism to report error
conditions. In most cases, JNI functions report error conditions by returning
an error code and throwing a Java exception. The error code is usually a
special return value (such as NULL) that is outside of the range of normal
return values. Therefore, the programmer can quickly check the return value of
the last JNI call to determine if an error has occurred, and call a function,
ExceptionOccurred(), to obtain the exception object that contains a more
detailed description of the error condition.
There are two cases where the programmer needs to check for exceptions without
being able to first check an error code:
[1] The JNI functions that invoke a Java method return the result of the Java
method. The programmer must call ExceptionOccurred() to check for possible
exceptions that occurred during the execution of the Java method.
[2] Some of the JNI array access functions do not return an error code, but may
throw an ArrayIndexOutOfBoundsException or ArrayStoreException.
In all other cases, a non-error return value guarantees that no exceptions have
been thrown.
{quote}
Here is a running list of issues:
* {{classNameOfObject}} in {{jni_helper.c}} calls {{CallObjectMethod}} but does
not check if an exception has occurred, it only checks if the result of the
method (in this case {{Class#getName(String)}}) returns {{NULL}}
* Exception handling in {{get_current_thread_id}} (both
{{posix/thread_local_storage.c}} and {{windows/thread_local_storage.c}}) seems
to have several issues; lots of JNI methods are called without checking for
exceptions
* Most of the calls to {{GetObjectArrayElement}} and {{GetByteArrayRegion}} in
{{hdfs.c}} do not check for exceptions properly
** e.g. for {{GetObjectArrayElement}} they only check if the result of the
operation is {{NULL}}, but they should call {{ExceptionOccurred}} to look for
pending exceptions as well
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