THRIFT-4555 Optionally disable copies of binary fields in Java constructors, getters, and setters

[bpodgursky]

THRIFT-2233 added safeguards when working with binary fields by performing TBaseHelper.copyBinary on the input bytes in relevant constructors, getters and setters in the Java client. While this is safer, it incurs a heavy overhead cost in GC churn by unnecessarily creating and destroying byte arrays when the input does happen to be safe.

This PR introduces a flag to disable these copies of binary fields, to improve performance in situations where developers are sure that the input (or output) will not later be mutated.

This builds without issue for me locally. This does not currently have any tests; I can add tests if this new flag is plausibly acceptable to the maintainers.

[dcelasun]

Sounds reasonable to me, but I'd like to get a few more +1s before I merge this.

And yes, please add tests.

[bpodgursky]

@dcelasun I have added tests. Let me know if anything else would be helpful.

Is there anyone else I should tag to pull in a couple other +1s?

[dcelasun]

There seems to be a related CI failure:

FAILED: lib/java/CMakeFiles/ThriftJava 
cd /thrift/src/thrift-1.0.0-dev/lib/java && /thrift/src/thrift-1.0.0-dev/lib/java/gradlew assemble --console=plain --no-daemon -Prelease=true -Pthrift.version=1.0.0 -Pbuild.dir=/thrift/src/thrift-1.0.0-dev/cmake_build/lib/java/build

[...]

FAILURE: Build failed with an exception.
* Where:
Script '/thrift/src/thrift-1.0.0-dev/lib/java/gradle/generateTestThrift.gradle' line: 40
* What went wrong:
A problem occurred evaluating script.
> assert thriftFile.exists()
         |          |
         |          false
         /thrift/src/thrift-1.0.0-dev/test/UnsafeTypes.thrift

[bpodgursky]

Is there a way to force a rebuild? I'm unable to reproduce this error locally, and that file is definitely in the PR. Maybe travis got confused by a rebase?

[dcelasun]

Just restarted the build, let's see how it goes.

[bpodgursky]

Ok, I actually had missed one place where the thrift file needed to be referenced. The CI builds are all passing now.

[dcelasun]

LGTM, merged.

[bpodgursky]

Thanks!