John Sirois created THRIFT-3583:
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Summary: Add support for generating immutable java stubs for
structs and unions
Key: THRIFT-3583
URL: https://issues.apache.org/jira/browse/THRIFT-3583
Project: Thrift
Issue Type: New Feature
Components: Java - Compiler, Java - Library
Reporter: John Sirois
In certain domains and depending on consuming project coding style, having
thrift entities (structs and unions) be immutable by default is advantageous to
both reasoning about code safety and correctness as well as certain performance
optimizations. An example of such a domain/project is found in Apache Aurora
which uses thrift to define its core data model, RPC API and as its medium for
stable storage serialization. Aurora must ensure thrift structs used as keys
in sets and maps are immutable and it must be able to perform bulk calculations
against these objects efficiently. Both requirements are hindered by the
thrift java generated code which is fundamentally mutable. Today Aurora works
around this by generating immutable wrappers with a custom python script, but
ideally it could just say {{thrift --gen java:immutable}} or {{thrift --gen
java_immut}} and opt in to immutable generated entities. An experiment writing
an immutable code generator using the Facebook swift library is discussed
[here|http://markmail.org/message/a6sdqcelgokw6mwz] and implemented
[here|https://reviews.apache.org/r/42748]. Performance improvements for the
Aurora use cases are documented [here|https://goo.gl/gR8zgu].
The concrete proposal is to add a new mode of java codegen (I think a new gen
lang, like {{java_immut}} will probably be needed vs another option to the
existing {{java}} gen lang) that generates immutable thrift entities. This is
harder than it sounds given the goal of leveraging the existing java support
lib as much as possible since the existing supporting thrift java lib assumes
mutable entities at its core with wide ripple. This starts in
[TBase|https://github.com/apache/thrift/blob/master/lib/java/src/org/apache/thrift/TBase.java#L37]
and flows from there up through the [deserialization
stack|https://github.com/apache/thrift/blob/master/lib/java/src/org/apache/thrift/TDeserializer.java#L70-L86].
Although not insurmountable, some thought will need to be given to a
restructuring of these mutable-assuming APIs into read and write parts that the
existing interfaces can be re-composed on top of to make way for the immutable
option. The alternative is to write a whole new support lib like {{javame}}
has done - not a 1st choice!
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