Garret Wilson created THRIFT-4857:
-------------------------------------
Summary: Java field hash code implementation inconsistent with
equals.
Key: THRIFT-4857
URL: https://issues.apache.org/jira/browse/THRIFT-4857
Project: Thrift
Issue Type: Bug
Components: Java - Library
Affects Versions: 0.12.0
Reporter: Garret Wilson
The {{TField}} hash code implementation is inconsistent with equals, which is a
breaking bug. If you know what hash codes are and are familiar with the Java
{{Object}} API, then you already know what I'm talking about. Basically Java
_requires_ that, if you override {{hashCode()}} and {{equals()}}, then for any
two objects that are equals they _must_ return the same has code.
The {{TField}} class API contract isn't clear about what is considered
equality, but according to the {{TField.equals()}} implementation, fields are
equal if and only if:
* Both objects are a {{TField}} (I'm generalizing here; there's another subtle
bug lurking with class checking, but that's another story).
* The fields both have the same {{type}} and {{id}}.
In other words, fields are equal _without regard to name_. And this follows the
overall Thrift architecture, in which field names are little more than window
dressing, and the IDs carry the semantics.
Unfortunately {{TField.hashCode()}} includes the name in the hash code
calculation! This completely breaks the {{Object}} contract. It makes the hash
code inconsistent with equality. To put it another way, two fields {{foo}} and
{{bar}} could have the same type and ID, and {{foo.equals(bar)}} would return
{{true}}, but they would be given different hash codes!!
This is completely forbidden, and means that with this bug you cannot use a
{{TField}} as the key in a map, for example, or even keep a {{Set<TField>}} of
fields! If you were to store {{foo} and {{bar}} as keys in a map, for example,
the different hash codes would put them in different buckets, even though they
were considered equal, providing inconsistent and strange lookup results,
depending on the name of the field you used to query with.
This is simply broken as per the Java {{Object}} API contract.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
