RFR: JDK-8227831: Avoid using volatile for write-once, read-many class field
OGATAK at jp.ibm.com
Wed Jul 17 06:48:44 UTC 2019
May I have a review for "JDK-8227831: Avoid using volatile for write-once,
read-many class field"?
In jdk.internal.reflect.ReflectionFactory, there is a private class field
named "langReflectAccess", which is referenced every time when the library
handles various reflective operations. This field is initialized on the
first access to the ReflectionFactory class. This field is declared as
volatile to avoid (or reduce) race condition between initialization and
references to the field.
On the platforms with weak memory model (i.e, POWER and ARM), reading a
volatile variable requires memory fence and incurs overhead. So it is
preferable to avoid use of volatile for such a write-once, read-many
langReflectAccess can be modified only in setLangReflectAccess() method.
So we can avoid using volatile by modifying setLangReflectAccess() to use
a synchronized block to avoid race condition. This change reduced elapsed
time of a micro benchmark by 9%, which repeatedly invoke
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