Bug 50265

Summary:	FormatDateSupport.dateFormatCache lazy init is not safe
Product:	Taglibs	Reporter:	Sebb <sebb>
Component:	Standard Taglib	Assignee:	Tomcat Developers Mailing List <dev>
Status:	RESOLVED FIXED
Severity:	normal
Priority:	P2
Version:	unspecified
Target Milestone:	---
Hardware:	PC
OS:	Windows XP
Bug Depends on:	32311
Bug Blocks:

Description Sebb 2010-11-13 06:53:23 UTC

FormatDateSupport.dateFormatCache is private and static.

It is initialised in the createFormatter method, however access is not synchronised, so the field might not be published correctly.

This can result in different threads getting different instances.
If this is acceptable, then this should be documented in the code.
Otherwise consider using IODH idiom.

Comment 1 Jeremy Boynes 2011-01-01 15:18:25 UTC

The caching was added to resolve 32311, which was opened due to contention issues with DateFormat.getTimeInstance() calling Calendar.getInstance() which was synchronized. However, the synchronized keyword was removed with Java 1.4 so this should no longer be an issue for us.

#32311 also notes that the calls to format() on the cached formatters are not thread safe and need to be synchronized; this is missing from the current implementation. However, in many applications the date/time patterns and Locale are likely to be the same and the cache only holds one instance of the formatter. By synchronizing on it we will introduce a contention point just like the the fix was trying to avoid.

Comment 2 Jeremy Boynes 2011-01-02 12:35:46 UTC

Addressed by reverting the addition of the cache added to address #32311.