Alexander Falb created JOHNZON-293:
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Summary: Potential Memleak in DateConverter
Key: JOHNZON-293
URL: https://issues.apache.org/jira/browse/JOHNZON-293
Project: Johnzon
Issue Type: Bug
Components: Mapper
Reporter: Alexander Falb
[DateConverter|https://github.com/apache/johnzon/blob/master/johnzon-mapper/src/main/java/org/apache/johnzon/mapper/converter/DateConverter.java]
creates a new SimpleDateFormat for every instance for every thread the
instance is used on and never cleans them up. This may cause a high memory
usage, if lots of those converters are created instead of reused.
Two approaches to get rid of them are on my mind:
# Create a new SimpleDateFormat within the toString and fromString methods as
method variable instead of a class field.
# Use java.time.DateTimeFormatter as class field, because it is immutable and
thread-safe, and do some object conversion from java.util.Date to/from
java.time.ZonedDateTime.
I did some JMH performance tests for both (full project can be found here
[https://github.com/elexx/dateconverter-benchmark]):
{noformat}
Benchmark Mode Cnt Score Error
Units
JavaTimeDateFormatterBenchmark.formatNewFormat avgt 5 828,623 ± 8,836
ns/op
JavaTimeDateFormatterBenchmark.formatReuseFormat avgt 5 496,916 ± 5,150
ns/op
JavaTimeDateFormatterBenchmark.parseNewFormat avgt 5 1430,276 ± 11,084
ns/op
JavaTimeDateFormatterBenchmark.parseReuseFormat avgt 5 990,648 ± 280,983
ns/op
SimpleDateFormatterBenchmark.formatNewFormat avgt 5 1308,144 ± 13,993
ns/op
SimpleDateFormatterBenchmark.formatReuseFormat avgt 5 392,236 ± 3,219
ns/op
SimpleDateFormatterBenchmark.parseNewFormat avgt 5 1848,772 ± 19,412
ns/op
SimpleDateFormatterBenchmark.parseReuseFormat avgt 5 1121,955 ± 12,417
ns/op
{noformat}
In this quick test it looks like creating a new SimpleDateFormatter in each
method is quite slow (1308ns/op + 1848ns/op).
Reusing the SimpleDateFormatter is faster (392ns/op + 1121ns/op), but no option
because it is not thread-safe.
Reusing the Java8-DateTimeFormatter is equivalent (496ns/op + 990ns/op) to
Reusing SimpleDateFormatter (parsing is faster, formatting is slower, avg is
about the same)
And just for completeness: Creating a Java8-DateTimeFormatter, which is
nonsense, because it is immutable and thread-safe.
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