On 11/05/2012 00:11, Mike Duigou wrote:
Hello all;
A benign but potentially expensive race condition was discovered in
java.util.UUID. The initialization of numberGenerator may cause the creation of
a number of SecureRandom instances if multiple threads are attempting to
initialize the field at the same time. This can happen because creation of the
SecureRandom instances, depending upon system configuration and state, may take
a significant amount of time.
Using a shared SecureRandom instance for the numberGenerator is an
optimization--nothing bad happens as a result of each thread using it's own
instance. However, creation of multiple SecureRandom instances, especially
during system startup, may be expensive or have high latency if no previous
SecureRandom instances have been created.
Accordingly, a holder class is used to ensure that only a single SecureRandom
instance is created. The holder also serves to defer initialization of
numberGenerator until randomUUID() is first called.
Webrev:
http://cr.openjdk.java.net/~mduigou/7071826/0/webrev/
This issue will be proposed for backport to Java 7u6 once integrated into Java 8
The implementation change looks good to me. For the javadoc change then
could you link to RFC 4122 on the IEFT site?
I don't quite get the test update, it improves the test but I don't see
how it might demonstrate the race condition. Minor consistency comment
is that the if statements use braces whereas the existing code doesn't,
also missing space in "if(".
-Alan.
