NullPointerExceptions - CommonLogger.legacyLogger is not thread-safe

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I've been running load tests using jain-sip and I've found a concurrence 
problem on CommonLogger. Running lots of instances of SipStackImpl causes 
NullPointerExceptions on loggers.

If I comment 723 line of SipStackImpl 
(https://code.google.com/p/jain-sip/source/browse/src/gov/nist/javax/sip/SipStac
kImpl.java):

// CommonLogger.legacyLogger = stackLogger;

the problem is solved.

Doing a quick analysis, we can verify that the variable 
CommonLogger.legacyLogger
is not thread safe


What version of the product are you using? On what operating system?
- Jain-sip-ri version 1.2.170
- Windows 7 64 bits

Original issue reported on code.google.com by joaosavio on 2 Jun 2014 at 7:17