struts2 - Java Thread Safety Issue in Struts ScopeInterceptor class? -

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i'm trying understand if there thread-safety issue inside of struts2 scopeinterceptor class (/org/apache/struts2/interceptor/scopeinterceptor.java), here's code in question:

    private static map locks = new identityhashmap();  static final void lock(object o, actioninvocation invocation) throws exception {     synchronized (o) {         int count = 3;         object previous = null;         while ((previous = locks.get(o)) != null) {             if (previous == invocation) {                 return;             }             if (count-- <= 0) {                 locks.remove(o);                 o.notify();                  throw new strutsexception("deadlock in session lock");             }             o.wait(10000);         }         ;         locks.put(o, invocation);     } }  static final void unlock(object o) {     synchronized (o) {         locks.remove(o);         o.notify();     } }

i have websphere application showing 45 stalled threads, high cpu usage. 33 threads stalled @ "locks.remove(o)" inside of "unlock" method. other 12 threads stalled inside of "locks.get(o)" inside of "lock" method.

it seems me usage of identityhashmap thread-unsafe. wrapping identityhashmap collections.synchronizedmap() solve problem?:

    private static map locks = collections.synchronizedmap(new identityhashmap());  static final void lock(object o, actioninvocation invocation) throws exception {     synchronized (o) {         int count = 3;         object previous = null;         while ((previous = locks.get(o)) != null) {             if (previous == invocation) {                 return;             }             if (count-- <= 0) {                 locks.remove(o);                 o.notify();                  throw new strutsexception("deadlock in session lock");             }             o.wait(10000);         }         ;         locks.put(o, invocation);     } }  static final void unlock(object o) {     synchronized (o) {         locks.remove(o);         o.notify();     } }

it seems me author tried "fix" identityhashmap's synchronization problem using synchronized code blocks, doesn't protect against multiple threads if object "o" thread-specific object. and, since code blocks within lock , unlock separate, identityhashmap (and does!) called simultaneously more 1 thread (as per our java core evidence).

is collections.synchronizedmap() wrapper correct fix, or missing something?

i believe right, , there appears thread safety issue. developer attempting thread safe synchronizing on object "o", looks object session object rather scoped more widely. believe change needs to synchronize on locks object.


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