STM on Android

[zhou...@163.com]

I've tryed SillyClock on android and works but when I proceed to more complex transaction involving both writeTVar and orElse, the App crashed because putIfAbsent was not implemented, so I replace java.util.Map to java.util.ConcurrentHashMap and it works again

[Dierk König]

Ok, thanks a lot!

I have to look more closely into this, esp wrt contention 

and effect on performance. 

Cool to see Frege STM on Android!

all the best

Dierk

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[V]

The log must be ordered to make the Two Phase Locking work correctly. The method putIfAbsent should be rebuild in the TransactionLog locally to make it downwards compatible with older Java library versions.

[V]

In more detail:

As far as I know, ConcurrentHashMap does not make any statement about the order of the elements. Two Phase Locking relies on the order of locks to avoid dead locks. Thus, if you have many concurrent processes on the same variables and you use a non ordered map for log, you may experience dead locks. Furthermore, if you use ConcurrentHashMap, you have overhead for synchronization, as the TransactionLog does not need to be synchronized because it is thread local. The methods of the TransactionLog will never be called concurrently.

Sorry for the long delay and the first sketchy answer.