Re: PATCHES: start adding Mercurial backend (HgOutputOption)

Greg Ward wrote:
> [from my patches]
>>     txn = self.repo.transaction()
>>     try:
>>       node = self.repo.commitctx(mctx)
>>       txn.close()
>>     finally:
>>       del txn
>>     return node
> 
> [Michael inquires]
>> I don't understand the point of the try...finally here.  "del txn" does
>> not force txn.__del__() to be run; it only unbinds the local "txn"
>> variable
> 
> [I plead ignorance]
>> I'll ask on mercurial-devel about this idiom.
> 
> Got the answer.  Without the "finally: del txn", an exception thrown
> from the "try" clause creates a traceback object that retains
> references to every stack frame.  That includes references to all
> local variables in each stack frame.  So in that case, the txn
> destructor is invoked much later and far away from here.  The "del
> txn" removes it from the current stack frame, ensuring that it's not
> kept around in case of an exception.

Yes, good point.  Thanks for researching this.

Michael

------------------------------------------------------
http://cvs2svn.tigris.org/ds/viewMessage.do?dsForumId=1667&dsMessageId=2403387

To unsubscribe from this discussion, e-mail: [[email protected]].