Am Thursday 21 January 2010 23:56:07 schrieb Vicente Botet Escriba:
I understand the intent of lazy constructing the local transactions. IMO this lazy construction can be done, but as soon as a resource has already a transaction, any global nested transaction should create a local transaction on it. All the resources have the same nested level of transaction except those that have none. This should solve the preceding issue, and let STM check for rollback only as soon as possible.
ok, that STM can check on each access makes it even easier: let's introduce a ResourceManager::check(transaction &) function, which is called by the TransactionManager every time a transaction is created or committed(or on every access?). then there is no need to create empty nested transactions, is there? this could even be exposed to the user as basic_transaction<>::check(), which checks each resource, so he can do something like this: transaction tx; //modify res tx.check(); //do something unrelated, non-transactional, that takes a while //continue modifying res
if (instance_==0) { scoped_lock<mutex> lk(mtx_); if (instance_==0) instance_ = new txmgr(...); } // here instance_!= 0
I used something like that in basic_transaction_manager::resource_transaction before, but I believe this is invalid code. what stops the compiler from inlining the txmgr constructor and decomposing it into code like this? if(instance_==0){ scoped_lock<mutex> lk(mtx_); if(instance_==0){ instance_=operator new(sizeof(txmgr)); //construct the txmgr in instance_; } }
return *instance_; } static char *db_filename; ... }; char * txmgr::db_filename="file.db";
I put that in main() because configuration options might be determined at runtime. but ok, that might be quite rare. I'd still prefer that it's the user's obligation to construct a transaction manager, but maybe that's also just a difference in style. what exactly is your issue with that? that the user could make a programming error by omitting the construction?
int main(){ basic_transaction<txmgr> tx; ... tx.commit(); }
Can you found this code on your book? ;-)
no, not there :)