Re: [boost] Boost library submission (poll for interest)

Subject: Re: [boost] Boost library submission (poll for interest)
From: strasser_at_[hidden]
Date: 2010-01-18 05:34:45

Zitat von "vicente.botet" <vicente.botet_at_[hidden]>:
>> what do you think about the basic_* and alias approach? is that feasible for
>> your library?
>
> Yes I think so.

great. Bob, what about your library?

> Does TransactionManager::begin_transaction makes a transaction or  
> registers the stack allocated one?

undefined.
the basic_transaction_manager implementation does neither(see below).

> unspecified TM::begin_transaction() ;
> what about
> void TM::begin_transaction(TM::transaction&) ;

I considered that, but this approach has some problems(transaction  
must be DefaultConstructible, deferred "construction", ...) and the  
current approach is as powerful.
note that using a return value does not mean that the transaction has  
to be CopyConstructible, the only requirement is that

TransactionManager::transaction(txmgr.begin_transaction())

is a valid expression.

you can for example do the following and still comply with the concept:

class transaction_manager{
   struct construct_tag{};
public:
   construct_tag begin_transaction(){ return construct_tag(); }
   class transaction : noncopyable{
     explicit transaction(construct_tag);
   }
};

in case you asked this question because of dynamic allocation, there  
is not a single allocation caused e.g. by the following code (if the  
accessed object is already loaded from disk):

transaction tx;
pinned_loc<pers_type const> l;
std::cerr << l->value;
tx.commit();

whatever you store in ResourceManager::transaction of your resource  
manager resides on the user´s stack.

>
> I would like to see something in the line of
>
> namespace this_transaction {
>     transaction* current();
>     ...
> }
>
> or
>
> namespace current_transaction {
>     ...
> }

what´s your point of this? that you´d like to have a simple syntax to  
obtain the current transaction?

a namespace doesn´t provide the type of the transaction manager  
configured by the user.

the syntax to obtain the global transaction currently is:

TxMgr::active().active_transaction()

as in, obtain the active transaction manager, and then obtain the  
active transaction from the manager.

the return value is of type (TxMgr::transaction &).