From: Curt Arnold [mailto:[EMAIL PROTECTED]
Sent: Thu 3/24/2005 00:52
To: Log4CXX User
Subject: Re: Head vs 0.9.7
Ron Ohmer wrote:
>I am working with the latest CVS
build...
>
>I am running into issues with Pools. Which are now
required for different adapters..
>
>In our EventLogger instance, I
am trying to create a pool...
>
>My code
is:
>
>_logPool=new log4cxx::helpers::Pool();
>
>where
_logPool is defined as:
>log4cxx::helpers::Pool
*_logPool;
>
>
>
>But that is no cutting
it.
>
>are there any examples (New examples that use pools)? I
am not finding
any...
>
>
>Thanks!
>
>Ron
>
>----------------------------------------------------------------------
>Startuj
z INTERIA.PL!!! >>> http://link.interia.pl/f1837
>
>
I'm
curious why you think you need to create one.
Pools are internal detail,
hopefully most users will never need to know
that they exist.
Methods
in Apache Portable Runtime (APR) take an apr_pool_t* parameter
when they
might allocate memory to perform the function. Since
dispatching a
logging event might call APR methods that might allocate
memory, a
log4cxx::Pool instance is allocated on the stack before
dispatching the event
and passed down to the appenders. At then end of
the dispatch, the
log4cxx::Pool is destructed which will cause all
memory allocated from the
pool to go out of scope.
log4cxx::Pool& was used in the method
signature instead of apr_pool_t*
to avoid requiring log4cxx using
applications to have to have APR
include files in their include path.
The apr_pool_t* within a
log4cxx::Pool can be retrived using
getAPRPool().
There are two patterns in Pool use within
log4cxx.
Some log4cxx objects need to create a long-lived APR objects,
like a
file, socket, mutex, etc. Since the APR objects are reclaimed
when
their pool is destroyed, the pool must live at least as long as the
file
or socket. In these cases, the Appender (or other log4cxx
instance)
will contain a Pool member variable that is used to allocate
resources
that have comparable lifetimes to the log4cxx object. So
you'd have
something like:
class MyWidget {
private:
log4cxx::helpers::Pool p;
};
The other
use of pools are for transient objects or memory blocks. The
Pool in
StringHelper::toString(int, Pool&) is there since apr_itoa takes
a
apr_pool_t* parameter. The intent is that most of these calls
occur
during event dispatching and the Pool& passed into the appender
in
doAppend() is used for these allocations If you need to create
a
short-lived pool for a short-lived allocation, you would do something
like:
Pool p;
std::wstring dst;
StringHelper::toString(i, dst,
p);
