APR::Pool - Perl API for APR pools
use APR::Pool ();
my $sp = $r->pool->new;
my $sp2 = APR::Pool->new;
# $sp3 is a subpool of $sp,
# which in turn is a subpool of $r->pool
$sp3 = $sp->new;
print '$r->pool is an ancestor of $sp3'
if $r->pool->is_ancestor($sp3);
# but sp2 is not a sub-pool of $r->pool
print '$r->pool is not an ancestor of $sp2'
unless $r->pool->is_ancestor($sp2);
# $sp4 and $sp are the same pool (though you can't
# compare the handle as variables)
my $sp4 = $sp3->parent_get;
# register a dummy cleanup function
# that just prints the passed args
$sp->cleanup_register(sub { print @{ $_[0] || [] } }, [1..3]);
# tag the pool
$sp->tag("My very best pool");
# clear the pool
$sp->clear();
# destroy sub pool
$sp2->destroy;
"APR::Pool" provides an access to APR pools, which are used for an
easy memory management.
Different pools have different life scopes and therefore one doesn't need to
free allocated memory explicitly, but instead it's done when the pool's life
is getting to an end. For example a request pool is created at the beginning
of a request and destroyed at the end of it, and all the memory allocated
during the request processing using the request pool is freed at once at the
end of the request.
Most of the time you will just pass various pool objects to the methods that
require them. And you must understand the scoping of the pools, since if you
pass a long lived server pool to a method that needs the memory only for a
short scoped request, you are going to leak memory. A request pool should be
used in such a case. And vice versa, if you need to allocate some memory for a
scope longer than a single request, then a request pool is inappropriate,
since when the request will be over, the memory will be freed and bad things
may happen.
If you need to create a new pool, you can always do that via the
"new()" method.
"APR::Pool" provides the following functions and/or methods:
Register cleanup callback to run
$pool->cleanup_register($callback);
$pool->cleanup_register($callback, $arg);
- obj: $pool ( "APR::Pool object" )
- The pool object to register the cleanup callback for
- arg1: $callback ( CODE ref or sub name )
- a cleanup callback CODE reference or just a name of the
subroutine (fully qualified unless defined in the current package).
- opt arg2: $arg ( SCALAR )
- If this optional argument is passed, the $callback function
will receive it as the first and only argument when executed.
To pass more than one argument, use an ARRAY or a HASH reference
- ret: no return value
- excpt:
- If a registered callback dies or throws an exception $@ is
stringified and passed to "warn()". Usually, this results in
printing it to the error_log. However, a $SIG{__WARN__} handler can
be used to catch them.
$pool->cleanup_register(sub {die "message1\n"});
$pool->cleanup_register(sub {die "message2\n"});
my @warnings;
{
local $SIG{__WARN__}=sub {push @warnings, @_};
$pool->destroy; # or simply undef $pool
}
Both of the cleanups above are executed at the time
"$pool->destroy" is called. @warnings contains
"message2\n" and "message1\n" afterwards.
"$pool->destroy" itself does not throw an exception. Any
value of $@ is preserved.
- since: 2.0.00
If there is more than one callback registered (when "cleanup_register"
is called more than once on the same pool object), the last registered
callback will be executed first (LIFO).
Examples:
No arguments, using anon sub as a cleanup callback:
$r->pool->cleanup_register(sub { warn "running cleanup" });
One or more arguments using a cleanup code reference:
$r->pool->cleanup_register(\&cleanup, $r);
$r->pool->cleanup_register(\&cleanup, [$r, $foo]);
sub cleanup {
my @args = (@_ && ref $_[0] eq ARRAY) ? @{ +shift } : shift;
my $r = shift @args;
warn "cleaning up";
}
No arguments, using a function name as a cleanup callback:
$r->pool->cleanup_register('foo');
Clear all memory in the pool and run all the registered cleanups. This also
destroys all sub-pools.
$pool->clear();
- obj: $pool ( "APR::Pool object" )
- The pool to clear
- ret: no return value
- since: 2.0.00
This method differs from "destroy()" in that it is not freeing the
previously allocated, but allows the pool to re-use it for the future memory
allocations.
"DESTROY" is an alias to "destroy". It's there so that
custom "APR::Pool" objects will get properly cleaned up, when the
pool object goes out of scope. If you ever want to destroy an
"APR::Pool" object before it goes out of scope, use
"destroy".
- since: 2.0.00
Destroy the pool.
$pool->destroy();
- obj: $pool ( "APR::Pool object" )
- The pool to destroy
- ret: no return value
- since: 2.0.00
This method takes a similar action to "clear()" and then frees all the
memory.
Determine if pool a is an ancestor of pool b
$ret = $pool_a->is_ancestor($pool_b);
- obj: $pool_a ( "APR::Pool object" )
- The pool to search
- arg1: $pool_b ( "APR::Pool object" )
- The pool to search for
- ret: $ret ( integer )
- True if $pool_a is an ancestor of $pool_b.
- since: 2.0.00
For example create a sub-pool of a given pool and check that the pool is an
ancestor of that sub-pool:
use APR::Pool ();
my $pp = $r->pool;
my $sp = $pp->new();
$pp->is_ancestor($sp) or die "Don't mess with genes!";
Create a new sub-pool
my $pool_child = $pool_parent->new;
my $pool_child = APR::Pool->new;
- obj: $pool_parent ( "APR::Pool object" )
- The parent pool.
If you don't have a parent pool to create the sub-pool from, you can use
this object method as a class method, in which case the sub-pool will be
created from the global pool:
my $pool_child = APR::Pool->new;
- ret: $pool_child ( "APR::Pool object" )
- The child sub-pool
- since: 2.0.00
Get the parent pool
$parent_pool = $child_pool->parent_get();
- obj: $child_pool ( "APR::Pool object" )
- the child pool
- ret: $parent_pool ( "APR::Pool object" )
- the parent pool. "undef" if there is no parent
pool (which is the case for the top-most global pool).
- since: 2.0.00
Example: Calculate how big is the pool's ancestry:
use APR::Pool ();
sub ancestry_count {
my $child = shift;
my $gen = 0;
while (my $parent = $child->parent_get) {
$gen++;
$child = $parent;
}
return $gen;
}
Tag a pool (give it a name)
$pool->tag($tag);
- obj: $pool ( "APR::Pool object" )
- The pool to tag
- arg1: $tag ( string )
- The tag (some unique string)
- ret: no return value
- since: 2.0.00
Each pool can be tagged with a unique label. This can prove useful when doing
low level apr_pool C tracing (when apr is compiled with
"-DAPR_POOL_DEBUG"). It allows you to
grep(1) for the tag you
have set, to single out the traces relevant to you.
Though there is no way to get read the tag value, since APR doesn't provide such
an accessor method.
"APR::Pool" also provides auto-generated Perl interface for a few
other methods which aren't tested at the moment and therefore their API is a
subject to change. These methods will be finalized later as a need arises. If
you want to rely on any of the following methods please contact the the
mod_perl development mailing list so we can help each other take the steps
necessary to shift the method to an officially supported API.
META: Autogenerated - needs to be reviewed/completed
Preparing for
exec() --- close files, etc., but *don't* flush I/O
buffers, *don't* wait for subprocesses, and *don't* free any memory. Run all
of the child_cleanups, so that any unnecessary files are closed because we are
about to exec a new program
- ret: no return value
- since: subject to change
mod_perl 2.0 documentation.
mod_perl 2.0 and its core modules are copyrighted under The Apache Software
License, Version 2.0.
The mod_perl development team and numerous contributors.