Re: Avoiding mutual retain cycles
Re: Avoiding mutual retain cycles
- Subject: Re: Avoiding mutual retain cycles
- From: Marcel Weiher <email@hidden>
- Date: Mon, 21 Jul 2008 21:21:46 -0700
On Jul 21, 2008, at 13:03 , Philippe Mougin wrote:
Le 21 juil. 08 à 20:50, Markus Spoettl a écrit :
I'm wondering if there is a general rule or mechanism that suggests
what to do in such a case. For instance, how are delegates
implemented in AppKit, are they retained? If so, when are they
released. It can't be in -dealloc, otherwise everything would lock
itself out of deallocation?
In the general case, there is no rule or mechanism to deal with
retain cycles other than implementing something equivalent to a
garbage collector. In some situations, however, the specific
semantics and life-cycle of the objects you are dealing with allow
implementing more simpler, ad hoc solutions (e.g., ownership
management in the view hierarchy). Still, this requires notable
housekeeping efforts and is often error prone. If you are in a
situation where you can make use of Cocoa's garbage collector, you
should go for it. It will free you from a bunch of low-level memory
management tasks, including having to care about cyclic references.
http://portal.acm.org/citation.cfm?id=1035292.1028982
"Tracing and reference counting are uniformly viewed as being
fundamentally different approaches to garbage collection that possess
very distinct performance properties. We have implemented high-
performance collectors of both types, and in the process observed that
the more we optimized them, the more similarly they behaved - that
they seem to share some deep structure.
We present a formulation of the two algorithms that shows that they
are in fact duals of each other. Intuitively, the difference is that
tracing operates on live objects, or "matter", while reference
counting operates on dead objects, or "anti-matter". For every
operation performed by the tracing collector, there is a precisely
corresponding anti-operation performed by the reference counting
collector.
Using this framework, we show that all high-performance collectors
(for example, deferred reference counting and generational collection)
are in fact hybrids of tracing and reference counting. We develop a
uniform cost-model for the collectors to quantify the trade-offs that
result from choosing different hybridizations of tracing and reference
counting. This allows the correct scheme to be selected based on
system performance requirements and the expected properties of the
target application."
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