Application root in garbage collection
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Troubleshoot performance issues in Java environment. I'd like to suggest a slightly different method that occured to me, I don't know if it has any official name:. Objects by themeselves don't have a reference counter. Instead, groups of one or more objects have a single reference counter for the entire group, which defines the lifetime of all the objects in the group.
A reference to an object affects the reference count of the object's group only if it's the reference external to the group. If two objects form a circular reference, they should be made a part of the same group. If two groups create a circular reference, they should be united into a single group. Bigger groups allow more reference-freedom, but objects of the group have more potential of staying alive while not needed.
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I have always redesigned to avoid the issue. One of the common cases where this comes up is the parent child relationship where the child needs to know about the parent. There are 2 solutions to this. Convert the parent to a service, the parent then does not know about the children and the parent dies when there are no more children or the main program drops the parent reference. If the parent must have access to the children, then have a register method on the parent which accepts a pointer that is not reference counted, such as an object pointer, and a corresponding unregister method.
The child will need to call the register and unregister method. When the parent needs to access a child then it type casts the object pointer to the reference counted interface. Augment naive reference counting with a cycle detector: counts decremented to non-zero values are considered to be potential sources of cycles and the heap topology around them is searched for cycles.
Constrain the language such that its programs can only ever produce acyclic aka unidirectional heaps. Erlang and Mathematica do this. Replace references with dictionary lookups and then implement your own garbage collector that can collect cycles. Note: You can replace the word achievements with orders if you don't like achievements. But who doesn't like achievements?
The idea was going to be that as something interesting happened, the system would call the IAchievementController and notify them that something interesting happend:. And when an event happens, the controller will iterate through each child and notify them of the event through their own Notify method:. If the Achievement object decides the event is something it would be interested in it will notify its child criteria:.
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But what happens when the achievement's criteria have been met? Meaning that the Criteria will need a reference to its parent; the who are now referencing each other - memory leak. And when an achievement is finally completed, it is going to have to notify its parent controller, so it can update views:. Now the Controller and its child Achievements circularly reference each other - more memory leaks. But we still have a circular reference, it just takes longer:.
Now the World of Warcraft api is not object-oriented friendly. But it does solve any circular references:. Do not pass references to the Controller. Have a single, global, singleton, Controller class.
That way an achievement doesn't have to reference the controller, just use it. Cons: Makes testing, and mocking, impossible - because you have to have a known global variable.
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An achievement doesn't know its list of criteria. If you want the Criteria for an Achievement you ask the Controller for them:. Cons: An Achievement can no longer decide to pass notifications to it's Criteria , because it doesn't have any criteria. You now have to register Criteria with the Controller. When a Criteria is completed, it notifies the Controller , who notifies the Achievement :. Having weak references is one solution.
The only other solution I know of is to avoid circular owning references all together. If you have shared pointers to objects, then this means semantically that you own that object in a shared manner. If you use shared pointers only in this way, then you can hardly get cyclic references. It does not occur very often that objects own each other in a cyclic manner, instead objects are usually connected through a hierarchical tree-like structure.
This is the case I'll describe next. If you have a tree with objects having a parent-child relationship, then the child does not need an owning reference to its parent, since the parent will outlive the child anyways. Hence a non-owning raw back pointer will do. This also applies to elements pointing to a container in which they are situated.
The container should, if possible, use unique pointers or values instead of shared pointers anyways, if possible.
NodeJS et le Garbage Collector
If you have a bunch of objects that can wildly point to each other and you want to clean up as soon as some objects are not reachable, then you might want to build a container for them and an array of root references in order to do garbage collection manually. In the real world I have found that the actual use cases of shared pointers are very limited and they should be avoided in favor of unique pointers, raw pointers, or -- even better -- just value types.
Shared pointers are usually used when you have multiple references pointing to a shared variable. Sharing causes friction and contention and should be avoided in the first place, if possible. However, sometimes shared pointers are needed.
Shared pointers are also used in order to extend the lifetime of an object. This does usually not lead to cyclic references.
La taille des segments alloués par le garbage collector est spécifique à l'implémentation et susceptible de changer à tout moment, y compris les mises à jour périodiques. The size of segments allocated by the garbage collector is implementation-specific and is subject to change at any time, including in periodic updates. Votre application ne doit jamais faire d'hypothèses concernant une taille de segment particulière, ni dépendre de celle-ci. Elle ne doit pas non plus tenter de configurer la quantité de mémoire disponible pour les allocations de segments. Your app should never make assumptions about or depend on a particular segment size, nor should it attempt to configure the amount of memory available for segment allocations.
Moins il y a d'objets alloués sur le tas, moins le garbage collector a à faire. The fewer objects allocated on the heap, the less work the garbage collector has to do. Lorsque vous allouez des objets, n'utilisez pas de valeurs arrondies qui dépassent vos besoins, par exemple en allouant un tableau de 32 octets lorsque vous avez besoin de seulement 15 octets.
When you allocate objects, do not use rounded-up values that exceed your needs, such as allocating an array of 32 bytes when you need only 15 bytes. Lorsqu'un garbage collection est déclenché, le garbage collector libère la mémoire occupée par les objets morts. When a garbage collection is triggered, the garbage collector reclaims the memory that is occupied by dead objects. Le processus de libération compacte les objets vivants afin qu'ils soient déplacés ensemble, et l'espace inutilisé est supprimé, ce qui entraîne la diminution du tas.
The reclaiming process compacts live objects so that they are moved together, and the dead space is removed, thereby making the heap smaller. Les objets alloués ensemble restent ainsi ensemble sur le tas managé, pour conserver leur emplacement. This ensures that objects that are allocated together stay together on the managed heap, to preserve their locality.
Le déroulement fréquence et durée des garbage collection est le résultat du volume des allocations et de la quantité de mémoire restante sur le tas managé. The intrusiveness frequency and duration of garbage collections is the result of the volume of allocations and the amount of survived memory on the managed heap.
The heap can be considered as the accumulation of two heaps: the large object heap and the small object heap. The large object heap contains very large objects that are 85, bytes and larger. Ces objets du tas d'objets volumineux sont généralement des tableaux.