Questions tagged [weak-references]
A weak reference is a one that makes no claim of ownership. A weak reference keeps a reference to the object in question while it is in memory, but does not prevent the memory management system from reclaiming the associated memory when the referenced object is otherwise no longer needed. Many languages feature or support various levels of weak references, such as Swift, Objective-C, Java, C#, Python, Perl and Lisp.
weak-references
1,143
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What's the difference between SoftReference and WeakReference in Java?
What's the difference between java.lang.ref.WeakReference and java.lang.ref.SoftReference ?
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answers
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Always pass weak reference of self into block in ARC?
I am a little confused about block usage in Objective-C. I currently use ARC and I have quite a lot of blocks in my app, currently always referring to self instead of its weak reference. May that be ...
- 12.8k
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votes
8
answers
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What is the difference between a weak reference and an unowned reference?
Swift has:
Strong References
Weak References
Unowned References
How is an unowned reference different from a weak reference?
When is it safe to use an unowned reference?
Are unowned references a ...
- 51.5k
235
votes
18
answers
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views
How do I declare an array of weak references in Swift?
I'd like to store an array of weak references in Swift. The array itself should not be a weak reference - its elements should be. I think Cocoa NSPointerArray offers a non-typesafe version of this.
- 45.4k
214
votes
7
answers
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Java: difference between strong/soft/weak/phantom reference
I have read this article about different types of references in Java (strong, soft, weak, phantom), but I don't really understand it.
What is the difference between these reference types, and when ...
user1204873
190
votes
4
answers
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How to use WeakReference in Java and Android development?
I have been a Java developer for 2 years.
But I have never written a WeakReference in my code. How to use WeakReference to make my application more efficient, especially the Android application?
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votes
10
answers
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When would you use a WeakHashMap or a WeakReference?
The use of weak references is something that I've never seen an implementation of so I'm trying to figure out what the use case for them is and how the implementation would work. When have you needed ...
- 3,211
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votes
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Where does the weak self go?
I often do this,
let when = DispatchTime.now() + 2.0
DispatchQueue.main.asyncAfter(deadline: when) {
beep()
}
and in one app we often do this
tickle.fresh(){
msg in
paint()
}
but if you ...
- 17.9k
105
votes
9
answers
35k
views
Is it possible to create a "weak reference" in JavaScript?
Is there any way in JavaScript to create a "weak reference" to another object? Here is the wiki page describing what a weak reference is. Here is another article that describes them in Java. ...
- 14.3k
102
votes
8
answers
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Is there a practical use for weak references? [duplicate]
Possible Duplicate:
Weak references - how useful are they?
Since weak references can be claimed by the garbage collector at any time, is there any practical reason for using them?
- 84.7k
89
votes
11
answers
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Why can the keyword "weak" only be applied to class and class-bound protocol types
When I'm declaring variables as weak in Swift, I sometimes get the error message from Xcode:
'weak' may only be applied to class and class-bound protocol types
or
'weak' must not be applied to non-...
- 9,868
83
votes
2
answers
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Why does exist WeakHashMap, but absent WeakSet?
From J. Bloch
A ... source of memory leaks is
listeners
... The best way to ensure that
callbacks are garbage collected
promptly is to store only weak
references to them, for instance, by
...
- 15.7k
82
votes
4
answers
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views
What is the difference between a __weak and a __block reference?
I'm reading Xcode's documentation, and here is something that puzzles me:
__block typeof(self) tmpSelf = self;
[self methodThatTakesABlock:^ {
[tmpSelf doSomething];
}];
The following is copied ...
- 5,567
82
votes
4
answers
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Understanding Java's Reference classes: SoftReference, WeakReference, and PhantomReference
Can someone explain the difference between the three Reference classes (or post a link to a nice explanation)? SoftReference > WeakReference > PhantomReference, but when would I use each one? Why is ...
- 821
78
votes
2
answers
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How does weak_ptr work?
I understand how to use weak_ptr and shared_ptr. I understand how shared_ptr works, by counting the number of references in its object. How does weak_ptr work? I tried reading through the boost source ...
- 7,991
77
votes
14
answers
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Pros and Cons of Listeners as WeakReferences
What are the pros and cons of keeping listeners as WeakReferences?
The big 'Pro' of course is that:
Adding a listener as a WeakReference means the listener doesn't need to bother 'removing' itself.
...
- 44.4k
75
votes
5
answers
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Java's WeakHashMap and caching: Why is it referencing the keys, not the values?
Java's WeakHashMap is often cited as being useful for caching. It seems odd though that its weak references are defined in terms of the map's keys, not its values. I mean, it's the values I want to ...
- 43.2k
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votes
3
answers
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Weak reference benefits
Can someone explain the main benefits of different types of references in C#?
Weak references
Soft references
Phantom references
Strong references.
We have an application that is consuming a lot of ...
- 192k
71
votes
7
answers
25k
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Is there a SoftHashMap in Java?
I know there is a WeakHashMap in java.util, but since it uses WeakReferences for everything, which is only referenced by this Map, referenced objects will get lost on the next GC cycle. So it's nearly ...
- 1,876
61
votes
2
answers
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Using weak self in dispatch_async function
I read a lot of posts about using __weak self inside dispatch_async, and now I am a litle bit confused.
if I have :
self.myQueue = dispatch_queue_create("com.biview.core_data", NULL);
...
- 8,472
60
votes
3
answers
19k
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WeakReference/AsyncTask pattern in android
I have a question regarding this simple frequently occurring situation in android .
We have a main activity , we invoke an AsyncTask alongwith the reference of the mainactivity , so that that the ...
- 4,168
49
votes
6
answers
41k
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Strong and weak references in Swift
In Objective C you can define a property as having a strong or weak reference like so:
@property(strong)...
@property(weak)...
How is this done in swift?
- 6,941
49
votes
3
answers
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Cost of using weak references in Java
Has anyone researched the runtime costs involved in creating and garbage collecting Java WeakReference objects? Are there any performance issues (e.g. contention) for multi-threaded applications?
...
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votes
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Is Josh Smith's implementation of the RelayCommand flawed?
Consider the reference Josh Smith' article WPF Apps With The Model-View-ViewModel Design Pattern, specifically the example implementation of a RelayCommand (In Figure 3). (No need to read through the ...
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votes
1
answer
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How can you capture multiple arguments weakly in a Swift closure?
Is there a way to capture multiple arguments weakly in a swift closure? I know this is the syntax to capture one argument weakly:
{ [weak arg]
arg.doSomething()
}
How can I do this for two ...
- 5,034
42
votes
3
answers
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views
When to use weak references in Python?
Can anyone explain usage of weak references?
The documentation doesn't explain it precisely, it just says that the GC can destroy the object linked to via a weak reference at any time. Then what's ...
- 77.3k
42
votes
8
answers
12k
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Collections of zeroing weak references under ARC
How can I get an array of zeroing weak references under ARC? I don't want the array to retain the objects. And I'd like the array elements either to remove themselves when they're deallocated, or set ...
- 17.1k
41
votes
5
answers
12k
views
Weak references - how useful are they?
So I've been mulling over some automatic memory management ideas lately - specifically, I've been looking at implementing a memory manager based on reference counting. Of course, everyone knows that ...
- 19.1k
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votes
3
answers
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Android Asyntask: Use weak reference for context to avoid device rotate screen
In Apress Pro Android 4 the author has said that:
[...] context of currently running activity will no longer be valid when the device is rotated. [...] One approach is to use a weak reference to ...
- 30k
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votes
8
answers
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Good implementation of weak dictionary in .Net
Where can I find good implementation of IDictionary which uses weak references inside?
Dictionary should be holding only weak references to values and eventually clean up itself of dead references.
...
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votes
5
answers
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IBOutlet and viewDidUnload under ARC
There is a similar question to this on SO here, however I just want to clarify something that wasn't fully explained there.
I understand that all delegates and outlets - in fact any reference to a "...
- 36.9k
35
votes
1
answer
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JVM G1GC's mixed gc not collecting much old regions
My server is using 1.8.0_92 on CentOS 6.7, GC param is '-Xms16g -Xmx16g -XX:+UseG1GC'. So the default InitiatingHeapOccupancyPercent is 45, G1HeapWastePercent is 5 and G1MixedGCLiveThresholdPercent is ...
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answers
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Generic typeof for weak self references
I am trying to figure out a way to use typeof to create a weak reference to self for use in blocks to avoid retain cycles.
When I first read about this it seems that the convention was to use __block ...
- 10.9k
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votes
4
answers
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WeakReference and event handling
Is it a good practice to implement event handling through WeakReference if that event is the only thing holding the reference and that we would need the object to be garbage collected?
As an ...
33
votes
1
answer
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views
Should ConditionalWeakTable<TKey, TValue> be used for non-compiler purposes?
I've recently come across the ConditionalWeakTable<TKey,TValue> class in my search for an IDictionary which uses weak references, as suggested in answers here and here.
There is a definitive ...
- 1,659
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Is self captured within a nested function
With closures I usually append [weak self] onto my capture list and then do a null check on self:
func myInstanceMethod()
{
let myClosure =
{
[weak self] (result : Bool) in
if ...
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votes
2
answers
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views
weak or strong for IBOutlet and other [duplicate]
I have switched my project to ARC, and I don't understand if I have to use strong or weak for IBOutlets. Xcode do this: in interface builder, if a create a UILabel for example and I connect it with ...
- 9,203
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votes
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Using Java's ReferenceQueue
Do SoftReference and WeakReference really only help when created as instance variables? Is there any benefit to using them in method scope?
The other big part is ReferenceQueue. Besides being able to ...
- 1,879
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votes
5
answers
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What's the difference between ES6 Set and WeakSet?
ECMAScript 6 has these very similar collections: Set and WeakSet. What is the difference between them?
- 6,443
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votes
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answers
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views
HashMap with weak values
I'm implementing a cache for Objects stored persistently. The idea is:
Method getObjectFromPersistence(long id); ///Takes about 3 seconds
Method getObjectFromCache(long id) //Instantly
And have a ...
- 32.3k
29
votes
1
answer
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Set equivalent of WeakHashMap?
Is HashSet<WeakReference<T>> the Set equivalent of WeakHashMap<T>? That is, will entries be automatically deleted when they are no longer referenced?
If not, what is the equivalent?
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votes
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Weak events in .NET?
If object A listens to an event from object B, object B will keep object A alive.
Is there a standard implementation of weak events that would prevent this?
I know WPF has some mechanism but I am ...
- 4,102
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Why isn’t my weak reference cleared right after the strong ones are gone?
I am a little bit stubborn, but I want to understand weak and strong references well, so that's why I'm asking you once again.
Consider this:
__weak NSString* mySecondPointer = myText;
NSLog(@"...
- 4,627
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votes
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answers
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Using __block and __weak
I've read over this thread: What does the "__block" keyword mean? which discusses what __block is used for but I'm confused about one of the answers. It says __block is used to avoid retain ...
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votes
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answers
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How do events cause memory leaks in C# and how do Weak References help mitigate that?
There are two ways (that I know of) to cause an unintentional memory leak in C#:
Not disposing of resources that implement IDisposable
Referencing and de-referencing events incorrectly.
I don't ...
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Do capture lists of inner closures need to redeclare `self` as `weak` or `unowned`?
If I have a closure passed to a function like this:
someFunctionWithTrailingClosure { [weak self] in
anotherFunctionWithTrailingClosure { [weak self] in
self?.doSomething()
}
}
...
- 5,730
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Is it possible to create a truely weak-keyed dictionary in C#?
I'm trying to nut out the details for a true WeakKeyedDictionary<,> for C#... but I'm running into difficulties.
I realise this is a non-trivial task, but the seeming inability to declare a ...
- 1,728
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votes
6
answers
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Using objc_setAssociatedObject with weak references
I know that OBJC_ASSOCIATION_ASSIGN exists, but does it zero the reference if the target object is dealloced? Or is it like the old days where that reference needs to get nil-ed or we risk a bad ...
- 1,072
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votes
1
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Bitmap, Bitmap.recycle(), WeakReferences, and Garbage Collection
AFAIK on Android, it is recommended to reference Bitmap objects as WeakReferences in order to avoid memory leaks. When no more hard references are kept of a bitmap object, the garbage collector will ...
- 2,101
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votes
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Why does Django's signal handling use weak references for callbacks by default?
The Django docs say this on the subject:
Note also that Django stores signal
handlers as weak references by
default, so if your handler is a local
function, it may be garbage collected.
To ...
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