Java SoftReference strange behaviour
Map<E, SoftReference<T>> cache = new ConcurrentHashMap<E, SoftReference<T>>();
I have map declared a map like the above one which I'm using as a Cache.
The problem is I'm to perform all operations on the Cache immediately after adding an item to the Cache but not later.
For ex:
cache.add("Username", "Tom");
if(cache.contains("Username")) returns true but
String userName = (String)cache.get("Username") returns null.
This happens only after a long time.
If I get the value after a few hours of adding it to the cache, I get the value correctly.
If I get the value after a long time, say more than 15-20 hrs, I get null.
When GC clears SoftReference objects, will the key remain in HashMap? Is that the reason for this behaviour?
java garbage-collection soft-references
asked Dec 27 at 14:34
Forever NewUser
113
add a comment |
Map<E, SoftReference<T>> cache = new ConcurrentHashMap<E, SoftReference<T>>();
I have map declared a map like the above one which I'm using as a Cache.
The problem is I'm to perform all operations on the Cache immediately after adding an item to the Cache but not later.
For ex:
cache.add("Username", "Tom");
if(cache.contains("Username")) returns true but
String userName = (String)cache.get("Username") returns null.
This happens only after a long time.
If I get the value after a few hours of adding it to the cache, I get the value correctly.
If I get the value after a long time, say more than 15-20 hrs, I get null.
When GC clears SoftReference objects, will the key remain in HashMap? Is that the reason for this behaviour?
java garbage-collection soft-references
asked Dec 27 at 14:34
Forever NewUser
113
Is itcache.get("Username")that returns null, or is itcache.get("Username").get()that returns null? The former (which is what’s in your question) has nothing to do with SoftReferences, and is strictly a HashMap problem. The latter is simply the reference being no longer valid.
– VGR
Dec 27 at 15:42
You can use aReferenceQueueif you want to make at an effort at removing the entry from the map, but even this wont happen atomically.
– Tom Hawtin - tackline
Dec 27 at 19:32
add a comment |
Map<E, SoftReference<T>> cache = new ConcurrentHashMap<E, SoftReference<T>>();
I have map declared a map like the above one which I'm using as a Cache.
The problem is I'm to perform all operations on the Cache immediately after adding an item to the Cache but not later.
For ex:
cache.add("Username", "Tom");
if(cache.contains("Username")) returns true but
String userName = (String)cache.get("Username") returns null.
This happens only after a long time.
If I get the value after a few hours of adding it to the cache, I get the value correctly.
If I get the value after a long time, say more than 15-20 hrs, I get null.
When GC clears SoftReference objects, will the key remain in HashMap? Is that the reason for this behaviour?
java garbage-collection soft-references
asked Dec 27 at 14:34
Forever NewUser
113
Map<E, SoftReference<T>> cache = new ConcurrentHashMap<E, SoftReference<T>>();
I have map declared a map like the above one which I'm using as a Cache.
The problem is I'm to perform all operations on the Cache immediately after adding an item to the Cache but not later.
For ex:
cache.add("Username", "Tom");
if(cache.contains("Username")) returns true but
String userName = (String)cache.get("Username") returns null.
This happens only after a long time.
If I get the value after a few hours of adding it to the cache, I get the value correctly.
If I get the value after a long time, say more than 15-20 hrs, I get null.
When GC clears SoftReference objects, will the key remain in HashMap? Is that the reason for this behaviour?
java garbage-collection soft-references
java garbage-collection soft-references
asked Dec 27 at 14:34
Forever NewUser
113
asked Dec 27 at 14:34
Forever NewUser
113
asked Dec 27 at 14:34
Forever NewUser
113
asked Dec 27 at 14:34
Forever NewUser
113
asked Dec 27 at 14:34
Forever NewUser
113
113
Is itcache.get("Username")that returns null, or is itcache.get("Username").get()that returns null? The former (which is what’s in your question) has nothing to do with SoftReferences, and is strictly a HashMap problem. The latter is simply the reference being no longer valid.
– VGR
Dec 27 at 15:42
You can use aReferenceQueueif you want to make at an effort at removing the entry from the map, but even this wont happen atomically.
– Tom Hawtin - tackline
Dec 27 at 19:32
add a comment |
Is itcache.get("Username")that returns null, or is itcache.get("Username").get()that returns null? The former (which is what’s in your question) has nothing to do with SoftReferences, and is strictly a HashMap problem. The latter is simply the reference being no longer valid.
– VGR
Dec 27 at 15:42
You can use aReferenceQueueif you want to make at an effort at removing the entry from the map, but even this wont happen atomically.
– Tom Hawtin - tackline
Dec 27 at 19:32
Is it
cache.get("Username") that returns null, or is it cache.get("Username").get() that returns null? The former (which is what’s in your question) has nothing to do with SoftReferences, and is strictly a HashMap problem. The latter is simply the reference being no longer valid.– VGR
Dec 27 at 15:42
Is it
cache.get("Username") that returns null, or is it cache.get("Username").get() that returns null? The former (which is what’s in your question) has nothing to do with SoftReferences, and is strictly a HashMap problem. The latter is simply the reference being no longer valid.– VGR
Dec 27 at 15:42
You can use a
ReferenceQueue if you want to make at an effort at removing the entry from the map, but even this wont happen atomically.– Tom Hawtin - tackline
Dec 27 at 19:32
You can use a
ReferenceQueue if you want to make at an effort at removing the entry from the map, but even this wont happen atomically.– Tom Hawtin - tackline
Dec 27 at 19:32
add a comment |
2 Answers
2
active
oldest
votes
As per oracle docs
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError.
Yes When GC clears SoftReference objects, the key remain in HashMap. The key and corresponding value have no relation other than when they are inside a map. Make map's value a normal reference and they will always be in the map unless map is GC.
answered Dec 27 at 14:49
Yug Singh
1,2872725
add a comment |
Yes, that is normal behaviour.
The SoftReference is garbage collected, resulting in the value in the Map being set to null.
It is the same as setting the value of a certain key to null for other types of maps (eg. Map)
answered Dec 27 at 14:48
Bossk
12211
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
As per oracle docs
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError.
Yes When GC clears SoftReference objects, the key remain in HashMap. The key and corresponding value have no relation other than when they are inside a map. Make map's value a normal reference and they will always be in the map unless map is GC.
answered Dec 27 at 14:49
Yug Singh
1,2872725
add a comment |
As per oracle docs
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError.
Yes When GC clears SoftReference objects, the key remain in HashMap. The key and corresponding value have no relation other than when they are inside a map. Make map's value a normal reference and they will always be in the map unless map is GC.
answered Dec 27 at 14:49
Yug Singh
1,2872725
add a comment |
As per oracle docs
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError.
Yes When GC clears SoftReference objects, the key remain in HashMap. The key and corresponding value have no relation other than when they are inside a map. Make map's value a normal reference and they will always be in the map unless map is GC.
answered Dec 27 at 14:49
Yug Singh
1,2872725
As per oracle docs
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError.
Yes When GC clears SoftReference objects, the key remain in HashMap. The key and corresponding value have no relation other than when they are inside a map. Make map's value a normal reference and they will always be in the map unless map is GC.
answered Dec 27 at 14:49
Yug Singh
1,2872725
answered Dec 27 at 14:49
Yug Singh
1,2872725
answered Dec 27 at 14:49
Yug Singh
1,2872725
answered Dec 27 at 14:49
Yug Singh
1,2872725
1,2872725
add a comment |
add a comment |
Yes, that is normal behaviour.
The SoftReference is garbage collected, resulting in the value in the Map being set to null.
It is the same as setting the value of a certain key to null for other types of maps (eg. Map)
answered Dec 27 at 14:48
Bossk
12211
add a comment |
Yes, that is normal behaviour.
The SoftReference is garbage collected, resulting in the value in the Map being set to null.
It is the same as setting the value of a certain key to null for other types of maps (eg. Map)
answered Dec 27 at 14:48
Bossk
12211
add a comment |
Yes, that is normal behaviour.
The SoftReference is garbage collected, resulting in the value in the Map being set to null.
It is the same as setting the value of a certain key to null for other types of maps (eg. Map)
answered Dec 27 at 14:48
Bossk
12211
Yes, that is normal behaviour.
The SoftReference is garbage collected, resulting in the value in the Map being set to null.
It is the same as setting the value of a certain key to null for other types of maps (eg. Map)
answered Dec 27 at 14:48
Bossk
12211
answered Dec 27 at 14:48
Bossk
12211
answered Dec 27 at 14:48
Bossk
12211
answered Dec 27 at 14:48
Bossk
12211
12211
add a comment |
add a comment |
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Is it
cache.get("Username")that returns null, or is itcache.get("Username").get()that returns null? The former (which is what’s in your question) has nothing to do with SoftReferences, and is strictly a HashMap problem. The latter is simply the reference being no longer valid.– VGR
Dec 27 at 15:42
You can use a
ReferenceQueueif you want to make at an effort at removing the entry from the map, but even this wont happen atomically.– Tom Hawtin - tackline
Dec 27 at 19:32