Enforcing JVM GC - for a good reason (I hope)
Let's look at potential race condition related to garbage collection speed.
Initial state:
main => a
a => b
b => c
main program references object a, object a references b, b references c. Now, we want to make a reference c instead of b.
Good:
a => c
As b is no longer referenced, it can be garbage collected.
Bad:
a = null
a => c
In between these two steps (setting a to null and re-pointing it at c), b may become garbage collected together with c. I doubt these kind of errors may be picked up by unit tests, as GC most likely won't run quickly enough to run into troubles. One way to detect the problem would be to enforce GC, or at least increase its frequency. Is there any command line param or another means of doing it? If not, what other automated means of preventing such kind of errors have we got?
java garbage-collection jvm
asked Nov 12 at 13:41
automatictester
1,084622
add a comment |
Let's look at potential race condition related to garbage collection speed.
Initial state:
main => a
a => b
b => c
main program references object a, object a references b, b references c. Now, we want to make a reference c instead of b.
Good:
a => c
As b is no longer referenced, it can be garbage collected.
Bad:
a = null
a => c
In between these two steps (setting a to null and re-pointing it at c), b may become garbage collected together with c. I doubt these kind of errors may be picked up by unit tests, as GC most likely won't run quickly enough to run into troubles. One way to detect the problem would be to enforce GC, or at least increase its frequency. Is there any command line param or another means of doing it? If not, what other automated means of preventing such kind of errors have we got?
java garbage-collection jvm
asked Nov 12 at 13:41
automatictester
1,084622
1
It isn't easy to answer your question given the "hand waviness" of the description. A specific code example would be more useful. That said, just because there is no reference to "b" does not mean it is collectible. To be collectible "b" must be "unreachable" from any of the garbage collection roots. Here is a good discussion of how it works. dynatrace.com/resources/ebooks/javabook/…
– Steven W. Klassen
Nov 12 at 13:52
I would look into Java'sAtomicReference.
– Mike
Nov 12 at 13:56
1
How would you make the assignmenta = c;, if you hadn’t a reference toc?
– Holger
Nov 12 at 16:02
add a comment |
Let's look at potential race condition related to garbage collection speed.
Initial state:
main => a
a => b
b => c
main program references object a, object a references b, b references c. Now, we want to make a reference c instead of b.
Good:
a => c
As b is no longer referenced, it can be garbage collected.
Bad:
a = null
a => c
In between these two steps (setting a to null and re-pointing it at c), b may become garbage collected together with c. I doubt these kind of errors may be picked up by unit tests, as GC most likely won't run quickly enough to run into troubles. One way to detect the problem would be to enforce GC, or at least increase its frequency. Is there any command line param or another means of doing it? If not, what other automated means of preventing such kind of errors have we got?
java garbage-collection jvm
asked Nov 12 at 13:41
automatictester
1,084622
Let's look at potential race condition related to garbage collection speed.
Initial state:
main => a
a => b
b => c
main program references object a, object a references b, b references c. Now, we want to make a reference c instead of b.
Good:
a => c
As b is no longer referenced, it can be garbage collected.
Bad:
a = null
a => c
In between these two steps (setting a to null and re-pointing it at c), b may become garbage collected together with c. I doubt these kind of errors may be picked up by unit tests, as GC most likely won't run quickly enough to run into troubles. One way to detect the problem would be to enforce GC, or at least increase its frequency. Is there any command line param or another means of doing it? If not, what other automated means of preventing such kind of errors have we got?
java garbage-collection jvm
java garbage-collection jvm
asked Nov 12 at 13:41
automatictester
1,084622
asked Nov 12 at 13:41
automatictester
1,084622
asked Nov 12 at 13:41
automatictester
1,084622
asked Nov 12 at 13:41
automatictester
1,084622
asked Nov 12 at 13:41
automatictester
1,084622
1,084622
1
It isn't easy to answer your question given the "hand waviness" of the description. A specific code example would be more useful. That said, just because there is no reference to "b" does not mean it is collectible. To be collectible "b" must be "unreachable" from any of the garbage collection roots. Here is a good discussion of how it works. dynatrace.com/resources/ebooks/javabook/…
– Steven W. Klassen
Nov 12 at 13:52
I would look into Java'sAtomicReference.
– Mike
Nov 12 at 13:56
1
How would you make the assignmenta = c;, if you hadn’t a reference toc?
– Holger
Nov 12 at 16:02
add a comment |
1
It isn't easy to answer your question given the "hand waviness" of the description. A specific code example would be more useful. That said, just because there is no reference to "b" does not mean it is collectible. To be collectible "b" must be "unreachable" from any of the garbage collection roots. Here is a good discussion of how it works. dynatrace.com/resources/ebooks/javabook/…
– Steven W. Klassen
Nov 12 at 13:52
I would look into Java'sAtomicReference.
– Mike
Nov 12 at 13:56
1
How would you make the assignmenta = c;, if you hadn’t a reference toc?
– Holger
Nov 12 at 16:02
1
1
It isn't easy to answer your question given the "hand waviness" of the description. A specific code example would be more useful. That said, just because there is no reference to "b" does not mean it is collectible. To be collectible "b" must be "unreachable" from any of the garbage collection roots. Here is a good discussion of how it works. dynatrace.com/resources/ebooks/javabook/…
– Steven W. Klassen
Nov 12 at 13:52
It isn't easy to answer your question given the "hand waviness" of the description. A specific code example would be more useful. That said, just because there is no reference to "b" does not mean it is collectible. To be collectible "b" must be "unreachable" from any of the garbage collection roots. Here is a good discussion of how it works. dynatrace.com/resources/ebooks/javabook/…
– Steven W. Klassen
Nov 12 at 13:52
I would look into Java's
AtomicReference.– Mike
Nov 12 at 13:56
I would look into Java's
AtomicReference.– Mike
Nov 12 at 13:56
1
1
How would you make the assignment
a = c;, if you hadn’t a reference to c?– Holger
Nov 12 at 16:02
How would you make the assignment
a = c;, if you hadn’t a reference to c?– Holger
Nov 12 at 16:02
add a comment |
2 Answers
2
active
oldest
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You're plain wrong. Even "in between these two steps", there's a reference to c somewhere (hint: google for GC roots).
What you describe would imply a sure and fast crash for all java-running servers, but there's no such problem.
answered Nov 12 at 15:54
maaartinus
26.8k2193226
add a comment |
If you are setting a reference within A to refer to C, how is it possible that C does not have a reference already in your program (a local variable or something at the very least) Are you getting C from thin air? The Garbage Collector won't even consider C for garbage collection.
answered Nov 12 at 16:04
jbx
10.4k1057109
add a comment |
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2 Answers
2
active
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2 Answers
2
active
oldest
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votes
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oldest
votes
You're plain wrong. Even "in between these two steps", there's a reference to c somewhere (hint: google for GC roots).
What you describe would imply a sure and fast crash for all java-running servers, but there's no such problem.
answered Nov 12 at 15:54
maaartinus
26.8k2193226
add a comment |
You're plain wrong. Even "in between these two steps", there's a reference to c somewhere (hint: google for GC roots).
What you describe would imply a sure and fast crash for all java-running servers, but there's no such problem.
answered Nov 12 at 15:54
maaartinus
26.8k2193226
add a comment |
You're plain wrong. Even "in between these two steps", there's a reference to c somewhere (hint: google for GC roots).
What you describe would imply a sure and fast crash for all java-running servers, but there's no such problem.
answered Nov 12 at 15:54
maaartinus
26.8k2193226
You're plain wrong. Even "in between these two steps", there's a reference to c somewhere (hint: google for GC roots).
What you describe would imply a sure and fast crash for all java-running servers, but there's no such problem.
answered Nov 12 at 15:54
maaartinus
26.8k2193226
answered Nov 12 at 15:54
maaartinus
26.8k2193226
answered Nov 12 at 15:54
maaartinus
26.8k2193226
answered Nov 12 at 15:54
maaartinus
26.8k2193226
26.8k2193226
add a comment |
add a comment |
If you are setting a reference within A to refer to C, how is it possible that C does not have a reference already in your program (a local variable or something at the very least) Are you getting C from thin air? The Garbage Collector won't even consider C for garbage collection.
answered Nov 12 at 16:04
jbx
10.4k1057109
add a comment |
If you are setting a reference within A to refer to C, how is it possible that C does not have a reference already in your program (a local variable or something at the very least) Are you getting C from thin air? The Garbage Collector won't even consider C for garbage collection.
answered Nov 12 at 16:04
jbx
10.4k1057109
add a comment |
If you are setting a reference within A to refer to C, how is it possible that C does not have a reference already in your program (a local variable or something at the very least) Are you getting C from thin air? The Garbage Collector won't even consider C for garbage collection.
answered Nov 12 at 16:04
jbx
10.4k1057109
If you are setting a reference within A to refer to C, how is it possible that C does not have a reference already in your program (a local variable or something at the very least) Are you getting C from thin air? The Garbage Collector won't even consider C for garbage collection.
answered Nov 12 at 16:04
jbx
10.4k1057109
answered Nov 12 at 16:04
jbx
10.4k1057109
answered Nov 12 at 16:04
jbx
10.4k1057109
answered Nov 12 at 16:04
jbx
10.4k1057109
10.4k1057109
add a comment |
add a comment |
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1
It isn't easy to answer your question given the "hand waviness" of the description. A specific code example would be more useful. That said, just because there is no reference to "b" does not mean it is collectible. To be collectible "b" must be "unreachable" from any of the garbage collection roots. Here is a good discussion of how it works. dynatrace.com/resources/ebooks/javabook/…
– Steven W. Klassen
Nov 12 at 13:52
I would look into Java's
AtomicReference.– Mike
Nov 12 at 13:56
1
How would you make the assignment
a = c;, if you hadn’t a reference toc?– Holger
Nov 12 at 16:02