What is a `monitor` in JVM(Hotspot), a specific object? [duplicate]
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This question already has an answer here:
What's a monitor in Java?
7 answers
Semaphore vs. Monitors - what's the difference?
6 answers
In Java Language Spec, Section 17.1: Synchronization, it says
Each object in Java is associated with a monitor, which a thread can lock or unlock.
Section 17.2:
Every object, in addition to having an associated monitor, has an associated wait set. A wait set is a set of threads.
When an object is first created, its wait set is empty. Elementary actions that add threads to and remove threads from wait sets are atomic. Wait sets are manipulated solely through the methods
Object.wait,Object.notify, andObject.notifyAll.
A question here is, what is monitor, seems it is an object which contain a wait set?
I have take a look at a similar question What's a monitor in Java? on stackoverflow, but the answers were not so clearly.
A monitor is mechanism to control concurrent access to an object.
A monitor is an entity that possesses both a lock and a wait set. In Java, any Object can serve as a monitor.
I got some more info on Hotspot runtime overview
Per-object synchronization state is encoded in the first word (
the so-called mark word) of the VM's object representation. For several states, the mark word is multiplexed to point to additional synchronization metadata. (As an aside, in addition, the mark word is also multiplexed to contain GC age data, and the object's identity hashCode value.) The states are:
Neutral: Unlocked
Biased: Locked/Unlocked + Unshared
Stack-Locked: Locked + Shared but uncontended The mark points to
displaced mark word on the owner thread's stack.Inflated: Locked/Unlocked + Shared and contended Threads are blocked
in monitorenter or wait(). The mark points to heavy-weight
"objectmonitor" structure.[8]
I guess if a monitor is a objectmonitor structure? But objectmonitor does not created at first, only used when heavy weight lock is used due to contention.
java multithreading jvm-hotspot
asked Dec 28 '18 at 3:26
Jacky
1,350825
marked as duplicate by shmosel java
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Dec 28 '18 at 3:28
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
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This question already has an answer here:
What's a monitor in Java?
7 answers
Semaphore vs. Monitors - what's the difference?
6 answers
In Java Language Spec, Section 17.1: Synchronization, it says
Each object in Java is associated with a monitor, which a thread can lock or unlock.
Section 17.2:
Every object, in addition to having an associated monitor, has an associated wait set. A wait set is a set of threads.
When an object is first created, its wait set is empty. Elementary actions that add threads to and remove threads from wait sets are atomic. Wait sets are manipulated solely through the methods
Object.wait,Object.notify, andObject.notifyAll.
A question here is, what is monitor, seems it is an object which contain a wait set?
I have take a look at a similar question What's a monitor in Java? on stackoverflow, but the answers were not so clearly.
A monitor is mechanism to control concurrent access to an object.
A monitor is an entity that possesses both a lock and a wait set. In Java, any Object can serve as a monitor.
I got some more info on Hotspot runtime overview
Per-object synchronization state is encoded in the first word (
the so-called mark word) of the VM's object representation. For several states, the mark word is multiplexed to point to additional synchronization metadata. (As an aside, in addition, the mark word is also multiplexed to contain GC age data, and the object's identity hashCode value.) The states are:
Neutral: Unlocked
Biased: Locked/Unlocked + Unshared
Stack-Locked: Locked + Shared but uncontended The mark points to
displaced mark word on the owner thread's stack.Inflated: Locked/Unlocked + Shared and contended Threads are blocked
in monitorenter or wait(). The mark points to heavy-weight
"objectmonitor" structure.[8]
I guess if a monitor is a objectmonitor structure? But objectmonitor does not created at first, only used when heavy weight lock is used due to contention.
java multithreading jvm-hotspot
asked Dec 28 '18 at 3:26
Jacky
1,350825
marked as duplicate by shmosel java
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Dec 28 '18 at 3:28
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
add a comment |
This question already has an answer here:
What's a monitor in Java?
7 answers
Semaphore vs. Monitors - what's the difference?
6 answers
In Java Language Spec, Section 17.1: Synchronization, it says
Each object in Java is associated with a monitor, which a thread can lock or unlock.
Section 17.2:
Every object, in addition to having an associated monitor, has an associated wait set. A wait set is a set of threads.
When an object is first created, its wait set is empty. Elementary actions that add threads to and remove threads from wait sets are atomic. Wait sets are manipulated solely through the methods
Object.wait,Object.notify, andObject.notifyAll.
A question here is, what is monitor, seems it is an object which contain a wait set?
I have take a look at a similar question What's a monitor in Java? on stackoverflow, but the answers were not so clearly.
A monitor is mechanism to control concurrent access to an object.
A monitor is an entity that possesses both a lock and a wait set. In Java, any Object can serve as a monitor.
I got some more info on Hotspot runtime overview
Per-object synchronization state is encoded in the first word (
the so-called mark word) of the VM's object representation. For several states, the mark word is multiplexed to point to additional synchronization metadata. (As an aside, in addition, the mark word is also multiplexed to contain GC age data, and the object's identity hashCode value.) The states are:
Neutral: Unlocked
Biased: Locked/Unlocked + Unshared
Stack-Locked: Locked + Shared but uncontended The mark points to
displaced mark word on the owner thread's stack.Inflated: Locked/Unlocked + Shared and contended Threads are blocked
in monitorenter or wait(). The mark points to heavy-weight
"objectmonitor" structure.[8]
I guess if a monitor is a objectmonitor structure? But objectmonitor does not created at first, only used when heavy weight lock is used due to contention.
java multithreading jvm-hotspot
asked Dec 28 '18 at 3:26
Jacky
1,350825
This question already has an answer here:
What's a monitor in Java?
7 answers
Semaphore vs. Monitors - what's the difference?
6 answers
In Java Language Spec, Section 17.1: Synchronization, it says
Each object in Java is associated with a monitor, which a thread can lock or unlock.
Section 17.2:
Every object, in addition to having an associated monitor, has an associated wait set. A wait set is a set of threads.
When an object is first created, its wait set is empty. Elementary actions that add threads to and remove threads from wait sets are atomic. Wait sets are manipulated solely through the methods
Object.wait,Object.notify, andObject.notifyAll.
A question here is, what is monitor, seems it is an object which contain a wait set?
I have take a look at a similar question What's a monitor in Java? on stackoverflow, but the answers were not so clearly.
A monitor is mechanism to control concurrent access to an object.
A monitor is an entity that possesses both a lock and a wait set. In Java, any Object can serve as a monitor.
I got some more info on Hotspot runtime overview
Per-object synchronization state is encoded in the first word (
the so-called mark word) of the VM's object representation. For several states, the mark word is multiplexed to point to additional synchronization metadata. (As an aside, in addition, the mark word is also multiplexed to contain GC age data, and the object's identity hashCode value.) The states are:
Neutral: Unlocked
Biased: Locked/Unlocked + Unshared
Stack-Locked: Locked + Shared but uncontended The mark points to
displaced mark word on the owner thread's stack.Inflated: Locked/Unlocked + Shared and contended Threads are blocked
in monitorenter or wait(). The mark points to heavy-weight
"objectmonitor" structure.[8]
I guess if a monitor is a objectmonitor structure? But objectmonitor does not created at first, only used when heavy weight lock is used due to contention.
This question already has an answer here:
What's a monitor in Java?
7 answers
Semaphore vs. Monitors - what's the difference?
6 answers
java multithreading jvm-hotspot
java multithreading jvm-hotspot
asked Dec 28 '18 at 3:26
Jacky
1,350825
asked Dec 28 '18 at 3:26
Jacky
1,350825
edited Dec 28 '18 at 3:33
asked Dec 28 '18 at 3:26
Jacky
1,350825
asked Dec 28 '18 at 3:26
Jacky
1,350825
asked Dec 28 '18 at 3:26
Jacky
1,350825
1,350825
marked as duplicate by shmosel java
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Dec 28 '18 at 3:28
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This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
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1 Answer
1
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oldest
votes
A monitor is a concept on which you can perform certain operations. Anything that implements the abstract operations of the concept of a monitor is a good implementation.
The concept is implemented in HotSpot in the mark word plus everything described in the text that you quoted about the mark word. It is not a single data structure.
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
1
Does that meanEvery object, in addition to having an associated monitor, has an associated wait set. its wait set is empty.is just a conceptual description, not involved with implementation details.
– Jacky
Dec 28 '18 at 3:38
1
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
A monitor is a concept on which you can perform certain operations. Anything that implements the abstract operations of the concept of a monitor is a good implementation.
The concept is implemented in HotSpot in the mark word plus everything described in the text that you quoted about the mark word. It is not a single data structure.
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
1
Does that meanEvery object, in addition to having an associated monitor, has an associated wait set. its wait set is empty.is just a conceptual description, not involved with implementation details.
– Jacky
Dec 28 '18 at 3:38
1
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
add a comment |
A monitor is a concept on which you can perform certain operations. Anything that implements the abstract operations of the concept of a monitor is a good implementation.
The concept is implemented in HotSpot in the mark word plus everything described in the text that you quoted about the mark word. It is not a single data structure.
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
1
Does that meanEvery object, in addition to having an associated monitor, has an associated wait set. its wait set is empty.is just a conceptual description, not involved with implementation details.
– Jacky
Dec 28 '18 at 3:38
1
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
add a comment |
A monitor is a concept on which you can perform certain operations. Anything that implements the abstract operations of the concept of a monitor is a good implementation.
The concept is implemented in HotSpot in the mark word plus everything described in the text that you quoted about the mark word. It is not a single data structure.
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
A monitor is a concept on which you can perform certain operations. Anything that implements the abstract operations of the concept of a monitor is a good implementation.
The concept is implemented in HotSpot in the mark word plus everything described in the text that you quoted about the mark word. It is not a single data structure.
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
edited Dec 28 '18 at 4:01
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
answered Dec 28 '18 at 3:32
Erwin Bolwidt
23.8k123858
23.8k123858
1
Does that meanEvery object, in addition to having an associated monitor, has an associated wait set. its wait set is empty.is just a conceptual description, not involved with implementation details.
– Jacky
Dec 28 '18 at 3:38
1
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
add a comment |
1
Does that meanEvery object, in addition to having an associated monitor, has an associated wait set. its wait set is empty.is just a conceptual description, not involved with implementation details.
– Jacky
Dec 28 '18 at 3:38
1
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
1
1
Does that mean
Every object, in addition to having an associated monitor, has an associated wait set. its wait set is empty. is just a conceptual description, not involved with implementation details.– Jacky
Dec 28 '18 at 3:38
Does that mean
Every object, in addition to having an associated monitor, has an associated wait set. its wait set is empty. is just a conceptual description, not involved with implementation details.– Jacky
Dec 28 '18 at 3:38
1
1
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Yes, that's correct.
– Louis Wasserman
Dec 28 '18 at 3:46
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
Indeed that's correct
– Erwin Bolwidt
Dec 28 '18 at 4:01
add a comment |
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