Class ParallelSequence
- All Implemented Interfaces:
Serializable
,Steppable
For example, keep in mind that the random number generator is unsynchronized. If you access the random number generator from within a ParallelSequence, or indeed from multiple threads you've spawned in other situations, you need to remember to lock on the random number generator itself.
In the same vein, if you use a RandomSequence within a ParallelSequence, you need to let the RandomSequence know this so that it will lock on the random number generator properly. This is done by setting the shouldSynchronize flag in the RandomSequence.
ParallelSequences are lightweight: they reuse the same threads if stepped repeatedly. This means that you must never attach a ParallelSequence inside itself -- that'd be an infinite loop, but it also would create weird thread errors.
While ParallelSequences might LOOK cool, generally speaking the only time you should ever think to use them is if you actually HAVE multiple CPUs on your computer. Otherwise they're almost certainly not the solution to your odd multiple-thread needs.
Important Note Because ParallelSequences are lightweight, their threads are persistent, even after your step() method has completed (this allows them to be reused for the next step() method. If the ParallelSequence is garbage collected, we automatically delete all its threads in its finalize() method. And that's the rub: even if you get rid of your ParallelSequence, it's often the case that its garbage collection is delayed, or even that the VM will never garbage collect it.
Thus when you're done with your ParallelSequence and wish to throw it away, you should always call cleanup(), which deletes the threads manually. Otherwise the thread resources will leak and quickly consume all your available memory.
Alternatively you can call setDestroysThreads(true) on your ParallelSequence. This will cause the ParallelSequence to destroy its threads every single time the ParallelSequence's step() method completes. This is expensive but you don't have to keep track of the ParallelSequence at the end of the run to call cleanup() on it. It's not a bad idea for a ParallelSequence which is one-shot rather than repeating.
Be sure to read the class documentation on sim.engine.Sequence
- See Also:
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Field Summary
Modifier and TypeFieldDescriptionstatic final int
Indicates that MASON should determine how many threads to use based on the number of CPUs.static final int
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Constructor Summary
ConstructorDescriptionParallelSequence
(Collection steps) Creates an immutable ParallelSequence with one thread per steppable in the collection.ParallelSequence
(Collection steps, int threads) Creates an immutable ParallelSequence with the specified number of threads, or if threads==ParallelSequence.CPUS, then the number of threads is determined at runtime based on the number of CPUs or cores on the system, or if threads == ParallelSequence.STEPPABLES, then the number of threads is the size of the collection passed in (and may change as the collection grows or shrinks).ParallelSequence
(Steppable[] steps) Creates an immutable ParallelSequence with one thread per steppable.ParallelSequence
(Steppable[] steps, int threads) Creates an immutable ParallelSequence with the specified number of threads, or if threads==ParallelSequence.CPUS, then the number of threads is determined at runtime based on the number of CPUs or cores on the system, or if threads == ParallelSequence.STEPPABLES, then the number of threads is the size of the steps array passed in. -
Method Summary
Modifier and TypeMethodDescriptionvoid
addSteppable
(Steppable steppable) Requests that the provided Steppable be added to the Sequence prior to the next step() call.void
addSteppables
(Collection steppables) Requests that the provided Steppables be added to the Sequence prior to the next step() call.void
addSteppables
(Steppable[] steppables) Requests that the provided Steppables be added to the Sequence prior to the next step() call.protected boolean
If your subclass does not respect order, override this method to return false, and Sequence will ignore the ensuresOrder result.void
cleanup()
Call this just before you get rid of a ParallelSequence: for example, one good place is the stop() method of your simulation.boolean
boolean
Returns whether the order among the remaining Steppables in the internal array is maintained after removing Steppables via removeSteppable() or removeSteppables().boolean
Returns whether the Sequence uses a Set internally to manage the internal array.void
removeSteppable
(Steppable steppable) Requests that the provided Steppable be removed from the Sequence prior to the next step() call.void
removeSteppables
(Collection steppables) Requests that the provided Steppables be removed from the Sequence prior to the next step() call.void
removeSteppables
(Steppable[] steppables) Requests that the provided Steppables be removed from the Sequence prior to the next step() call.void
replaceSteppables
(Collection collection) Requests that the provided Steppables replace the existing Steppables in the internal array prior to the next step() call.void
replaceSteppables
(Steppable[] steppables) Requests that the provided Steppables replace the existing Steppables in the internal array prior to the next step() call.void
setDestroysThreads
(boolean val) void
setEnsuresOrder
(boolean val) Sets whether the order among the remaining Steppables in the internal array is maintained after removing Steppables via removeSteppable() or removeSteppables().void
setUsesSets
(boolean val) Sets whether the Sequence uses a Set internally to manage the internal array.void
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Field Details
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CPUS
public static final int CPUSIndicates that MASON should determine how many threads to use based on the number of CPUs.- See Also:
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STEPPABLES
public static final int STEPPABLES- See Also:
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Constructor Details
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ParallelSequence
Creates an immutable ParallelSequence with the specified number of threads, or if threads==ParallelSequence.CPUS, then the number of threads is determined at runtime based on the number of CPUs or cores on the system, or if threads == ParallelSequence.STEPPABLES, then the number of threads is the size of the steps array passed in. -
ParallelSequence
Creates an immutable ParallelSequence with one thread per steppable. -
ParallelSequence
Creates an immutable ParallelSequence with the specified number of threads, or if threads==ParallelSequence.CPUS, then the number of threads is determined at runtime based on the number of CPUs or cores on the system, or if threads == ParallelSequence.STEPPABLES, then the number of threads is the size of the collection passed in (and may change as the collection grows or shrinks). -
ParallelSequence
Creates an immutable ParallelSequence with one thread per steppable in the collection.
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Method Details
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getDestroysThreads
public boolean getDestroysThreads() -
setDestroysThreads
public void setDestroysThreads(boolean val) -
getCleaner
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cleanup
public void cleanup()Call this just before you get rid of a ParallelSequence: for example, one good place is the stop() method of your simulation. Never call this method inside the ParallelSequence's own step() method. This method deletes the threads so the ParallelSequence is ready to be thrown away. We also do this in finalize() but finalize() is not guaranteed to be called at any particular time, which can result in unexpected memory leaks. Think of this method as the same kind of thing as a Graphics or Window's dispose() method. -
canEnsureOrder
protected boolean canEnsureOrder()Description copied from class:Sequence
If your subclass does not respect order, override this method to return false, and Sequence will ignore the ensuresOrder result.- Overrides:
canEnsureOrder
in classSequence
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step
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replaceSteppables
Description copied from class:Sequence
Requests that the provided Steppables replace the existing Steppables in the internal array prior to the next step() call.- Overrides:
replaceSteppables
in classSequence
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replaceSteppables
Description copied from class:Sequence
Requests that the provided Steppables replace the existing Steppables in the internal array prior to the next step() call.- Overrides:
replaceSteppables
in classSequence
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addSteppable
Description copied from class:Sequence
Requests that the provided Steppable be added to the Sequence prior to the next step() call.- Overrides:
addSteppable
in classSequence
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addSteppables
Description copied from class:Sequence
Requests that the provided Steppables be added to the Sequence prior to the next step() call.- Overrides:
addSteppables
in classSequence
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addSteppables
Description copied from class:Sequence
Requests that the provided Steppables be added to the Sequence prior to the next step() call.- Overrides:
addSteppables
in classSequence
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removeSteppable
Description copied from class:Sequence
Requests that the provided Steppable be removed from the Sequence prior to the next step() call.- Overrides:
removeSteppable
in classSequence
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removeSteppables
Description copied from class:Sequence
Requests that the provided Steppables be removed from the Sequence prior to the next step() call.- Overrides:
removeSteppables
in classSequence
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removeSteppables
Description copied from class:Sequence
Requests that the provided Steppables be removed from the Sequence prior to the next step() call.- Overrides:
removeSteppables
in classSequence
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getEnsuresOrder
public boolean getEnsuresOrder()Description copied from class:Sequence
Returns whether the order among the remaining Steppables in the internal array is maintained after removing Steppables via removeSteppable() or removeSteppables(). Note that this value may be entirely ignored by subclasses for which maintaining order doesn't make sense (such as parallel or random sequences). Also if you use sets (via setUsesSets(true)), then order is never ensured regardless.- Overrides:
getEnsuresOrder
in classSequence
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setEnsuresOrder
public void setEnsuresOrder(boolean val) Description copied from class:Sequence
Sets whether the order among the remaining Steppables in the internal array is maintained after removing Steppables via removeSteppable() or removeSteppables(). Note that this value may be entirely ignored by subclasses for which maintaining order doesn't make sense (such as parallel or random sequences). Also if you use sets (via setUsesSets(true)), then order is never ensured regardless.- Overrides:
setEnsuresOrder
in classSequence
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getUsesSets
public boolean getUsesSets()Description copied from class:Sequence
Returns whether the Sequence uses a Set internally to manage the internal array. This is faster, often much faster, for large numbers of removals (perhaps more than 5 or so), but requires that each Steppable in the internal array be unique.- Overrides:
getUsesSets
in classSequence
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setUsesSets
public void setUsesSets(boolean val) Description copied from class:Sequence
Sets whether the Sequence uses a Set internally to manage the internal array. This is faster, often much faster, for large numbers of removals (perhaps more than 5 or so), but requires that each Steppable in the internal array be unique.- Overrides:
setUsesSets
in classSequence
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