sim.engine
Class ParallelSequence

java.lang.Object
  extended by sim.engine.Sequence
      extended by sim.engine.ParallelSequence
All Implemented Interfaces:
java.io.Serializable, Steppable

public class ParallelSequence
extends Sequence

Spawns all the sequence elements in parallel on separate threads. This should ONLY be used if you know that all of the elements in the sequence can be executed independently of one another without any race conditions. No synchronization on the model data is done -- you're responsible for that if you need it.

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:
Serialized Form

Field Summary
static int CPUS
          Indicates that MASON should determine how many threads to use based on the number of CPUs.
static int STEPPABLES
           
 
Fields inherited from class sim.engine.Sequence
size, steps
 
Constructor Summary
ParallelSequence(java.util.Collection steps)
          Creates an immutable ParallelSequence with one thread per steppable in the collection.
ParallelSequence(java.util.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
protected  boolean canEnsureOrder()
          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.
protected  void finalize()
           
 Steppable getCleaner()
           
 boolean getDestroysThreads()
           
 void setDestroysThreads(boolean val)
           
 void step(SimState state)
           
 
Methods inherited from class sim.engine.Sequence
addSteppable, addSteppables, addSteppables, getEnsuresOrder, getUsesSets, loadSteps, removeSteppable, removeSteppables, removeSteppables, replaceSteppables, replaceSteppables, setEnsuresOrder, setUsesSets
 
Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

CPUS

public static final int CPUS
Indicates that MASON should determine how many threads to use based on the number of CPUs.

See Also:
Constant Field Values

STEPPABLES

public static final int STEPPABLES
See Also:
Constant Field Values
Constructor Detail

ParallelSequence

public 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.


ParallelSequence

public ParallelSequence(Steppable[] steps)
Creates an immutable ParallelSequence with one thread per steppable.


ParallelSequence

public ParallelSequence(java.util.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

public ParallelSequence(java.util.Collection steps)
Creates an immutable ParallelSequence with one thread per steppable in the collection.

Method Detail

getDestroysThreads

public boolean getDestroysThreads()

setDestroysThreads

public void setDestroysThreads(boolean val)

getCleaner

public Steppable getCleaner()

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.


finalize

protected void finalize()
                 throws java.lang.Throwable
Overrides:
finalize in class java.lang.Object
Throws:
java.lang.Throwable

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 class Sequence

step

public void step(SimState state)
Specified by:
step in interface Steppable
Overrides:
step in class Sequence