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. You should not embed RandomSequences inside a ParallelSequence unless you've set their shouldSynchronize value to true, and elsewhere in your embedded steppables you're synchronizing on the Schedule first (the Schedule is the basic lock point for MASON's models).

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.

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.
 
Fields inherited from class sim.engine.Sequence
steps
 
Constructor Summary
ParallelSequence(Steppable[] steps)
          Creates a ParallelSequence with one thread per steppable.
ParallelSequence(Steppable[] sequence, int threads)
          Creates a 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.
 
Method Summary
 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 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
Constructor Detail

ParallelSequence

public ParallelSequence(Steppable[] sequence,
                        int threads)
Creates a 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. The steppable objects are divided approximately evenly among the various threads.


ParallelSequence

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

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

step

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