edu.mines.jtk.util

Class Parallel.Unsafe<T>

java.lang.Object

edu.mines.jtk.util.Parallel.Unsafe<T>

Enclosing class:

Parallel

public static class Parallel.Unsafe<T>
extends java.lang.Object

A wrapper for objects that are not thread-safe. Such objects have methods that cannot safely be executed concurrently in multiple threads. To use an unsafe object within a parallel computation, first construct an instance of this wrapper. Then, within the compute method, get the unsafe object; if null, construct and set a new unsafe object in this wrapper, before using the unsafe object to perform the computation. This pattern ensures that each thread computes using a distinct unsafe object. For example,

 final Parallel.Unsafe<Worker> nts = new Parallel.Unsafe<Worker>();
 Parallel.loop(count,new Parallel.LoopInt() {
   public void compute(int i) {
     Worker w = nts.get(); // get worker for the current thread
     if (w==null) nts.set(w=new Worker()); // if null, make one
     w.work(); // the method work need not be thread-safe
   }
 });
 

This wrapper is most useful when (1) the cost of constructing an unsafe object is high, relative to the cost of each call to compute, and (2) the number of threads calling compute is significantly lower than the total number of such calls. Otherwise, if either of these conditions is false, then simply construct a new unsafe object within the compute method.

This wrapper works much like the Java standard class ThreadLocal, except that an object within this wrapper can be garbage-collected before its thread dies. This difference is important because fork-join worker threads are pooled and will typically die only when a program ends.

Constructor Summary

Constructors

Constructor and Description
Parallel.Unsafe() Constructs a wrapper for objects that are not thread-safe.

Method Summary

Methods

Modifier and Type	Method and Description
T	get() Gets the object in this wrapper for the current thread.
java.util.Collection<T>	getAll() Returns a collection of all unsafe objects in this wrapper.
void	set(T object) Sets the object in this wrapper for the current thread.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Parallel.Unsafe

public Parallel.Unsafe()

Constructs a wrapper for objects that are not thread-safe.

Method Detail

get

public T get()

Gets the object in this wrapper for the current thread.

Returns:

the object; null, of not yet set for the current thread.

set

public void set(T object)

Sets the object in this wrapper for the current thread.

Parameters:

object - the object.

getAll

public java.util.Collection<T> getAll()

Returns a collection of all unsafe objects in this wrapper. This method is useful only after parallel loops have ended.

Returns:

the collection of unsafe objects.