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package org.gnu.glpk;
import java.util.LinkedList;
/**
* This class manages callbacks from the MIP solver.
* <p>The GLPK MIP solver calls method {@link #callback(long) callback} in
* the branch-and-cut algorithm. A listener to the callback can be used to
* influence the sequence in which nodes of the search tree are evaluated, or
* to supply a heuristic solution. To find out why the callback is issued
* use method {@link GLPK#glp_ios_reason(glp_tree) GLPK.glp_ios_reason}.
* <p>The list of listeners is thread local. Each thread has to register its
* own listener.
*/
public final class GlpkCallback {
/**
* List of callback listeners.
*/
private static ThreadLocal<LinkedList<GlpkCallbackListener>> listeners
= new ThreadLocal<LinkedList<GlpkCallbackListener>>() {
@Override
protected LinkedList<GlpkCallbackListener> initialValue() {
return new LinkedList<GlpkCallbackListener>();
}
};
/**
* Constructor.
*/
private GlpkCallback() {
}
/**
* Callback method called by native library.
* @param cPtr pointer to search tree
*/
public static void callback(final long cPtr) {
glp_tree tree;
tree = new glp_tree(cPtr, false);
for (GlpkCallbackListener listener : listeners.get()) {
listener.callback(tree);
}
}
/**
* Adds a listener for callbacks.
* @param listener listener for callbacks
*/
public static void addListener(final GlpkCallbackListener listener) {
listeners.get().add(listener);
}
/**
* Removes first occurance of a listener for callbacks.
* @param listener listener for callbacks
* @return true if the listener was found
*/
public static boolean removeListener(final GlpkCallbackListener listener) {
return listeners.get().remove(listener);
}
}
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