The number of essential/relevant cycles can be exponential for some m…

…olecules - e.g. cyclo-phanes.

We know how many there are before generating them so we can et a reasonable limit which just fails if this
limit is reached. This limit can be configured by a system property.

base/core/src/main/java/org/openscience/cdk/graph/Cycles.java

@@ -32,6 +32,7 @@
 import org.openscience.cdk.interfaces.IRing;
 import org.openscience.cdk.interfaces.IRingSet;
 import org.openscience.cdk.ringsearch.RingSearch;
+import org.openscience.cdk.tools.LoggingToolFactory;
 
 import java.util.ArrayDeque;
 import java.util.ArrayList;
@@ -90,6 +91,22 @@
  */
 public final class Cycles {
 
+    private static final String CDK_MAX_RELEVANT_CYCLES_KEY = "cdk.maxRelevantCycles";
+    private static final long MAX_RELEVANT_CYCLES = getSystemInteger(CDK_MAX_RELEVANT_CYCLES_KEY, 512000);
+
+    private static long getSystemInteger(String key, long val) {
+        String prop = System.getProperty(key);
+        if (prop == null)
+            return val;
+        try {
+            return Long.parseLong(prop);
+        } catch (NumberFormatException ex) {
+            LoggingToolFactory.createLoggingTool(Cycles.class)
+                              .error("Error - Invalid number for system property=" + key);
+        }
+        return val;
+    }
+
     /** Vertex paths for each cycle. */
     private final int[][]        paths;
 
@@ -861,19 +878,23 @@ int[][] apply(int[][] graph, int length) {
 
             /** {@inheritDoc} */
             @Override
-            int[][] apply(int[][] graph, int length) {
+            int[][] apply(int[][] graph, int length) throws Intractable {
                 InitialCycles ic = InitialCycles.ofBiconnectedComponent(graph, length);
                 RelevantCycles rc = new RelevantCycles(ic);
-                return new EssentialCycles(rc, ic).paths();
+                numberOfCyclesCheck(rc);
+                EssentialCycles essentialCycles = new EssentialCycles(rc, ic);
+                return essentialCycles.paths();
             }
         },
         RELEVANT {
 
             /** {@inheritDoc} */
             @Override
-            int[][] apply(int[][] graph, int length) {
+            int[][] apply(int[][] graph, int length) throws Intractable {
                 InitialCycles ic = InitialCycles.ofBiconnectedComponent(graph, length);
-                return new RelevantCycles(ic).paths();
+                RelevantCycles rc = new RelevantCycles(ic);
+                numberOfCyclesCheck(rc);
+                return rc.paths();
             }
         },
         ALL {
@@ -1024,6 +1045,12 @@ public Cycles find(IAtomContainer molecule, int[][] graph, int length) throws In
         }
     }
 
+    private static void numberOfCyclesCheck(RelevantCycles rc) throws Intractable {
+        if (rc.size() > MAX_RELEVANT_CYCLES)
+            throw new Intractable("Too many relevant cycles cycles! max=" + MAX_RELEVANT_CYCLES + " was=" + rc.size() + "." +
+                                  " Increase this limit with System property -D" + CDK_MAX_RELEVANT_CYCLES_KEY + "=<num>");
+    }
+
     /**
      * Internal - lifts a path in a subgraph back to the original graph.
      *