[core] Add CoreWorkload.createOperationGenerator() for use in other workloads.

Eventually it would be nice to move this out into a proper generator with enums to
save space, but as users may have extended CoreWorkload and could be using the
"operationchooser" field, we'll just break it out into a static function so as to
avoid breaking anyone's code.

core/src/main/java/com/yahoo/ycsb/workloads/CoreWorkload.java

 /**
- * Copyright (c) 2010 Yahoo! Inc. All rights reserved.
+ * Copyright (c) 2010 Yahoo! Inc., Copyright (c) 2016 YCSB contributors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you
  * may not use this file except in compliance with the License. You
@@ -371,17 +371,7 @@ public class CoreWorkload extends Workload {
       fieldnames.add("field" + i);
     }
     fieldlengthgenerator = CoreWorkload.getFieldLengthGenerator(p);
-
-    double readproportion = Double.parseDouble(
-        p.getProperty(READ_PROPORTION_PROPERTY, READ_PROPORTION_PROPERTY_DEFAULT));
-    double updateproportion = Double.parseDouble(
-        p.getProperty(UPDATE_PROPORTION_PROPERTY, UPDATE_PROPORTION_PROPERTY_DEFAULT));
-    double insertproportion = Double.parseDouble(
-        p.getProperty(INSERT_PROPORTION_PROPERTY, INSERT_PROPORTION_PROPERTY_DEFAULT));
-    double scanproportion = Double.parseDouble(
-        p.getProperty(SCAN_PROPORTION_PROPERTY, SCAN_PROPORTION_PROPERTY_DEFAULT));
-    double readmodifywriteproportion = Double.parseDouble(p.getProperty(
-        READMODIFYWRITE_PROPORTION_PROPERTY, READMODIFYWRITE_PROPORTION_PROPERTY_DEFAULT));
+    
     recordcount =
         Integer.parseInt(p.getProperty(Client.RECORD_COUNT_PROPERTY, Client.DEFAULT_RECORD_COUNT));
     if (recordcount == 0)
@@ -429,26 +419,7 @@ public class CoreWorkload extends Workload {
     }
 
     keysequence = new CounterGenerator(insertstart);
-    operationchooser = new DiscreteGenerator();
-    if (readproportion > 0) {
-      operationchooser.addValue(readproportion, "READ");
-    }
-
-    if (updateproportion > 0) {
-      operationchooser.addValue(updateproportion, "UPDATE");
-    }
-
-    if (insertproportion > 0) {
-      operationchooser.addValue(insertproportion, "INSERT");
-    }
-
-    if (scanproportion > 0) {
-      operationchooser.addValue(scanproportion, "SCAN");
-    }
-
-    if (readmodifywriteproportion > 0) {
-      operationchooser.addValue(readmodifywriteproportion, "READMODIFYWRITE");
-    }
+    operationchooser = createOperationGenerator(p);
 
     transactioninsertkeysequence = new AcknowledgedCounterGenerator(recordcount);
     if (requestdistrib.compareTo("uniform") == 0) {
@@ -463,7 +434,8 @@ public class CoreWorkload extends Workload {
       // plus the number of predicted keys as the total keyspace. then, if the generator picks a key
       // that hasn't been inserted yet, will just ignore it and pick another key. this way, the size of
       // the keyspace doesn't change from the perspective of the scrambled zipfian generator
-
+      final double insertproportion = Double.parseDouble(
+          p.getProperty(INSERT_PROPORTION_PROPERTY, INSERT_PROPORTION_PROPERTY_DEFAULT));
       int opcount = Integer.parseInt(p.getProperty(Client.OPERATION_COUNT_PROPERTY));
       int expectednewkeys = (int) ((opcount) * insertproportion * 2.0); // 2 is fudge factor
 
@@ -801,4 +773,51 @@ public class CoreWorkload extends Workload {
       transactioninsertkeysequence.acknowledge(keynum);
     }
   }
-}
+
+  /**
+   * Creates a weighted discrete values with database operations for a workload to perform.
+   * Weights/proportions are read from the properties list and defaults are used
+   * when values are not configured.
+   * Current operations are "READ", "UPDATE", "INSERT", "SCAN" and "READMODIFYWRITE".
+   * @param p The properties list to pull weights from.
+   * @return A generator that can be used to determine the next operation to perform.
+   * @throws IllegalArgumentException if the properties object was null.
+   */
+  public static DiscreteGenerator createOperationGenerator(final Properties p) {
+    if (p == null) {
+      throw new IllegalArgumentException("Properties object cannot be null");
+    }
+    final double readproportion = Double.parseDouble(
+        p.getProperty(READ_PROPORTION_PROPERTY, READ_PROPORTION_PROPERTY_DEFAULT));
+    final double updateproportion = Double.parseDouble(
+        p.getProperty(UPDATE_PROPORTION_PROPERTY, UPDATE_PROPORTION_PROPERTY_DEFAULT));
+    final double insertproportion = Double.parseDouble(
+        p.getProperty(INSERT_PROPORTION_PROPERTY, INSERT_PROPORTION_PROPERTY_DEFAULT));
+    final double scanproportion = Double.parseDouble(
+        p.getProperty(SCAN_PROPORTION_PROPERTY, SCAN_PROPORTION_PROPERTY_DEFAULT));
+    final double readmodifywriteproportion = Double.parseDouble(p.getProperty(
+        READMODIFYWRITE_PROPORTION_PROPERTY, READMODIFYWRITE_PROPORTION_PROPERTY_DEFAULT));
+    
+    final DiscreteGenerator operationchooser = new DiscreteGenerator();
+    if (readproportion > 0) {
+      operationchooser.addValue(readproportion, "READ");
+    }
+
+    if (updateproportion > 0) {
+      operationchooser.addValue(updateproportion, "UPDATE");
+    }
+
+    if (insertproportion > 0) {
+      operationchooser.addValue(insertproportion, "INSERT");
+    }
+
+    if (scanproportion > 0) {
+      operationchooser.addValue(scanproportion, "SCAN");
+    }
+
+    if (readmodifywriteproportion > 0) {
+      operationchooser.addValue(readmodifywriteproportion, "READMODIFYWRITE");
+    }
+    return operationchooser;
+  }
+}
\ No newline at end of file

core/src/test/java/com/yahoo/ycsb/workloads/TestCoreWorkload.java

+/**                                                                                                                                                                                
+ * Copyright (c) 2016 YCSB contributors. All rights reserved.                                                                                                                             
+ *                                                                                                                                                                                 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you                                                                                                             
+ * may not use this file except in compliance with the License. You                                                                                                                
+ * may obtain a copy of the License at                                                                                                                                             
+ *                                                                                                                                                                                 
+ * http://www.apache.org/licenses/LICENSE-2.0                                                                                                                                      
+ *                                                                                                                                                                                 
+ * Unless required by applicable law or agreed to in writing, software                                                                                                             
+ * distributed under the License is distributed on an "AS IS" BASIS,                                                                                                               
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or                                                                                                                 
+ * implied. See the License for the specific language governing                                                                                                                    
+ * permissions and limitations under the License. See accompanying                                                                                                                 
+ * LICENSE file.                                                                                                                                                                   
+ */
+package com.yahoo.ycsb.workloads;
+
+import static org.testng.Assert.assertTrue;
+
+import java.util.Properties;
+
+import org.testng.annotations.Test;
+
+import com.yahoo.ycsb.generator.DiscreteGenerator;
+
+public class TestCoreWorkload {
+
+  @Test
+  public void createOperationChooser() {
+    final Properties p = new Properties();
+    p.setProperty(CoreWorkload.READ_PROPORTION_PROPERTY, "0.20");
+    p.setProperty(CoreWorkload.UPDATE_PROPORTION_PROPERTY, "0.20");
+    p.setProperty(CoreWorkload.INSERT_PROPORTION_PROPERTY, "0.20");
+    p.setProperty(CoreWorkload.SCAN_PROPORTION_PROPERTY, "0.20");
+    p.setProperty(CoreWorkload.READMODIFYWRITE_PROPORTION_PROPERTY, "0.20");
+    final DiscreteGenerator generator = CoreWorkload.createOperationGenerator(p);
+    final int[] counts = new int[5];
+    
+    for (int i = 0; i < 100; ++i) {
+      switch (generator.nextString()) {
+      case "READ":
+        ++counts[0];
+        break;
+      case "UPDATE":
+        ++counts[1];
+        break;
+      case "INSERT": 
+        ++counts[2];
+        break;
+      case "SCAN":
+        ++counts[3];
+        break;
+      default:
+        ++counts[4];
+      } 
+    }
+    
+    for (int i : counts) {
+      // Doesn't do a wonderful job of equal distribution, but in a hundred, if we 
+      // don't see at least one of each operation then the generator is really broke.
+      assertTrue(i > 1);
+    }
+  }
+  
+  @Test (expectedExceptions = IllegalArgumentException.class)
+  public void createOperationChooserNullProperties() {
+    CoreWorkload.createOperationGenerator(null);
+  }
+}
\ No newline at end of file