fix PcpMmvWriter strings leak

`PcpMmvWriter` leaks strings through its `PcpStringStore` when the
writer is reset. The fix is to clear the store in the reset method.
However, the `metricInfoStore` and `instanceDomainStore` rely on
putting values in the string store when MMV2 is used. As such, these
stores must also be cleared so that the strings can be recreated.

Author: pwinckles

dxm/pom.xml

@@ -76,7 +76,10 @@
       <artifactId>hamcrest-all</artifactId>
       <scope>test</scope>
     </dependency>
-
-
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-simple</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 </project>

dxm/src/main/java/io/pcp/parfait/dxm/PcpMmvWriter.java

@@ -339,6 +339,9 @@ public void reset() {
         started = false;
         metricData.clear();
         perMetricByteBuffers.clear();
+        instanceDomainStore.clear();
+        metricInfoStore.clear();
+        stringStore.clear();
     }
 
     @Override
@@ -764,6 +767,11 @@ synchronized Collection<T> all() {
         synchronized int size() {
             return byName.size();
         }
+
+        synchronized void clear() {
+            byId.clear();
+            byName.clear();
+        }
     }
 
     @Override

dxm/src/main/java/io/pcp/parfait/dxm/PcpString.java

@@ -81,6 +81,9 @@ Collection<PcpString> getStrings() {
             return stringInfo;
         }
 
+        void clear() {
+            stringInfo.clear();
+        }
     }
 
 }

dxm/src/test/java/io/pcp/parfait/dxm/PcpMmvWriterIntegrationTest.java

@@ -21,11 +21,14 @@
 import org.junit.BeforeClass;
 import org.junit.Test;
 
+import java.lang.reflect.Field;
+
 import static io.pcp.parfait.dxm.IdentifierSourceSet.DEFAULT_SET;
 import static io.pcp.parfait.dxm.MmvVersion.MMV_VERSION1;
 import static io.pcp.parfait.dxm.MmvVersion.MMV_VERSION2;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertEquals;
 import static tech.units.indriya.AbstractUnit.ONE;
 
 public class PcpMmvWriterIntegrationTest {
@@ -79,11 +82,45 @@ public void mmvVersion2ShouldSupportInstanceNamesOver63Characters() throws Excep
         assertMetric("mmv.v2.integer[instance_name_over_63_characters_instance_name_over_63_characters_instance]", is("11.000"));
     }
 
+    @Test
+    public void resetShouldClearStrings() throws Exception {
+        pcpMmvWriterV1.reset();
+        assertStringsCount(pcpMmvWriterV1, 0);
+        pcpMmvWriterV1.addMetric(MetricName.parse("v1.string"), Semantics.DISCRETE, null, "test1");
+        pcpMmvWriterV1.start();
+
+        pcpMmvWriterV2.reset();
+        assertStringsCount(pcpMmvWriterV2, 0);
+        pcpMmvWriterV2.addMetric(MetricName.parse("v2.string"), Semantics.DISCRETE, null, "test2");
+        pcpMmvWriterV2.start();
+
+        waitForReload();
+
+        assertMetric("mmv.v1.string", is("\"test1\""));
+        assertMetric("mmv.v2.string", is("\"test2\""));
+
+        assertStringsCount(pcpMmvWriterV1, 1);
+        assertStringsCount(pcpMmvWriterV2, 2);
+
+        pcpMmvWriterV1.reset();
+        assertStringsCount(pcpMmvWriterV1, 0);
+
+        pcpMmvWriterV2.reset();
+        assertStringsCount(pcpMmvWriterV2, 0);
+    }
+
     private void assertMetric(String metricName, Matcher<String> expectedValue) throws Exception {
         String actual = pcpClient.getMetric(metricName);
         assertThat(actual, expectedValue);
     }
 
+    private void assertStringsCount(PcpMmvWriter writer, int expectedCount) throws NoSuchFieldException, IllegalAccessException {
+        Field field = PcpMmvWriter.class.getDeclaredField("stringStore");
+        field.setAccessible(true);
+        PcpString.PcpStringStore stringStore = (PcpString.PcpStringStore) field.get(writer);
+        assertEquals(expectedCount, stringStore.getStrings().size());
+    }
+
     private void waitForReload() throws InterruptedException {
         Thread.sleep(1000);
     }