HADOOP-18429. fix infinite loop in MutableGaugeFloat#incr(float) (#4823)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/lib/MutableGaugeFloat.java

@@ -69,7 +69,7 @@ public class MutableGaugeFloat extends MutableGauge {
 
   private void incr(float delta) {
     while (true) {
-      float current = value.get();
+      float current = Float.intBitsToFloat(value.get());
       float next = current + delta;
       if (compareAndSet(current, next)) {
         setChanged();

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/metrics2/lib/TestMutableMetrics.java

@@ -18,6 +18,7 @@
 
 package org.apache.hadoop.metrics2.lib;
 
+import static org.apache.hadoop.metrics2.impl.MsInfo.Context;
 import static org.apache.hadoop.metrics2.lib.Interns.info;
 import static org.apache.hadoop.test.MetricsAsserts.*;
 import static org.mockito.AdditionalMatchers.eq;
@@ -500,4 +501,15 @@ public class TestMutableMetrics {
     verify(mb, times(2)).addGauge(
         info("FooNumOps", "Number of ops for stat with 5s interval"), (long) 0);
   }
+
+  /**
+   * Test {@link MutableGaugeFloat#incr()}.
+   */
+  @Test(timeout = 30000)
+  public void testMutableGaugeFloat() {
+    MutableGaugeFloat mgf = new MutableGaugeFloat(Context, 3.2f);
+    assertEquals(3.2f, mgf.value(), 0.0);
+    mgf.incr();
+    assertEquals(4.2f, mgf.value(), 0.0);
+  }
 }