Simplify TimeValue Serialization (#62023)

This can be done without map lookups => less code and much smaller methods => better inlining potentially.

server/src/main/java/org/elasticsearch/common/io/stream/StreamInput.java

@@ -94,25 +94,6 @@ import static org.elasticsearch.ElasticsearchException.readStackTrace;
  */
 public abstract class StreamInput extends InputStream {
 
-    private static final Map<Byte, TimeUnit> BYTE_TIME_UNIT_MAP;
-
-    static {
-        final Map<Byte, TimeUnit> byteTimeUnitMap = new HashMap<>();
-        byteTimeUnitMap.put((byte)0, TimeUnit.NANOSECONDS);
-        byteTimeUnitMap.put((byte)1, TimeUnit.MICROSECONDS);
-        byteTimeUnitMap.put((byte)2, TimeUnit.MILLISECONDS);
-        byteTimeUnitMap.put((byte)3, TimeUnit.SECONDS);
-        byteTimeUnitMap.put((byte)4, TimeUnit.MINUTES);
-        byteTimeUnitMap.put((byte)5, TimeUnit.HOURS);
-        byteTimeUnitMap.put((byte)6, TimeUnit.DAYS);
-
-        for (TimeUnit value : TimeUnit.values()) {
-            assert byteTimeUnitMap.containsValue(value) : value;
-        }
-
-        BYTE_TIME_UNIT_MAP = Collections.unmodifiableMap(byteTimeUnitMap);
-    }
-
     private Version version = Version.CURRENT;
 
     /**
@@ -1312,12 +1293,22 @@ public abstract class StreamInput extends InputStream {
      */
     protected abstract void ensureCanReadBytes(int length) throws EOFException;
 
+    private static final TimeUnit[] TIME_UNITS = TimeUnit.values();
+
+    static {
+        // assert the exact form of the TimeUnit values to ensure we're not silently broken by a JDK change
+        if (Arrays.equals(TIME_UNITS, new TimeUnit[]{TimeUnit.NANOSECONDS, TimeUnit.MICROSECONDS, TimeUnit.MILLISECONDS,
+            TimeUnit.SECONDS, TimeUnit.MINUTES, TimeUnit.HOURS, TimeUnit.DAYS}) == false) {
+            throw new AssertionError("Incompatible JDK version used that breaks assumptions on the structure of the TimeUnit enum");
+        }
+    }
+
     /**
      * Read a {@link TimeValue} from the stream
      */
     public TimeValue readTimeValue() throws IOException {
         long duration = readZLong();
-        TimeUnit timeUnit = BYTE_TIME_UNIT_MAP.get(readByte());
+        TimeUnit timeUnit = TIME_UNITS[readByte()];
         return new TimeValue(duration, timeUnit);
     }
 

server/src/main/java/org/elasticsearch/common/io/stream/StreamOutput.java

@@ -62,9 +62,7 @@ import java.time.ZoneId;
 import java.time.ZonedDateTime;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Date;
-import java.util.EnumMap;
 import java.util.EnumSet;
 import java.util.Iterator;
 import java.util.LinkedHashMap;
@@ -72,7 +70,6 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.concurrent.TimeUnit;
 import java.util.function.IntFunction;
 
 import static java.util.Map.entry;
@@ -90,26 +87,8 @@ import static java.util.Map.entry;
  */
 public abstract class StreamOutput extends OutputStream {
 
-    private static final Map<TimeUnit, Byte> TIME_UNIT_BYTE_MAP;
     private static final int MAX_NESTED_EXCEPTION_LEVEL = 100;
 
-    static {
-        final Map<TimeUnit, Byte> timeUnitByteMap = new EnumMap<>(TimeUnit.class);
-        timeUnitByteMap.put(TimeUnit.NANOSECONDS, (byte)0);
-        timeUnitByteMap.put(TimeUnit.MICROSECONDS, (byte)1);
-        timeUnitByteMap.put(TimeUnit.MILLISECONDS, (byte)2);
-        timeUnitByteMap.put(TimeUnit.SECONDS, (byte)3);
-        timeUnitByteMap.put(TimeUnit.MINUTES, (byte)4);
-        timeUnitByteMap.put(TimeUnit.HOURS, (byte)5);
-        timeUnitByteMap.put(TimeUnit.DAYS, (byte)6);
-
-        for (TimeUnit value : TimeUnit.values()) {
-            assert timeUnitByteMap.containsKey(value) : value;
-        }
-
-        TIME_UNIT_BYTE_MAP = Collections.unmodifiableMap(timeUnitByteMap);
-    }
-
     private Version version = Version.CURRENT;
 
     /**
@@ -1280,7 +1259,7 @@ public abstract class StreamOutput extends OutputStream {
      */
     public void writeTimeValue(TimeValue timeValue) throws IOException {
         writeZLong(timeValue.duration());
-        writeByte(TIME_UNIT_BYTE_MAP.get(timeValue.timeUnit()));
+        writeByte((byte) timeValue.timeUnit().ordinal());
     }
 
     /**