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SOLR-14579: Comment SolrJ 'Utils' generic map functions

This commit is contained in:
Erick Erickson 2020-09-01 10:04:44 -04:00
parent c077185943
commit b421878b77
1 changed files with 39 additions and 3 deletions
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42
solr/solrj/src/java/org/apache/solr/common/util/Utils.java
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@ -94,7 +94,44 @@ import static java.util.Collections.unmodifiableList;
import static java.util.Collections.unmodifiableSet;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
public class Utils {
// Why static lambdas? Even though they require SuppressWarnings? This is
// purely an optimization. Comparing:
//
// mapObject.computeIfAbsent(key, o -> new HashMap<>());
//
// vs.
//
// mapObject.computeIfAbsent(key, Utils.NEW_HASHMAP_FUN)
//
//
// The first code fragment is executed as following
//
// s.computeIfAbsent(key, new Function() {
// @Override
// public Object apply(String key) {
// return new HashMap<>();
// }
// }
//
// So, there are two problems with this
//
// A new anonymous inner class is created for that lambda. This one extra
// class becomes a part of your binary a new instance of that class is
// created everytime the computeIfAbsent() method is invoked, irrespective
// of whether the value is absent for that key or not. Now imagine that
// method getting called millions of times and creating millions of such
// objects for no reason
//
// OTOH
//
// Utils.NEW_HASHMAP_FUN
// Only a single anonymous class is created for the entire codebase
// Only single instance of that object is created in the VM
//
// See SOLR-14579.
@SuppressWarnings({"rawtypes"})
public static final Function NEW_HASHMAP_FUN = o -> new HashMap<>();
@SuppressWarnings({"rawtypes"})
@ -236,7 +273,7 @@ public class Utils {
}
@Override
@SuppressWarnings({"unchecked", "rawtypes"})
@SuppressWarnings({"rawtypes"})
public void handleUnknownClass(Object o) {
if (o instanceof MapWriter) {
Map m = ((MapWriter) o).toMap(new LinkedHashMap<>());
@ -404,7 +441,6 @@ public class Utils {
return getObjectByPath(root, onlyPrimitive, parts);
}
@SuppressWarnings({"unchecked"})
public static boolean setObjectByPath(Object root, String hierarchy, Object value) {
List<String> parts = StrUtils.splitSmart(hierarchy, '/', true);
return setObjectByPath(root, parts, value);
@ -693,7 +729,7 @@ public class Utils {
* @param input the json with new values
* @return whether there was any change made to sink or not.
*/
@SuppressWarnings({"unchecked", "rawtypes"})
@SuppressWarnings({"unchecked"})
public static boolean mergeJson(Map<String, Object> sink, Map<String, Object> input) {
boolean isModified = false;
for (Map.Entry<String, Object> e : input.entrySet()) {