HADOOP-15554. Improve JIT performance for Configuration parsing. Contributed by Todd Lipcon.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java

@@ -41,6 +41,7 @@
 import java.lang.ref.WeakReference;
 import java.net.InetSocketAddress;
 import java.net.JarURLConnection;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;
 import java.util.ArrayList;
@@ -2981,24 +2982,117 @@ private Resource loadResource(Properties properties,
       if(returnCachedProperties) {
         toAddTo = new Properties();
       }
+
+      List<ParsedItem> items = new Parser(reader, wrapper, quiet).parse();
+      for (ParsedItem item : items) {
+        loadProperty(toAddTo, item.name, item.key, item.value,
+            item.isFinal, item.sources);
+      }
+      reader.close();
+
+      if (returnCachedProperties) {
+        overlay(properties, toAddTo);
+        return new Resource(toAddTo, name, wrapper.isParserRestricted());
+      }
+      return null;
+    } catch (IOException e) {
+      LOG.error("error parsing conf " + name, e);
+      throw new RuntimeException(e);
+    } catch (XMLStreamException e) {
+      LOG.error("error parsing conf " + name, e);
+      throw new RuntimeException(e);
+    }
+  }
+
+  private static class ParsedItem {
+    String name;
+    String key;
+    String value;
+    boolean isFinal;
+    String[] sources;
+
+    ParsedItem(String name, String key, String value,
+        boolean isFinal, String[] sources) {
+      this.name = name;
+      this.key = key;
+      this.value = value;
+      this.isFinal = isFinal;
+      this.sources = sources;
+    }
+  }
+
+  /**
+   * Parser to consume SAX stream of XML elements from a Configuration.
+   */
+  private class Parser {
+    private final XMLStreamReader2 reader;
+    private final Resource wrapper;
+    private final String name;
+    private final String[] nameSingletonArray;
+    private final boolean isRestricted;
+    private final boolean quiet;
+
     DeprecationContext deprecations = deprecationContext.get();
 
-      StringBuilder token = new StringBuilder();
+    private StringBuilder token = new StringBuilder();
-      String confName = null;
+    private String confName = null;
-      String confValue = null;
+    private String confValue = null;
-      String confInclude = null;
+    private String confInclude = null;
-      String confTag = null;
+    private String confTag = null;
-      boolean confFinal = false;
+    private boolean confFinal = false;
-      boolean fallbackAllowed = false;
+    private boolean fallbackAllowed = false;
-      boolean fallbackEntered = false;
+    private boolean fallbackEntered = false;
-      boolean parseToken = false;
+    private boolean parseToken = false;
-      LinkedList<String> confSource = new LinkedList<String>();
+    private List<String> confSource = new ArrayList<>();
+    private List<ParsedItem> results = new ArrayList<>();
 
+    Parser(XMLStreamReader2 reader,
+           Resource wrapper,
+           boolean quiet) {
+      this.reader = reader;
+      this.wrapper = wrapper;
+      this.name = wrapper.getName();
+      this.nameSingletonArray = new String[]{ name };
+      this.isRestricted = wrapper.isParserRestricted();
+      this.quiet = quiet;
+
+    }
+
+    List<ParsedItem> parse() throws IOException, XMLStreamException {
       while (reader.hasNext()) {
-        switch (reader.next()) {
+        parseNext();
-        case XMLStreamConstants.START_ELEMENT:
+      }
+      return results;
+    }
+
+    private void handleStartElement() throws MalformedURLException {
       switch (reader.getLocalName()) {
       case "property":
+        handleStartProperty();
+        break;
+
+      case "name":
+      case "value":
+      case "final":
+      case "source":
+      case "tag":
+        parseToken = true;
+        token.setLength(0);
+        break;
+      case "include":
+        handleInclude();
+        break;
+      case "fallback":
+        fallbackEntered = true;
+        break;
+      case "configuration":
+        break;
+      default:
+        break;
+      }
+    }
+
+    private void handleStartProperty() {
       confName = null;
       confValue = null;
       confFinal = false;
@@ -3025,19 +3119,12 @@ private Resource loadResource(Properties properties,
               .weakIntern(reader.getAttributeValue(i));
         }
       }
-            break;
+    }
-          case "name":
+
-          case "value":
+    private void handleInclude() throws MalformedURLException {
-          case "final":
-          case "source":
-          case "tag":
-            parseToken = true;
-            token.setLength(0);
-            break;
-          case "include":
       // Determine href for xi:include
       confInclude = null;
-            attrCount = reader.getAttributeCount();
+      int attrCount = reader.getAttributeCount();
       for (int i = 0; i < attrCount; i++) {
         String attrName = reader.getAttributeLocalName(i);
         if ("href".equals(attrName)) {
@@ -3045,7 +3132,7 @@ private Resource loadResource(Properties properties,
         }
       }
       if (confInclude == null) {
-              break;
+        return;
       }
       if (isRestricted) {
         throw new RuntimeException("Error parsing resource " + wrapper
@@ -3058,7 +3145,11 @@ private Resource loadResource(Properties properties,
       if (include != null) {
         Resource classpathResource = new Resource(include, name,
             wrapper.isParserRestricted());
+        // This is only called recursively while the lock is already held
+        // by this thread, but synchronizing avoids a findbugs warning.
+        synchronized (Configuration.this) {
           loadResource(properties, classpathResource, quiet);
+        }
       } else {
         URL url;
         try {
@@ -3074,53 +3165,42 @@ private Resource loadResource(Properties properties,
           if (!href.exists()) {
             // Resource errors are non-fatal iff there is 1 xi:fallback
             fallbackAllowed = true;
-                  break;
+            return;
           }
           url = href.toURI().toURL();
         }
         Resource uriResource = new Resource(url, name,
             wrapper.isParserRestricted());
+        // This is only called recursively while the lock is already held
+        // by this thread, but synchronizing avoids a findbugs warning.
+        synchronized (Configuration.this) {
           loadResource(properties, uriResource, quiet);
         }
-            break;
-          case "fallback":
-            fallbackEntered = true;
-            break;
-          case "configuration":
-            break;
-          default:
-            break;
       }
-          break;
-
-        case XMLStreamConstants.CHARACTERS:
-          if (parseToken) {
-            char[] text = reader.getTextCharacters();
-            token.append(text, reader.getTextStart(), reader.getTextLength());
     }
-          break;
 
-        case XMLStreamConstants.END_ELEMENT:
+    void handleEndElement() throws IOException {
+      String tokenStr = token.toString();
       switch (reader.getLocalName()) {
       case "name":
         if (token.length() > 0) {
-              confName = StringInterner.weakIntern(token.toString().trim());
+          confName = StringInterner.weakIntern(tokenStr.trim());
         }
         break;
       case "value":
         if (token.length() > 0) {
-              confValue = StringInterner.weakIntern(token.toString());
+          confValue = StringInterner.weakIntern(tokenStr);
         }
         break;
       case "final":
-            confFinal = "true".equals(token.toString());
+        confFinal = "true".equals(tokenStr);
         break;
       case "source":
-            confSource.add(StringInterner.weakIntern(token.toString()));
+        confSource.add(StringInterner.weakIntern(tokenStr));
         break;
       case "tag":
         if (token.length() > 0) {
-              confTag = StringInterner.weakIntern(token.toString());
+          confTag = StringInterner.weakIntern(tokenStr);
         }
         break;
       case "include":
@@ -3133,49 +3213,63 @@ private Resource loadResource(Properties properties,
         fallbackEntered = false;
         break;
       case "property":
-            if (confName == null || (!fallbackAllowed && fallbackEntered)) {
+        handleEndProperty();
+        break;
+      default:
         break;
       }
+    }
+
+    void handleEndProperty() {
+      if (confName == null || (!fallbackAllowed && fallbackEntered)) {
+        return;
+      }
+      String[] confSourceArray;
+      if (confSource.isEmpty()) {
+        confSourceArray = nameSingletonArray;
+      } else {
         confSource.add(name);
+        confSourceArray = confSource.toArray(new String[confSource.size()]);
+      }
+
       // Read tags and put them in propertyTagsMap
       if (confTag != null) {
-              readTagFromConfig(confTag, confName, confValue, confSource);
+        readTagFromConfig(confTag, confName, confValue, confSourceArray);
       }
 
       DeprecatedKeyInfo keyInfo =
           deprecations.getDeprecatedKeyMap().get(confName);
+
       if (keyInfo != null) {
         keyInfo.clearAccessed();
         for (String key : keyInfo.newKeys) {
           // update new keys with deprecated key's value
-                loadProperty(toAddTo, name, key, confValue, confFinal,
+          results.add(new ParsedItem(
-                    confSource.toArray(new String[confSource.size()]));
+              name, key, confValue, confFinal, confSourceArray));
         }
       } else {
-              loadProperty(toAddTo, name, confName, confValue, confFinal,
+        results.add(new ParsedItem(name, confName, confValue, confFinal,
-                  confSource.toArray(new String[confSource.size()]));
+            confSourceArray));
-            }
-            break;
-          default:
-            break;
-          }
-        default:
-          break;
       }
     }
-      reader.close();
 
-      if (returnCachedProperties) {
+    void parseNext() throws IOException, XMLStreamException {
-        overlay(properties, toAddTo);
+      switch (reader.next()) {
-        return new Resource(toAddTo, name, wrapper.isParserRestricted());
+      case XMLStreamConstants.START_ELEMENT:
+        handleStartElement();
+        break;
+      case XMLStreamConstants.CHARACTERS:
+        if (parseToken) {
+          char[] text = reader.getTextCharacters();
+          token.append(text, reader.getTextStart(), reader.getTextLength());
+        }
+        break;
+      case XMLStreamConstants.END_ELEMENT:
+        handleEndElement();
+        break;
+      default:
+        break;
       }
-      return null;
-    } catch (IOException e) {
-      LOG.error("error parsing conf " + name, e);
-      throw new RuntimeException(e);
-    } catch (XMLStreamException e) {
-      LOG.error("error parsing conf " + name, e);
-      throw new RuntimeException(e);
     }
   }
 
@@ -3225,7 +3319,7 @@ public void addTags(Properties prop) {
    * @param confSource
    */
   private void readTagFromConfig(String attributeValue, String confName, String
-      confValue, List<String> confSource) {
+      confValue, String[] confSource) {
     for (String tagStr : attributeValue.split(",")) {
       try {
         tagStr = tagStr.trim();
@@ -3243,7 +3337,7 @@ private void readTagFromConfig(String attributeValue, String confName, String
       } catch (Exception ex) {
         // Log the exception at trace level.
         LOG.trace("Tag '{}' for property:{} Source:{}", tagStr, confName,
-            Arrays.toString(confSource.toArray()), ex);
+            confSource, ex);
       }
     }
   }