[performance] Avoid reading SourceFile twice

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/Compiler.java

@@ -422,7 +422,15 @@ protected void reportWorked(int workIncrement, int currentUnitIndex) {
 	}
 
 	public void compile(ICompilationUnit[] sourceUnits) {
-		compile(sourceUnits, false);
+		try {
+			compile(sourceUnits, false);
+		} finally {
+			for (ICompilationUnit cu:sourceUnits) {
+				if (cu != null) {
+					cu.releaseContent();
+				}
+			}
+		}
 	}
 	/**
 	 * General API
@@ -851,30 +859,31 @@ protected void internalBeginToCompile(ICompilationUnit[] sourceUnits, int maxUni
 			for (int i = 0; i < maxUnits; i++) {
 				CompilationResult unitResult = null;
 				try {
+					ICompilationUnit sourceUnit = sourceUnits[i];
 					if (this.options.verbose) {
 						this.out.println(
 							Messages.bind(Messages.compilation_request,
 							new String[] {
 								String.valueOf(i + 1),
 								String.valueOf(maxUnits),
-								new String(sourceUnits[i].getFileName())
+								new String(sourceUnit.getFileName())
 							}));
 					}
 					// diet parsing for large collection of units
 					CompilationUnitDeclaration parsedUnit;
-					unitResult = new CompilationResult(sourceUnits[i], i, maxUnits, this.options.maxProblemsPerUnit);
+					unitResult = new CompilationResult(sourceUnit, i, maxUnits, this.options.maxProblemsPerUnit);
 					long parseStart = System.currentTimeMillis();
 					if (this.totalUnits < this.parseThreshold) {
-						parsedUnit = this.parser.parse(sourceUnits[i], unitResult);
+						parsedUnit = this.parser.parse(sourceUnit, unitResult);
 					} else {
-						parsedUnit = this.parser.dietParse(sourceUnits[i], unitResult);
+						parsedUnit = this.parser.dietParse(sourceUnit, unitResult);
 					}
 					long resolveStart = System.currentTimeMillis();
 					this.stats.parseTime += resolveStart - parseStart;
 					// initial type binding creation
 					this.lookupEnvironment.buildTypeBindings(parsedUnit, null /*no access restriction*/);
 					this.stats.resolveTime += System.currentTimeMillis() - resolveStart;
-					addCompilationUnit(sourceUnits[i], parsedUnit);
+					addCompilationUnit(sourceUnit, parsedUnit);
 					ImportReference currentPackage = parsedUnit.currentPackage;
 					if (currentPackage != null) {
 						unitResult.recordPackageName(currentPackage.tokens);

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/env/ICompilationUnit.java

@@ -37,6 +37,11 @@ public interface ICompilationUnit extends IDependent {
  * CharOperation.NO_CHAR being the candidate of choice.
  */
 char[] getContents();
+
+/** if {@link #getContents()} keeps a cached copy that cache can be released with this method **/
+default void releaseContent() {
+	// nothing
+}
 /**
  * Answer the name of the top level public type.
  * For example, {Hashtable}.

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/parser/Parser.java

@@ -11693,6 +11693,7 @@ public void getMethodBodies(CompilationUnitDeclaration unit) {
 	char[] contents = this.readManager != null
 		? this.readManager.getContents(compilationResult.compilationUnit)
 		: compilationResult.compilationUnit.getContents();
+	compilationResult.compilationUnit.releaseContent();
 	this.scanner.setSource(contents, compilationResult);
 
 	if (this.javadocParser != null && this.javadocParser.checkDocComment) {

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/builder/SourceFile.java

@@ -13,6 +13,8 @@
  *******************************************************************************/
 package org.eclipse.jdt.internal.core.builder;
 
+import java.lang.ref.SoftReference;
+
 import org.eclipse.core.resources.IFile;
 import org.eclipse.core.runtime.IPath;
 import org.eclipse.core.runtime.CoreException;
@@ -29,6 +31,7 @@ public class SourceFile implements ICompilationUnit {
 ClasspathMultiDirectory sourceLocation;
 String initialTypeName;
 boolean updateClassFile;
+private volatile SoftReference<char[]> contentRef;
 
 public SourceFile(IFile resource, ClasspathMultiDirectory sourceLocation) {
 	this.resource = resource;
@@ -80,12 +83,27 @@ String extractTypeName() {
 
 @Override
 public char[] getContents() {
-
+	SoftReference<char[]> cr = this.contentRef;
+	if (cr != null) {
+		char[] cachedContents = cr.get();
+		if (cachedContents != null) {
+			return cachedContents;
+		}
+	}
+	char[] contents;
 	try {
-		return Util.getResourceContentsAsCharArray(this.resource);
+		contents = Util.getResourceContentsAsCharArray(this.resource);
 	} catch (CoreException e) {
 		throw new AbortCompilation(true, new MissingSourceFileException(this.resource.getFullPath().toString()));
 	}
+	// softly cache the result:
+	this.contentRef = new SoftReference<>(contents);
+	return contents;
+}
+
+@Override
+public void releaseContent() {
+	this.contentRef = null;
 }
 
 /**

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/util/ResourceCompilationUnit.java

@@ -66,6 +66,11 @@ public char[] getContents() {
 		return contents;
 	}
 
+	@Override
+	public void releaseContent() {
+		this.contentRef = null;
+	}
+
 	@Override
 	public char[] getFileName() {
 		return this.fileName;