### Eclipse Workspace Patch 1.0
#P org.eclipse.jdt.core
Index: model/org/eclipse/jdt/internal/core/CompilationUnit.java
===================================================================
RCS file: /cvsroot/eclipse/org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/CompilationUnit.java,v
retrieving revision 1.231
diff -u -r1.231 CompilationUnit.java
--- model/org/eclipse/jdt/internal/core/CompilationUnit.java	20 Jun 2006 11:33:14 -0000	1.231
+++ model/org/eclipse/jdt/internal/core/CompilationUnit.java	21 Jun 2006 10:09:53 -0000
@@ -1021,43 +1021,50 @@
 protected IBuffer openBuffer(IProgressMonitor pm, Object info) throws JavaModelException {
 
 	// create buffer
+	BufferManager bufManager = getBufferManager();
 	boolean isWorkingCopy = isWorkingCopy();
 	IBuffer buffer = 
 		isWorkingCopy 
 			? this.owner.createBuffer(this) 
-			: BufferManager.getDefaultBufferManager().createBuffer(this);
+			: bufManager.createBuffer(this);
 	if (buffer == null) return null;
 	
-	// set the buffer source
-	if (buffer.getCharacters() == null) {
-		if (isWorkingCopy) {
-			ICompilationUnit original;
-			if (!isPrimary() 
-					&& (original = new CompilationUnit((PackageFragment)getParent(), getElementName(), DefaultWorkingCopyOwner.PRIMARY)).isOpen()) {
-				buffer.setContents(original.getSource());
-			} else {
-				IFile file = (IFile)getResource();
-				if (file == null || !file.exists()) {
-					// initialize buffer with empty contents
-					buffer.setContents(CharOperation.NO_CHAR);
+	// synchronize to ensure that 2 threads are not putting 2 different buffers at the same time
+	// see https://bugs.eclipse.org/bugs/show_bug.cgi?id=146331
+	synchronized(bufManager) {
+		IBuffer existingBuffer = bufManager.getBuffer(this);
+		if (existingBuffer != null)
+			return existingBuffer;
+		
+		// set the buffer source
+		if (buffer.getCharacters() == null) {
+			if (isWorkingCopy) {
+				ICompilationUnit original;
+				if (!isPrimary() 
+						&& (original = new CompilationUnit((PackageFragment)getParent(), getElementName(), DefaultWorkingCopyOwner.PRIMARY)).isOpen()) {
+					buffer.setContents(original.getSource());
 				} else {
-					buffer.setContents(Util.getResourceContentsAsCharArray(file));
+					IFile file = (IFile)getResource();
+					if (file == null || !file.exists()) {
+						// initialize buffer with empty contents
+						buffer.setContents(CharOperation.NO_CHAR);
+					} else {
+						buffer.setContents(Util.getResourceContentsAsCharArray(file));
+					}
 				}
+			} else {
+				IFile file = (IFile)this.getResource();
+				if (file == null || !file.exists()) throw newNotPresentException();
+				buffer.setContents(Util.getResourceContentsAsCharArray(file));
 			}
-		} else {
-			IFile file = (IFile)this.getResource();
-			if (file == null || !file.exists()) throw newNotPresentException();
-			buffer.setContents(Util.getResourceContentsAsCharArray(file));
 		}
-	}
-
-	// add buffer to buffer cache
-	BufferManager bufManager = getBufferManager();
-	bufManager.addBuffer(buffer);
-			
-	// listen to buffer changes
-	buffer.addBufferChangedListener(this);
 	
+		// add buffer to buffer cache
+		bufManager.addBuffer(buffer);
+				
+		// listen to buffer changes
+		buffer.addBufferChangedListener(this);
+	}	
 	return buffer;
 }
 protected void openParent(Object childInfo, HashMap newElements, IProgressMonitor pm) throws JavaModelException {