Index: core/src/org/netbeans/core/NbTopManager.java
===================================================================
RCS file: /cvs/core/src/org/netbeans/core/NbTopManager.java,v
retrieving revision 1.122
diff -u -r1.122 NbTopManager.java
--- core/src/org/netbeans/core/NbTopManager.java	5 Oct 2001 16:01:40 -0000	1.122
+++ core/src/org/netbeans/core/NbTopManager.java	10 Oct 2001 15:42:45 -0000
@@ -755,7 +755,8 @@
     public ClassLoader systemClassLoader () {
         ModuleSystem ms = getModuleSystem();
         if (ms != null) {
-            return ms.getManager().getClassLoader();
+            // #16265: do not go straight to ModuleManager
+            return ms.getSystemClassLoader();
         } else {
             // This can be called very early: if lookup asks for ClassLoader.
             // For now, just give the startup classloader.
Index: core/src/org/netbeans/core/modules/ModuleManager.java
===================================================================
RCS file: /cvs/core/src/org/netbeans/core/modules/ModuleManager.java,v
retrieving revision 1.14
diff -u -r1.14 ModuleManager.java
--- core/src/org/netbeans/core/modules/ModuleManager.java	11 Sep 2001 20:28:37 -0000	1.14
+++ core/src/org/netbeans/core/modules/ModuleManager.java	10 Oct 2001 15:42:47 -0000
@@ -52,7 +52,8 @@
     
     private final ModuleInstaller installer;
     
-    private SystemClassLoader classLoader = null;
+    private SystemClassLoader classLoader = new SystemClassLoader(new ClassLoader[0]);
+    private final Object classLoaderLock = "ModuleManager.classLoaderLock"; // NOI18N
     
     private final Events ev;
     
@@ -198,41 +199,45 @@
     /** Get a classloader capable of loading from any
      * of the enabled modules or their declared extensions.
      * Should be used as the result of TopManager.systemClassLoader.
-     * <strong>Note:</strong> must be called from within write, not
-     * just read, access.
+     * Thread-safe.
      * @see #PROP_CLASS_LOADER
      */
     public ClassLoader getClassLoader() {
-        if (classLoader == null) {
-            // Set, not List, because if we have >1 bootstrap module (using Plain),
-            // it is likely that some of these classloaders will overlap.
-            Set parents = new HashSet(modules.size() * 4 / 3 + 1); // Set<ClassLoader>
-            Iterator it = modules.iterator();
-            while (it.hasNext()) {
-                Module m = ((Module)it.next());
-                if (! m.isEnabled()) {
-                    continue;
-                }
-                parents.add(m.getClassLoader());
-            }
-            ClassLoader[] parentCLs = (ClassLoader[])parents.toArray(new ClassLoader[parents.size()]);
-            try {
-                classLoader = new SystemClassLoader(parentCLs);
-            } catch (IllegalArgumentException iae) {
-                Util.err.notify(iae);
-                classLoader = new SystemClassLoader(new ClassLoader[0]);
-            }
+        // #16265: should not require mutex to get at. Many pieces of the IDE
+        // require the correct result immediately.
+        synchronized (classLoaderLock) {
+            return classLoader;
         }
-        return classLoader;
     }
     
-    /** Mark the current class loader as invalid. */
+    /** Mark the current class loader as invalid and make a new one. */
     private void invalidateClassLoader() {
-        if (classLoader != null) {
+        synchronized (classLoaderLock) {
             classLoader.destroy(); // probably has no effect, but just in case...
-            classLoader = null;
-            firer.change(new ChangeFirer.Change(this, PROP_CLASS_LOADER, null, null));
         }
+        // Set, not List, because if we have >1 bootstrap module (using Plain),
+        // it is likely that some of these classloaders will overlap.
+        Set parents = new HashSet(modules.size() * 4 / 3 + 1); // Set<ClassLoader>
+        Iterator it = modules.iterator();
+        while (it.hasNext()) {
+            Module m = ((Module)it.next());
+            if (! m.isEnabled()) {
+                continue;
+            }
+            parents.add(m.getClassLoader());
+        }
+        ClassLoader[] parentCLs = (ClassLoader[])parents.toArray(new ClassLoader[parents.size()]);
+        SystemClassLoader nue;
+        try {
+            nue = new SystemClassLoader(parentCLs);
+        } catch (IllegalArgumentException iae) {
+            Util.err.notify(iae);
+            nue = new SystemClassLoader(new ClassLoader[0]);
+        }
+        synchronized (classLoaderLock) {
+            classLoader = nue;
+        }
+        firer.change(new ChangeFirer.Change(this, PROP_CLASS_LOADER, null, null));
     }
     
     /** A classloader giving access to all the module classloaders at once. */
Index: core/src/org/netbeans/core/modules/ModuleSystem.java
===================================================================
RCS file: /cvs/core/src/org/netbeans/core/modules/ModuleSystem.java,v
retrieving revision 1.10
diff -u -r1.10 ModuleSystem.java
--- core/src/org/netbeans/core/modules/ModuleSystem.java	20 Jul 2001 18:12:50 -0000	1.10
+++ core/src/org/netbeans/core/modules/ModuleSystem.java	10 Oct 2001 15:42:48 -0000
@@ -131,12 +131,8 @@
             }
             mgr.addPropertyChangeListener(new ListenerFirer());
         }
-        mgr.mutexPrivileged().enterWriteAccess();
-        try {
-            return mgr.getClassLoader();
-        } finally {
-            mgr.mutexPrivileged().exitWriteAccess();
-        }
+        // #16265: no need for write mutex any more.
+        return mgr.getClassLoader();
     }
     private boolean addedClassLoaderListener = false;