Revert^8 "Make sure that const-class linkage is preserved."

Replaced two ReaderMutexLocks with WriterMutexLocks.
Removed some unnecessary debugging output.

Test: m test-art-host
Bug: 30627598
Original-Change-Id: Ie9b721464b4e9a5dcce8df8095548e983bba1fe8

This reverts commit 2c8c6b63da6ecb2ac701cc30f9b4fa4a8eea5cc8.

Change-Id: I3a1aeecf64e4b202cef61cceb248d48106a2f4a6
diff --git a/test/626-const-class-linking/src/DefiningLoader.java b/test/626-const-class-linking/src/DefiningLoader.java
new file mode 100644
index 0000000..b17ab77
--- /dev/null
+++ b/test/626-const-class-linking/src/DefiningLoader.java
@@ -0,0 +1,239 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+import java.lang.reflect.InvocationTargetException;
+
+/**
+ * A class loader with atypical behavior: we try to load a private
+ * class implementation before asking the system or boot loader.  This
+ * is used to create multiple classes with identical names in a single VM.
+ *
+ * If DexFile is available, we use that; if not, we assume we're not in
+ * Dalvik and instantiate the class with defineClass().
+ *
+ * The location of the DEX files and class data is dependent upon the
+ * test framework.
+ */
+public class DefiningLoader extends ClassLoader {
+    static {
+        // For JVM, register as parallel capable.
+        // Android treats all class loaders as parallel capable and makes this a no-op.
+        registerAsParallelCapable();
+    }
+
+    /* this is where the .class files live */
+    static final String CLASS_PATH1 = "classes/";
+    static final String CLASS_PATH2 = "classes2/";
+
+    /* this is the DEX/Jar file */
+    static final String DEX_FILE = System.getenv("DEX_LOCATION") + "/626-const-class-linking.jar";
+
+    /* on Dalvik, this is a DexFile; otherwise, it's null */
+    private Class<?> mDexClass;
+
+    private Object mDexFile;
+
+    /**
+     * Construct DefiningLoader, grabbing a reference to the DexFile class
+     * if we're running under Dalvik.
+     */
+    public DefiningLoader(ClassLoader parent) {
+        super(parent);
+
+        try {
+            mDexClass = parent.loadClass("dalvik.system.DexFile");
+        } catch (ClassNotFoundException cnfe) {
+            // ignore -- not running Dalvik
+        }
+    }
+
+    /**
+     * Finds the class with the specified binary name.
+     *
+     * We search for a file in CLASS_PATH or pull an entry from DEX_FILE.
+     * If we don't find a match, we throw an exception.
+     */
+    protected Class<?> findClass(String name) throws ClassNotFoundException
+    {
+        if (mDexClass != null) {
+            return findClassDalvik(name);
+        } else {
+            return findClassNonDalvik(name);
+        }
+    }
+
+    /**
+     * Finds the class with the specified binary name, from a DEX file.
+     */
+    private Class<?> findClassDalvik(String name)
+        throws ClassNotFoundException {
+
+        if (mDexFile == null) {
+            synchronized (DefiningLoader.class) {
+                Constructor<?> ctor;
+                /*
+                 * Construct a DexFile object through reflection.
+                 */
+                try {
+                    ctor = mDexClass.getConstructor(String.class);
+                } catch (NoSuchMethodException nsme) {
+                    throw new ClassNotFoundException("getConstructor failed",
+                        nsme);
+                }
+
+                try {
+                    mDexFile = ctor.newInstance(DEX_FILE);
+                } catch (InstantiationException ie) {
+                    throw new ClassNotFoundException("newInstance failed", ie);
+                } catch (IllegalAccessException iae) {
+                    throw new ClassNotFoundException("newInstance failed", iae);
+                } catch (InvocationTargetException ite) {
+                    throw new ClassNotFoundException("newInstance failed", ite);
+                }
+            }
+        }
+
+        /*
+         * Call DexFile.loadClass(String, ClassLoader).
+         */
+        Method meth;
+
+        try {
+            meth = mDexClass.getMethod("loadClass", String.class, ClassLoader.class);
+        } catch (NoSuchMethodException nsme) {
+            throw new ClassNotFoundException("getMethod failed", nsme);
+        }
+
+        try {
+            meth.invoke(mDexFile, name, this);
+        } catch (IllegalAccessException iae) {
+            throw new ClassNotFoundException("loadClass failed", iae);
+        } catch (InvocationTargetException ite) {
+            throw new ClassNotFoundException("loadClass failed",
+                ite.getCause());
+        }
+
+        return null;
+    }
+
+    /**
+     * Finds the class with the specified binary name, from .class files.
+     */
+    private Class<?> findClassNonDalvik(String name)
+        throws ClassNotFoundException {
+
+        String[] pathNames = { CLASS_PATH1 + name + ".class", CLASS_PATH2 + name + ".class" };
+
+        String pathName = null;
+        RandomAccessFile raf = null;
+
+        for (String pn : pathNames) {
+            pathName = pn;
+            try {
+                //System.out.println("--- Defining: looking for " + pathName);
+                raf = new RandomAccessFile(new File(pathName), "r");
+                break;
+            } catch (FileNotFoundException fnfe) {
+            }
+        }
+        if (raf == null) {
+            throw new ClassNotFoundException("Not found: " + pathNames[0] + ":" + pathNames[1]);
+        }
+
+        /* read the entire file in */
+        byte[] fileData;
+        try {
+            fileData = new byte[(int) raf.length()];
+            raf.readFully(fileData);
+        } catch (IOException ioe) {
+            throw new ClassNotFoundException("Read error: " + pathName);
+        } finally {
+            try {
+                raf.close();
+            } catch (IOException ioe) {
+                // drop
+            }
+        }
+
+        /* create the class */
+        //System.out.println("--- Defining: defining " + name);
+        try {
+            return defineClass(name, fileData, 0, fileData.length);
+        } catch (Throwable th) {
+            throw new ClassNotFoundException("defineClass failed", th);
+        }
+    }
+
+    /**
+     * Load a class.
+     *
+     * Normally a class loader wouldn't override this, but we want our
+     * version of the class to take precedence over an already-loaded
+     * version.
+     *
+     * We still want the system classes (e.g. java.lang.Object) from the
+     * bootstrap class loader.
+     */
+    synchronized protected Class<?> loadClass(String name, boolean resolve)
+        throws ClassNotFoundException
+    {
+        Class<?> res;
+
+        /*
+         * 1. Invoke findLoadedClass(String) to check if the class has
+         * already been loaded.
+         *
+         * This doesn't change.
+         */
+        res = findLoadedClass(name);
+        if (res != null) {
+            // System.out.println("FancyLoader.loadClass: " + name + " already loaded");
+            if (resolve)
+                resolveClass(res);
+            return res;
+        }
+
+        /*
+         * 3. Invoke the findClass(String) method to find the class.
+         */
+        try {
+            res = findClass(name);
+            if (resolve)
+                resolveClass(res);
+        }
+        catch (ClassNotFoundException e) {
+            // we couldn't find it, so eat the exception and keep going
+        }
+
+        /*
+         * 2. Invoke the loadClass method on the parent class loader.  If
+         * the parent loader is null the class loader built-in to the
+         * virtual machine is used, instead.
+         *
+         * (Since we're not in java.lang, we can't actually invoke the
+         * parent's loadClass() method, but we passed our parent to the
+         * super-class which can take care of it for us.)
+         */
+        res = super.loadClass(name, resolve);   // returns class or throws
+        return res;
+    }
+}