WM Tests: Use a separate WindowManager instance per test

Fixes a bunch of flakes, where the WindowManagerService instance
was reused between tests, which caused delayed callbacks from a
previous test affecting state of a future test.

Also introduces a DexmakerShareClassLoaderRule to manage
the 'dexmaker.share_classloader' property instead of sprinkling
error prone System.setProperty() invocations all over the tests.

Change-Id: Ic9445d1b2cef594e79365c425632aabced6343a9
Fixes: 76111404
Fixes: 75991352
Fixes: 75991878
Fixes: 75992153
Test: atest services/tests/servicestests DexmakerShareClassLoaderRuleTest packages/SystemUI/tests packages/SystemUI/shared/tests

1 files changed, 129 insertions, 0 deletions

diff --git a/tests/testables/src/android/testing/DexmakerShareClassLoaderRule.java b/tests/testables/src/android/testing/DexmakerShareClassLoaderRule.java
new file mode 100644
index 000000000000..1b8e58c3050d
--- /dev/null
+++ b/tests/testables/src/android/testing/DexmakerShareClassLoaderRule.java
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+package android.testing;
+
+import android.util.Log;
+
+import com.android.internal.annotations.VisibleForTesting;
+
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runners.model.Statement;
+
+import java.util.ConcurrentModificationException;
+
+
+/**
+ * Runs the test such that mocks created in it don't use a dedicated classloader.
+ *
+ * This allows mocking package-private methods.
+ *
+ * WARNING: This is absolutely incompatible with running tests in parallel!
+ */
+public class DexmakerShareClassLoaderRule implements TestRule {
+
+    private static final String TAG = "ShareClassloaderRule";
+    @VisibleForTesting
+    static final String DEXMAKER_SHARE_CLASSLOADER_PROPERTY = "dexmaker.share_classloader";
+
+    private static Thread sOwningThread = null;
+
+    @Override
+    public Statement apply(Statement base, Description description) {
+        return apply(base::evaluate).toStatement();
+    }
+
+    /**
+     * Runs the runnable such that mocks created in it don't use a dedicated classloader.
+     *
+     * This allows mocking package-private methods.
+     *
+     * WARNING: This is absolutely incompatible with running tests in parallel!
+     */
+    public static void runWithDexmakerShareClassLoader(Runnable r) {
+        apply(r::run).run();
+    }
+
+    /**
+     * Returns a statement that first makes sure that only one thread at the time is modifying
+     * the property. Then actually sets the property, and runs the statement.
+     */
+    private static <T extends Throwable> ThrowingRunnable<T> apply(ThrowingRunnable<T> r) {
+        return wrapInMutex(wrapInSetAndClearProperty(r));
+    }
+
+    private static <T extends Throwable> ThrowingRunnable<T> wrapInSetAndClearProperty(
+            ThrowingRunnable<T> r) {
+        return () -> {
+            final String previousValue = System.getProperty(DEXMAKER_SHARE_CLASSLOADER_PROPERTY);
+            try {
+                System.setProperty(DEXMAKER_SHARE_CLASSLOADER_PROPERTY, "true");
+                r.run();
+            } finally {
+                if (previousValue != null) {
+                    System.setProperty(DEXMAKER_SHARE_CLASSLOADER_PROPERTY, previousValue);
+                } else {
+                    System.clearProperty(DEXMAKER_SHARE_CLASSLOADER_PROPERTY);
+                }
+            }
+        };
+    }
+
+    /**
+     * Runs the given statement, and while doing so prevents other threads from running statements.
+     */
+    private static <T extends Throwable> ThrowingRunnable<T> wrapInMutex(ThrowingRunnable<T> r) {
+        return () -> {
+            final boolean isOwner;
+            synchronized (DexmakerShareClassLoaderRule.class) {
+                isOwner = (sOwningThread == null);
+                if (isOwner) {
+                    sOwningThread = Thread.currentThread();
+                } else if (sOwningThread != Thread.currentThread()) {
+                    final RuntimeException e = new ConcurrentModificationException(
+                            "Tried to set dexmaker.share_classloader from " + Thread.currentThread()
+                                    + ", but was already set from " + sOwningThread);
+                    // Also log in case exception gets swallowed.
+                    Log.e(TAG, e.getMessage(), e);
+                    throw e;
+                }
+            }
+            try {
+                r.run();
+            } finally {
+                synchronized (DexmakerShareClassLoaderRule.class) {
+                    if (isOwner) {
+                        sOwningThread = null;
+                    }
+                }
+            }
+        };
+    }
+
+    private interface ThrowingRunnable<T extends Throwable> {
+        void run() throws T;
+
+        default Statement toStatement() {
+            return new Statement() {
+                @Override
+                public void evaluate() throws Throwable {
+                    ThrowingRunnable.this.run();
+                }
+            };
+        }
+    }
+}