1 files changed, 58 insertions, 0 deletions
diff --git a/src/com/android/documentsui/ThreadHelper.java b/src/com/android/documentsui/ThreadHelper.java
new file mode 100644
index 000000000..bb123b69b
--- /dev/null
+++ b/src/com/android/documentsui/ThreadHelper.java
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2020 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 com.android.documentsui;
+
+import android.os.Looper;
+
+/** Class for handler/thread utils. */
+public final class ThreadHelper {
+    private ThreadHelper() {
+    }
+
+    static final String MUST_NOT_ON_MAIN_THREAD_MSG =
+            "This method should not be called on main thread.";
+    static final String MUST_ON_MAIN_THREAD_MSG =
+            "This method should only be called on main thread.";
+
+    /** Verifies that current thread is not the UI thread. */
+    public static void assertNotOnMainThread() {
+        if (Looper.getMainLooper().getThread() == Thread.currentThread()) {
+            fatalAssert(MUST_NOT_ON_MAIN_THREAD_MSG);
+        }
+    }
+
+    /** Verifies that current thread is the UI thread. */
+    public static void assertOnMainThread() {
+        if (Looper.getMainLooper().getThread() != Thread.currentThread()) {
+            fatalAssert(MUST_ON_MAIN_THREAD_MSG);
+        }
+    }
+
+    /**
+     * Exceptions thrown in background threads are silently swallowed on Android. Use the
+     * uncaught exception handler of the UI thread to force the app to crash.
+     */
+    public static void fatalAssert(final String message) {
+        crashMainThread(new AssertionError(message));
+    }
+
+    private static void crashMainThread(Throwable t) {
+        Thread.UncaughtExceptionHandler uiThreadExceptionHandler =
+                Looper.getMainLooper().getThread().getUncaughtExceptionHandler();
+        uiThreadExceptionHandler.uncaughtException(Thread.currentThread(), t);
+    }
+}