Make thread related utility methods available for use in all modules.

core-util/src/main/java/org/signal/core/util/ThreadUtil.java

@@ -0,0 +1,90 @@
+package org.signal.core.util;
+
+import android.os.Handler;
+import android.os.Looper;
+
+import androidx.annotation.NonNull;
+
+import java.util.concurrent.CountDownLatch;
+
+/**
+ * Thread related utility functions.
+ */
+public final class ThreadUtil {
+
+  private static volatile Handler handler;
+
+  private ThreadUtil() {}
+
+  private static Handler getHandler() {
+    if (handler == null) {
+      synchronized (ThreadUtil.class) {
+        if (handler == null) {
+          handler = new Handler(Looper.getMainLooper());
+        }
+      }
+    }
+    return handler;
+  }
+
+  public static boolean isMainThread() {
+    return Looper.myLooper() == Looper.getMainLooper();
+  }
+
+  public static void assertMainThread() {
+    if (!isMainThread()) {
+      throw new AssertionError("Must run on main thread.");
+    }
+  }
+
+  public static void assertNotMainThread() {
+    if (isMainThread()) {
+      throw new AssertionError("Cannot run on main thread.");
+    }
+  }
+
+  public static void postToMain(final @NonNull Runnable runnable) {
+    getHandler().post(runnable);
+  }
+
+  public static void runOnMain(final @NonNull Runnable runnable) {
+    if (isMainThread()) runnable.run();
+    else                getHandler().post(runnable);
+  }
+
+  public static void runOnMainDelayed(final @NonNull Runnable runnable, long delayMillis) {
+    getHandler().postDelayed(runnable, delayMillis);
+  }
+
+  public static void cancelRunnableOnMain(@NonNull Runnable runnable) {
+    getHandler().removeCallbacks(runnable);
+  }
+
+  public static void runOnMainSync(final @NonNull Runnable runnable) {
+    if (isMainThread()) {
+      runnable.run();
+    } else {
+      final CountDownLatch sync = new CountDownLatch(1);
+      runOnMain(() -> {
+        try {
+          runnable.run();
+        } finally {
+          sync.countDown();
+        }
+      });
+      try {
+        sync.await();
+      } catch (InterruptedException ie) {
+        throw new AssertionError(ie);
+      }
+    }
+  }
+
+  public static void sleep(long millis) {
+    try {
+      Thread.sleep(millis);
+    } catch (InterruptedException e) {
+      throw new AssertionError(e);
+    }
+  }
+}