public void monitorEnter(Local<?> monitor) {
    addInstruction(
        new ThrowingInsn(
            Rops.MONITOR_ENTER, sourcePosition, RegisterSpecList.make(monitor.spec()), catches));
  }
Awaits the lock on {@code monitor}, and acquires it.
android/android_framework/dex-maker/src/main/java/com/android/dx/Code.java