in src/main/java/com/googlesource/gerrit/plugins/readonly/ReadOnlyState.java [40:46]
public void setReadOnly(boolean readOnly) throws IOException {
if (readOnly && !marker.exists()) {
Files.newOutputStream(marker.toPath(), StandardOpenOption.CREATE).close();
} else if (!readOnly && marker.exists()) {
Files.delete(marker.toPath());
}
}