Keep ChangeLock inteface and its only implementation in one file

shared/src/main/java/org/odk/collect/shared/locks/ChangeLock.kt

@@ -14,3 +14,36 @@ interface ChangeLock {
 
     fun unlock()
 }
+
+class ThreadSafeBooleanChangeLock : ChangeLock {
+    private var locked = false
+
+    override fun <T> withLock(function: Function<Boolean, T>): T {
+        val acquired = tryLock()
+
+        return try {
+            function.apply(acquired)
+        } finally {
+            if (acquired) {
+                unlock()
+            }
+        }
+    }
+
+    override fun tryLock(): Boolean {
+        return synchronized(this) {
+            if (locked) {
+                false
+            } else {
+                locked = true
+                true
+            }
+        }
+    }
+
+    override fun unlock() {
+        synchronized(this) {
+            locked = false
+        }
+    }
+}