Fix CompositeMutex concurrent locking

app/src/test/java/org/koitharu/kotatsu/utils/CompositeMutexTest.kt

@@ -0,0 +1,39 @@
+package org.koitharu.kotatsu.utils
+
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.withTimeoutOrNull
+import kotlinx.coroutines.yield
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class CompositeMutexTest {
+
+	@Test
+	fun testSingleLock() = runTest {
+		val mutex = CompositeMutex<Int>()
+		mutex.lock(1)
+		mutex.lock(2)
+		mutex.unlock(1)
+		assert(mutex.size == 1)
+		mutex.unlock(2)
+		assert(mutex.isEmpty())
+	}
+
+	@Test
+	fun testDoubleLock() = runTest {
+		val mutex = CompositeMutex<Int>()
+		repeat(2) {
+			launch(Dispatchers.Default) {
+				mutex.lock(1)
+			}
+		}
+		yield()
+		mutex.unlock(1)
+		val tryLock = withTimeoutOrNull(1000) {
+			mutex.lock(1)
+		}
+		assertNull(tryLock)
+	}
+}