kotlinify thread pool (#18366)

chore: Kotlinify thread pool

modules/react-native-status/android/src/main/java/im/status/ethereum/module/StatusThreadPoolExecutor.kt

@@ -0,0 +1,47 @@
+package im.status.ethereum.module
+
+import java.util.concurrent.*
+
+/**
+ * Uses an unbounded queue but allows timeout of core threads
+ * (modified case 2 in
+ * https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ThreadPoolExecutor.html )
+ */
+class StatusThreadPoolExecutor private constructor() {
+    private val NUMBER_OF_CORES: Int = Runtime.getRuntime().availableProcessors()
+    private val THREADS_TO_CORES_RATIO: Int = 100
+    private val KEEP_ALIVE_TIME: Int = 1
+    private val KEEP_ALIVE_TIME_UNIT: TimeUnit = TimeUnit.SECONDS
+
+    private val mQueue: BlockingQueue<Runnable> = LinkedBlockingQueue()
+    private val mThreadPool: ThreadPoolExecutor
+
+    init {
+        mThreadPool = ThreadPoolExecutor(
+                THREADS_TO_CORES_RATIO * NUMBER_OF_CORES,
+                THREADS_TO_CORES_RATIO * NUMBER_OF_CORES,
+                KEEP_ALIVE_TIME.toLong(),
+                KEEP_ALIVE_TIME_UNIT,
+                mQueue
+        )
+
+        // Allow pool to drain
+        mThreadPool.allowCoreThreadTimeOut(true)
+    }
+
+    /** Singleton holder */
+    private object Holder {
+        val instance = StatusThreadPoolExecutor()
+    }
+
+    companion object {
+        @JvmStatic
+        fun getInstance(): StatusThreadPoolExecutor {
+            return Holder.instance
+        }
+    }
+
+    fun execute(r: Runnable) {
+        mThreadPool.execute(r)
+    }
+}