Initial Upload

app/src/main/java/com/josh/trackcovid19v2/AppExecutors.java

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+package com.josh.trackcovid19v2;
+
+import android.os.Handler;
+import android.os.Looper;
+
+import androidx.annotation.NonNull;
+
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+
+/**
+ * Global executor pools for the whole application.
+ * <p>
+ * Grouping tasks like this avoids the effects of task starvation (e.g. disk reads don't wait behind
+ * webservice requests).
+ * <p>
+ * Creating a class like this is a way for android apps to handle non-trivial threading.
+ */
+public class AppExecutors {
+
+    // For Singleton instantiation
+    private static final Object LOCK = new Object();
+    private static AppExecutors sInstance;
+    private final Executor diskIO;
+    private final Executor mainThread;
+    private final Executor networkIO;
+
+    private AppExecutors(Executor diskIO, Executor networkIO, Executor mainThread) {
+        this.diskIO = diskIO;
+        this.networkIO = networkIO;
+        this.mainThread = mainThread;
+    }
+
+    public static AppExecutors getInstance() {
+        if (sInstance == null) {
+            synchronized (LOCK) {
+                sInstance = new AppExecutors(Executors.newSingleThreadExecutor(), Executors
+                        .newFixedThreadPool(3), new MainThreadExecutor());
+            }
+        }
+        return sInstance;
+    }
+
+    public Executor diskIO() {
+        return diskIO;
+    }
+
+    public Executor mainThread() {
+        return mainThread;
+    }
+
+    public Executor networkIO() {
+        return networkIO;
+    }
+
+    private static class MainThreadExecutor implements Executor {
+        private Handler mainThreadHandler = new Handler(Looper.getMainLooper());
+
+        @Override
+        public void execute(@NonNull Runnable command) {
+            mainThreadHandler.post(command);
+        }
+    }
+}