1 /*
2  * Copyright (C) 2017 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package androidx.arch.core.executor;
18 
19 import android.os.Build;
20 import android.os.Handler;
21 import android.os.Looper;
22 
23 import androidx.annotation.RequiresApi;
24 import androidx.annotation.RestrictTo;
25 
26 import org.jspecify.annotations.NonNull;
27 import org.jspecify.annotations.Nullable;
28 
29 import java.lang.reflect.InvocationTargetException;
30 import java.util.concurrent.ExecutorService;
31 import java.util.concurrent.Executors;
32 import java.util.concurrent.ThreadFactory;
33 import java.util.concurrent.atomic.AtomicInteger;
34 
35 /**
36  */
37 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP_PREFIX)
38 public class DefaultTaskExecutor extends TaskExecutor {
39 
40     private final Object mLock = new Object();
41 
42     private final ExecutorService mDiskIO = Executors.newFixedThreadPool(4, new ThreadFactory() {
43         private static final String THREAD_NAME_STEM = "arch_disk_io_";
44 
45         private final AtomicInteger mThreadId = new AtomicInteger(0);
46 
47         @Override
48         public Thread newThread(Runnable r) {
49             Thread t = new Thread(r);
50             t.setName(THREAD_NAME_STEM + mThreadId.getAndIncrement());
51             return t;
52         }
53     });
54 
55     private volatile @Nullable Handler mMainHandler;
56 
57     @Override
executeOnDiskIO(@onNull Runnable runnable)58     public void executeOnDiskIO(@NonNull Runnable runnable) {
59         mDiskIO.execute(runnable);
60     }
61 
62     @Override
postToMainThread(@onNull Runnable runnable)63     public void postToMainThread(@NonNull Runnable runnable) {
64         if (mMainHandler == null) {
65             synchronized (mLock) {
66                 if (mMainHandler == null) {
67                     mMainHandler = createAsync(Looper.getMainLooper());
68                 }
69             }
70         }
71         //noinspection ConstantConditions
72         mMainHandler.post(runnable);
73     }
74 
75     @Override
isMainThread()76     public boolean isMainThread() {
77         return Looper.getMainLooper().getThread() == Thread.currentThread();
78     }
79 
80     @SuppressWarnings("JavaReflectionMemberAccess")
createAsync(@onNull Looper looper)81     private static @NonNull Handler createAsync(@NonNull Looper looper) {
82         if (Build.VERSION.SDK_INT >= 28) {
83             return Api28Impl.createAsync(looper);
84         } else {
85             try {
86                 // This constructor was added as private in JB MR1:
87                 // https://android.googlesource.com/platform/frameworks/base/+/refs/heads/jb-mr1-release/core/java/android/os/Handler.java
88                 return Handler.class.getDeclaredConstructor(Looper.class, Handler.Callback.class,
89                         boolean.class)
90                         .newInstance(looper, null, true);
91             } catch (IllegalAccessException ignored) {
92             } catch (InstantiationException ignored) {
93             } catch (NoSuchMethodException ignored) {
94             } catch (InvocationTargetException e) {
95                 return new Handler(looper);
96             }
97         }
98         return new Handler(looper);
99     }
100 
101     @RequiresApi(28)
102     private static class Api28Impl {
Api28Impl()103         private Api28Impl() {
104             // Non-instantiable.
105         }
106 
createAsync(@onNull Looper looper)107         public static @NonNull Handler createAsync(@NonNull Looper looper) {
108             return Handler.createAsync(looper);
109         }
110     }
111 }
112