1 /*
2  * Copyright (C) 2013 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 com.android.server;
18 
19 import android.os.Handler;
20 import android.os.HandlerExecutor;
21 import android.os.Looper;
22 import android.os.Trace;
23 
24 import java.util.concurrent.Executor;
25 
26 /**
27  * Shared singleton foreground thread for the system.  This is a thread for regular
28  * foreground service operations, which shouldn't be blocked by anything running in
29  * the background.  In particular, the shared background thread could be doing
30  * relatively long-running operations like saving state to disk (in addition to
31  * simply being a background priority), which can cause operations scheduled on it
32  * to be delayed for a user-noticeable amount of time.
33  */
34 public final class FgThread extends ServiceThread {
35     private static final long SLOW_DISPATCH_THRESHOLD_MS = 100;
36     private static final long SLOW_DELIVERY_THRESHOLD_MS = 200;
37 
38     private static FgThread sInstance;
39     private static Handler sHandler;
40     private static HandlerExecutor sHandlerExecutor;
41 
FgThread()42     private FgThread() {
43         super("android.fg", android.os.Process.THREAD_PRIORITY_DEFAULT, true /*allowIo*/);
44     }
45 
ensureThreadLocked()46     private static void ensureThreadLocked() {
47         if (sInstance == null) {
48             sInstance = new FgThread();
49             sInstance.start();
50             final Looper looper = sInstance.getLooper();
51             looper.setTraceTag(Trace.TRACE_TAG_SYSTEM_SERVER);
52             looper.setSlowLogThresholdMs(
53                     SLOW_DISPATCH_THRESHOLD_MS, SLOW_DELIVERY_THRESHOLD_MS);
54             sHandler = makeSharedHandler(sInstance.getLooper());
55             sHandlerExecutor = new HandlerExecutor(sHandler);
56         }
57     }
58 
get()59     public static FgThread get() {
60         synchronized (FgThread.class) {
61             ensureThreadLocked();
62             return sInstance;
63         }
64     }
65 
getHandler()66     public static Handler getHandler() {
67         synchronized (FgThread.class) {
68             ensureThreadLocked();
69             return sHandler;
70         }
71     }
72 
getExecutor()73     public static Executor getExecutor() {
74         synchronized (FgThread.class) {
75             ensureThreadLocked();
76             return sHandlerExecutor;
77         }
78     }
79 }
80