Android之看“马达”如何贯通Android系统 (从硬件设计 --> 驱动 --> HAL --> JNI --> Framework --> Application)

在Android 2.3(Gingerbread) 系统的时候，我写过一篇关于“Android 震动马达系统“的文章，当时的Linux内核还是2.6版本的。写那篇文章的目的，是想彻底的了解从硬件到驱动，再到应用的运作流程。完成了之后，文章一直仍在草稿箱里面没发表；今天看到，决定整理一下，重新发表。目的是想和大家分享自己对Android系统的一点认识：以马达为代表，来考究“Android是如何一步步工作的。它从硬件设计，到Linux驱动，再到HAL，再到JNI，再到Framework，最后到被应用调用，这整套的流程到底是怎么样的！”

转载请注明出处：http://www.cnblogs.com/skywang12345/p/3404808.html

Part 1 马达的硬件设计

马达的震动原理很简单，给马达通电，马达就能震动。至于马达是如何工作，如何将电能转化为机械能，这不是我们关心的重点。但是，我们要需要了解如何控制马达的通电。在硬件上，我们是通过一个IO口(GPIO)去控制；对于马达而言，我们可以将IO理解为一个开关。当开关合上时，马达震动；开关断开，马达停止震动。

GPIO(General Purpose Input Output)，称为通用输入/输出。它可以被配置为中断、输入、输出等类型，从而对各个IO进行控制。对于马达而已，GPIO就相当于一个开关。下面看看硬件原理图中的马达部分，如下图：

注：上面原理图对应CPU是“三星A8”。不同平台的马达，马达的接法和GPIO都不一样；但原理都是类似的。

原理图中红线标注部分的含义：GPH3_3是马达的GPIO。三星A8中有很多组GPIO，而马达对应和GPH3_3连接。

Part 2 马达的驱动代码

知道马达的硬件设计之后，我们就可以进行Linux Driver开发工作，也就是编写马达的驱动。Linux的一个非常重要的特点，一切都是文件！而我们进行Linux Driver开发的目的，就是将硬件设备映射成一个文件；然后，我们可以通过操作文件，来操作对应的硬件设备。

OK！理解了驱动的作用和原理之后，我们接下来开发讲解马达的驱动开发。

1. Datasheet中相关信息

我们知道，马达是通过GPIO去控制；接下来，我们就是找到马达对应的GPIO信息，然后控制该GPIO即可。

通过马达的原理图，我们知道马达和GPH3_3相连接。我们查阅“三星A8 的Datasheet”，查找GPH3_3的相关信息。

   所谓Datasheet，就是CPU芯片的数据手册。
   上面记载了CPU的功能特性和操作方式等信息。任何一个厂家在发布它的芯片时，都会提供对应的Datasheet给它的客户；客户根据Datasheet上面所描述的CPU的特性，就可以进行相关的开发(当然，实际开发中可能还需要芯片厂商的支持)。例如，国内手机都是采用MTK平台，对于MTK方案开发商来说，它要开发MTK6577的产品。那么首先，MTK原厂会提供一份MTK6577的BSP包，BSP包中包括了MTK6577的Datasheet，也就是该芯片的数据手册。方案开发商有任何关于MTK6577的问题，都可以查阅该Datasheet。

三星A8的Datasheet中，关于GPH3_3的信息如下：

说明：

(01) GPH3_3对应CPU中的寄存器是GPH3CON[3]。

(02) [15:12] 表示寄存器的第12~15位，一个寄存器共32 bits。而第三列的 0000, 0001, 0010, 0011, 1111表示“寄存器取不同值的时候，该GPIO的功能”。

例如， 0000表示将该GPIO作为输入，0001表示将GPIO作为输出，1111表示将该GPIO作为中断。

前面，我们已经说过，操作马达就是相当与将它作为一个开关操作。因此，我们需要将马达的GPIO设为“输入”类型；然后输入1，相当于开启马达；输入0，则是关闭马达！

下面，我们需要做的就是在Driver中将GPH3_3(也就是GPH3CON[3])映射为一个文件节点，并将它配置为“输入”类型，即将GPH3CON[3]的寄存器值设为0000。

2. 马达的驱动

我们编写马达驱动(drivers/misc/misc_sysfs.c)，将马达(vibrator)注册道platform总线上。源码如下：

  1 #include <linux/kernel.h>
  2 #include <linux/types.h>
  3 #include <linux/module.h>
  4 #include <linux/device.h>
  5 #include <linux/platform_device.h>
  6 #include <linux/delay.h>
  7 #include <linux/irq.h>
  8 #include <linux/interrupt.h>
  9 #include <linux/sysfs.h>
 10 #include <linux/input.h>
 11 #include <mach/gpio.h>
 12 
 13 // vibrator 对应的GPIO
 14 #define  VIBRATOR_POWER_PORT (S5PV210_GPH3(3))
 15 
 16 typedef struct combo_module__t    {
 17     unsigned char            status_vibrator;
 18 }    combo_module_t    ;
 19 
 20 static combo_module_t combo_module;
 21 
 22 /*
 23  * vibrator初始化函数：申请GPIO，并初始化vibrator状态。
 24  */
 25 static void combo_module_init(void)
 26 {
 27     if(gpio_request(VIBRATOR_POWER_PORT, "vibrator power"))    {
 28         printk("misc_sysfs.c request vibrator gpio failse.
");
 29     }
 30     gpio_pull_updown(VIBRATOR_POWER_PORT, PullDisable);
 31       gpio_direction_output(VIBRATOR_POWER_PORT, GPIO_LOW);    
 32 
 33     combo_module.status_vibrator  = 0;
 34 }
 35 
 36 /*
 37  * vibrator控制函数
 38  */
 39 staticvoid combo_module_control(void)
 40 {
 41     if(combo_module.status_vibrator)
 42     {
 43         gpio_direction_output(VIBRATOR_POWER_PORT, GPIO_HIGH);
 44     }
 45     else    
 46     {
 47         gpio_direction_output(VIBRATOR_POWER_PORT, GPIO_LOW);
 48     }
 49 
 50 }
 51 
 52 
 53 ///////////////////////////////////////////////////////////////////////////////////////////////////////////
 54 
 55 static ssize_t show_vibrator_onoff (struct device *dev, struct device_attribute *attr, char *buf)
 56 {
 57     return    sprintf(buf, "%d
", combo_module.status_vibrator);
 58 }
 59 
 60 static ssize_t set_vibrator_onoff (struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
 61 {
 62      unsigned int    val;
 63 
 64     if(!(sscanf(buf, "%u
", &val)))     return    -EINVAL;
 65 
 66     //printk("set_vibrator_onoff:%d
",val);
 67 
 68     if(!val )    
 69     {
 70         combo_module.status_vibrator = 0;
 71         combo_module_control();
 72     }
 73     else        
 74     {
 75         combo_module.status_vibrator = 1;
 76         combo_module_control();
 77 
 78         msleep(val);
 79 
 80         combo_module.status_vibrator = 0;
 81         combo_module_control();
 82     }
 83     
 84     return count;
 85 }
 86 
 87 static    ssize_t show_vibrator_onoff    (struct device *dev, struct device_attribute *attr, char *buf);
 88 static     ssize_t set_vibrator_onoff    (struct device *dev, struct device_attribute *attr, const char *buf, size_t count);
 89 // 将vibrator注册到sysfs文件系统。
 90 // 参数说明：
 91 //       vibrator_onoff      : vibrator对应在sysfs下的文件节点名称
 92 //       S_IRWXUGO           : 文件节点的属性
 93 //       show_vibrator_onoff : 对应的读函数
 94 //       set_vibrator_onoff  : 对应的写函数
 95 static DEVICE_ATTR(vibrator_onoff, S_IRWXUGO, show_vibrator_onoff, set_vibrator_onoff);
 96 
 97 
 98 static struct attribute *control_sysfs_entries[] = {
 99     &dev_attr_vibrator_onoff.attr,
100     NULL
101 };
102 
103 static struct attribute_group control_sysfs_attr_group = {
104     .name   = NULL,
105     .attrs  = control_sysfs_entries,
106 };
107 
108 static int control_sysfs_probe(struct platform_device *pdev)    
109 {
110     printk("vibrator probe");
111     combo_module_init();
112     combo_module_control();
113     return    sysfs_create_group(&pdev->dev.kobj, &control_sysfs_attr_group);
114 }
115 
116 staticint control_sysfs_remove(struct platform_device *pdev)    
117 {
118     sysfs_remove_group(&pdev->dev.kobj, &control_sysfs_attr_group);
119     
120     return    0;
121 }
122 
123 #ifdef CONFIG_PM
124 static int control_sysfs_resume(struct platform_device *dev)
125 {
126 
127     combo_module_control();
128 
129     return  0;
130 }
131 
132 static int control_sysfs_suspend(struct platform_device *dev, pm_message_t state)
133 {
134     
135     combo_module_control();
136     
137     return  0;
138 }
139 #else
140 #define control_sysfs_suspend NULL
141 #define control_sysfs_resume NULL
142 #endif
143 
144 
145 static struct platform_driver control_sysfs_driver = {
146     .driver = {
147         .name = "misc_ctl",
148         .owner = THIS_MODULE,
149     },
150     .probe         = control_sysfs_probe,
151     .remove     = control_sysfs_remove,
152     .suspend    = control_sysfs_suspend,
153     .resume        = control_sysfs_resume,
154 };
155 
156 static int __init control_sysfs_init(void)
157 {    
158     // 将vibrator注册到platform总线
159     printk("vibrator init");
160     return platform_driver_register(&control_sysfs_driver);
161 }
162 
163 static void __exit control_sysfs_exit(void)
164 {
165    platform_driver_unregister(&control_sysfs_driver);
166 }
167 
168 
169 module_init(control_sysfs_init);
170 module_exit(control_sysfs_exit);
171 
172 
173 MODULE_DESCRIPTION("misc control driver");
174 MODULE_AUTHOR("other");
175 MODULE_LICENSE("GPL");

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说明：

若您熟悉驱动开发，应该很容易理解上面的代码。不熟悉也不要紧，您只需要了解“Linux系统中，一切都是文件”，上面代码的作用是，

将马达(vibrator)映射到“/sys/devices/platform/misc_ctl/vibrator_onoff”文件上，我们可以通过读写vibrator_onoff来操作马达的开启和关闭。

有了马达的源码之后，我们还需要将该源码编译到Linux内核中。这就是通过Kconfig和Makefile来完成的，关于Kconfig和Makefile的知识，这里就不过多说明了。目前您只需要了解，通过Kconfig和Makefile，我们能将马达驱动编译到内核中，该驱动会在驱动加载的时候自动运行就可以了！

马达对应的Kconfig(driver/misc/Kconfig)内容如下：

config MISC_VIBRATOR
       tristate"misc vabrator"
       default y

马达对应的Makefile(driver/misc/Makefile)内容如下：

obj-$(CONFIG_MISC_VIBRATOR)   += misc_sysfs.o

至此，我们已经完成马达的驱动开发了！也就是说，我们已经成功的将马达映射到文件节点上；接下来，我们通过操作文件节点，就可以操作马达了。下面从HAL层到Framework曾，都是基于Android4.2系统进行说明的。

Part 3 马达的HAL实现

HAL (Hardware Abstraction Layer), 又称为“硬件抽象层”。在Linux驱动中，我们已经将马达设为映射为文件了；而该HAL层的存在的意义，就是“对设备文件进行操作，从而相当于硬件进行操作”。HAL层的作用，一是操作硬件设备，二是操作接口封装，外界能方便的使用HAL提供的接口直接操作硬件设备。

理解了HAL之后，我们看看Android中如何在HAL层对马达进行操作。

在Android系统中，我们在libhardware_legacy中，实现马达的HAL层控制。
马达在HAL中的代码路径：hardware/libhardware_legacy/vibrator/vibrator.c

vibrator.c的代码如下：

 1 /*
 2  * Copyright (C) 2008 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 #include <hardware_legacy/vibrator.h>
17 #include "qemu.h"
18 
19 #include <stdio.h>
20 #include <unistd.h>
21 #include <fcntl.h>
22 #include <errno.h>
23 
24 #define THE_DEVICE "/sys/devices/platform/misc_ctl/vibrator_onoff"
25 
26 int vibrator_exists()
27 {
28     int fd;
29 
30 #ifdef QEMU_HARDWARE
31     if (qemu_check()) {
32         return 1;
33     }
34 #endif
35 
36     fd = open(THE_DEVICE, O_RDWR);
37     if(fd < 0)
38         return 0;
39     close(fd);
40     return 1;
41 }
42 
43 static int sendit(int timeout_ms)
44 {
45     int nwr, ret, fd;
46     char value[20];
47 
48 #ifdef QEMU_HARDWARE
49     if (qemu_check()) {
50         return qemu_control_command( "vibrator:%d", timeout_ms );
51     }
52 #endif
53 
54     fd = open(THE_DEVICE, O_RDWR);
55     if(fd < 0)
56         return errno;
57 
58     nwr = sprintf(value, "%d
", timeout_ms);
59     ret = write(fd, value, nwr);
60 
61     close(fd);
62 
63     return (ret == nwr) ? 0 : -1;
64 }
65 
66 int vibrator_on(int timeout_ms)
67 {
68     /* constant on, up to maximum allowed time */
69     return sendit(timeout_ms);
70 }
71 
72 int vibrator_off()
73 {
74     return sendit(0);
75 }

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在kernel的驱动中，我们已经将马达注册到sys文件系统中(/sys/devices/platform/misc_ctl/vibrator_onoff)。在vibrator.c中，我们就是通过读写“vibrator_onoff文件节点”来实现对马达的操作。

Part 4 马达的JNI部分

1 马达的JNI实现

JNI(Java Native Interface)，中文是“Java本地接口”。

JNI是Java中一种技术，它存在的意义，是保证本地代码(C/C++代码)能在任何Java虚拟机下工作。简单点说，Java通过JNI接口，能够调用到C/C++代码。关于“JNI的更多内容”，请参考“Android JNI和NDK学习系列文章”。

在了解了vibrator的HAL层实现之后，我们再来看看android是如何通过JNI将震动马达注册到android系统中。马达对应的JNI层代码路径如下：frameworks/base/services/jni/com_android_server_VibratorService.cpp

com_android_server_VibratorService.cpp的源码如下：

 1 /*
 2  * Copyright (C) 2009 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 #define LOG_TAG "VibratorService"
18 
19 #include "jni.h"
20 #include "JNIHelp.h"
21 #include "android_runtime/AndroidRuntime.h"
22 
23 #include <utils/misc.h>
24 #include <utils/Log.h>
25 #include <hardware_legacy/vibrator.h>
26 
27 #include <stdio.h>
28 
29 namespace android
30 {
31 
32 static jboolean vibratorExists(JNIEnv *env, jobject clazz)
33 {
34     return vibrator_exists() > 0 ? JNI_TRUE : JNI_FALSE;
35 }
36 
37 static void vibratorOn(JNIEnv *env, jobject clazz, jlong timeout_ms)
38 {
39     // ALOGI("vibratorOn
");
40     vibrator_on(timeout_ms);
41 }
42 
43 static void vibratorOff(JNIEnv *env, jobject clazz)
44 {
45     // ALOGI("vibratorOff
");
46     vibrator_off();
47 }
48 
49 static JNINativeMethod method_table[] = {
50     { "vibratorExists", "()Z", (void*)vibratorExists },
51     { "vibratorOn", "(J)V", (void*)vibratorOn },
52     { "vibratorOff", "()V", (void*)vibratorOff }
53 };
54 
55 int register_android_server_VibratorService(JNIEnv *env)
56 {
57     return jniRegisterNativeMethods(env, "com/android/server/VibratorService",
58             method_table, NELEM(method_table));
59 }
60 
61 };

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下面，对这部分的JNI代码进行简单说明。

(01) 通过 jniRegisterNativeMethods()，我们将method_table中的方法注册到 com.android.server.VibratorService.java 中。配对表格如下：

---------------------------------------------------++++-------------------------------------------
             VibratorService.java                          com_android_server_VibratorService.cpp   
native static boolean vibratorExists();                static jboolean vibratorExists(JNIEnv *env, jobject clazz)
native static void vibratorOn(long milliseconds);      static void vibratorOn(JNIEnv *env, jobject clazz, jlong timeout_ms)
native static void vibratorOff();                      static void vibratorOff(JNIEnv *env, jobject clazz)

通过JNI，我们就能将Java层和HAL层的代码联系起来。
以vibratorOff()来说，我们在VibratorService.java中调用vibratorOff()；实际上会调用到com_android_server_VibratorService.cpp中的vibratorOff()函数；进一步会调用到vibrator_off()函数，而vibrator_off()是我们在 “HAL层的vibrator.c中的接口”。

2 马达的JNI如何和HAL关联方式

在继续接下来的研究之前，我们先搞清楚：JNI如何和HAL层代码关联起来的。即com_android_server_VibratorService.cpp是如何调用到vibrator.c中的代码的。
实际上道理很简单，我们先将vibrator.c封装成.so库；然后在com_android_server_VibratorService.cpp中导入该库，就可以调用vibrator.c的接口了。下面，看看Android中具体是如何做到的。

(01) vibrator.c封装到libhardware_legacy.so中的步骤

在hardware/libhardware_legacy/vibrator/Android.mk中，会将vibrator.c添加到 LOCAL_SRC_FILES 变量中。
hardware/libhardware_legacy/vibrator/Android.mk源码如下：

LOCAL_SRC_FILES += vibrator/vibrator.c

在hardware/libhardware_legacy/Android.mk中，它会调用子目录的Android.mk并将它们导入当前的Android.mk中。
hardware/libhardware_legacy/Android.mk源码如下：

legacy_modules := power uevent vibrator wifi qemu qemu_tracing

SAVE_MAKEFILES := $(call all-named-subdir-makefiles,$(legacy_modules))
LEGACY_AUDIO_MAKEFILES := $(call all-named-subdir-makefiles,audio)

include $(SAVE_MAKEFILES)

...

LOCAL_MODULE:= libhardware_legacy

include $(BUILD_SHARED_LIBRARY)

在“我们编译Android系统”或“通过 mmm hardware/libhardware_legacy进行模块编译”的时候，就会生成库libhardware_legacy.so；而且vibrator.c被包含在该库中。

(02) 在 com_android_server_VibratorService.cpp 对应的Android.mk中，会导入libhardware_legacy.so。
com_android_server_VibratorService.cpp 对应的frameworks/base/services/jni/Android.mk 的源码如下：

LOCAL_SRC_FILES:= 
com_android_server_VibratorService.cpp 
...

LOCAL_SHARED_LIBRARIES := 
libhardware_legacy 
...


LOCAL_MODULE:= libandroid_servers

include $(BUILD_SHARED_LIBRARY)

Part 5 马达的Framework层实现

应用层操作马达，是通过马达服务进行操作的。而马达服务是通过aidl实现的，aidl是Android进程间的通信方式。关于aidl的更多说明可以参考“Android Service总结06 之AIDL”。

马达服务涉及的主要文件如下：

1 frameworks/base/services/java/com/android/server/SystemServer.java
2 frameworks/base/services/java/com/android/server/VibratorService.java
3 frameworks/base/core/java/android/os/IVibratorService.aidl
4 frameworks/base/core/java/android/os/Vibrator.java
5 frameworks/base/core/java/android/os/SystemVibrator.java

下面，对这几个文件的功能进行简要说明。

文件1: SystemServer.java
它是系统服务，作用是启动、管理系统服务，包括“马达服务、Wifi服务、Activity管理服务”等等。
SystemServer是通过Zygote启动的，而Zygote又是在init中启动的，init则是kernel加载完毕之后启动的第一个进程。在这里，我们只需要知道“SystemServer是用来启动/管理马达服务即可。”

文件2: IVibratorService.aidl
它是马达服务对应的aidl配置文件。我们在aidl中定义了其它进程可以访问的外部接口；然后再通过VibratorService.java实现这些接口。

文件3: VibratorService.java
它是马达服务对应的aidl接口的实现程序。它实现IVibratorService.aidl的接口，从而实现马达服务；它的函数接口，是通过调用JNI层对应的马达控制函数来实现的。

文件4: Vibrator.java
它是马达服务开放给应用层的调用类。理论上讲，我们完全可以通过aidl直接调用马达服务，而不需要Vibrator.java类。但是！既然它存在，就肯定有它的理由。事实的确如此，Google之所以这么做。有以下几个原因：
第一，提供统一而且方便的服务调用方式。这里的“统一”，是指和所有其它的系统服务一样，我们调用服务时，需先通过getSystemService()获取服务，然后再调用服务的函数接口。这里的“方便”，是指若我们直接通过aidl调用，操作比较繁琐(若你用过aidl就会知道，需要先实现ServiceConnection接口以获取IBinder对象，然后再通过IBinder对象调用aidl的接口)；而Vibrator.java封装之后的接口，将许多细节都隐藏了，非常便于应用者调用！
第二，基于安全的考虑。Vibrator.java封装隐藏了许多细节，而这些都是应用开发者不必要知道的。
第三，Vibrator是抽象类。它便于我们支持不同类型的马达：包括“将马达直接映射到文件”以及“将马达注册到输入子系统”中。

文件5: SystemVibrator.java
它是Vibrator.java的子类，实现了马达的服务接口。

下面，我们继续Read The Fucking Source Code，加深对上面知识的理解。

1 SystemServer.java

在frameworks/base/services/java/com/android/server/SystemServer.java中关于马达的代码如下：

 1 {
 2     VibratorService vibrator = null;
 3 
 4     Slog.i(TAG, "Vibrator Service");
 5     vibrator = new VibratorService(context);
 6     ServiceManager.addService("vibrator", vibrator);
 7 
 8     ...
 9 
10     try {
11         vibrator.systemReady();
12     } catch (Throwable e) {
13         reportWtf("making Vibrator Service ready", e);
14     }
15 }

从中，我们知道：
(01) SystemServer中会通过VibratorService()新建马达服务，并将其添加到ServiceManager中。
(02) 在Android系统启动完成之后，SystemServer会调用vibrator.systemReady()。

2 IVibratorService.aidl

在查看VibratorService.java之前，我们先看看它对应的aidl文件。frameworks/base/core/java/android/os/IVibratorService.aidl源码如下：

 1 package android.os;
 2 
 3 /** {@hide} */
 4 interface IVibratorService
 5 {
 6     boolean hasVibrator();
 7     void vibrate(long milliseconds, IBinder token);
 8     void vibratePattern(in long[] pattern, int repeat, IBinder token);
 9     void cancelVibrate(IBinder token);
10 }

3 VibratorService.java

frameworks/base/services/java/com/android/server/VibratorService.java源码如下：

  1 /*
  2  * Copyright (C) 2008 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.content.BroadcastReceiver;
 20 import android.content.Context;
 21 import android.content.Intent;
 22 import android.content.IntentFilter;
 23 import android.content.pm.PackageManager;
 24 import android.database.ContentObserver;
 25 import android.hardware.input.InputManager;
 26 import android.os.Handler;
 27 import android.os.IVibratorService;
 28 import android.os.PowerManager;
 29 import android.os.Process;
 30 import android.os.RemoteException;
 31 import android.os.IBinder;
 32 import android.os.Binder;
 33 import android.os.SystemClock;
 34 import android.os.UserHandle;
 35 import android.os.Vibrator;
 36 import android.os.WorkSource;
 37 import android.provider.Settings;
 38 import android.provider.Settings.SettingNotFoundException;
 39 import android.util.Slog;
 40 import android.view.InputDevice;
 41 
 42 import java.util.ArrayList;
 43 import java.util.LinkedList;
 44 import java.util.ListIterator;
 45 
 46 public class VibratorService extends IVibratorService.Stub
 47         implements InputManager.InputDeviceListener {
 48     private static final String TAG = "VibratorService";
 49 
 50     private final LinkedList<Vibration> mVibrations;
 51     private Vibration mCurrentVibration;
 52     private final WorkSource mTmpWorkSource = new WorkSource();
 53     private final Handler mH = new Handler();
 54 
 55     private final Context mContext;
 56     private final PowerManager.WakeLock mWakeLock;
 57     private InputManager mIm;
 58 
 59     volatile VibrateThread mThread;
 60 
 61     // mInputDeviceVibrators lock should be acquired after mVibrations lock, if both are
 62     // to be acquired
 63     private final ArrayList<Vibrator> mInputDeviceVibrators = new ArrayList<Vibrator>();
 64     private boolean mVibrateInputDevicesSetting; // guarded by mInputDeviceVibrators
 65     private boolean mInputDeviceListenerRegistered; // guarded by mInputDeviceVibrators
 66 
 67     native static boolean vibratorExists();
 68     native static void vibratorOn(long milliseconds);
 69     native static void vibratorOff();
 70 
 71     private class Vibration implements IBinder.DeathRecipient {
 72         private final IBinder mToken;
 73         private final long    mTimeout;
 74         private final long    mStartTime;
 75         private final long[]  mPattern;
 76         private final int     mRepeat;
 77         private final int     mUid;
 78 
 79         Vibration(IBinder token, long millis, int uid) {
 80             this(token, millis, null, 0, uid);
 81         }
 82 
 83         Vibration(IBinder token, long[] pattern, int repeat, int uid) {
 84             this(token, 0, pattern, repeat, uid);
 85         }
 86 
 87         private Vibration(IBinder token, long millis, long[] pattern,
 88                 int repeat, int uid) {
 89             mToken = token;
 90             mTimeout = millis;
 91             mStartTime = SystemClock.uptimeMillis();
 92             mPattern = pattern;
 93             mRepeat = repeat;
 94             mUid = uid;
 95         }
 96 
 97         public void binderDied() {
 98             synchronized (mVibrations) {
 99                 mVibrations.remove(this);
100                 if (this == mCurrentVibration) {
101                     doCancelVibrateLocked();
102                     startNextVibrationLocked();
103                 }
104             }
105         }
106 
107         public boolean hasLongerTimeout(long millis) {
108             if (mTimeout == 0) {
109                 // This is a pattern, return false to play the simple
110                 // vibration.
111                 return false;
112             }
113             if ((mStartTime + mTimeout)
114                     < (SystemClock.uptimeMillis() + millis)) {
115                 // If this vibration will end before the time passed in, let
116                 // the new vibration play.
117                 return false;
118             }
119             return true;
120         }
121     }
122 
123     VibratorService(Context context) {
124         // Reset the hardware to a default state, in case this is a runtime
125         // restart instead of a fresh boot.
126         vibratorOff();
127 
128         mContext = context;
129         PowerManager pm = (PowerManager)context.getSystemService(
130                 Context.POWER_SERVICE);
131         mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "*vibrator*");
132         mWakeLock.setReferenceCounted(true);
133 
134         mVibrations = new LinkedList<Vibration>();
135 
136         IntentFilter filter = new IntentFilter();
137         filter.addAction(Intent.ACTION_SCREEN_OFF);
138         context.registerReceiver(mIntentReceiver, filter);
139     }
140 
141     public void systemReady() {
142         mIm = (InputManager)mContext.getSystemService(Context.INPUT_SERVICE);
143 
144         mContext.getContentResolver().registerContentObserver(
145                 Settings.System.getUriFor(Settings.System.VIBRATE_INPUT_DEVICES), true,
146                 new ContentObserver(mH) {
147                     @Override
148                     public void onChange(boolean selfChange) {
149                         updateInputDeviceVibrators();
150                     }
151                 }, UserHandle.USER_ALL);
152 
153         mContext.registerReceiver(new BroadcastReceiver() {
154             @Override
155             public void onReceive(Context context, Intent intent) {
156                 updateInputDeviceVibrators();
157             }
158         }, new IntentFilter(Intent.ACTION_USER_SWITCHED), null, mH);
159 
160         updateInputDeviceVibrators();
161     }
162 
163     public boolean hasVibrator() {
164         return doVibratorExists();
165     }
166 
167     public void vibrate(long milliseconds, IBinder token) {
168         if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.VIBRATE)
169                 != PackageManager.PERMISSION_GRANTED) {
170             throw new SecurityException("Requires VIBRATE permission");
171         }
172         int uid = Binder.getCallingUid();
173         // We're running in the system server so we cannot crash. Check for a
174         // timeout of 0 or negative. This will ensure that a vibration has
175         // either a timeout of > 0 or a non-null pattern.
176         if (milliseconds <= 0 || (mCurrentVibration != null
177                 && mCurrentVibration.hasLongerTimeout(milliseconds))) {
178             // Ignore this vibration since the current vibration will play for
179             // longer than milliseconds.
180             return;
181         }
182 
183         Vibration vib = new Vibration(token, milliseconds, uid);
184         synchronized (mVibrations) {
185             removeVibrationLocked(token);
186             doCancelVibrateLocked();
187             mCurrentVibration = vib;
188             startVibrationLocked(vib);
189         }
190     }
191 
192     private boolean isAll0(long[] pattern) {
193         int N = pattern.length;
194         for (int i = 0; i < N; i++) {
195             if (pattern[i] != 0) {
196                 return false;
197             }
198         }
199         return true;
200     }
201 
202     public void vibratePattern(long[] pattern, int repeat, IBinder token) {
203         if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.VIBRATE)
204                 != PackageManager.PERMISSION_GRANTED) {
205             throw new SecurityException("Requires VIBRATE permission");
206         }
207         int uid = Binder.getCallingUid();
208         // so wakelock calls will succeed
209         long identity = Binder.clearCallingIdentity();
210         try {
211             if (false) {
212                 String s = "";
213                 int N = pattern.length;
214                 for (int i=0; i<N; i++) {
215                     s += " " + pattern[i];
216                 }
217                 Slog.i(TAG, "vibrating with pattern: " + s);
218             }
219 
220             // we're running in the server so we can't fail
221             if (pattern == null || pattern.length == 0
222                     || isAll0(pattern)
223                     || repeat >= pattern.length || token == null) {
224                 return;
225             }
226 
227             Vibration vib = new Vibration(token, pattern, repeat, uid);
228             try {
229                 token.linkToDeath(vib, 0);
230             } catch (RemoteException e) {
231                 return;
232             }
233 
234             synchronized (mVibrations) {
235                 removeVibrationLocked(token);
236                 doCancelVibrateLocked();
237                 if (repeat >= 0) {
238                     mVibrations.addFirst(vib);
239                     startNextVibrationLocked();
240                 } else {
241                     // A negative repeat means that this pattern is not meant
242                     // to repeat. Treat it like a simple vibration.
243                     mCurrentVibration = vib;
244                     startVibrationLocked(vib);
245                 }
246             }
247         }
248         finally {
249             Binder.restoreCallingIdentity(identity);
250         }
251     }
252 
253     public void cancelVibrate(IBinder token) {
254         mContext.enforceCallingOrSelfPermission(
255                 android.Manifest.permission.VIBRATE,
256                 "cancelVibrate");
257 
258         // so wakelock calls will succeed
259         long identity = Binder.clearCallingIdentity();
260         try {
261             synchronized (mVibrations) {
262                 final Vibration vib = removeVibrationLocked(token);
263                 if (vib == mCurrentVibration) {
264                     doCancelVibrateLocked();
265                     startNextVibrationLocked();
266                 }
267             }
268         }
269         finally {
270             Binder.restoreCallingIdentity(identity);
271         }
272     }
273 
274     private final Runnable mVibrationRunnable = new Runnable() {
275         public void run() {
276             synchronized (mVibrations) {
277                 doCancelVibrateLocked();
278                 startNextVibrationLocked();
279             }
280         }
281     };
282 
283     // Lock held on mVibrations
284     private void doCancelVibrateLocked() {
285         if (mThread != null) {
286             synchronized (mThread) {
287                 mThread.mDone = true;
288                 mThread.notify();
289             }
290             mThread = null;
291         }
292         doVibratorOff();
293         mH.removeCallbacks(mVibrationRunnable);
294     }
295 
296     // Lock held on mVibrations
297     private void startNextVibrationLocked() {
298         if (mVibrations.size() <= 0) {
299             mCurrentVibration = null;
300             return;
301         }
302         mCurrentVibration = mVibrations.getFirst();
303         startVibrationLocked(mCurrentVibration);
304     }
305 
306     // Lock held on mVibrations
307     private void startVibrationLocked(final Vibration vib) {
308         if (vib.mTimeout != 0) {
309             doVibratorOn(vib.mTimeout);
310             mH.postDelayed(mVibrationRunnable, vib.mTimeout);
311         } else {
312             // mThread better be null here. doCancelVibrate should always be
313             // called before startNextVibrationLocked or startVibrationLocked.
314             mThread = new VibrateThread(vib);
315             mThread.start();
316         }
317     }
318 
319     // Lock held on mVibrations
320     private Vibration removeVibrationLocked(IBinder token) {
321         ListIterator<Vibration> iter = mVibrations.listIterator(0);
322         while (iter.hasNext()) {
323             Vibration vib = iter.next();
324             if (vib.mToken == token) {
325                 iter.remove();
326                 unlinkVibration(vib);
327                 return vib;
328             }
329         }
330         // We might be looking for a simple vibration which is only stored in
331         // mCurrentVibration.
332         if (mCurrentVibration != null && mCurrentVibration.mToken == token) {
333             unlinkVibration(mCurrentVibration);
334             return mCurrentVibration;
335         }
336         return null;
337     }
338 
339     private void unlinkVibration(Vibration vib) {
340         if (vib.mPattern != null) {
341             // If Vibration object has a pattern,
342             // the Vibration object has also been linkedToDeath.
343             vib.mToken.unlinkToDeath(vib, 0);
344         }
345     }
346 
347     private void updateInputDeviceVibrators() {
348         synchronized (mVibrations) {
349             doCancelVibrateLocked();
350 
351             synchronized (mInputDeviceVibrators) {
352                 mVibrateInputDevicesSetting = false;
353                 try {
354                     mVibrateInputDevicesSetting = Settings.System.getIntForUser(
355                             mContext.getContentResolver(),
356                             Settings.System.VIBRATE_INPUT_DEVICES, UserHandle.USER_CURRENT) > 0;
357                 } catch (SettingNotFoundException snfe) {
358                 }
359 
360                 if (mVibrateInputDevicesSetting) {
361                     if (!mInputDeviceListenerRegistered) {
362                         mInputDeviceListenerRegistered = true;
363                         mIm.registerInputDeviceListener(this, mH);
364                     }
365                 } else {
366                     if (mInputDeviceListenerRegistered) {
367                         mInputDeviceListenerRegistered = false;
368                         mIm.unregisterInputDeviceListener(this);
369                     }
370                 }
371 
372                 mInputDeviceVibrators.clear();
373                 if (mVibrateInputDevicesSetting) {
374                     int[] ids = mIm.getInputDeviceIds();
375                     for (int i = 0; i < ids.length; i++) {
376                         InputDevice device = mIm.getInputDevice(ids[i]);
377                         Vibrator vibrator = device.getVibrator();
378                         if (vibrator.hasVibrator()) {
379                             mInputDeviceVibrators.add(vibrator);
380                         }
381                     }
382                 }
383             }
384 
385             startNextVibrationLocked();
386         }
387     }
388 
389     @Override
390     public void onInputDeviceAdded(int deviceId) {
391         updateInputDeviceVibrators();
392     }
393 
394     @Override
395     public void onInputDeviceChanged(int deviceId) {
396         updateInputDeviceVibrators();
397     }
398 
399     @Override
400     public void onInputDeviceRemoved(int deviceId) {
401         updateInputDeviceVibrators();
402     }
403 
404     private boolean doVibratorExists() {
405         // For now, we choose to ignore the presence of input devices that have vibrators
406         // when reporting whether the device has a vibrator.  Applications often use this
407         // information to decide whether to enable certain features so they expect the
408         // result of hasVibrator() to be constant.  For now, just report whether
409         // the device has a built-in vibrator.
410         //synchronized (mInputDeviceVibrators) {
411         //    return !mInputDeviceVibrators.isEmpty() || vibratorExists();
412         //}
413         return vibratorExists();
414     }
415 
416     private void doVibratorOn(long millis) {
417         synchronized (mInputDeviceVibrators) {
418             final int vibratorCount = mInputDeviceVibrators.size();
419             if (vibratorCount != 0) {
420                 for (int i = 0; i < vibratorCount; i++) {
421                     mInputDeviceVibrators.get(i).vibrate(millis);
422                 }
423             } else {
424                 vibratorOn(millis);
425             }
426         }
427     }
428 
429     private void doVibratorOff() {
430         synchronized (mInputDeviceVibrators) {
431             final int vibratorCount = mInputDeviceVibrators.size();
432             if (vibratorCount != 0) {
433                 for (int i = 0; i < vibratorCount; i++) {
434                     mInputDeviceVibrators.get(i).cancel();
435                 }
436             } else {
437                 vibratorOff();
438             }
439         }
440     }
441 
442     private class VibrateThread extends Thread {
443         final Vibration mVibration;
444         boolean mDone;
445 
446         VibrateThread(Vibration vib) {
447             mVibration = vib;
448             mTmpWorkSource.set(vib.mUid);
449             mWakeLock.setWorkSource(mTmpWorkSource);
450             mWakeLock.acquire();
451         }
452 
453         private void delay(long duration) {
454             if (duration > 0) {
455                 long bedtime = duration + SystemClock.uptimeMillis();
456                 do {
457                     try {
458                         this.wait(duration);
459                     }
460                     catch (InterruptedException e) {
461                     }
462                     if (mDone) {
463                         break;
464                     }
465                     duration = bedtime - SystemClock.uptimeMillis();
466                 } while (duration > 0);
467             }
468         }
469 
470         public void run() {
471             Process.setThreadPriority(Process.THREAD_PRIORITY_URGENT_DISPLAY);
472             synchronized (this) {
473                 int index = 0;
474                 long[] pattern = mVibration.mPattern;
475                 int len = pattern.length;
476                 int repeat = mVibration.mRepeat;
477                 long duration = 0;
478 
479                 while (!mDone) {
480                     // add off-time duration to any accumulated on-time duration
481                     if (index < len) {
482                         duration += pattern[index++];
483                     }
484 
485                     // sleep until it is time to start the vibrator
486                     delay(duration);
487                     if (mDone) {
488                         break;
489                     }
490 
491                     if (index < len) {
492                         // read on-time duration and start the vibrator
493                         // duration is saved for delay() at top of loop
494                         duration = pattern[index++];
495                         if (duration > 0) {
496                             VibratorService.this.doVibratorOn(duration);
497                         }
498                     } else {
499                         if (repeat < 0) {
500                             break;
501                         } else {
502                             index = repeat;
503                             duration = 0;
504                         }
505                     }
506                 }
507                 mWakeLock.release();
508             }
509             synchronized (mVibrations) {
510                 if (mThread == this) {
511                     mThread = null;
512                 }
513                 if (!mDone) {
514                     // If this vibration finished naturally, start the next
515                     // vibration.
516                     mVibrations.remove(mVibration);
517                     unlinkVibration(mVibration);
518                     startNextVibrationLocked();
519                 }
520             }
521         }
522     };
523 
524     BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
525         public void onReceive(Context context, Intent intent) {
526             if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
527                 synchronized (mVibrations) {
528                     doCancelVibrateLocked();
529 
530                     int size = mVibrations.size();
531                     for(int i = 0; i < size; i++) {
532                         unlinkVibration(mVibrations.get(i));
533                     }
534 
535                     mVibrations.clear();
536                 }
537             }
538         }
539     };
540 }

View Code

其中，VibratorService实际上是通过“本地方法”去控制马达的。例如，hasVibratora()最终是通过vibratorExists()来判断马达是否存在的。

4 Vibrator.java

frameworks/base/core/java/android/os/Vibrator.java源码如下：

 1 package android.os;
 2 
 3 import android.content.Context;
 4 
 5 public abstract class Vibrator {
 6 
 7     public Vibrator() {
 8     }
 9 
10     public abstract boolean hasVibrator();
11     
12     public abstract void vibrate(long milliseconds);
13 
14     public abstract void vibrate(long[] pattern, int repeat);
15 
16     public abstract void cancel();
17 }

5 SystemVibrator.java

frameworks/base/core/java/android/os/SystemVibrator.java源码如下：

 1 /*
 2  * Copyright (C) 2012 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 android.os;
18 
19 import android.util.Log;
20 
21 /**
22  * Vibrator implementation that controls the main system vibrator.
23  *
24  * @hide
25  */
26 public class SystemVibrator extends Vibrator {
27     private static final String TAG = "Vibrator";
28 
29     private final IVibratorService mService;
30     private final Binder mToken = new Binder();
31 
32     public SystemVibrator() {
33         mService = IVibratorService.Stub.asInterface(
34                 ServiceManager.getService("vibrator"));
35     }
36 
37     @Override
38     public boolean hasVibrator() {
39         if (mService == null) {
40             Log.w(TAG, "Failed to vibrate; no vibrator service.");
41             return false;
42         }
43         try {
44             return mService.hasVibrator();
45         } catch (RemoteException e) {
46         }
47         return false;
48     }
49 
50     @Override
51     public void vibrate(long milliseconds) {
52         if (mService == null) {
53             Log.w(TAG, "Failed to vibrate; no vibrator service.");
54             return;
55         }
56         try {
57             mService.vibrate(milliseconds, mToken);
58         } catch (RemoteException e) {
59             Log.w(TAG, "Failed to vibrate.", e);
60         }
61     }
62 
63     @Override
64     public void vibrate(long[] pattern, int repeat) {
65         if (mService == null) {
66             Log.w(TAG, "Failed to vibrate; no vibrator service.");
67             return;
68         }
69         // catch this here because the server will do nothing.  pattern may
70         // not be null, let that be checked, because the server will drop it
71         // anyway
72         if (repeat < pattern.length) {
73             try {
74                 mService.vibratePattern(pattern, repeat, mToken);
75             } catch (RemoteException e) {
76                 Log.w(TAG, "Failed to vibrate.", e);
77             }
78         } else {
79             throw new ArrayIndexOutOfBoundsException();
80         }
81     }
82 
83     @Override
84     public void cancel() {
85         if (mService == null) {
86             return;
87         }
88         try {
89             mService.cancelVibrate(mToken);
90         } catch (RemoteException e) {
91             Log.w(TAG, "Failed to cancel vibration.", e);
92         }
93     }
94 }

View Code

说明：
(01) 在构造函数SystemVibrator()中，我们通过 IVibratorService.Stub.asInterface(ServiceManager.getService("vibrator")) 获取马达服务，实际上获取的是VibratorService对象。
(02) SystemVibrator的接口都是调用VibratorService接口实现的。

在讲解“应用层如何通过getSystemService(VIBRATOR_SERVICE)获取马达服务，然后进一步的操作马达”之前，我们先看看应用层的马达操作示例！

Part 6 马达的应用示例

1 权限

调用马达服务，需要在manifest中添加相应的权限：

<!-- 震动马达权限 -->
<uses-permission android:name="android.permission.VIBRATE"/>

2 源码

源码如下：

 1 package com.test;
 2 
 3 import android.app.Activity;
 4 import android.os.Bundle;
 5 import android.os.Vibrator;
 6 import android.view.View;
 7 import android.view.View.OnClickListener;
 8 import android.widget.Button;
 9 import android.widget.ToggleButton;
10 import android.util.Log;
11 
12 public class VibratorTest extends Activity {
13     private static final String TAG = "skywang-->VibratorTest";
14 
15     private Vibrator mVibrator;
16     private Button mOnce = null;
17     private ToggleButton mEndless = null;
18 
19     @Override
20     protected void onCreate(Bundle savedInstanceState) {
21         super.onCreate(savedInstanceState);
22         setContentView(R.layout.main);
23 
24         // 获取震动马达服务
25         mVibrator= (Vibrator) getSystemService(VIBRATOR_SERVICE);
26 
27         mOnce = (Button) findViewById(R.id.vib_once);
28         mOnce.setOnClickListener(new View.OnClickListener() {
29             
30             @Override
31             public void onClick(View view) {
32                 //震动指定时间
33                 mVibrator.vibrate(100);
34             }
35         });
36 
37         mEndless = (ToggleButton) findViewById(R.id.vib_endless);
38         mEndless.setOnClickListener(new OnClickListener() {
39             @Override
40             public void onClick(View v) {
41                 if (mEndless.isChecked()) {
42                     //等待100ms后，按数组所给数值间隔震动；其后为重复次数，-1为不重复，0一直震动
43                     mVibrator.vibrate(new long[]{100,20,100,40,100,60}, 0);
44                 } else {
45                     // 取消震动 
46                     mVibrator.cancel();
47                 }
48             }
49         });
50 
51     }
52 
53     @Override
54     protected void onStop() {
55         super.onStop();
56         if (mVibrator != null)
57             mVibrator= null;
58     }
59 }

点击下载：Android马达应用代码

Part 7 马达的应用如何调用到马达服务的

接下来，我们分析一下如何获取马达服务的：即 mVibrator= (Vibrator) getSystemService(VIBRATOR_SERVICE) 的工作原理。

1. Context.java中的getSystemService()

getSystemService()定义在frameworks/base/core/java/android/content/Context.java中，源码如下：

public abstract Object getSystemService(String name);

Context.java中的getSystemService() 是个抽象方法，它的实现在ContextImpl.java中。

2. ContextImpl.java中的getSystemService()

frameworks/base/core/java/android/app/ContextImpl.java中的 getSystemService() 源码如下：

1 @Override
2 public Object getSystemService(String name) {
3     ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
4     return fetcher == null ? null : fetcher.getService(this);
5 }

3. ContextImpl.java中的SYSTEM_SERVICE_MAP

SYSTEM_SERVICE_MAP是一个HashMap对象，它的相关代码如下：

 1 private static final HashMap<String, ServiceFetcher> SYSTEM_SERVICE_MAP =
 2         new HashMap<String, ServiceFetcher>();
 3 
 4 SYSTEM_SERVICE_MAP的初始化，是在ContextImpl.java通过static静态模块完成的。源码如下：
 5 static {
 6 
 7     ...
 8 
 9     // 注册“传感器服务”
10     registerService(SENSOR_SERVICE, new ServiceFetcher() {
11             public Object createService(ContextImpl ctx) {
12                 return new SystemSensorManager(ctx.mMainThread.getHandler().getLooper());
13             }});
14 
15     // 注册其它服务 ...
16 
17     // 注册马达服务
18     registerService(VIBRATOR_SERVICE, new ServiceFetcher() {
19             public Object createService(ContextImpl ctx) {
20                 return new SystemVibrator();
21             }});
22 
23     ...
24 }

说明：在上面的static静态模块中，会通过registerService()注册一系列的服务，包括马达服务。注册服务是通过registerService()实现的，下面我们看看registerService()的定义。

1 private static int sNextPerContextServiceCacheIndex = 0;
2 private static void registerService(String serviceName, ServiceFetcher fetcher) {
3     if (!(fetcher instanceof StaticServiceFetcher)) {
4         fetcher.mContextCacheIndex = sNextPerContextServiceCacheIndex++;
5     }
6     SYSTEM_SERVICE_MAP.put(serviceName, fetcher);
7 }

从中，我们知道，在registerService()中，会通过 SYSTEM_SERVICE_MAP.put(serviceName, fetcher) 将serviceName和fetcher添加到哈希表SYSTEM_SERVICE_MAP中。
对马达服务而言，添加到哈希表SYSTEM_SERVICE_MAP中的key-value中的key是VIBRATOR_SERVICE，value则是ServiceFetcher对象；而且该匿名ServiceFetcher对象的createService()方法会“通过new SystemVibrator()”返回SystemVibrator对象。而SystemVibrator我们在前面已经介绍过了，它是马达服务对外提供接口的类。

OK，接着往下看。

3. ContextImpl.java中的fetcher.getService(this)

1 public Object getSystemService(String name) {
2     ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
3     return fetcher == null ? null : fetcher.getService(this);
4 }

我们已经知道SYSTEM_SERVICE_MAP是哈希表，通过SYSTEM_SERVICE_MAP.get(name)返回的是ServiceFetcher对象。
由于fetcher不为null，所以，getSystemService()会返回fetcher.getService(this)。我们看看ServiceFetcher中getService()源码：

 1 static class ServiceFetcher {
 2     int mContextCacheIndex = -1;
 3 
 4     public Object getService(ContextImpl ctx) {
 5         ArrayList<Object> cache = ctx.mServiceCache;
 6         Object service;
 7         synchronized (cache) {
 8             if (cache.size() == 0) {
 9 
10                 // “服务对象”缓冲
11                 for (int i = 0; i < sNextPerContextServiceCacheIndex; i++) {
12                     cache.add(null);
13                 }
14             } else {
15                 service = cache.get(mContextCacheIndex);
16                 if (service != null) {
17                     return service;
18                 }
19             }
20             service = createService(ctx);
21             cache.set(mContextCacheIndex, service);
22             return service;
23         }
24     }
25 
26     public Object createService(ContextImpl ctx) {
27         throw new RuntimeException("Not implemented");
28     }
29 }

从中，我们发现，getService()实际上返回的是“通过createService(ctx)创建的service对象”。
而在registerService()注册马达服务时，我们匿名实现了createService()方法：它实际上是通过 new SystemVibrator() 返回SystemVibrator对象。

至此，我们知道：getSystemService(VIBRATOR_SERVICE) 返回的是 SystemVibrator对象！SystemVibrator前面已经分析过，这里就不再说明了。

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原文地址：https://www.cnblogs.com/skywang12345/p/3404808.html

Android之 看“马达”如何贯通Android系统 (从硬件设计 --> 驱动 --> HAL --> JNI --> Framework --> Application)

Part 1 马达的硬件设计

Part 2 马达的驱动代码

Part 3 马达的HAL实现

Part 4 马达的JNI部分

Part 5 马达的Framework层实现

Part 6 马达的应用示例

Part 7 马达的应用如何调用到马达服务的

Android之看“马达”如何贯通Android系统 (从硬件设计 --> 驱动 --> HAL --> JNI --> Framework --> Application)