Android在标准linux基础上对休眠唤醒的实现(三)

四、android层源码解析

在linux之上经过android的软件堆层层封装,最终在上层的java应用程序中使用。休眠唤醒也是从最上层发出的命令，然后一层一层地将参数解析，往最底层传，最后走上标准linux的休眠唤醒之路。

这一部分将会初略分析休眠唤醒机制上linux之上所走的路线。

在linux之上，存在一个hal层，专门做和linux内核设备打交道的事情，这里也不例外。休眠唤醒机制的hal层源码位于：@hardware/libhardware_legacy/power/power.c

该文件源码比较简单，下面列举重点片段：

enum {

ACQUIRE_PARTIAL_WAKE_LOCK = 0,

RELEASE_WAKE_LOCK,

REQUEST_STATE,

OUR_FD_COUNT

};

const char * const NEW_PATHS[] = {

"/sys/power/wake_lock",

"/sys/power/wake_unlock",

"/sys/power/state"

};

static int g_initialized = 0;

static int g_fds[OUR_FD_COUNT];

static const char *off_state = "mem";

static const char *on_state = "on";

static int open_file_descriptors(const char * const paths[])

{

int i;

for (i=0; i<OUR_FD_COUNT; i++) {

int fd = open(paths[i], O_RDWR);

if (fd < 0) {

fprintf(stderr, "fatal error opening \"%s\"\n", paths[i]);

g_error = errno;

return -1;

}

g_fds[i] = fd;

}

g_error = 0;

return 0;

}

static inline void initialize_fds(void)

{

if (g_initialized == 0) {

if(open_file_descriptors(NEW_PATHS) < 0) {

open_file_descriptors(OLD_PATHS);

on_state = "wake";

off_state = "standby";

}

g_initialized = 1;

}

}

int acquire_wake_lock(int lock, const char* id)

{

initialize_fds();

if (g_error) return g_error;

int fd;

if (lock == PARTIAL_WAKE_LOCK) { // 上层传下来的lock type

fd = g_fds[ACQUIRE_PARTIAL_WAKE_LOCK];

}

else {

return EINVAL;

}

return write(fd, id, strlen(id));

}

int release_wake_lock(const char* id)

{

initialize_fds();

// LOGI("release_wake_lock id='%s'\n", id);

if (g_error) return g_error;

ssize_t len = write(g_fds[RELEASE_WAKE_LOCK], id, strlen(id));

return len >= 0;

}

int set_screen_state(int on)

{

QEMU_FALLBACK(set_screen_state(on));

LOGI("*** set_screen_state %d", on);

initialize_fds();

if (g_error) return g_error;

char buf[32];

int len;

if(on)

len = sprintf(buf, on_state);

else

len = sprintf(buf, off_state);

len = write(g_fds[REQUEST_STATE], buf, len);

if(len < 0) {

LOGE("Failed setting last user activity: g_error=%d\n", g_error);

}

return 0;

}

Hal层的代码在jni层中被使用，源码位于：frameworks/base/core/jni/android_os_Power.cpp，代码片段如下：

static void acquireWakeLock(JNIEnv *env, jobject clazz, jint lock, jstring idObj)

{

if (idObj == NULL) {

throw_NullPointerException(env, "id is null");

return ;

}

const char *id = env->GetStringUTFChars(idObj, NULL);

acquire_wake_lock(lock, id);

env->ReleaseStringUTFChars(idObj, id);

}// 对wakelock加锁函数

static void releaseWakeLock(JNIEnv *env, jobject clazz, jstring idObj)

{

if (idObj == NULL) {

throw_NullPointerException(env, "id is null");

return ;

}

const char *id = env->GetStringUTFChars(idObj, NULL);

release_wake_lock(id);

env->ReleaseStringUTFChars(idObj, id);

}// 对wakelock解锁函数

static int setScreenState(JNIEnv *env, jobject clazz, jboolean on)

{

return set_screen_state(on);

}// 休眠唤醒的函数

Jni的方法需要注册到上层才可以使用，同时也需要在上层的对应java类中声明了native才可以使用。那么这里的方法在java中对应的声明在哪里呢？frameworks/base/core/java/android/os/Power.java，该文件定义一个java类，如下：

public class Power

{

// can't instantiate this class

private Power()

{

}

/**

* Wake lock that ensures that the CPU is running. The screen might

* not be on.

*/

public static final int PARTIAL_WAKE_LOCK = 1;

/**

* Wake lock that ensures that the screen is on.

*/

public static final int FULL_WAKE_LOCK = 2;

public static native void acquireWakeLock(int lock, String id);

public static native void releaseWakeLock(String id);

…

/**

* Turn the screen on or off

*

* @param on Whether you want the screen on or off

*/

public static native int setScreenState(boolean on);

…

}

声明的jni接口应该是被java server在使用，这里就是专门的电源管理服务：PowerManagerService使用，具体源码位置在：frameworks/base/services/java/com/android/server/PowerManagerService.java。android在最上层还提供了现场的android.os.PowerManager类

(frameworks/base/core/java/android/os/PowerManager.java)来供app使用，PowerManager类会调用java服务PowerManagerService的方法来完成与wakelock相关的工作。

@ frameworks/base/core/java/android/os/PowerManager.java

类PowerManager中内嵌了一个WakeLock类，另外还定义了wakelock的类型，下面是代码片段：

public class PowerManager

{

private static final String TAG = "PowerManager";

…

/**

* Wake lock that ensures that the CPU is running. The screen might

* not be on.

*/

public static final int PARTIAL_WAKE_LOCK = WAKE_BIT_CPU_STRONG;

/**

* Wake lock that ensures that the screen and keyboard are on at

* full brightness.

*/

public static final int FULL_WAKE_LOCK = WAKE_BIT_CPU_WEAK | WAKE_BIT_SCREEN_BRIGHT | WAKE_BIT_KEYBOARD_BRIGHT;

/**

* Wake lock that ensures that the screen is on at full brightness;

* the keyboard backlight will be allowed to go off.

*/

public static final int SCREEN_BRIGHT_WAKE_LOCK = WAKE_BIT_CPU_WEAK | WAKE_BIT_SCREEN_BRIGHT;

/**

* Wake lock that ensures that the screen is on (but may be dimmed);

* the keyboard backlight will be allowed to go off.

*/

public static final int SCREEN_DIM_WAKE_LOCK = WAKE_BIT_CPU_WEAK | WAKE_BIT_SCREEN_DIM;

/**

* Wake lock that turns the screen off when the proximity sensor activates.

* Since not all devices have proximity sensors, use

* {@link #getSupportedWakeLockFlags() getSupportedWakeLockFlags()} to determine if

* this wake lock mode is supported.

*

* {@hide}

*/

public static final int PROXIMITY_SCREEN_OFF_WAKE_LOCK

= WAKE_BIT_PROXIMITY_SCREEN_OFF;

…

public class WakeLock

{

…

WakeLock(int flags, String tag)

{

switch (flags & LOCK_MASK) {

case PARTIAL_WAKE_LOCK:

case SCREEN_DIM_WAKE_LOCK:

case SCREEN_BRIGHT_WAKE_LOCK:

case FULL_WAKE_LOCK:

case PROXIMITY_SCREEN_OFF_WAKE_LOCK:

break;

default:

throw new IllegalArgumentException();

}

mFlags = flags;

mTag = tag;

mToken = new Binder();

}

public void acquire()

{

synchronized (mToken) {

if (!mRefCounted || mCount++ == 0) {

try {

mService.acquireWakeLock(mFlags, mToken, mTag);

} catch (RemoteException e) {

}

mHeld = true;

}

}

}

public void release(int flags)

{

synchronized (mToken) {

if (!mRefCounted || --mCount == 0) {

try {

mService.releaseWakeLock(mToken, flags);

} catch (RemoteException e) {

}

mHeld = false;

}

if (mCount < 0) {

throw new RuntimeException("WakeLock under-locked " + mTag);

}

}

}

…

}

…

public WakeLock newWakeLock(int flags, String tag)

{

if (tag == null) {

throw new NullPointerException("tag is

null in PowerManager.newWakeLock");

}

return new WakeLock(flags, tag);

}

public void goToSleep(long time)

{

try {

mService.goToSleep(time);

} catch (RemoteException e) {

}

}

…

public PowerManager(IPowerManager service, Handler handler)

{

mService = service;

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