//创建电源锁

[cpp] view plain copy

PowerManagerService.java

mWakeLockSuspendBlocker = createSuspendBlockerLocked("PowerManagerService.WakeLocks");

mDisplaySuspendBlocker = createSuspendBlockerLocked("PowerManagerService.Display");

private SuspendBlocker createSuspendBlockerLocked(String name) {
SuspendBlocker suspendBlocker = new SuspendBlockerImpl(name);
mSuspendBlockers.add(suspendBlocker);
return suspendBlocker;
}

//电源锁操作类的实现

[cpp] view plain copy

private final class SuspendBlockerImpl implements SuspendBlocker {
private final String mName;
private int mReferenceCount;

public SuspendBlockerImpl(String name) {
mName = name;
}

@Override
public void acquire() {
synchronized (this) {
mReferenceCount += 1;
if (mReferenceCount == 1) {
if (DEBUG_SPEW) {
Slog.d(TAG, "Acquiring suspend blocker \"" + mName + "\".");
}
nativeAcquireSuspendBlocker(mName);
}
}
}

@Override
public void release() {
synchronized (this) {
mReferenceCount -= 1;
if (mReferenceCount == 0) {
if (DEBUG_SPEW) {
Slog.d(TAG, "Releasing suspend blocker \"" + mName + "\".");
}
nativeReleaseSuspendBlocker(mName);
} else if (mReferenceCount < 0) {
Log.wtf(TAG, "Suspend blocker \"" + mName
+ "\" was released without being acquired!", new Throwable());
mReferenceCount = 0;
}
}
}

}

//JNI层函数实现电源锁的获取

[cpp] view plain copy

com_android_server_power_PowerManagerService.cpp

static void nativeAcquireSuspendBlocker(JNIEnv *env, jclass clazz, jstring nameStr) {
ScopedUtfChars name(env, nameStr);
acquire_wake_lock(PARTIAL_WAKE_LOCK, name.c_str());
}

//将电源锁写入到相应的文件中，相当于获得了电源锁

power.c

[cpp] view plain copy

int acquire_wake_lock(int lock, const char* id)
{
initialize_fds();
if (g_error) return g_error;

int fd;

if (lock == PARTIAL_WAKE_LOCK) {
fd = g_fds[ACQUIRE_PARTIAL_WAKE_LOCK];
}
else {
return EINVAL;
}

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

//打开记录电源锁的文件

[cpp] view plain copy

static inline void
initialize_fds(void)
{
if (g_initialized == 0) {
if(open_file_descriptors(NEW_PATHS) < 0)
open_file_descriptors(OLD_PATHS);
g_initialized = 1;
}
}

//记录电源锁的文件路径

[cpp] view plain copy

const char * const OLD_PATHS[] = {
"/sys/android_power/acquire_partial_wake_lock",
"/sys/android_power/release_wake_lock",
};

const char * const NEW_PATHS[] = {
"/sys/power/wake_lock",
"/sys/power/wake_unlock",
};

到现在为止，我们的代码流程已经走了一大半了，我们一开始介绍的android的上面几层Framework层、JNI层、HAL层都已经介绍了。下面就应该是和kernel层进行交互了。
但是在android/hardware/libhardware_legacy/power/power.c中的acquire_wake_lock()函数似乎没法和kernel层进行通信啊？最后的返回语句return write(fd, id, strlen(id))是一个系统调用，这里就实现了与kernel的交互。
kernel/power/main.c中的power_attr宏很多地方用到：

[cpp] view plain copy

1. #definepower_attr(_name)\
2. staticstructkobj_attribute_name##_attr={\
3. .attr={\
4. .name=__stringify(_name),\
5. .mode=0644,\
6. },\
7. .show=_name##_show,\
8. .store=_name##_store,\
9. }

[cpp] view plain copy

1. #ifdefCONFIG_USER_WAKELOCK
2. power_attr(wake_lock);
3. power_attr(wake_unlock);
4. #endif

default y
User-space wake lock api. Write "lockname" or "lockname timeout"
to /sys/power/wake_lock lock and if needed create a wake lock.
Write "lockname" to /sys/power/wake_unlock to unlock a user wake
lock.
[cpp] view plain copy

1. #ifdefCONFIG_PM_WAKELOCKS
2. power_attr(wake_lock);
3. power_attr(wake_unlock);
4. #endif

default n
Allow user space to create, activate and deactivate wakeup source
objects with the help of a sysfs-based interface.
宏展开，等价于：
[cpp] view plain copy

1. staticstructkobj_attributewake_lock_attr={
2. .attr={
3. .name=“wake_lock”,
4. .mode=0644,
5. },
6. .show=wake_lock_show,
7. .store=wake_lock_store,
8. }

[cpp] view plain copy

1. staticstructkobj_attributewake_unlock_attr={
2. .attr={
3. .name=“wake_unlock”,
4. .mode=0644,
5. },
6. .show=wake_unlock_show,
7. .store=wake_unlock_store,
8. }

show和store函数的源码位于kernel/power/userwakelock.c。
[cpp] view plain copy

1. staticstructattribute*g[]={
2. &state_attr.attr,
3. #ifdefCONFIG_PM_TRACE
4. &pm_trace_attr.attr,
5. &pm_trace_dev_match_attr.attr,
6. #endif
7. #ifdefCONFIG_PM_SLEEP
8. &pm_async_attr.attr,
9. &wakeup_count_attr.attr,
10. #ifdefCONFIG_USER_WAKELOCK
11. &wake_lock_attr.attr,
12. &wake_unlock_attr.attr,
13. #endif
14. #ifdefCONFIG_PM_AUTOSLEEP
15. &autosleep_attr.attr,
16. #endif
17. #ifdefCONFIG_PM_WAKELOCKS
18. &wake_lock_attr.attr,
19. &wake_unlock_attr.attr,
20. #endif
21. #ifdefCONFIG_PM_DEBUG
22. &pm_test_attr.attr,
23. #endif
24. #ifdefCONFIG_PM_SLEEP_DEBUG
25. &pm_print_times_attr.attr,
26. #endif
27. #endif
28. #ifdefCONFIG_FREEZER
29. &pm_freeze_timeout_attr.attr,
30. #endif
31. NULL,
32. };

[cpp] view plain copy

1. staticstructattribute_groupattr_group={
2. .attrs=g,
3. };

pm_init()->
error = sysfs_create_group(power_kobj, &attr_group);
好了，我们该回到原来我们产生疑问的地方了这时我们还得关注其中的另一个函数acquire_wake_lock()->initialize_fds()。 [cpp] view plain copy

1. initialize_fds(void)
2. {
3. //XXX:shouldbethis:
4. //pthread_once(&g_initialized,open_file_descriptors);
5. //XXX:notthis:
6. if(g_initialized==0){
7. if(open_file_descriptors(NEW_PATHS)<0)
8. open_file_descriptors(OLD_PATHS);
9. g_initialized=1;
10. }
11. }

其实这个函数中最核心的步骤就是open_file_descriptors(NEW_PATHS)，顺序打开NEW_PATHS[ ]中的文件：

[cpp] view plain copy

1. staticint
2. open_file_descriptors(constchar*constpaths[])
3. {
4. inti;
5. for(i=0;i<OUR_FD_COUNT;i++){
6. intfd=open(paths[i],O_RDWR);
7. if(fd<0){
8. fprintf(stderr,"fatalerroropening\"%s\"\n",paths[i]);
9. g_error=errno;
10. return-1;
11. }
12. g_fds[i]=fd;
13. }
15. g_error=0;
16. return0;
17. }

[cpp] view plain copy

1. constchar*constNEW_PATHS[]={
2. "/sys/power/wake_lock",
3. "/sys/power/wake_unlock",
4. };

总之经过着一系列的步骤后，最终我们将在 return write(fd, id, strlen(id));时调用android/kernel/kernel/power/userwakelock.c 中的 wake_lock_store()函数。

[cpp] view plain copy

1. ssize_twake_lock_store(
2. structkobject*kobj,structkobj_attribute*attr,
3. constchar*buf,size_tn)
4. {
5. longtimeout;
6. structuser_wake_lock*l;
8. mutex_lock(&tree_lock);
9. l=lookup_wake_lock_name(buf,1,&timeout);
10. if(IS_ERR(l)){
11. n=PTR_ERR(l);
12. gotobad_name;
13. }
15. if(debug_mask&DEBUG_ACCESS)
16. pr_info("wake_lock_store:%s,timeout%ld\n",l->name,timeout);
18. if(timeout)
19. wake_lock_timeout(&l->wake_lock,timeout);
20. else
21. wake_lock(&l->wake_lock);
22. bad_name:
23. mutex_unlock(&tree_lock);
24. returnn;
25. }

[cpp] view plain copy

1. structrb_rootuser_wake_locks;
2. staticstructuser_wake_lock*lookup_wake_lock_name(
3. constchar*buf,intallocate,long*timeoutptr)
4. {
5. structrb_node**p=&user_wake_locks.rb_node;
6. structrb_node*parent=NULL;
7. structuser_wake_lock*l;
8. intdiff;
9. u64timeout;
10. intname_len;
11. constchar*arg;
13. /*Findlengthoflocknameandstartofoptionaltimeoutstring*/
14. arg=buf;
15. while(*arg&&!isspace(*arg))
16. arg++;
17. //lockname的长度
18. name_len=arg-buf;
19. if(!name_len)
20. gotobad_arg;
21. while(isspace(*arg))
22. arg++;
24. /*Processtimeoutstring*/
25. if(timeoutptr&&*arg){
26. //(char**)&arg存储的是解析string的结束字符
27. timeout=simple_strtoull(arg,(char**)&arg,0);
28. while(isspace(*arg))
29. arg++;
30. //如果解析string的结束字符不是’\0’
31. if(*arg)
32. gotobad_arg;
33. /*converttimeoutfromnanosecondstojiffies>0*/
34. timeout+=(NSEC_PER_SEC/HZ)-1;
35. //do_div(a,b)的返回值是余数，商保存到a中
36. do_div(timeout,(NSEC_PER_SEC/HZ));
37. if(timeout<=0)
38. timeout=1;
39. *timeoutptr=timeout;
40. }elseif(*arg)
41. //timeoutptr为NULL
42. gotobad_arg;
43. elseif(timeoutptr)
44. //*arg为0，没有timeout
45. *timeoutptr=0;
47. /*Lookupwakelockinrbtree*/
48. //对于一颗空的红黑树，略过while。wakelock按照name从小到大的顺序存储到user_wake_locks红黑树中
49. while(*p){
50. parent=*p;
51. l=rb_entry(parent,structuser_wake_lock,node);
52. diff=strncmp(buf,l->name,name_len);
53. //如果buf是l->name的子串，那么l->name[name_len]就不会为0，但是buf[name_len]会为0
54. if(!diff&&l->name[name_len])
55. diff=-1;
56. if(debug_mask&DEBUG_ERROR)
57. pr_info("lookup_wake_lock_name:compare%.*s%s%d\n",
58. name_len,buf,l->name,diff);
60. if(diff<0)
61. p=&(*p)->rb_left;
62. elseif(diff>0)
63. p=&(*p)->rb_right;
64. else
65. returnl;
66. }
68. /*Allocateandaddnewwakelocktorbtree*/
69. //allocate为0，表示不需要分配新的wakelock，只在rbtree上查找，找不到就出错了
70. if(!allocate){
71. if(debug_mask&DEBUG_ERROR)
72. pr_info("lookup_wake_lock_name:%.*snotfound\n",
73. name_len,buf);
74. returnERR_PTR(-EINVAL);
75. }
76. l=kzalloc(sizeof(*l)+name_len+1,GFP_KERNEL);
77. if(l==NULL){
78. if(debug_mask&DEBUG_FAILURE)
79. pr_err("lookup_wake_lock_name:failedtoallocate"
80. "memoryfor%.*s\n",name_len,buf);
81. returnERR_PTR(-ENOMEM);
82. }
83. memcpy(l->name,buf,name_len);
84. if(debug_mask&DEBUG_NEW)
85. pr_info("lookup_wake_lock_name:newwakelock%s\n",l->name);
86. wake_lock_init(&l->wake_lock,WAKE_LOCK_SUSPEND,l->name);
87. //插入结点，并染成红色
88. rb_link_node(&l->node,parent,p);
89. rb_insert_color(&l->node,&user_wake_locks);
90. returnl;
92. bad_arg:
93. if(debug_mask&DEBUG_ERROR)
94. pr_info("lookup_wake_lock_name:wakelock,%.*s,badarg,%s\n",
95. name_len,buf,arg);
96. returnERR_PTR(-EINVAL);
97. }

wake_lock_store()执行的基本流程为：首先调用lookup_wake_lock_name()来获得指定的唤醒锁，若延迟参数timeout为零的话，就调用 wake_lock()否则就调用wake_lock_timeout()，但不管调用哪个最后都会调用到android/kernel/kernel/power/wakelock.c中的函数static void wake_lock_internal()。

[cpp] view plain copy

1. staticvoidwake_lock_internal(
2. structwake_lock*lock,longtimeout,inthas_timeout)
3. {
4. inttype;
5. unsignedlongirqflags;
6. longexpire_in;
8. spin_lock_irqsave(&list_lock,irqflags);
9. type=lock->flags&WAKE_LOCK_TYPE_MASK;
10. //检查type是否合法
11. BUG_ON(type>=WAKE_LOCK_TYPE_COUNT);
12. //检查是否初始化过
13. BUG_ON(!(lock->flags&WAKE_LOCK_INITIALIZED));
14. #ifdefCONFIG_WAKELOCK_STAT
15. if(type==WAKE_LOCK_SUSPEND&&wait_for_wakeup){
16. if(debug_mask&DEBUG_WAKEUP)
17. pr_info("wakeupwakelock:%s\n",lock->name);
18. wait_for_wakeup=0;
19. lock->stat.wakeup_count++;
20. }
21. if((lock->flags&WAKE_LOCK_AUTO_EXPIRE)&&
22. (long)(lock->expires-jiffies)<=0){
23. wake_unlock_stat_locked(lock,0);
24. lock->stat.last_time=ktime_get();
25. }
26. #endif
27. if(!(lock->flags&WAKE_LOCK_ACTIVE)){
28. lock->flags|=WAKE_LOCK_ACTIVE;
29. #ifdefCONFIG_WAKELOCK_STAT
30. lock->stat.last_time=ktime_get();
31. #endif
32. }
33. //从inactive_locks上删除
34. list_del(&lock->link);
35. if(has_timeout){
36. if(debug_mask&DEBUG_WAKE_LOCK)
37. pr_info("wake_lock:%s,type%d,timeout%ld.%03lu\n",
38. lock->name,type,timeout/HZ,
39. (timeout%HZ)*MSEC_PER_SEC/HZ);
40. lock->expires=jiffies+timeout;
41. lock->flags|=WAKE_LOCK_AUTO_EXPIRE;
42. list_add_tail(&lock->link,&active_wake_locks[type]);
43. }else{
44. if(debug_mask&DEBUG_WAKE_LOCK)
45. pr_info("wake_lock:%s,type%d\n",lock->name,type);
46. lock->expires=LONG_MAX;
47. lock->flags&=~WAKE_LOCK_AUTO_EXPIRE;
48. list_add(&lock->link,&active_wake_locks[type]);
49. }
50. if(type==WAKE_LOCK_SUSPEND){
51. current_event_num++;
52. #ifdefCONFIG_WAKELOCK_STAT
53. if(lock==&main_wake_lock)
54. update_sleep_wait_stats_locked(1);
55. elseif(!wake_lock_active(&main_wake_lock))
56. update_sleep_wait_stats_locked(0);
57. #endif
58. if(has_timeout)
59. expire_in=has_wake_lock_locked(type);
60. else
61. expire_in=-1;
62. if(expire_in>0){
63. if(debug_mask&DEBUG_EXPIRE)
64. pr_info("wake_lock:%s,startexpiretimer,"
65. "%ld\n",lock->name,expire_in);
66. mod_timer(&expire_timer,jiffies+expire_in);
67. }else{
68. if(del_timer(&expire_timer))
69. if(debug_mask&DEBUG_EXPIRE)
70. pr_info("wake_lock:%s,stopexpiretimer\n",
71. lock->name);
72. if(expire_in==0)
73. queue_work(suspend_work_queue,&suspend_work);
74. }
75. }
76. spin_unlock_irqrestore(&list_lock,irqflags);
77. }
    

//电源锁的使用

[cpp] view plain copy

/**
* Updates the suspend blocker that keeps the CPU alive.
*
* This function must have no other side-effects.
*/
private void updateSuspendBlockerLocked() {
final boolean needWakeLockSuspendBlocker = ((mWakeLockSummary & WAKE_LOCK_CPU) != 0);
final boolean needDisplaySuspendBlocker = needDisplaySuspendBlocker();

// First acquire suspend blockers if needed.
if (needWakeLockSuspendBlocker && !mHoldingWakeLockSuspendBlocker) {
mWakeLockSuspendBlocker.acquire();
mHoldingWakeLockSuspendBlocker = true;
}
if (needDisplaySuspendBlocker && !mHoldingDisplaySuspendBlocker) {
mDisplaySuspendBlocker.acquire();
mHoldingDisplaySuspendBlocker = true;
}

// Then release suspend blockers if needed.
if (!needWakeLockSuspendBlocker && mHoldingWakeLockSuspendBlocker) {
mWakeLockSuspendBlocker.release();
mHoldingWakeLockSuspendBlocker = false;
}
if (!needDisplaySuspendBlocker && mHoldingDisplaySuspendBlocker) {
mDisplaySuspendBlocker.release();
mHoldingDisplaySuspendBlocker = false;
}
}

//判断是否处于亮屏或者正在变化阶段

[cpp] view plain copy private boolean needDisplaySuspendBlocker() {

//正处于变化阶段
if (!mDisplayReady) {
return true;
}
if (mDisplayPowerRequest.screenState != DisplayPowerRequest.SCREEN_STATE_OFF) {

//有疑问？
// If we asked for the screen to be on but it is off due to the proximity
// sensor then we may suspend but only if the configuration allows it.
// On some hardware it may not be safe to suspend because the proximity
// sensor may not be correctly configured as a wake-up source.
if (!mDisplayPowerRequest.useProximitySensor || !mProximityPositive
|| !mSuspendWhenScreenOffDueToProximityConfig) {
return true;
}
}
return false;
}

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