1 重点知识
1.1 Alarm
当手机重启或者应用被杀死的时候，Alarm会被删除，因此，如果想通过Alarm来完成长久定时任务是不可靠的，如果非要完成长久定时任务，可以这样：将应用的所有Alarm信息存到数据库中，每次应用启动的时候都重新注册Alarm并更新Alarm的触发时间，通过这种方式就不存在Alarm丢失的情况了。

1.2 Android-N app seinfo设置流程
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
startProcessLocked() {
[…]
Process.ProcessStartResult startResult =
Process.start(entryPoint,
app.processName,
uid, uid, gids,
debugFlags, mountExternal,
app.info.targetSdkVersion,
app.info.seinfo,
requiredAbi, instructionSet,
app.info.dataDir, entryPointArgs);
[…]
}

frameworks/base/core/java/android/os/Process.java
start() {
try {
return startViaZygote(processClass,
niceName,
uid, gid, gids,
debugFlags, mountExternal,
targetSdkVersion, seInfo,
abi, instructionSet,
appDataDir, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
[…]
}

frameworks/base/core/jni/com_android_internal_os_Zygote.cpp
ForkAndSpecializeCommon() {
[…]
rc = selinux_android_setcontext(
uid, is_system_server,
se_info_c_str, se_name_c_str);
[…]
}

external/libselinux/src/android.c
int selinux_android_setcontext(
uid_t uid,
bool isSystemServer,
const char *seinfo,
const char *pkgname)
{
[…]
}

1.3 Launcher的启动
/* ActivityThread.java */
SystemServer.java
private void startOtherServices() {
[...]
mActivityManagerService.systemReady(
new Runnable() {
});
}

1.4 屏幕永不超时
frameworks/base/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java
frameworks/base/packages/SettingsProvider/res/values/defaults.xml
将def_screen_off_timeout的值改成2147483647（0x7fffffff）。

/data/system/users/0/settings_system.xml
adb shell settings put system screen_off_timeout 3600000 #一小时超时

1.5 禁止锁屏
frameworks/policies/base/phone/com/android/internal/policy/impl/KeyguardViewMediator.java
将mExternallyEnabled的值改成false。

1.6 tmpfs文件系统
mkdir /data/tmp
mount -t tmpfs -o size=100M tmpfs /data/tmp

1.7 apk signer
apk: private key signer
keystore: 密钥库

2 Android异常分析汇总
2.1 Android卡在开机动画
1）AudioFlinger反复重启
2）systemui ANR

2.2 framework反复重启
1）boot_progress|low-level shutdown|am_crash|checkScreenEnabled|ILL_ILLOPN

2.3 no window focus
ViewRootImpl.java
mAttachInfo.mHasWindowFocus = true

Activity中在dispatchKeyEvent()或者dispatchTouchEvent()方法里面，通过反射把mAttachInfo.mHasWindowFocus重置为true，可以解决no window focus。

@Override
public boolean dispatchTouchEvent(@NonNull KeyEvent event) {
try {
ViewParent viewRootImpl =
getWindow().getDecorView().getParent();
Class viewRootImplClass =
viewRootImpl.getClass();

Field mAttachInfoField =
viewRootImplClass.getDeclaredField(
"mAttachInfo");
mAttachInfoField.setAccessible(true);
Object mAttachInfo =
mAttachInfoField.get(viewRootImpl);
Class mAttachInfoClass =
mAttachInfo.getClass();

Field mHasWindowFocusField =
mAttachInfoClass.getDeclaredField(
"mHasWindowFocus");
mHasWindowFocusField.setAccessible(true);
mHasWindowFocusField.set(mAttachInfo,
true);
boolean mHasWindowFocus =
(boolean) mHasWindowFocusField.get(
mAttachInfo);

} catch (Exception e) {
e.printStackTrace();
}

return super.dispatchKeyEvent(event);
}

2.4 dumpsys gfxinfo
使用dumpsys gfxinfo命令可获取128帧的绘制信息，详细包括每一帧绘制的Draw、Process、Execute三个过程的耗时，如果这三个时间总和超过16.6ms即认为发生了卡顿。

2.5 Linux disk usage
查看当前目录下面所有文件夹所占的空间。
du -h -d 1

显示目录和目录下子目录和文件占用磁盘空间的大小。
du -h /data/data

2.6 提取log
import io
import re
import sys,os
import shutil

arg0_proc_name = ''
def print_usage():
print('\nUsage: python ' + arg0_proc_name +
' <DIR> <file_prefix> <match_string>')
print('refer to the below showcases '
'regarding match_string\n')
list = [
'boot_progress|shutdown',
'boot_progress|low-level shutdown|'
'am_crash',
'boot_progress|shutdown|am_crash|'
'bootinfo',
'checkScreenEnabled|ILL_ILLOPN',
'UIWDT',
]

for item in list:
print(' \"' + item + '\"')
print('')

def remove_dir(dir_path):
if os.path.isdir(dir_path):
for file in os.listdir(dir_path):
if (os.path.isdir(dir_path +
os.path.sep + file)):
remove_dir(dir_path +
os.path.sep + file)
else:
os.remove(dir_path +
os.path.sep + file)
os.removedirs(dir_path)

def write_file_string(file, line_string):
h = open(file, 'a+')
h.writelines(line_string)
h.close()

def write_line_string_to_log(src_file,
dst_file, match_string):
line_cnt = 1
fp = io.open(src_file, 'r', encoding='utf-8',
errors='ignore')
for line_string in fp:
if re.findall(match_string, line_string.lower()):
#if re.findall(match_string, line_string.lower(),
#re.I):
write_file_string(
dst_file, str(line_cnt) + ' ' + line_string)
line_cnt += 1

def find_string(dir_path, file_prefix, match_string):
remove_dir(dir_path + os.path.sep + 'my_out')
os.makedirs(dir_path + os.path.sep + 'my_out')

try:
for file in os.listdir(dir_path):
if (os.path.isfile(dir_path + os.path.sep +
file) and \
file.startswith(file_prefix)):
write_line_string_to_log(dir_path +
os.path.sep + file,
dir_path + os.path.sep +
'my_out' + os.path.sep + file,
match_string)
except KeyboardInterrupt:
print('Got ^C exit signal')

def main():
global arg0_proc_name
arg0_proc_name = sys.argv[0]
if sys.argv[0].rfind(os.path.sep) > 0 :
index = sys.argv[0].rfind(os.path.sep)
arg0_proc_name = sys.argv[0][index+1:]

if len(sys.argv) < 4:
print_usage()
sys.exit(0)

print('to be found: ' + sys.argv[2])
find_string(sys.argv[1], sys.argv[2],
sys.argv[3])

if __name__ == '__main__':
main()

3 USB异步API
development/samples/USB/AdbTest
import static java.lang.Integer.toHexString;
Integer.toHexString(USB_VID)

USB gadget state is not attached

MTP/mass_storage
Maybe the USB cable|idVendor=1d6b|idVendor=12d1|usb disconnect|over-current|nearby|wwan0, isUp is:

1) Choose xxx-Domain, then click Create to create a new page BBB under xxx-Domain.
2) Add Link to xxx-Domain, Edit - copy other line to get prefix format - Insert Link - Search BBB.

4 ART
adb shell oatdump --oat-file=/data/dalvik-cache/xxx/xxx.dex

Linux：
readelf -a xxx.dex

5 Abbreviations
Android PMS LI、LIF、LPw、LPr：要想弄明白方法名中的LI、LIF、LPw、LPr的含义，需要先了解PackageManagerService内部使用的两个锁。因为LI、LIF、LPw、LPr中的L，指的是Lock，而后面跟的I和P指的是两个锁，I表示mInstallLock同步锁；P表示mPackages同步锁。LPw、LPr中的w表示writing，r表示reading。LIF中的F表示Freeze。
ILL_ILLOPN：illegal operand
scanDirLI()：scanDir Lock mInstallLock