Android重量级开发之--提高android启动速度研究


http://www.eoeandroid.com/thread-29953-1-1.html

Android重量级开发之--提高android启动速度研究

www.eoeandroid.com首发，作者：Tigertang2@gmail.com

大家都知道启动速度慢是智能操作系统的一个通病，Android也不例外，启动速度大概在1分钟左右，虽然日本有一个叫quick boot的一秒启动android的产品，但是毕竟是旁门左道。所以从常规来提高android的启动速度成了大家研究的重点，也是难点。下面将初步研究的一下经验跟大家分享一下。

首先看一下android系统的启动流程：
bootloader

引导程序
kernel

内核
init

init初始化（这个大家都比较熟悉了，不要多说）

loads several daemons and services, including zygote

see /init.rc and init.<platform>.rc

zygote

这个是占用时间最多的，重点修理对象

preloads classes

装载了一千多个类，妈呀！！！
starts package manager
扫描package(下面详细介绍)

service manager

start services
（启动多个服务）

从实际的测试数据来看，有两个地方时最耗时间的，一个是zygote的装载一千多个类和初始化堆栈的过程，用了20秒左右。另一个是扫描
/system/app,

/system/framework,

/data/app,

/data/app-private.

这几个目录下面的package用了大概10秒，所以我们重点能够修理的就是这两个老大的。

一、首先是调试工具的使用，可以测试哪些类和那些过程占用了多少时间，
主要工具为

stopwatch

Message loggers

grabserial

参考http://elinux.org/Grabserial

printk times
参考http://elinux.org/Printk_Times

logcat

Android自带

bootchart
参考http://elinux.org/Bootchart
和
http://elinux.org/Bootchart

strace

AOSP的一部分（Eclair及以上版本）

使用例子
在init.rc中为了调试zygote

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server改为

service zygote /system/xbin/strace -tt -o/data/boot.strace /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server

method tracer*

ftrace*

详细使用可看提供的文档和网页介绍

上面的工具如果不用详细的分析不一定都用到，也可以使用logcat就可以,在代码中加一点计算时间和一些类的调试信息也可以达到很好效果。

二、zygote
装载1千多个类

首先，我们可以添加一点调试信息，以获得具体转载情况。

diff --git a/core/java/com/android/internal/os/ZygoteInit.java b/core/java/com/android/internal/os/ZygoteInit.java

index 404c513..f2b573c 100644

--- a/core/java/com/android/internal/os/ZygoteInit.java

+++ b/core/java/com/android/internal/os/ZygoteInit.java

@@ -259,6 +259,8 @@ public class ZygoteInit {

} else {

Log.i(TAG, "Preloading classes...");

long startTime = SystemClock.uptimeMillis();

+ long lastTime = SystemClock.uptimeMillis();

+ long nextTime = SystemClock.uptimeMillis();

// Drop root perms while running static initializers.

setEffectiveGroup(UNPRIVILEGED_GID);

@@ -292,12 +294,24 @@ public class ZygoteInit {

if (Config.LOGV) {

Log.v(TAG, "Preloading " + line + "...");

}

+ //if (count%5==0) {

+ // Log.v(TAG, "Preloading " + line + "...");

+ //}

+ Log.v(TAG, "Preloading " + line + "...");

Class.forName(line);

+ nextTime = SystemClock.uptimeMillis();

+ if (nextTime-lastTime >50) {

+ Log.i(TAG, "Preloading " + line + "... took " + (nextTime-lastTime) + "ms.");

+ }

+ lastTime = nextTime;

+

if (Debug.getGlobalAllocSize() > PRELOAD_GC_THRESHOLD) {

if (Config.LOGV) {

Log.v(TAG,

" GC at " + Debug.getGlobalAllocSize());

}

+ Log.i(TAG,

+ " GC at " + Debug.getGlobalAllocSize());

runtime.gcSoftReferences();

runtime.runFinalizationSync();

Debug.resetGlobalAllocSize();

上面+代表添加的代码，这样就可以很容易的得到在装载类的过程中具体装载了哪些类，耗费了多久。具体装载的类在文件platform/frameworks/base/
preloaded-classes

内容类似：
android.R$styleable

android.accounts.AccountMonitor

android.accounts.AccountMonitor$AccountUpdater

android.app.Activity

android.app.ActivityGroup

android.app.ActivityManager$MemoryInfo$1

android.app.ActivityManagerNative

android.app.ActivityManagerProxy

android.app.ActivityThread

android.app.ActivityThread$ActivityRecord

android.app.ActivityThread$AppBindData

android.app.ActivityThread$ApplicationThread

android.app.ActivityThread$ContextCleanupInfo

android.app.ActivityThread$GcIdler

android.app.ActivityThread$H

android.app.ActivityThread$Idler

而这个文件是由文件WritePreloadedClassFile.java中的WritePreloadedClassFile类自动生成

/**

* Writes /frameworks/base/preloaded-classes. Also updates

* {@link LoadedClass#preloaded} fields and writes over compiled log file.

*/
public
class WritePreloadedClassFile

/**

* Preload any class that take longer to load than MIN_LOAD_TIME_MICROS us.
*/

static final int MIN_LOAD_TIME_MICROS = 1250;//这个代表了装载时间小于1250us即1.25ms的类将不予装载，也许可以改这个参数减少一下类的装载

//这里可以看到什么样的类会被装载

A:启动必须装载的类，比如系统级的类

B：刚才说的装载时间大于1.25ms的类

C：被使用一次以上或被应用装载的类

仔细看看筛选类的具体实现，可以帮助我们认识哪些类比较重要，哪些可以去掉。
筛选规则是

第一 isPreloadable，

/**Reports if the given class should be preloaded. */

public static boolean isPreloadable(LoadedClass clazz) {
return clazz.systemClass && !EXCLUDED_CLASSES.contains(clazz.name);
}
意思是指除了EXCLUDED_CLASSES包含的类之外的所有系统装载的类。
EXCLUDED_CLASSES包含
/**

* Classes which we shouldn't load from the Zygote.

*/

private static final Set<String> EXCLUDED_CLASSES

= new HashSet<String>(Arrays.asList(

// Binders

"android.app.AlarmManager",

"android.app.SearchManager",

"android.os.FileObserver",

"com.android.server.PackageManagerService$AppDirObserver",
// Threads

"android.os.AsyncTask",

"android.pim.ContactsAsyncHelper",

"java.lang.ProcessManager"

));
目前是跟Binders跟Threads有关的不会被预装载。

第二 clazz.medianTimeMicros() > MIN_LOAD_TIME_MICROS装载时间大于1.25ms。

第三 names.size() > 1 ，既是被processes一次以上的。

上面的都是指的system class,另外还有一些application class需要被装载
规则是fromZygote而且不是服务

proc.fromZygote() && !Policy.isService(proc.name)

fromZygote指的除了com.android.development的zygote类
public boolean fromZygote() {

return parent != null && parent.name.equals("zygote")

&& !name.equals("com.android.development");

}

/除了常驻内存的服务

/**

* Long running services. These are restricted in their contribution to the

* preloader because their launch time is less critical.

*/

// TODO: Generate this automatically from package manager.

private static final Set<String> SERVICES = new HashSet<String>(Arrays.asList(

"system_server",

"com.google.process.content",

"android.process.media",

"com.android.bluetooth",

"com.android.calendar",

"com.android.inputmethod.latin",

"com.android.phone",

"com.google.android.apps.maps.FriendService", // pre froyo

"com.google.android.apps.maps:FriendService", // froyo

"com.google.android.apps.maps.LocationFriendService",

"com.google.android.deskclock",

"com.google.process.gapps",

"android.tts"

));

好了。要转载的就是这些类了。虽然preloaded-classes是在下载源码的时候已经确定了的，也就是对我们来说WritePreloadedClassFile类是没用到的，我们可以做的就是在preloaded-classes文件中，把不预装载的类去掉，试了把所有类去掉，启动确实很快跳过那个地方，但是启动HOME的时候就会很慢了。所以最好的方法就是只去掉那些没怎么用到的，不过要小心处理。至于该去掉哪些，还在摸索，稍后跟大家分享。有兴趣的朋友可以先把preloaded-classes这个文件里面全部清空，启动快了很多，但在启动apk的时候会慢了点。当然了，也可以把android相关的类全部去掉，剩下java的类，试过了也是可以提高速度。

三，系统服务初始化和package
扫描

在启动系统服务的init2()时会启动应用层（Java层）的所有服务。

public static void main(String[] args) {

System.loadLibrary("android_servers");

init1(args); //init1 初始化，完成之后会回调init2()

}

在init2()中会启动一个线程来启动所有服务
public static final void init2() {

Log.i(TAG, "Entered the Android system server!");

Thread thr = new ServerThread();

thr.setName("android.server.ServerThread");

thr.start();

}

class ServerThread extends Thread {
。。。
public void run() {
。。。
关键服务：
ServiceManager.addService("entropy", new EntropyService());
ServiceManager.addService(Context.POWER_SERVICE, power);
context = ActivityManagerService.main(factoryTest);
ServiceManager.addService("telephony.registry", new TelephonyRegistry(context));

PackageManagerService.main(context,

factoryTest != SystemServer.FACTORY_TEST_OFF);//apk扫描的服务
ServiceManager.addService(Context.ACCOUNT_SERVICE,

new AccountManagerService(context));
ContentService.main(context,

factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL);
battery = new BatteryService(context);

ServiceManager.addService("battery", battery);

hardware = new HardwareService(context);

ServiceManager.addService("hardware", hardware);

AlarmManagerService alarm = new AlarmManagerService(context);

ServiceManager.addService(Context.ALARM_SERVICE, alarm);

ServiceManager.addService(Context.SENSOR_SERVICE, new SensorService(context));

WindowManagerService.main(context, power,

factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL);

ServiceManager.addService(Context.WINDOW_SERVICE, wm);

上面这些都是关键服务，不建议进行裁剪。

下面的这些不是很关键，可以进行裁剪，当是必须相应的修改framework部分的代码，工作量比较大和复杂。我去掉了20个服务，大概需要相应修改大概20多个文件。

statusBar = new StatusBarService(context);

ServiceManager.addService("statusbar", statusBar);

ServiceManager.addService("clipboard", new ClipboardService(context));

imm = new InputMethodManagerService(context, statusBar);

ServiceManager.addService(Context.INPUT_METHOD_SERVICE, imm);

ServiceManager.addService("netstat", new NetStatService(context));

connectivity = ConnectivityService.getInstance(context);

ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);

ServiceManager.addService(Context.ACCESSIBILITY_SERVICE,

new AccessibilityManagerService(context));

notification = new NotificationManagerService(context, statusBar, hardware);

ServiceManager.addService(Context.NOTIFICATION_SERVICE, notification);

ServiceManager.addService("mount", new MountService(context));

ServiceManager.addService(DeviceStorageMonitorService.SERVICE,

new DeviceStorageMonitorService(context));

ServiceManager.addService(Context.LOCATION_SERVICE, new LocationManagerService(context));

ServiceManager.addService( Context.SEARCH_SERVICE, new SearchManagerService(context) );

if (INCLUDE_DEMO) {

Log.i(TAG, "Installing demo data...");

(new DemoThread(context)).start();

}

Intent intent = new Intent().setComponent(new ComponentName(

"com.google.android.server.checkin",

"com.google.android.server.checkin.CheckinService"));

ServiceManager.addService("checkin", new FallbackCheckinService(context));

wallpaper = new WallpaperManagerService(context);

ServiceManager.addService(Context.WALLPAPER_SERVICE, wallpaper);

ServiceManager.addService(Context.AUDIO_SERVICE, new AudioService(context));

headset = new HeadsetObserver(context);

dock = new DockObserver(context, power);

ServiceManager.addService(Context.BACKUP_SERVICE, new BackupManagerService(context));

ServiceManager.addService(Context.APPWIDGET_SERVICE, appWidget);

package 扫描部分，整个流程为下图所示：

最终的zip文件（apk）读取是在下面这两个函数：

/*

* Open the specified file read-only. We memory-map the entire thing and

* close the file before returning.

*/

status_t ZipFileRO::open(const char* zipFileName)

{

int fd = -1;

off_t length;
assert(mFileMap == NULL);

LOGD("opening zip '%s'\n", zipFileName);
/*

* Open and map the specified file.

*/
fd = ::open(zipFileName, O_RDONLY);

if (fd < 0) {

LOGW("Unable to open zip '%s': %s\n", zipFileName, strerror(errno));

return NAME_NOT_FOUND;

}
length = lseek(fd, 0, SEEK_END);

if (length < 0) {

close(fd);

return UNKNOWN_ERROR;

}

mFileMap = new FileMap();

if (mFileMap == NULL) {

close(fd);

return NO_MEMORY;

}

if (!mFileMap->create(zipFileName, fd, 0, length, true)) {

LOGW("Unable to map '%s': %s\n", zipFileName, strerror(errno));

close(fd);

return UNKNOWN_ERROR;

}

mFd = fd;
/*

* Got it mapped, verify it and create data structures for fast access.

*/

if (!parseZipArchive()) {

mFileMap->release();

mFileMap = NULL;

return UNKNOWN_ERROR;

}

LOGD("done opening zip\n");

return OK;

}

/*

* Parse the Zip archive, verifying its contents and initializing internal

* data structures.

*/

bool ZipFileRO::parseZipArchive(void)

{

#define CHECK_OFFSET(_off) { \

if ((unsigned int) (_off) >= maxOffset) { \

LOGE("ERROR: bad offset %u (max %d): %s\n", \

(unsigned int) (_off), maxOffset, #_off); \

goto bail; \

} \

}

const unsigned char* basePtr = (const unsigned char*)mFileMap->getDataPtr();

const unsigned char* ptr;

size_t length = mFileMap->getDataLength();

bool result = false;

unsigned int i, numEntries, cdOffset;

unsigned int val;
/*

* The first 4 bytes of the file will either be the local header

* signature for the first file (kLFHSignature) or, if the archive doesn't

* have any files in it, the end-of-central-directory signature

* (kEOCDSignature).

*/

val = get4LE(basePtr);

if (val == kEOCDSignature) {

LOGI("Found Zip archive, but it looks empty\n");

goto bail;

} else if (val != kLFHSignature) {

LOGV("Not a Zip archive (found 0x%08x)\n", val);

goto bail;

}
/*

* Find the EOCD. We'll find it immediately unless they have a file

* comment.

*/

ptr = basePtr + length - kEOCDLen;
while (ptr >= basePtr) {

if (*ptr == (kEOCDSignature & 0xff) && get4LE(ptr) == kEOCDSignature)

break;

ptr--;

}

if (ptr < basePtr) {

LOGI("Could not find end-of-central-directory in Zip\n");

goto bail;

}
/*

* There are two interesting items in the EOCD block: the number of

* entries in the file, and the file offset of the start of the

* central directory.

*

* (There's actually a count of the #of entries in this file, and for

* all files which comprise a spanned archive, but for our purposes

* we're only interested in the current file. Besides, we expect the

* two to be equivalent for our stuff.)

*/

numEntries = get2LE(ptr + kEOCDNumEntries);

cdOffset = get4LE(ptr + kEOCDFileOffset);
/* valid offsets are [0,EOCD] */

unsigned int maxOffset;

maxOffset = (ptr - basePtr) +1;
LOGV("+++ numEntries=%d cdOffset=%d\n", numEntries, cdOffset);

if (numEntries == 0 || cdOffset >= length) {

LOGW("Invalid entries=%d offset=%d (len=%zd)\n",

numEntries, cdOffset, length);

goto bail;

}
/*

* Create hash table. We have a minimum 75% load factor, possibly as

* low as 50% after we round off to a power of 2.

*/

mNumEntries = numEntries;

mHashTableSize = roundUpPower2(1 + ((numEntries * 4) / 3));

mHashTable = (HashEntry*) calloc(1, sizeof(HashEntry) * mHashTableSize);
/*

* Walk through the central directory, adding entries to the hash

* table.

*/

ptr = basePtr + cdOffset;

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

unsigned int fileNameLen, extraLen, commentLen, localHdrOffset;

const unsigned char* localHdr;

unsigned int hash;
if (get4LE(ptr) != kCDESignature) {

LOGW("Missed a central dir sig (at %d)\n", i);

goto bail;

}

if (ptr + kCDELen > basePtr + length) {

LOGW("Ran off the end (at %d)\n", i);

goto bail;

}
localHdrOffset = get4LE(ptr + kCDELocalOffset);

CHECK_OFFSET(localHdrOffset);

fileNameLen = get2LE(ptr + kCDENameLen);

extraLen = get2LE(ptr + kCDEExtraLen);

commentLen = get2LE(ptr + kCDECommentLen);
//LOGV("+++ %d: localHdr=%d fnl=%d el=%d cl=%d\n",

// i, localHdrOffset, fileNameLen, extraLen, commentLen);

//LOGV(" '%.*s'\n", fileNameLen, ptr + kCDELen);
/* add the CDE filename to the hash table */

hash = computeHash((const char*)ptr + kCDELen, fileNameLen);

addToHash((const char*)ptr + kCDELen, fileNameLen, hash);

// localHdr = basePtr + localHdrOffset;

// if (get4LE(localHdr) != kLFHSignature) {

// LOGW("Bad offset to local header: %d (at %d)\n",

// localHdrOffset, i);

// goto bail;

// }
ptr += kCDELen + fileNameLen + extraLen + commentLen;

CHECK_OFFSET(ptr - basePtr);

}
result = true;
bail:

return result;

#undef CHECK_OFFSET

}

红色部分是修改后的代码，大家可以对比一下。(未完。。。)

参考资料推荐：http://elinux.org/Improving_Android_Boot_Time

http://jollen.org/wiki/Improving_Android_Boot_Time