問題背景
最近跟群友討論一個技術(shù)問題:
一個應(yīng)用開啟了多進(jìn)程溯祸,最終到底會創(chuàng)建幾個application對象羽嫡,執(zhí)行幾次onCreate()
方法本姥?
有的群友根據(jù)自己的想法給出了猜想
甚至有的群友直接咨詢起了ChatGPT
但至始至終都沒有一個最終的結(jié)論。于是乎杭棵,為了弄清這個問題婚惫,我決定先寫個demo測試得出結(jié)論,然后從源碼著手分析原因
Demo驗(yàn)證
首先創(chuàng)建了一個app項(xiàng)目魂爪,開啟多進(jìn)程
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools">
<application android:name=".DemoApplication" android:allowBackup="true" android:dataExtractionRules="@xml/data_extraction_rules" android:fullBackupContent="@xml/backup_rules" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/Theme.Demo0307" tools:targetApi="31">
<!--android:process 開啟多進(jìn)程并設(shè)置進(jìn)程名-->
<activity android:name=".MainActivity" android:exported="true" android:process=":remote">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
然后在DemoApplication的onCreate()
方法打印application對象的地址先舷,當(dāng)前進(jìn)程名稱
public class DemoApplication extends Application {
private static final String TAG = "jasonwan";
@Override
public void onCreate() {
super.onCreate();
Log.d(TAG, "Demo application onCreate: " + this + ", processName=" + getProcessName(this));
}
private String getProcessName(Application app) {
int myPid = Process.myPid();
ActivityManager am = (ActivityManager) app.getApplicationContext().getSystemService(Context.ACTIVITY_SERVICE); List<ActivityManager.RunningAppProcessInfo> runningAppProcesses = am.getRunningAppProcesses();
for (ActivityManager.RunningAppProcessInfo runningAppProcess : runningAppProcesses) {
if (runningAppProcess.pid == myPid) {
return runningAppProcess.processName;
}
}
return "null";
}
}
運(yùn)行,得到的日志如下
2023-03-07 11:15:27.785 19563-19563/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote
查看當(dāng)前應(yīng)用所有進(jìn)程
說明此時app只有一個進(jìn)程滓侍,且只有一個application對象蒋川,對象地址為@fb06c2d
現(xiàn)在我們將進(jìn)程增加到多個,看看情況如何
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools">
<application android:name=".DemoApplication" android:allowBackup="true" android:dataExtractionRules="@xml/data_extraction_rules" android:fullBackupContent="@xml/backup_rules" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/Theme.Demo0307" tools:targetApi="31">
<!--android:process 開啟多進(jìn)程并設(shè)置進(jìn)程名-->
<activity android:name=".MainActivity" android:exported="true" android:process=":remote">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".TwoActivity" android:process=":remote2" />
<activity android:name=".ThreeActivity" android:process=":remote3" />
<activity android:name=".FourActivity" android:process=":remote4" />
<activity android:name=".FiveActivity" android:process=":remote5" />
</application>
</manifest>
邏輯是點(diǎn)擊MainActivity啟動TwoActivity粗井,點(diǎn)擊TwoActivity啟動ThreeActivity尔破,以此類推。最后我們運(yùn)行浇衬,啟動所有Activity得到的日志如下
2023-03-07 11:25:35.433 19955-19955/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote
2023-03-07 11:25:43.795 20001-20001/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote2
2023-03-07 11:25:45.136 20046-20046/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote3
2023-03-07 11:25:45.993 20107-20107/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote4
2023-03-07 11:25:46.541 20148-20148/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote5
查看當(dāng)前應(yīng)用所有進(jìn)程
此時app有5個進(jìn)程懒构,但application對象地址均為@fb06c2d
,地址相同意味著它們是同一個對象耘擂。
那是不是就可以得出結(jié)論胆剧,無論啟動多少個進(jìn)程都只會創(chuàng)建一個application對象呢?并不能妄下此定論醉冤,我們將MainActivity的process屬性去掉再運(yùn)行秩霍,得到的日志如下
2023-03-07 11:32:10.156 20318-20318/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@5d49e29, processName=com.jason.demo0307
2023-03-07 11:32:15.143 20375-20375/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote
22023-03-07 11:32:16.477 20417-20417/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote
32023-03-07 11:32:17.582 20463-20463/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote4
2023-03-07 11:32:18.882 20506-20506/com.jason.demo0307 D/jasonwan: Demo application onCreate: com.jason.demo0307.DemoApplication@fb06c2d, processName=com.jason.demo0307:remote5
查看當(dāng)前應(yīng)用所有進(jìn)程
此時app有5個進(jìn)程,但有2個application對象蚁阳,對象地址為@5d49e29
和@fb06c2d
铃绒,且子進(jìn)程的application對象都相同。
上述所有進(jìn)程的父進(jìn)程ID為678螺捐,而此進(jìn)程正是zygote進(jìn)程
根據(jù)上面的測試結(jié)果我們目前能得出的結(jié)論:
- 結(jié)論1:單進(jìn)程只創(chuàng)建一個Application對象颠悬,執(zhí)行一次
onCreate()
方法矮燎; - 結(jié)論2:多進(jìn)程至少創(chuàng)建2個Application對象,執(zhí)行多次
onCreate()
方法赔癌,幾個進(jìn)程就執(zhí)行幾次诞外;
結(jié)論2為什么說至少創(chuàng)建2個,因?yàn)槲以诩闪薐Push的商業(yè)項(xiàng)目中測試發(fā)現(xiàn)灾票,JPush創(chuàng)建的進(jìn)程跟我自己創(chuàng)建的進(jìn)程峡谊,Application地址是不同的。
這里三個進(jìn)程刊苍,分別創(chuàng)建了三個Application對象既们,對象地址分別是@f31ba9d
,@2c586f3
班缰,@fb06c2d
源碼分析
Application 的創(chuàng)建位于 frameworks/base/core/java/android/app/ActivityThread.java 的handleBindApplication()
方法中
@UnsupportedAppUsage private void handleBindApplication(AppBindData data) {
long st_bindApp = SystemClock.uptimeMillis();
//省略部分代碼
// Note when this process has started.
//設(shè)置進(jìn)程啟動時間
Process.setStartTimes(SystemClock.elapsedRealtime(), SystemClock.uptimeMillis());
//省略部分代碼
// send up app name; do this *before* waiting for debugger
//設(shè)置進(jìn)程名稱
Process.setArgV0(data.processName);
//省略部分代碼
// Allow disk access during application and provider setup. This could
// block processing ordered
broadcasts, but later processing would
// probably end up doing the same disk access.
Application app;
final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();
final StrictMode.ThreadPolicy writesAllowedPolicy = StrictMode.getThreadPolicy();
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
//此處開始創(chuàng)建application對象贤壁,注意參數(shù)2為null
app = data.info.makeApplication(data.restrictedBackupMode, null);
//省略部分代碼
try {
if ("com.jason.demo0307".equals(app.getPackageName())){
Log.d("jasonwan", "execute app onCreate(), app=:"+app+", processName="+getProcessName(app)+", pid="+Process.myPid());
}
//執(zhí)行application的onCreate方法()
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
} finally {
// If the app targets < O-MR1, or doesn't change the thread policy
// during startup, clobber the policy to maintain behavior of b/36951662
if (data.appInfo.targetSdkVersion < Build.VERSION_CODES.O_MR1
||
StrictMode.getThreadPolicy().equals(writesAllowedPolicy)) {
StrictMode.setThreadPolicy(savedPolicy);
} }
//省略部分代碼
}
實(shí)際創(chuàng)建過程在 frameworks/base/core/java/android/app/LoadedApk.java 中的makeApplication()
方法中,LoadedApk 顧名思義就是加載好的Apk文件埠忘,里面包含Apk所有信息,像包名馒索、Application對象莹妒,app所在的目錄等,這里直接看application的創(chuàng)建過程
@UnsupportedAppUsage
public Application makeApplication(boolean forceDefaultAppClass, Instrumentation instrumentation) {
if ("com.jason.demo0307".equals(mApplicationInfo.packageName)) {
Log.d("jasonwan", "makeApplication: mApplication="+mApplication+", pid="+Process.myPid());
}
//如果已經(jīng)創(chuàng)建過了就不再創(chuàng)建
if (mApplication != null) {
return mApplication;
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "makeApplication");
Application app = null;
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
if (!mPackageName.equals("android")) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "initializeJavaContextClassLoader");
initializeJavaContextClassLoader();
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
//反射創(chuàng)建application對象
app = mActivityThread.mInstrumentation.newApplication( cl, appClass, appContext);
if("com.jason.demo0307.DemoApplication".equals(appClass)){
Log.d("jasonwan", "create application, app="+app+", processName="+mActivityThread.getProcessName()+", pid="+Process.myPid());
}
appContext.setOuterContext(app);
} catch (Exception e) {
Log.d("jasonwan", "fail to create application, "+e.getMessage());
if (!mActivityThread.mInstrumentation.onException(app, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw new RuntimeException(
"Unable to instantiate application " + appClass
+ ": " + e.toString(), e);
}
}
mActivityThread.mAllApplications.add(app);
mApplication = app;
if (instrumentation != null) {
try {
//第一次啟動創(chuàng)建時绰上,instrumentation為null旨怠,不會執(zhí)行onCreate()方法 instrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if
(!instrumentation.onException(app, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
}
// 省略部分代碼
return app;
}
為了看清application到底被創(chuàng)建了幾次,我在關(guān)鍵地方埋下了log蜈块,TAG為jasonwan的log是我自己加的鉴腻,編譯驗(yàn)證,得到如下log
啟動app百揭,進(jìn)入MainActivity
03-08 17:20:29.965 4069 4069 D jasonwan: makeApplication: mApplication=null, pid=4069
//創(chuàng)建application對象爽哎,地址為@c2f8311,當(dāng)前進(jìn)程id為4069
03-08 17:20:29.967 4069 4069 D jasonwan: create application, app=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307, pid=4069
03-08 17:20:29.988 4069 4069 D jasonwan: execute app onCreate(), app=:com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307, pid=4069
03-08 17:20:29.989 4069 4069 D jasonwan: DemoApplication=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307, pid=4069
03-08 17:20:36.614 4069 4069 D jasonwan: makeApplication: mApplication=com.jason.demo0307.DemoApplication@c2f8311, pid=4069
點(diǎn)擊MainActivity器一,跳轉(zhuǎn)到TwoActivity
03-08 17:20:39.686 4116 4116 D jasonwan: makeApplication: mApplication=null, pid=4116
//創(chuàng)建application對象课锌,地址為@c2f8311,當(dāng)前進(jìn)程id為4116
03-08 17:20:39.687 4116 4116 D jasonwan: create application, app=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote2, pid=4116
03-08 17:20:39.688 4116 4116 D jasonwan: execute app onCreate(), app=:com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote2, pid=4116
03-08 17:20:39.688 4116 4116 D jasonwan: DemoApplication=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote2, pid=4116
03-08 17:20:39.733 4116 4116 D jasonwan: makeApplication: mApplication=com.jason.demo0307.DemoApplication@c2f8311, pid=4116
點(diǎn)擊TwoActivity祈秕,跳轉(zhuǎn)到ThreeActivity
03-08 17:20:41.473 4147 4147 D jasonwan: makeApplication: mApplication=null, pid=4147
//創(chuàng)建application對象渺贤,地址為@c2f8311,當(dāng)前進(jìn)程id為4147
03-08 17:20:41.475 4147 4147 D jasonwan: create application, app=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote3, pid=4147
03-08 17:20:41.475 4147 4147 D jasonwan: execute app onCreate(), app=:com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote3, pid=4147
03-08 17:20:41.476 4147 4147 D jasonwan: DemoApplication=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote3, pid=4147
03-08 17:20:41.519 4147 4147 D jasonwan: makeApplication: mApplication=com.jason.demo0307.DemoApplication@c2f8311, pid=4147
點(diǎn)擊ThreeActivity请毛,跳轉(zhuǎn)到FourActivity
03-08 17:20:42.966 4174 4174 D jasonwan: makeApplication: mApplication=null, pid=4174
//創(chuàng)建application對象志鞍,地址為@c2f8311,當(dāng)前進(jìn)程id為4174
03-08 17:20:42.968 4174 4174 D jasonwan: create application, app=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote4, pid=4174
03-08 17:20:42.969 4174 4174 D jasonwan: execute app onCreate(), app=:com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote4, pid=4174
03-08 17:20:42.969 4174 4174 D jasonwan: DemoApplication=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote4, pid=4174
03-08 17:20:43.015 4174 4174 D jasonwan: makeApplication: mApplication=com.jason.demo0307.DemoApplication@c2f8311, pid=4174
點(diǎn)擊FourActivity方仿,跳轉(zhuǎn)到FiveActivity
03-08 17:20:44.426 4202 4202 D jasonwan: makeApplication: mApplication=null, pid=4202
//創(chuàng)建application對象固棚,地址為@c2f8311统翩,當(dāng)前進(jìn)程id為4202
03-08 17:20:44.428 4202 4202 D jasonwan: create application, app=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote5, pid=4202
03-08 17:20:44.429 4202 4202 D jasonwan: execute app onCreate(), app=:com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote5, pid=4202
03-08 17:20:44.430 4202 4202 D jasonwan: DemoApplication=com.jason.demo0307.DemoApplication@c2f8311, processName=com.jason.demo0307:remote5, pid=4202
03-08 17:20:44.473 4202 4202 D jasonwan: makeApplication: mApplication=com.jason.demo0307.DemoApplication@c2f8311, pid=4202
結(jié)果很震驚,我們在5個進(jìn)程中創(chuàng)建的application對象玻孟,地址均為@c2f8311
唆缴,也就是至始至終創(chuàng)建的都是同一個Application對象,那么上面的結(jié)論2顯然并不成立黍翎,只是測試的偶然性導(dǎo)致的面徽。
可真的是這樣子的嗎,這也太顛覆我的三觀了匣掸,為此我跟群友討論了這個問題:
不同進(jìn)程中的多個對象趟紊,內(nèi)存地址相同,是否代表這些對象都是同一個對象碰酝?
群友的想法是霎匈,java中獲取的都是虛擬內(nèi)存地址,虛擬內(nèi)存地址相同送爸,不代表是同一個對象铛嘱,必須物理內(nèi)存地址相同,才表示是同一塊內(nèi)存空間袭厂,也就意味著是同一個對象墨吓,物理內(nèi)存地址和虛擬內(nèi)存地址存在一個映射關(guān)系,同時給出了java中獲取物理內(nèi)存地址的方法Android獲取對象地址纹磺,主要是利用Unsafe這個類來操作帖烘,這個類有一個作用就是直接訪問系統(tǒng)內(nèi)存資源。因?yàn)檫@種操作是不安全的橄杨,所以被標(biāo)為了私有秘症,但我們可以通過反射去調(diào)用此API, 然后我又去請教了部門搞寄存器的大佬式矫,大佬肯定了群友的想法乡摹,于是我添加代碼,嘗試獲取對象的物理內(nèi)存地址衷佃,看看是否相同
public class DemoApplication extends Application {
public static final String TAG = "jasonwan";
@Override
public void onCreate() {
super.onCreate();
Log.d(TAG, "DemoApplication=" + this + ", address=" + addressOf(this) + ", pid=" + Process.myPid());
}
//獲取對象的真實(shí)物理地址
public static long addressOf(Object o) {
Object[] array = new Object[]{o};
long objectAddress = -1;
try {
Class cls = Class.forName("sun.misc.Unsafe");
Field field = cls.getDeclaredField("theUnsafe");
field.setAccessible(true);
Object unsafe = field.get(null);
Class unsafeCls = unsafe.getClass();
Method arrayBaseOffset = unsafeCls.getMethod("arrayBaseOffset", Object.class.getClass());
int baseOffset = (int) arrayBaseOffset.invoke(unsafe, Object[].class);
Method size = unsafeCls.getMethod("addressSize");
int addressSize = (int) size.invoke(unsafe);
switch (addressSize) {
case 4:
Method getInt = unsafeCls.getMethod("getInt", Object.class, long.class);
objectAddress = (int) getInt.invoke(unsafe, array, baseOffset);
break;
case 8:
Method getLong = unsafeCls.getMethod("getLong", Object.class, long.class);
objectAddress = (long) getLong.invoke(unsafe, array, baseOffset);
break;
default:
throw new Error("unsupported address size: " + addressSize);
}
} catch (Exception e) {
e.printStackTrace();
}
return objectAddress;
}
}
運(yùn)行后得到如下日志
2023-03-10 11:01:54.043 6535-6535/com.jason.demo0307 D/jasonwan:
DemoApplication=com.jason.demo0307.DemoApplication@930d275, address=8050489105119022792, pid=6535
2023-03-10 11:02:22.610 6579-6579/com.jason.demo0307 D/jasonwan:
DemoApplication=com.jason.demo0307.DemoApplication@331b3b9, address=8050489105119027136, pid=6579
2023-03-10 11:02:36.369 6617-6617/com.jason.demo0307 D/jasonwan:
DemoApplication=com.jason.demo0307.DemoApplication@331b3b9, address=8050489105119029912, pid=6617
2023-03-10 11:02:39.244 6654-6654/com.jason.demo0307 D/jasonwan:
DemoApplication=com.jason.demo0307.DemoApplication@331b3b9, address=8050489105119032760, pid=6654
2023-03-10 11:02:40.841 6692-6692/com.jason.demo0307 D/jasonwan:
DemoApplication=com.jason.demo0307.DemoApplication@331b3b9, address=8050489105119036016, pid=6692
2023-03-10 11:02:52.429 6729-6729/com.jason.demo0307 D/jasonwan:
DemoApplication=com.jason.demo0307.DemoApplication@331b3b9, address=8050489105119038720, pid=6729
可以看到趟卸,雖然Application的虛擬內(nèi)存地址相同,都是331b3b9
氏义,但它們的真實(shí)物理地址卻不同锄列。
至此,我們可以得出最終結(jié)論:
- 單進(jìn)程惯悠,創(chuàng)建1個application對象邻邮,執(zhí)行一次
onCreate()
方法 - 多進(jìn)程(N),創(chuàng)建N個application對象克婶,執(zhí)行N次
onCreate()
方法