framework——應用程式啟動流程

little_fat_sheep發表於2020-12-31

1 前言

2 原始碼分析

2.1 ActivityManagerInternal 初始化流程

（1）請求啟動應用程式的入口

/frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java

void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
	final WindowProcessController wpc = mService.getProcessController(r.processName, r.info.applicationInfo.uid);
	...
    //判斷應用程式是否已建立，即 IApplicationThread 是否為空
	if (wpc != null && wpc.hasThread()) {
		try {
            //啟動 Activity
			realStartActivityLocked(r, wpc, andResume, checkConfig);
			return;
		}
	}
	try {
		...
		//應用程式不存在，通知建立應用程式，mService 為 ATMS；mService.mAmInternal 為 ActivityManagerInternal 
		final Message msg = PooledLambda.obtainMessage(
				ActivityManagerInternal::startProcess, mService.mAmInternal, r.processName,
				r.info.applicationInfo, knownToBeDead, "activity", r.intent.getComponent());
		mService.mH.sendMessage(msg);
	}
	...
}

ActivityStackSupervisor 物件在 ATMS 的 initialize() 方法中建立，並將 ATMS 物件注入到 ActivityStackSupervisor 中。

PooledLambda.obtainMessage() 獲取一個 Message，併為其指定 Callback，即執行 mService.mAmInternal 物件的 ActivityManagerInternal::startProcess 函式，函式入參為 r.processName、r.info.applicationInfo 等5個引數。由此可知，ActivityManagerInternal 的 startProcess() 方法是請求啟動應用程式的起點。

ActivityManagerInternal 是抽象類，其實現類是 AMS 的內部類 LocalService。接下來將分析 ActivityManagerInternal 的建立流程和 ATMS 獲取起物件的流程。

（2）ActivityManagerInternal 的建立

/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

private void start() {
	...
	LocalServices.addService(ActivityManagerInternal.class, new LocalService());
    //呼叫 ATMS 的 onActivityManagerInternalAdded 方法進一步初始化
	mActivityTaskManager.onActivityManagerInternalAdded();
	...
}

start() 方法被 AMS.Lifecycle 的 onStart() 方法呼叫，onStart() 方法又被 SystemServiceManager 的 startService() 方法呼叫。

（3）ATMS 獲取 ActivityManagerInternal

/frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java

public void onActivityManagerInternalAdded() {
	synchronized (mGlobalLock) {
		mAmInternal = LocalServices.getService(ActivityManagerInternal.class);
		...
	}
}

（4）LocalServices

public final class LocalServices {
    ...

    private static final ArrayMap<Class<?>, Object> sLocalServiceObjects = new ArrayMap<Class<?>, Object>();

    public static <T> T getService(Class<T> type) {
        synchronized (sLocalServiceObjects) {
            return (T) sLocalServiceObjects.get(type);
        }
    }

    public static <T> void addService(Class<T> type, T service) {
        synchronized (sLocalServiceObjects) {
            ...
            sLocalServiceObjects.put(type, service);
        }
    }
	
	...
}

2.2 AMS 到 ZygoteState

（1）startProcess

/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.LocalService.java

public void startProcess(String processName, ApplicationInfo info, boolean knownToBeDead, String hostingType, ComponentName hostingName) {
	try {
		...
		synchronized (ActivityManagerService.this) {
			startProcessLocked(processName, info, knownToBeDead, 0 , new HostingRecord(hostingType, hostingName), false, false, true);
		}
	}
	...
}

（2）startProcessLocked

/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

final ProcessRecord startProcessLocked(String processName, ApplicationInfo info, boolean knownToBeDead, int intentFlags, 
			HostingRecord hostingRecord, boolean allowWhileBooting, boolean isolated, boolean keepIfLarge) {
    //mProcessList 在定義時就被初始化，即：final ProcessList mProcessList = new ProcessList()
	return mProcessList.startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingRecord, 
			allowWhileBooting, isolated, 0, keepIfLarge, null, null, null, null);
}

（3）startProcessLocked