android activity 管理器AMS----概述

AMS & WMS，应该是app端打交道最多的2个framwork层的service。

ActivityManagerService 是android提供给用于管理Activity运行状态的系统进程。

本系列共分3个部分，概述，ActivityStatck & Activiy Task.

AMS 主要用于管理Activity之间的交互问题。

核心问题有以下几个：

1.activity 生命周期管理

2.intent是怎么传递数据的。（可能跨进程，以及双向传递）

3.launchmode是怎么使用的。（Task的概念）

一. AMS概述

首先AMS 是一个同我们开发的service非常相似的一个service，只不过它的作用是管理activity。

所以AMS是一个进程，并且当开机以后，它就常驻在系统里面，归ServiceManager调度。

而AMS启动后，它开始有一个线程监听处理客户的需求。

一下为android5.0 的代码：

\frameworks\base\services\java\com\android\server\SystemServera.java

public ActivityManagerService(Context systemContext) {
mContext = systemContext;
mFactoryTest = FactoryTest.getMode();
mSystemThread = ActivityThread.currentActivityThread();

Slog.i(TAG, "Memory class: " + ActivityManager.staticGetMemoryClass());

mHandlerThread = new ServiceThread(TAG,
android.os.Process.THREAD_PRIORITY_FOREGROUND, false /*allowIo*/);
mHandlerThread.start();
mHandler = new MainHandler(mHandlerThread.getLooper());

mFgBroadcastQueue = new BroadcastQueue(this, mHandler,
"foreground", BROADCAST_FG_TIMEOUT, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandler,
"background", BROADCAST_BG_TIMEOUT, true);
mBroadcastQueues[0] = mFgBroadcastQueue;
mBroadcastQueues[1] = mBgBroadcastQueue;

mServices = new ActiveServices(this);
mProviderMap = new ProviderMap(this);

// TODO: Move creation of battery stats service outside of activity manager service.
File dataDir = Environment.getDataDirectory();
File systemDir = new File(dataDir, "system");
systemDir.mkdirs();
mBatteryStatsService = new BatteryStatsService(systemDir, mHandler);
mBatteryStatsService.getActiveStatistics().readLocked();
mBatteryStatsService.getActiveStatistics().writeAsyncLocked();
mOnBattery = DEBUG_POWER ? true
: mBatteryStatsService.getActiveStatistics().getIsOnBattery();
mBatteryStatsService.getActiveStatistics().setCallback(this);

mProcessStats = new ProcessStatsService(this, new File(systemDir, "procstats"));

mAppOpsService = new AppOpsService(new File(systemDir, "appops.xml"), mHandler);

mGrantFile = new AtomicFile(new File(systemDir, "urigrants.xml"));

// User 0 is the first and only user that runs at boot.
mStartedUsers.put(0, new UserStartedState(new UserHandle(0), true));
mUserLru.add(Integer.valueOf(0));
updateStartedUserArrayLocked();

GL_ES_VERSION = SystemProperties.getInt("ro.opengles.version",
ConfigurationInfo.GL_ES_VERSION_UNDEFINED);

mConfiguration.setToDefaults();
mConfiguration.setLocale(Locale.getDefault());

mConfigurationSeq = mConfiguration.seq = 1;
mProcessCpuTracker.init();

mCompatModePackages = new CompatModePackages(this, systemDir, mHandler);
mIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler);
mStackSupervisor = new ActivityStackSupervisor(this);
mTaskPersister = new TaskPersister(systemDir, mStackSupervisor);

mProcessCpuThread = new Thread("CpuTracker") {
@Override
public void run() {
while (true) {
try {
try {
synchronized(this) {
final long now = SystemClock.uptimeMillis();
long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now;
long nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now;
//Slog.i(TAG, "Cpu delay=" + nextCpuDelay
//        + ", write delay=" + nextWriteDelay);
if (nextWriteDelay < nextCpuDelay) {
nextCpuDelay = nextWriteDelay;
}
if (nextCpuDelay > 0) {
mProcessCpuMutexFree.set(true);
this.wait(nextCpuDelay);
}
}
} catch (InterruptedException e) {
}
updateCpuStatsNow();
} catch (Exception e) {
Slog.e(TAG, "Unexpected exception collecting process stats", e);
}
}
}
};

mLockToAppRequest = new LockToAppRequestDialog(mContext, this);

Watchdog.getInstance().addMonitor(this);
Watchdog.getInstance().addThread(mHandler);
}

ActivityManagerService

mStackSupervisor = new ActivityStackSupervisor(this);
mTaskPersister = new TaskPersister(systemDir, mStackSupervisor);

这两句是ActivityStack & ActivityTask设置的地方。

public void setSystemProcess()就比较简单了，它不仅注册了自己一个server， 还注册了其他的server。

ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);
ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
ServiceManager.addService("meminfo", new MemBinder(this));
ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
ServiceManager.addService("dbinfo", new DbBinder(this));
if (MONITOR_CPU_USAGE) {
ServiceManager.addService("cpuinfo", new CpuBinder(this));
}
ServiceManager.addService("permission", new PermissionController(this));

二.Activit状态管理---ActivityStack

1.ActivityState

定义了如下状态：



状态变化图。

三：startActivity

startActivity@ActivityManagerService.java

startActivityAsUser@ActivityManagerService.java

startActivityMayWait@ActivityStack.java

startActivityLocked@ActivityStack.java

sartActivityUncheckedLocked@ActivityStack.java

这5个函数先后关系，就是上面的顺序。

public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options) {
return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
resultWho, requestCode, startFlags, profilerInfo, options,
UserHandle.getCallingUserId());
}

多了一个

UserHandle.getCallingUserId()

调用者的Userid值，通过bind机制获得的。

@Override
public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {
enforceNotIsolatedCaller("startActivity");
userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
false, ALLOW_FULL_ONLY, "startActivity", null);
// TODO: Switch to user app stacks here.
return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
profilerInfo, null, null, options, false, userId, null, null);
}

enforceNotIsolatedCaller 的目的是确认当前用户是否属于被隔离的对象。



接下来是 startActivityMayWait

ActivityStackSupervisor.startActivityMayWait