Android ActivityThread(主线程或UI线程)简介 _Activity

登山则情满于山，观海则意溢于海。这篇文章主要讲述Android ActivityThread(主线程或UI线程)简介相关的知识，希望能为你提供帮助。
1. ActivityThread功能它管理应用进程的主线程的执行(相当于普通Java程序的main入口函数)，并根据AMS的要求（通过IApplicationThread接口，AMS为Client、ActivityThread.ApplicationThread为Server）负责调度和执行activities、broadcasts和其它操作。
在Android系统中，在默认情况下，一个应用程序内的各个组件(如Activity、BroadcastReceiver、Service)都会在同一个进程(Process)里执行，且由此进程的【主线程】负责执行。
在android系统中，如果有特别指定(通过android:process)，也可以让特定组件在不同的进程中运行。无论组件在哪一个进程中运行，默认情况下，他们都由此进程的【主线程】负责执行。
【主线程】既要处理Activity组件的UI事件，又要处理Service后台服务工作，通常会忙不过来。为了解决此问题，主线程可以创建多个子线程来处理后台服务工作，而本身专心处理UI画面的事件。
【主线程】的主要责任：
? 快速处理UI事件。而且只有它才处理UI事件，其它线程还不能存取UI画面上的对象(如TextView等)，此时，主线程就叫做UI线程。基本上，Android希望UI线程能根据用户的要求做出快速响应，如果UI线程花太多时间处理后台的工作，当UI事件发生时，让用户等待时间超过5秒而未处理，Android系统就会给用户显示ANR提示信息。
只有UI线程才能执行View派生类的onDraw()函数。
? 快速处理Broadcast消息。【主线程】除了处理UI事件之外，还要处理Broadcast消息。所以在BroadcastReceiver的onReceive()函数中，不宜占用太长的时间，否则导致【主线程】无法处理其它的Broadcast消息或UI事件。如果占用时间超过10秒， Android系统就会给用户显示ANR提示信息。
注意事项：
? 尽量避免让【主线程】执行耗时的操作，让它能快速处理UI事件和Broadcast消息。
? BroadcastReceiver的子类都是无状态的，即每次启动时，才会创建其对象，然后调用它的onReceive()函数，当执行完onReceive()函数时，就立即删除此对象。由于每次调用其函数时，会重新创建一个新的对象，所以对象里的属性值，是无法让各函数所共享。
1.1 Thread与SurfaceView View组件由UI线程(主线程)所执行。如果需要迅速更新UI画面或UI画图需要较长时间，则需要使用SurfaceView。它可由后台线程(background thread)来执行，而View只能由UI(主)线程执行。SurfaceView内有高效的rendering机制，可以让后台线程快速刷新Surface的内容。
View ---> UI(主)线程
SurfaceView ---> 后台线程

2. Android应用程序主线程stack 在一个只有Activity派生类的应用程序中，它包含如下线程:

文章图片

main线程stack如下：

[java] view plain copy

文章图片

at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:118)
at android.os.Looper.loop(Looper.java:118)
at android.app.ActivityThread.main(ActivityThread.java:4424) // Java main入口函数
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)

JDWP线程stack如下：

[java] view plain copy

文章图片

at org.apache.harmony.dalvik.ddmc.DdmVmInternal.getStackTraceById(Native Method)
at android.ddm.DdmHandleThread.handleSTKL(DdmHandleThread.java:131)
at android.ddm.DdmHandleThread.handleChunk(DdmHandleThread.java:77)
at org.apache.harmony.dalvik.ddmc.DdmServer.dispatch(DdmServer.java:171)
at dalvik.system.NativeStart.run(Native Method)

3. IApplicationThread关系图

文章图片

4. ActivityThread类 ActivityThread类即代表Application主线程。
4.1 类中关键信息【Android ActivityThread(主线程或UI线程)简介】
[java] view plain copy

文章图片

/**
* This manages the execution of the main thread in an
* application process, scheduling and executing activities,
* broadcasts, and other operations on it as the activity
* manager requests.
*
* {@hide}
*/
public final class ActivityThread {
static ContextImpl mSystemContext = null;
static IPackageManager sPackageManager;
// 创建ApplicationThread实例，以接收AMS指令并执行
final ApplicationThread mAppThread = new ApplicationThread();
final Looper mLooper = Looper.myLooper();
final H mH = new H();
final HashMap< IBinder, ActivityClientRecord> mActivities
= new HashMap< IBinder, ActivityClientRecord> ();
// List of new activities (via ActivityRecord.nextIdle) that should
// be reported when next we idle.
ActivityClientRecord mNewActivities = null;
// Number of activities that are currently visible on-screen.
int mNumVisibleActivities = 0;
final HashMap< IBinder, Service> mServices
= new HashMap< IBinder, Service> ();
Application mInitialApplication;
final ArrayList< Application> mAllApplications
= new ArrayList< Application> ();
static final ThreadLocal< ActivityThread> sThreadLocal = new ThreadLocal< ActivityThread> ();
Instrumentation mInstrumentation;
static Handler sMainThreadHandler; // set once in main()
static final class ActivityClientRecord {
IBinder token;
int ident;
Intent intent;
Bundle state;
Activity activity;
Window window;
Activity parent;
String embeddedID;
Activity.NonConfigurationInstances lastNonConfigurationInstances;
boolean paused;
boolean stopped;
boolean hideForNow;
Configuration newConfig;
Configuration createdConfig;
ActivityClientRecord nextIdle;
String profileFile;
ParcelFileDescriptor profileFd;
boolean autoStopProfiler;
ActivityInfo activityInfo;
CompatibilityInfo compatInfo;
LoadedApk packageInfo; //包信息，通过调用ActivityThread.getPapckageInfo而获得
List< ResultInfo> pendingResults;
List< Intent> pendingIntents;
boolean startsNotResumed;
boolean isForward;
int pendingConfigChanges;
boolean onlyLocalRequest;
View mPendingRemoveWindow;
WindowManager mPendingRemoveWindowManager;
...
}
private class ApplicationThread extends ApplicationThreadNative {
private void updatePendingConfiguration(Configuration config) {
synchronized (mPackages) {
if (mPendingConfiguration == null ||
mPendingConfiguration.isOtherSeqNewer(config)) {
mPendingConfiguration = config;
}
}
}
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges) {
queueOrSendMessage(
finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
token,
(userLeaving ? 1 : 0),
configChanges);
}
// we use token to identify this activity without having to send the
// activity itself back to the activity manager. (matters more with ipc)
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, CompatibilityInfo compatInfo,
Bundle state, List< ResultInfo> pendingResults,
List< Intent> pendingNewIntents, boolean notResumed, boolean isForward,
String profileName, ParcelFileDescriptor profileFd, boolean autoStopProfiler) {
ActivityClientRecord r = new ActivityClientRecord();
r.token = token;
r.ident = ident;
r.intent = intent;
r.activityInfo = info;
r.compatInfo = compatInfo;
r.state = state;
r.pendingResults = pendingResults;
r.pendingIntents = pendingNewIntents;
r.startsNotResumed = notResumed;
r.isForward = isForward;
r.profileFile = profileName;
r.profileFd = profileFd;
r.autoStopProfiler = autoStopProfiler;
updatePendingConfiguration(curConfig);
queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}
...
}
private class H extends Handler {
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, "> > > handling: " + codeToString(msg.what));
switch (msg.what) {
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo, r.compatInfo);
handleLaunchActivity(r, null);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
...
}
if (DEBUG_MESSAGES) Slog.v(TAG, "< < < done: " + codeToString(msg.what));
}
...
}
public static ActivityThread currentActivityThread() {
return sThreadLocal.get();
}
public static void main(String[] args) {
SamplingProfilerIntegration.start();
// CloseGuard defaults to true and can be quite spammy. We
// disable it here, but selectively enable it later (via
// StrictMode) on debug builds, but using DropBox, not logs.
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
// Set the reporter for event logging in libcore
EventLogger.setReporter(new EventLoggingReporter());
Process.setArgV0("< pre-initialized> ");
Looper.prepareMainLooper();
// 创建ActivityThread实例
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
AsyncTask.init();
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
}