ANR 可能是大家平时开发过程中，相对比较少的一类的问题，从考核过程中就能看出来，很少有同学能够回答完善。既然我们在开发中会遇到，那么我们至少需要知道 Framework 层的原理，ANR 怎么监控？ANR 怎么分析解决？这三个维度。
ANR 大致分为这么两种：四大组件启动超时和 Input 响应超时，它们之间的底层实现原理也是有些差别的，四大组件启动超时 ANR 是一个埋炸弹拆炸弹的过程，而 Input 响应超时 ANR 是一个排雷的过程。四大组件启动超时的原理我相信大家都能看懂，但 Input 响应超时可能就未必了，因为它需要一定的 C++ 基础。
1. 四大组件启动超时 ANR
我们在 Framework 源码分析篇中详细介绍过 Service 启动流程。其中在 Service 进程 attach 到 system_server 进程的过程中会调用 realStartServiceLocked() 方法来埋下炸弹.
private final void realStartServiceLocked(ServiceRecord r, ProcessRecord app, boolean execInFg) throws RemoteException {
...
// 发送delay消息 (SERVICE_TIMEOUT_MSG)
bumpServiceExecutingLocked(r, execInFg, "create");
try {
...
// 最终创建 Service 并执行服务的 onCreate() 方法
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
} catch (DeadObjectException e) {
mAm.appDiedLocked(app);
throw e;
} finally {
...
}
}
private final void bumpServiceExecutingLocked(ServiceRecord r, boolean fg, String why) {
...
scheduleServiceTimeoutLocked(r.app);
}
void scheduleServiceTimeoutLocked(ProcessRecord proc) {
if (proc.executingServices.size() == 0 || proc.thread == null) {
return;
}
long now = SystemClock.uptimeMillis();
Message msg = mAm.mHandler.obtainMessage(
ActivityManagerService.SERVICE_TIMEOUT_MSG);
msg.obj = proc;
// 当超时后仍没有 remove 该 SERVICE_TIMEOUT_MSG 消息，则执行 service Timeout 流程
mAm.mHandler.sendMessageAtTime(msg,
proc.execServicesFg ? (now+SERVICE_TIMEOUT) : (now+ SERVICE_BACKGROUND_TIMEOUT));
}
该方法的主要工作发送 delay 消息 (SERVICE_TIMEOUT_MSG)。炸弹已埋下, 我们并不希望炸弹被引爆, 那么就需要在炸弹爆炸之前拆除炸弹。
private void handleCreateService(CreateServiceData data) {
...
// 反射创建 Service 对象
java.lang.ClassLoader cl = packageInfo.getClassLoader();
Service service = (Service) cl.loadClass(data.info.name).newInstance();
...
try {
// 创建 ContextImpl 对象
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
// 创建 Application 对象
Application app = packageInfo.makeApplication(false, mInstrumentation);
service.attach(context, this, data.info.name, data.token, app,
ActivityManagerNative.getDefault());
// 调用服务 onCreate() 方法
service.onCreate();
// 拆除炸弹引线
ActivityManagerNative.getDefault().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
} catch (Exception e) {
...
}
}
private void serviceDoneExecutingLocked(ServiceRecord r, boolean inDestroying, boolean finishing) {
...
if (r.executeNesting <= 0) {
if (r.app != null) {
r.app.execServicesFg = false;
r.app.executingServices.remove(r);
if (r.app.executingServices.size() == 0) {
//当前服务所在进程中没有正在执行的service
mAm.mHandler.removeMessages(ActivityManagerService.SERVICE_TIMEOUT_MSG, r.app);
...
}
...
}
如果整个启动过程中一切正常那么就会 removeMessages ，如果不正常则会引爆炸弹
final class MainHandler extends Handler {
public void handleMessage(Message msg) {
switch (msg.what) {
case SERVICE_TIMEOUT_MSG: {
...
mServices.serviceTimeout((ProcessRecord)msg.obj);
} break;
...
}
...
}
}
void serviceTimeout(ProcessRecord proc) {
String anrMessage = null;
synchronized(mAm) {
if (proc.executingServices.size() == 0 || proc.thread == null) {
return;
}
final long now = SystemClock.uptimeMillis();
final long maxTime = now -
(proc.execServicesFg ? SERVICE_TIMEOUT : SERVICE_BACKGROUND_TIMEOUT);
ServiceRecord timeout = null;
long nextTime = 0;
for (int i=proc.executingServices.size()-1; i>=0; i--) {
ServiceRecord sr = proc.executingServices.valueAt(i);
if (sr.executingStart < maxTime) {
timeout = sr;
break;
}
if (sr.executingStart > nextTime) {
nextTime = sr.executingStart;
}
}
if (timeout != null && mAm.mLruProcesses.contains(proc)) {
Slog.w(TAG, "Timeout executing service: " + timeout);
StringWriter sw = new StringWriter();
PrintWriter pw = new FastPrintWriter(sw, false, 1024);
pw.println(timeout);
timeout.dump(pw, " ");
pw.close();
mLastAnrDump = sw.toString();
mAm.mHandler.removeCallbacks(mLastAnrDumpClearer);
mAm.mHandler.postDelayed(mLastAnrDumpClearer, LAST_ANR_LIFETIME_DURATION_MSECS);
anrMessage = "executing service " + timeout.shortName;
}
}
if (anrMessage != null) {
// 当存在timeout的service，则执行appNotResponding
mAm.appNotResponding(proc, null, null, false, anrMessage);
}
}
2. Input 响应超时 ANR
在正式开始分析 Input 事件的 ANR 触发原理以及触发场景之前，大家需要先回顾一下 Input 事件的分发流程，这个也在 Framework 源码分析篇中。
Input ANR 时间区间便是指当前这次的事件 dispatch 过程中执行 findFocusedWindowTargetsLocked() 方法到下一次执行 resetANRTimeoutsLocked() 的时间区间。看源码有 5 个时机会 reset。都位于InputDispatcher.cpp 文件:
void InputDispatcher::dispatchOnceInnerLocked(nsecs_t* nextWakeupTime) {
// Ready to start a new event.
// If we don't already have a pending event, go grab one.
if (! mPendingEvent) {
......
// Get ready to dispatch the event.
resetANRTimeoutsLocked();
}
......
switch (mPendingEvent->type) {
case EventEntry::TYPE_MOTION: {
......
done = dispatchMotionLocked(currentTime, typedEntry,
&dropReason, nextWakeupTime);
break;
}
......
}
int32_t InputDispatcher::findFocusedWindowTargetsLocked(nsecs_t currentTime,
const EventEntry* entry, Vector<InputTarget>& inputTargets, nsecs_t* nextWakeupTime) {
int32_t injectionResult;
String8 reason;
// If there is no currently focused window and no focused application
// then drop the event.
if (mFocusedWindowHandle == NULL) {
if (mFocusedApplicationHandle != NULL) {
injectionResult = handleTargetsNotReadyLocked(currentTime, entry,
mFocusedApplicationHandle, NULL, nextWakeupTime,
"Waiting because no window has focus but there is a "
"focused application that may eventually add a window "
"when it finishes starting up.");
goto Unresponsive;
}
goto Failed;
}
......
return injectionResult;
}
int32_t InputDispatcher::handleTargetsNotReadyLocked(nsecs_t currentTime,
const EventEntry* entry,
const sp<InputApplicationHandle>& applicationHandle,
const sp<InputWindowHandle>& windowHandle,
nsecs_t* nextWakeupTime, const char* reason) {
if (applicationHandle == NULL && windowHandle == NULL) {
...
} else {
if (mInputTargetWaitCause != INPUT_TARGET_WAIT_CAUSE_APPLICATION_NOT_READY) {
if (windowHandle != NULL) {
timeout = windowHandle->getDispatchingTimeout(DEFAULT_INPUT_DISPATCHING_TIMEOUT);
} else if (applicationHandle != NULL) {
timeout = applicationHandle->getDispatchingTimeout(
DEFAULT_INPUT_DISPATCHING_TIMEOUT);
} else {
timeout = DEFAULT_INPUT_DISPATCHING_TIMEOUT;
}
mInputTargetWaitCause = INPUT_TARGET_WAIT_CAUSE_APPLICATION_NOT_READY;
mInputTargetWaitStartTime = currentTime;
// 这个就是超时时间了
mInputTargetWaitTimeoutTime = currentTime + timeout;
mInputTargetWaitTimeoutExpired = false;
mInputTargetWaitApplicationHandle.clear();
if (windowHandle != NULL) {
mInputTargetWaitApplicationHandle = windowHandle->inputApplicationHandle;
}
if (mInputTargetWaitApplicationHandle == NULL && applicationHandle != NULL) {
mInputTargetWaitApplicationHandle = applicationHandle;
}
}
}
if (mInputTargetWaitTimeoutExpired) {
return INPUT_EVENT_INJECTION_TIMED_OUT;
}
}
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视频密码: l5df
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