startService.png
概述:
Ams在整個(gè)流程中充當(dāng)server端的作用, ActivityManagerNative兩次調(diào)用AMS,第一次調(diào)用創(chuàng)建service運(yùn)行的process，第二次調(diào)用創(chuàng)建具體的service
一.從主進(jìn)程調(diào)用到ActivityManagerService進(jìn)程中，完成新進(jìn)程的創(chuàng)建；
二. 從新進(jìn)程調(diào)用到ActivityManagerService進(jìn)程中，獲取要在新進(jìn)程啟動(dòng)的服務(wù)的相關(guān)信息；
三. 從ActivityManagerService進(jìn)程又回到新進(jìn)程中，最終將服務(wù)啟動(dòng)起來(lái)。
一.從contextimpl的startServiceCommon方法進(jìn)入到ActivityManangerService的startService方法.
ComponentName res = mServices.startServiceLocked(caller, service,
resolvedType, callingPid, callingUid, callingPackage, userId);
二.從AMS進(jìn)入到ActivityServices中的startServiceLocked方法
在該方法中首先確定該服務(wù)是前臺(tái)服務(wù)還是后臺(tái)服務(wù),
final boolean callerFg;
if (caller != null) {
final ProcessRecord callerApp = mAm.getRecordForAppLocked(caller);
if (callerApp == null) {
throw new SecurityException(
"Unable to find app for caller " + caller
+ " (pid=" + Binder.getCallingPid()
+ ") when starting service " + service);
}
callerFg = callerApp.setSchedGroup != Process.THREAD_GROUP_BG_NONINTERACTIVE;
} else {
callerFg = true;
}
取出一個(gè)ServiceLookupResult對(duì)象
ServiceLookupResult res =
retrieveServiceLocked(service, resolvedType,
callingPid, callingUid, userId, true, callerFg);
ServiceLookupResult對(duì)象包括一個(gè)ServiceRecord對(duì)象和一個(gè)permission字符串
private final class ServiceLookupResult {
final ServiceRecord record;
final String permission;
ServiceLookupResult(ServiceRecord _record, String _permission) {
record = _record;
permission = _permission;
}
}
三.如果ActiveServices中沒有存儲(chǔ)service的引用,會(huì)生成一個(gè)新的ServiceRecord進(jìn)行存儲(chǔ),并將service從PendingServices隊(duì)列中去除，并且重新開始這個(gè)service.
if (r == null && createIfNeeded) {
Intent.FilterComparison filter
= new Intent.FilterComparison(service.cloneFilter());
ServiceRestarter res = new ServiceRestarter();
BatteryStatsImpl.Uid.Pkg.Serv ss = null;
BatteryStatsImpl stats = mAm.mBatteryStatsService.getActiveStatistics();
synchronized (stats) {
ss = stats.getServiceStatsLocked(
sInfo.applicationInfo.uid, sInfo.packageName,
sInfo.name);
}
r = new ServiceRecord(mAm, ss, name, filter, sInfo, callingFromFg, res);
res.setService(r);
smap.mServicesByName.put(name, r);
smap.mServicesByIntent.put(filter, r);
// Make sure this component isn't in the pending list.
for (int i=mPendingServices.size()-1; i>=0; i--) {
ServiceRecord pr = mPendingServices.get(i);
if (pr.serviceInfo.applicationInfo.uid == sInfo.applicationInfo.uid
&& pr.name.equals(name)) {
mPendingServices.remove(i);
}
}
如果callerApp運(yùn)行在后臺(tái),service有可能因?yàn)楹笈_(tái)啟動(dòng)隊(duì)列已滿而暫緩啟動(dòng),但如果callerApp運(yùn)行在前臺(tái)則沒有這種情況
if (r.delayed) {
// This service is already scheduled for a delayed start; just leave
// it still waiting.
if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "Continuing to delay: " + r);
return r.name;
}
if (smap.mStartingBackground.size() >= mMaxStartingBackground) {
// Something else is starting, delay!
Slog.i(TAG_SERVICE, "Delaying start of: " + r);
smap.mDelayedStartList.add(r);
r.delayed = true;
return r.name;
}
四,進(jìn)入startServiceInnerLocked函數(shù)
如果此時(shí)
if (r.app != null && r.app.thread != null) {
sendServiceArgsLocked(r, execInFg, false);
return null;
}
ServiceRecord對(duì)象中的app和app對(duì)象中的thread均不為null,則調(diào)用bringUpServiceLocked()函數(shù),并返回null值,也就是service已經(jīng)啟動(dòng)的情況
String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false);
在bringUpServiceLocked()函數(shù)中：
1>
首先會(huì)調(diào)用
sendServiceArgsLocked函數(shù)
在這里出現(xiàn)一個(gè)StartItem的數(shù)據(jù)結(jié)構(gòu)，這個(gè)類記錄了一次service的啟動(dòng)過程的相關(guān)參數(shù)
final ArrayList<StartItem> pendingStarts = new ArrayList<StartItem>();
// start() arguments that haven't yet been delivered.
接著調(diào)用
bumpServiceExecutingLocked(r, execInFg, "start");
在這個(gè)函數(shù)中主要對(duì)處于executing狀態(tài)的service進(jìn)行判斷，看是否已經(jīng)超時(shí)，前臺(tái)service是20秒，后臺(tái)servie是200s
之后會(huì)執(zhí)行scheduleServiceArgs()函數(shù),在該函數(shù)中跳轉(zhuǎn)到handleServiceArgs函數(shù)中
handleServiceArgs((ServiceArgsData)msg.obj);
在handleServiceArgs中主要執(zhí)行了onStartCommand和onTaskRemoved兩個(gè)回調(diào)函數(shù)
res = s.onStartCommand(data.args, data.flags, data.startId);
s.onTaskRemoved(data.args);
通過binder通信回到AMS中執(zhí)行serviceDoneExecuting()函數(shù)
2>
再回到bringUpServieLocked()函數(shù)中,判斷該service是否處于正在準(zhǔn)備restart的狀態(tài)，或者service處在restart隊(duì)列就強(qiáng)制把它移除該隊(duì)列.再判斷service是否處于延遲開始狀態(tài),
if (!whileRestarting && r.restartDelay > 0) {
// If waiting for a restart, then do nothing.
return null;
}
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Bringing up " + r + " " + r.intent);
// We are now bringing the service up, so no longer in the
// restarting state.
if (mRestartingServices.remove(r)) {
r.resetRestartCounter();
clearRestartingIfNeededLocked(r);
}
// Make sure this service is no longer considered delayed, we are starting it now.
if (r.delayed) {
if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "REM FR DELAY LIST (bring up): " + r);
getServiceMap(r.userId).mDelayedStartList.remove(r);
r.delayed = false;
}
// Make sure that the user who owns this service is started. If not,
// we don't want to allow it to run.
if (mAm.mStartedUsers.get(r.userId) == null) {
String msg = "Unable to launch app "
+ r.appInfo.packageName + "/"
+ r.appInfo.uid + " for service "
+ r.intent.getIntent() + ": user " + r.userId + " is stopped";
Slog.w(TAG, msg);
bringDownServiceLocked(r);
return msg;
}
3>之后判斷該service是否要運(yùn)行在一個(gè)單獨(dú)的進(jìn)程中,如果運(yùn)行在當(dāng)前進(jìn)程并且進(jìn)程已經(jīng)啟動(dòng)，就直接調(diào)用realStartServiceLocked()方法:
realStartServiceLocked(r, app, execInFg);
如果要運(yùn)行在單獨(dú)的進(jìn)程中,會(huì)調(diào)用startProcessLocked()方法開啟一個(gè)新的進(jìn)程.
觀察startProcessLocked()方法:
如果service會(huì)運(yùn)行在當(dāng)前進(jìn)程中，就會(huì)調(diào)用getProcessLocked()方法得到一個(gè)ProcessRecord對(duì)象。
下面代碼中有一段邏輯,如果啟動(dòng)service的intent由后臺(tái)發(fā)出，那么一旦判斷目前的進(jìn)程時(shí)bad進(jìn)程就會(huì)直接返回一個(gè)null值.
badProcess是指在一段時(shí)間內(nèi)發(fā)生兩次以上crash的進(jìn)程,AMS中有一個(gè)隊(duì)列來(lái)存儲(chǔ)這些bad進(jìn)程,而一旦該進(jìn)程被restart了，那么它就會(huì)從bad隊(duì)列中去除掉.
if (!isolated) {
app = getProcessRecordLocked(processName, info.uid, keepIfLarge);
checkTime(startTime, "startProcess: after getProcessRecord");
if ((intentFlags & Intent.FLAG_FROM_BACKGROUND) != 0) {
// If we are in the background, then check to see if this process
// is bad. If so, we will just silently fail.
if (mBadProcesses.get(info.processName, info.uid) != null) {
if (DEBUG_PROCESSES) Slog.v(TAG, "Bad process: " + info.uid
+ "/" + info.processName);
return null;
}
} else {
// When the user is explicitly starting a process, then clear its
// crash count so that we won't make it bad until they see at
// least one crash dialog again, and make the process good again
// if it had been bad.
if (DEBUG_PROCESSES) Slog.v(TAG, "Clearing bad process: " + info.uid
+ "/" + info.processName);
mProcessCrashTimes.remove(info.processName, info.uid);
if (mBadProcesses.get(info.processName, info.uid) != null) {
EventLog.writeEvent(EventLogTags.AM_PROC_GOOD,
UserHandle.getUserId(info.uid), info.uid,
info.processName);
mBadProcesses.remove(info.processName, info.uid);
if (app != null) {
app.bad = false;
}
}
}
} else {
// If this is an isolated process, it can't re-use an existing process.
app = null;
}
最終進(jìn)入到startProcessLocked()方法調(diào)用Process.start()方法開啟一個(gè)新的進(jìn)程.
checkTime(startTime, "startProcess: asking zygote to start proc");
Process.ProcessStartResult startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
app.info.dataDir, entryPointArgs);
/ We don't have to do anything more if:
// (1) There is an existing application record; and
// (2) The caller doesn't think it is dead, OR there is no thread
// object attached to it so we know it couldn't have crashed; and
// (3) There is a pid assigned to it, so it is either starting or
// already running.
創(chuàng)建新新進(jìn)程后，會(huì)把service加入到等待啟動(dòng)的隊(duì)列中
if (!mPendingServices.contains(r)) {
mPendingServices.add(r);
}
當(dāng)新進(jìn)程啟動(dòng)后，會(huì)調(diào)用attachApplicationLocked方法調(diào)用ActiveService中的realStartService()方法啟動(dòng)該service,在方法內(nèi)部繼續(xù)調(diào)用ActivityThread的scheduleCreateService方法.
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
