1, startService
啟動一個服務至少需要在2個程序之間進行跨程序通信,
1,程序A向AMS發送一個請求
2,AMS處理之後,到程序A所啟動的服務所在的程序。
1,應用程序
用戶端apk調用startService方法調用流程圖如下,
Context的startService方法如下,
public ComponentName startService(Intent service) {
warnIfCallingFromSystemProcess();
return startServiceCommon(service, mUser);
}
startServiceCommon方法如下,
private ComponentName startServiceCommon(Intent service, UserHandle user) {
try {
validateServiceIntent(service);
service.prepareToLeaveProcess();
ComponentName cn = ActivityManagerNative.getDefault().startService(
mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
getContentResolver()), getOpPackageName(), user.getIdentifier());
if (cn != null) {
•••
}
return cn;
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
}
不用說,直接利用binder機制,跨程序調用AMS的startservice方法
2 AMS程序
在AMS服務所在的程序調用流程圖如下,
AMS的startService方法如下,
public ComponentName startService(IApplicationThread caller, Intent service,
String resolvedType, String callingPackage, int userId)
throws TransactionTooLargeException {
enforceNotIsolatedCaller("startService");
•••
synchronized(this) {
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
ComponentName res = mServices.startServiceLocked(caller, service,
resolvedType, callingPid, callingUid, callingPackage, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}
mServices是ActiveServices類型的對象,其startServiceLocked方法如下所示,
ComponentName startServiceLocked(IApplicationThread caller, Intent service, String
resolvedType, int callingPid, int callingUid, String callingPackage, int userId)
throws TransactionTooLargeException {
•••
ServiceLookupResult res =retrieveServiceLocked(service, resolvedType,
callingPackage, callingPid, callingUid, userId, true, callerFg);
if (res == null) {
return null;
}
•••
ServiceRecord r = res.record;
if (!mAm.getUserManagerLocked().exists(r.userId)) {
Slog.d(TAG, "Trying to start service with non-existent user! " + r.userId);
return null;
}
•••
return startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
}
startServiceLocked做2件事情,首先通過retrieveServiceLocked方法找到（或建立）一個ServiceRecord節點，然後才能
執行後續的啟動service的動作。
retrieveServiceLocked方法如下,
private ServiceLookupResult retrieveServiceLocked(Intent service,
String resolvedType, String callingPackage, int callingPid, int callingUid, int userId,
boolean createIfNeeded, boolean callingFromFg) {
ServiceRecord r = null;
•••
ServiceMap smap = getServiceMap(userId);
final ComponentName comp = service.getComponent();
if (comp != null) {
r = smap.mServicesByName.get(comp);
}
if (r == null) {
Intent.FilterComparison filter = new Intent.FilterComparison(service);
r = smap.mServicesByIntent.get(filter);
}
if (r == null) {
try {
ResolveInfo rInfo =
AppGlobals.getPackageManager().resolveService(
service, resolvedType,
ActivityManagerService.STOCK_PM_FLAGS, userId);
ServiceInfo sInfo =
rInfo != null ? rInfo.serviceInfo : null;
if (sInfo == null) {
Slog.w(TAG_SERVICE, "Unable to start service " + service + " U=" + userId +
": not found");
return null;
}
ComponentName name = new ComponentName(
sInfo.applicationInfo.packageName, sInfo.name);
if (userId > 0) {
if (mAm.isSingleton(sInfo.processName, sInfo.applicationInfo,
sInfo.name, sInfo.flags)
&& mAm.isValidSingletonCall(callingUid, sInfo.applicationInfo.uid)) {
userId = 0;
smap = getServiceMap(0);
}
sInfo = new ServiceInfo(sInfo);
sInfo.applicationInfo = mAm.getAppInfoForUser(sInfo.applicationInfo, userId);
}
r = smap.mServicesByName.get(name);
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);
•••
} catch (RemoteException ex) {
// pm is in same process, this will never happen.
}
}
•••
if (!mAm.mIntentFirewall.checkService(r.name, service, callingUid, callingPid,
resolvedType, r.appInfo)) {
return null;
}
return new ServiceLookupResult(r, null);
}
return null;
}
代碼較長, 在AMS内部的相關表格裡找到對應的ServiceRecord節點，如果找不到，就建立一個新節點，并插入到相應的表格中。
示意圖如下:
startServiceInnerLocked方法如下,
ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ServiceRecord r,
boolean callerFg, boolean addToStarting) throws TransactionTooLargeException {
ProcessStats.ServiceState stracker = r.getTracker();
if (stracker != null) {
stracker.setStarted(true, mAm.mProcessStats.getMemFactorLocked(), r.lastActivity);
}
r.callStart = false;
synchronized (r.stats.getBatteryStats()) {
r.stats.startRunningLocked();
}
String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false);
if (error != null) {
return new ComponentName("!!", error);
}
•••
return r.name;
}
bringUpServiceLocked方法如下,
private final String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean
execInFg, boolean whileRestarting) throws TransactionTooLargeException {
if (r.app != null && r.app.thread != null) {
sendServiceArgsLocked(r, execInFg, false);
return null;
}
•••
try {
AppGlobals.getPackageManager().setPackageStoppedState(
r.packageName, false, r.userId);
} catch (RemoteException e) {
} catch (IllegalArgumentException e) {
Slog.w(TAG, "Failed trying to unstop package "
+ r.packageName + ": " + e);
}
final boolean isolated = (r.serviceInfo.flags&ServiceInfo.FLAG_ISOLATED_PROCESS) != 0;
final String procName = r.processName;
ProcessRecord app;
if (!isolated) {
app = mAm.getProcessRecordLocked(procName, r.appInfo.uid, false);
if (app != null && app.thread != null) {
try {
app.addPackage(r.appInfo.packageName, r.appInfo.versionCode, mAm.mProcessStats);
realStartServiceLocked(r, app, execInFg);
return null;
} catch (TransactionTooLargeException e) {
throw e;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting service " + r.shortName, e);
}
}
} else {
app = r.isolatedProc;
}
// Not running -- get it started, and enqueue this service record
// to be executed when the app comes up.
if (app == null) {
if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
"service", r.name, false, isolated, false)) == null) {
•••
}
return null;
}
在啟動一個服務時,分為三種情況:
1,該服務已經啟動了,最後會直接調用其onStartCommand方法
2,該服務所在的apk已經在運作,直接啟動該服務,調用其onCreate方法
3,該服務所在的apk還未啟動,則首先啟動該apk,然後啟動該服務。