进程间通信
Binder是什么
IPC间的通信机制。
Binder.jpg
什么时候需要进程间通信
大图片加载 // 防止出现内存不够
文件下载
系统服务进程
为什么要多进程
Android进程内存使用有限制，因此需要使用开启新的进程来做一些占内存的其他工作，来保证主进程的正常运行。
进程间通信为什么使用Binder
Binder在性能和安全性之前达到了平衡
| Binder | 共享内存 | Socket | |
|---|---|---|---|
| 性能 | 拷贝一次 | 无需拷贝 | 拷贝两次 |
| 特点 | 基于S/C架构，易用性高 | 控制复杂易用性差 | 基于S/C架构，作为一款通用接口，传输效率低，开销大，速度低 |
| 安全性 | 为每个APP分配UID，同时支持实名和匿名,通过Pid来进行访问控制 | 以来上层协议，访问控制不安全 | 以来上层协议，方位接入点开放，不安全 |
Binder源码分析
客户端为什么可以获得Binder
Bindler绑定流程
首先调用Context.bindService，代码走到ContextImpl中，调用ContextImpl.bindService，接着走到ComtextImpl.bindServiceCommon
handler, UserHandle user) {
// Keep this in sync with DevicePolicyManager.bindDeviceAdminServiceAsUser.
...........
try {
...............
// 最主要还是这一句
int res = ActivityManager.getService().bindService(
mMainThread.getApplicationThread(), getActivityToken(), service,
service.resolveTypeIfNeeded(getContentResolver()),
sd, flags, getOpPackageName(), user.getIdentifier());
if (res < 0) {
throw new SecurityException(
"Not allowed to bind to service " + service);
}
return res != 0;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
// 这里实际上是调用IActivityManger.Proxy.bindService, 但是最终还是通过binder调用到ActivityManagerService.bindService, 因为ActivityManaagerService是IActivityManager.Stub的实现类
接着分析 ** ActiityManager.getService().bindService **
ActivityManager.getService().bindService(
mMainThread.getApplicationThread(), getActivityToken(), service,
service.resolveTypeIfNeeded(getContentResolver()),
IActivityManager === ***.AIDL
ActivityManager.getService() -------> IActivityManager.Stub.Proxy ---->ActivityManagerProxy
IActivityManager.Stub -----------> ActivityManagerNative -------->(ActivityManagerService)
public static IActivityManager getService() {
return IActivityManagerSingleton.get();
}
private static final Singleton IActivityManagerSingleton =
new Singleton() {
@Override
protected IActivityManager create() {
final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
// 获取对象ActivityManager.Stub.Proxy 对象
final IActivityManager am = IActivityManager.Stub.asInterface(b);
return am;
}
};
//ActivityManagerNative 实际上就是IActivityManager.Stub的实现类， 因此看ActivityManagerNative的AasInterface方法。
/**
* Cast a Binder object into an activity manager interface, generating
* a proxy if needed.
*
* @deprecated use IActivityManager.Stub.asInterface instead.
*/
static public IActivityManager asInterface(IBinder obj) {
return IActivityManager.Stub.asInterface(obj);
}
}
// 但是实际的Proxy对象是谁呢 ？ 答案就是：ActivityManagerProxy，通过IActiviytManager客户端的bindService方法，调用到IActivityManager的服务端ActivityManagerService的bindServcie方法。
public int bindService(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, IServiceConnection connection, int flags, String callingPackage,
int userId) throws TransactionTooLargeException {
enforceNotIsolatedCaller("bindService");
// Refuse possible leaked file descriptors
if (service != null && service.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
if (callingPackage == null) {
throw new IllegalArgumentException("callingPackage cannot be null");
}
synchronized(this) {
return mServices.bindServiceLocked(caller, token, service,
resolvedType, connection, flags, callingPackage, userId);
}
}
这里的mServices实际上就是# ActivityServices #类
int bindServiceLocked(IApplicationThread caller, IBinder token, Intent service,
String resolvedType, final IServiceConnection connection, int flags,
String callingPackage, final int userId) throws TransactionTooLargeException {
.........
//这里最重要的还是两个方法：1\. bringUpServiceLocked
if ((flags&Context.BIND_AUTO_CREATE) != 0) {
s.lastActivity = SystemClock.uptimeMillis();
if (bringUpServiceLocked(s, service.getFlags(), callerFg, false,
permissionsReviewRequired) != null) {
return 0;
}
}
/// 然后说就是第二个 requestServiceBindingLocked
if (b.intent.apps.size() == 1 && b.intent.doRebind) {
requestServiceBindingLocked(s, b.intent, callerFg, true);
}
} else if (!b.intent.requested) {
requestServiceBindingLocked(s, b.intent, callerFg, false);
}
getServiceMapLocked(s.userId).ensureNotStartingBackgroundLocked(s);
} finally {
Binder.restoreCallingIdentity(origId);
}
return 1;
}
A进程访问B进程
- B进程没有启动
- B进程启动，但是Service没有启动
- B进程启动，Service已经启动，但是没有被绑定，回调onBind
- B进程启动，Service已经起来，被绑定过，回调onRebind
分析bringUpServiceLocked方法
如果目标app已经启动，调用realStartServiceLocked 方法，在realStartServiceLocked中调用
- app.thread.scheduleCreateService(r,r.serviceInfo,mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo), app.repProcState);*
----------->ActivityServices.bringUpServiceLocked --------> ActivityServices.realStartServiceLocked ------> app.thread.scheduleCreateService( )[app.Thread = ActivityThread.ApplicationThread];------> ApplicationThread.scheduleCreateService()----->ApplicationThread.handleCreateService()
boolean whileRestarting, boolean permissionsReviewRequired)
throws TransactionTooLargeException {
//Slog.i(TAG, "Bring up service:");
/////////////////////
if (!isolated) {
app = mAm.getProcessRecordLocked(procName, r.appInfo.uid, false);
if (DEBUG_MU) Slog.v(TAG_MU, "bringUpServiceLocked: appInfo.uid=" + r.appInfo.uid
+ " app=" + app);
////////////////////如果app已经起来，直接调用realStartServiceLocked方法。
if (app != null && app.thread != null) {
try {
app.addPackage(r.appInfo.packageName, r.appInfo.longVersionCode, mAm.mProcessStats);
// 这里主要调用了realStartService 这个方法
realStartServiceLocked(r, app, execInFg);
return null;
} catch (TransactionTooLargeException e) {
throw e;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting service " + r.shortName, e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
}
} else {
..................
如果APP没有启动
if (app == null && !permissionsReviewRequired) {
if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
hostingType, r.name, false, isolated, false)) == null) {
String msg = "Unable to launch app "
+ r.appInfo.packageName + "/"
+ r.appInfo.uid + " for service "
+ r.intent.getIntent() + ": process is bad";
Slog.w(TAG, msg);
bringDownServiceLocked(r);
return msg;
}
if (isolated) {
r.isolatedProc = app;
}
}
............
return null;
}
A 流程 ， 如果应用进程已经启动，但是目标Service没有启动查看方法 realStartServiceLocked
ProcessRecord app, boolean execInFg) throws RemoteException {
if (app.thread == null) {
throw new RemoteException();
}
try {
if (LOG_SERVICE_START_STOP) {
String nameTerm;
int lastPeriod = r.shortName.lastIndexOf('.');
nameTerm = lastPeriod >= 0 ? r.shortName.substring(lastPeriod) : r.shortName;
EventLogTags.writeAmCreateService(
r.userId, System.identityHashCode(r), nameTerm, r.app.uid, r.app.pid);
}
synchronized (r.stats.getBatteryStats()) {
r.stats.startLaunchedLocked();
}
mAm.notifyPackageUse(r.serviceInfo.packageName,
PackageManager.NOTIFY_PACKAGE_USE_SERVICE);
app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
// 调用ProcessRecord.ApplicationThread.shceduleCreateService.
app.thread.scheduleCreateService(r, r.serviceInfo,
mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo),
app.repProcState);
r.postNotification();
created = true;
} catch (DeadObjectException e) {
Slog.w(TAG, "Application dead when creating service " + r);
mAm.appDiedLocked(app);
throw e;
} finally {
}}
ProcessRecord.ApplicationThread.shceduleCreateService
public final void scheduleCreateService(IBinder token,
ServiceInfo info, CompatibilityInfo compatInfo, int processState) {
updateProcessState(processState, false);
CreateServiceData s = new CreateServiceData();
s.token = token;
s.info = info;
s.compatInfo = compatInfo;
sendMessage(H.CREATE_SERVICE, s);
}
// 2 处理启动Service
private void handleCreateService(CreateServiceData data) {
// If we are getting ready to gc after going to the background, well
// we are back active so skip it.
unscheduleGcIdler();
LoadedApk packageInfo = getPackageInfoNoCheck(
data.info.applicationInfo, data.compatInfo);
Service service = null;
try {
// 直接使用反射
java.lang.ClassLoader cl = packageInfo.getClassLoader();
service = packageInfo.getAppFactory()
.instantiateService(cl, data.info.name, data.intent);
} catch (Exception e) {
if (!mInstrumentation.onException(service, e)) {
throw new RuntimeException(
"Unable to instantiate service " + data.info.name
+ ": " + e.toString(), e);
}
}
try {
if (localLOGV) Slog.v(TAG, "Creating service " + data.info.name);
ContextImpl context = ContextImpl.createAppContext(this, packageInfo);
context.setOuterContext(service);
// MakeApplication
Application app = packageInfo.makeApplication(false, mInstrumentation);
// 将Service和Context进行链接
service.attach(context, this, data.info.name, data.token, app,
ActivityManager.getService());
service.onCreate();
// 将服务放进
mServices.put(data.token, service);
try {
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(service, e)) {
throw new RuntimeException(
"Unable to create service " + data.info.name
+ ": " + e.toString(), e);
}
}
}
B 流程，APPProcess没有启动，Service也没有启动
调用ActivityManagerService.startProcessLocked();
private boolean startProcessLocked(String hostingType, String hostingNameStr, String entryPoint,
ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
String seInfo, String requiredAbi, String instructionSet, String invokeWith,
long startTime) {
.....
// 调用startProcess方法
final ProcessStartResult startResult = startProcess(app.hostingType, entryPoint,
app, app.startUid, gids, runtimeFlags, mountExternal, app.seInfo,
requiredAbi, instructionSet, invokeWith, app.startTime);
synchronized (ActivityManagerService.this) {
handleProcessStartedLocked(app, startResult, startSeq);
}
} catch (RuntimeException e) {
......
} else {
try {
final ProcessStartResult startResult = startProcess(hostingType, entryPoint, app,
uid, gids, runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet,
invokeWith, startTime);
handleProcessStartedLocked(app, startResult.pid, startResult.usingWrapper,
startSeq, false);
} catch (RuntimeException e) {
Slog.e(TAG, "Failure starting process " + app.processName, e);
app.pendingStart = false;
forceStopPackageLocked(app.info.packageName, UserHandle.getAppId(app.uid),
false, false, true, false, false,
UserHandle.getUserId(app.userId), "start failure");
}
return app.pid > 0;
}
}
//startProcess 方法
ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
String seInfo, String requiredAbi, String instructionSet, String invokeWith,
long startTime) {
try {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
app.processName);
checkTime(startTime, "startProcess: asking zygote to start proc");
final ProcessStartResult startResult;
if (hostingType.equals("webview_service")) {
startResult = startWebView(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, null,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});
} else {
// 使用Process。start方法
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});
}
checkTime(startTime, "startProcess: returned from zygote!");
return startResult;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}
至此， app开始进入绑定流程。
启动进入请求绑定app
boolean execInFg, boolean rebind) throws TransactionTooLargeException {
if (r.app == null || r.app.thread == null) {
// If service is not currently running, can't yet bind.
return false;
}
if (DEBUG_SERVICE) Slog.d(TAG_SERVICE, "requestBind " + i + ": requested=" + i.requested
+ " rebind=" + rebind);
if ((!i.requested || rebind) && i.apps.size() > 0) {
try {
bumpServiceExecutingLocked(r, execInFg, "bind");
r.app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_SERVICE);
// 这里调用ApplicationThread的shceduleBindService
r.app.thread.scheduleBindService(r, i.intent.getIntent(), rebind,
r.app.repProcState);
if (!rebind) {
i.requested = true;
}
i.hasBound = true;
i.doRebind = false;
} catch (TransactionTooLargeException e) {
// Keep the executeNesting count accurate.
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Crashed while binding " + r, e);
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
throw e;
} catch (RemoteException e) {
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Crashed while binding " + r);
// Keep the executeNesting count accurate.
final boolean inDestroying = mDestroyingServices.contains(r);
serviceDoneExecutingLocked(r, inDestroying, inDestroying);
return false;
}
}
return true;
}
ApplicationThread
scheduleBindService
public final void scheduleBindService(IBinder token, Intent intent,
boolean rebind, int processState) {
updateProcessState(processState, false);
BindServiceData s = new BindServiceData();
s.token = token;
s.intent = intent;
s.rebind = rebind;
if (DEBUG_SERVICE)
Slog.v(TAG, "scheduleBindService token=" + token + " intent=" + intent + " uid="
+ Binder.getCallingUid() + " pid=" + Binder.getCallingPid());
sendMessage(H.BIND_SERVICE, s);
}
----------------------------------------
handleBindService
private void handleBindService(BindServiceData data) {
Service s = mServices.get(data.token);
if (DEBUG_SERVICE)
Slog.v(TAG, "handleBindService s=" + s + " rebind=" + data.rebind);
if (s != null) {
try {
data.intent.setExtrasClassLoader(s.getClassLoader());
data.intent.prepareToEnterProcess();
try {
if (!data.rebind) {
// 调用Service.onBinde, 获取binder 并进行返回
IBinder binder = s.onBind(data.intent);
ActivityManager.getService().publishService(
data.token, data.intent, binder);
} else {
s.onRebind(data.intent);
ActivityManager.getService().serviceDoneExecuting(
data.token, SERVICE_DONE_EXECUTING_ANON, 0, 0);
}
ensureJitEnabled();
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
} catch (Exception e) {
if (!mInstrumentation.onException(s, e)) {
throw new RuntimeException(
"Unable to bind to service " + s
+ " with " + data.intent + ": " + e.toString(), e);
}
}
}
}
ActivityManagerService.publishService
// Refuse possible leaked file descriptors
if (intent != null && intent.hasFileDescriptors() == true) {
throw new IllegalArgumentException("File descriptors passed in Intent");
}
synchronized(this) {
if (!(token instanceof ServiceRecord)) {
throw new IllegalArgumentException("Invalid service token");
}
mServices.publishServiceLocked((ServiceRecord)token, intent, service);
}
}
以上代码走到ActivityServices.publishService
final long origId = Binder.clearCallingIdentity();
try {
if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "PUBLISHING " + r
+ " " + intent + ": " + service);
if (r != null) {
Intent.FilterComparison filter
= new Intent.FilterComparison(intent);
IntentBindRecord b = r.bindings.get(filter);
if (b != null && !b.received) {
b.binder = service;
b.requested = true;
b.received = true;
for (int conni=r.connections.size()-1; conni>=0; conni--) {
ArrayList clist = r.connections.valueAt(conni);
for (int i=0; i 调用c.conn.connected(r.name, service, false);
conn = IServiceConnection.proxy -----------Stub = ServiceConnection
这里就走到的ServiceConnection的onServiceConnect方法。