service組件-bindService源碼分析

因為有前面分析startService的代碼實現過程，則對於bindService的代碼分析就不用那麼詳細介紹，在介紹流程的同時更關注一些細節上的部分。

首先，bindService也是通過 ContextWrapper.bindService，再到ContextImpl的bindService，然後是bindServiceCommon，需要注意的是，傳入的ServiceConnection被轉換成IServiceConnection類型，

private boolean bindServiceCommon(Intent service, ServiceConnection conn,
                                  int flags,
                                  UserHandle user)
{
    IServiceConnection sd;
    sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
                                           mMainThread.getHandler(), flags);

    int res = ActivityManagerNative.getDefault().bindService(
                  mMainThread.getApplicationThread(), getActivityToken(),
                  service, service.resolveTypeIfNeeded(getContentResolver()),
                  sd, flags, user.getIdentifier());
}

接下去是進入AMS的bindService，再調用ActiveServices.java 的bindServiceLocked，它會把IServiceConnection實例存放到ConnectionRecord裡面，並執行bringUpServiceLocked，

int bindServiceLocked(IApplicationThread caller, IBinder token,
                      Intent service, String resolvedType,
                      IServiceConnection connection, int flags, int userId)
{

    ConnectionRecord c = new ConnectionRecord(b, activity,
            connection, flags, clientLabel, clientIntent);

    IBinder binder = connection.asBinder();

    if ((flags & Context.BIND_AUTO_CREATE) != 0) {
        s.lastActivity = SystemClock.uptimeMillis();

        if (bringUpServiceLocked(s, service.getFlags(), callerFg, false) != null) {
            return 0;
        }
    }

    if (s.app != null && b.intent.received) {
        // Service is already running, so we can immediately
        // publish the connection.
        try {
            c.conn.connected(s.name, b.intent.binder);
        } catch (Exception e) {
            Slog.w(TAG, "Failure sending service " + s.shortName
                   + " to connection " + c.conn.asBinder()
                   + " (in " + c.binding.client.processName + ")", e);
        }

        // If this is the first app connected back to this binding,
        // and the service had previously asked to be told when
        // rebound, then do so.

        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);
    }
}

根據之前的分析ServiceLocked會調用realStartServiceLocked，而realStartServiceLocked則先調用scheduleCreateService，完成service的創建和Oncreate（）的執行，然後執行requestServiceBindingsLocked，這個是bind服務相關處理，最後是sendServiceArgsLocked，這個是Start服務的處理。

private final void realStartServiceLocked(ServiceRecord r,
        ProcessRecord app, boolean execInFg) throws RemoteException {
    app.thread.scheduleCreateService(r, r.serviceInfo, mAm.compatibilityInfoForPackageLocked(r.serviceInfo.applicationInfo), app.repProcState);
    requestServiceBindingsLocked(r, execInFg);
    sendServiceArgsLocked(r, execInFg, true);
}

requestServiceBindingsLocked再調用ActivityThread的方法scheduleBindService，在ActivityThread.java 中，它發出一個BIND_SERVICE事件，被handleBindService處理，

void publishServiceLocked(ServiceRecord r, Intent intent, IBinder service)
{
    for (int conni = r.connections.size() - 1; conni >= 0; conni--) {
        ArrayList<ConnectionRecord> clist = r.connections.valueAt(conni);
        for (int i = 0; i < clist.size(); i++) {
            ConnectionRecord c = clist.get(i);
            try {
                c.conn.connected(r.name, service);
            }
            serviceDoneExecutingLocked(r, mDestroyingServices.contains(r), false);
        }
    }
}

這裡主要調用到c.conn.connected，c就是ConnectionRecord，其成員conn是一個IServiceConnection類型實例，這在前面有提到，connected則是其實現類的方法。

對於IServiceConnection，它是一個接口，位置在(frameworks\base): core/java/android/app/IServiceConnection.aidl，aidl定義如下，它只有一個接口方法connected，

oneway interface IServiceConnection {
    void connected(in ComponentName name, IBinder service);
}

其服務端的實現在LoadedApk.java，如下，InnerConnection類是在ServiceDispatcher的內部類，並在ServiceDispatcher的構造函數裡面實例化的，其方法connected也是調用的ServiceDispatcher的方法connected，

private static class InnerConnection extendsIServiceConnection.Stub
{
    final WeakReference<LoadedApk.ServiceDispatcher> mDispatcher;
    InnerConnection(LoadedApk.ServiceDispatcher sd)
    {
        mDispatcher = new WeakReference<LoadedApk.ServiceDispatcher>(sd);
    }

    public void connected(ComponentName name,
                          IBinder service) throws RemoteException {
        LoadedApk.ServiceDispatcher sd = mDispatcher.get();
        if (sd != null)
        {
            sd.connected(name, service);
        }
    }
}

ServiceDispatcher(ServiceConnection conn,
                  Context context, Handler activityThread, int flags)
{
    mIServiceConnection = new InnerConnection(this);
    mConnection = conn;
    mContext = context;

    mActivityThread = activityThread;
    mLocation = new ServiceConnectionLeaked(null);
    mLocation.fillInStackTrace();
    mFlags = flags;
}

這裡就再回到我們前面的ContextImpl裡面bindServiceCommon方法裡面，這裡進行ServiceConnection轉化為IServiceConnection時，調用了mPackageInfo.getServiceDispatcher，mPackageInfo就是一個LoadedApk實例，

/*package*/ LoadedApk mPackageInfo;

private boolean bindServiceCommon(Intent service, ServiceConnection conn,
                                  int flags,
                                  UserHandle user)
{
    IServiceConnection sd;
    sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
                                           mMainThread.getHandler(), flags);
}

所以，getServiceDispatcher會創建一個ServiceDispatcher實例，並將ServiceDispatcher實例和ServiceConnection實例形成KV對，並在ServiceDispatcher的構造函數裡將ServiceConnection實例c賦值給ServiceConnection的成員變量mConnection，

public final IServiceConnection getServiceDispatcher(ServiceConnection c,
        Context context, Handler handler, int flags)
{
    synchronized(mServices) {
        LoadedApk.ServiceDispatcher sd = null;
        ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher> map = mServices.get(
                    context);

        if (map != null) {
            sd = map.get(c);
        }

        if (sd == null) {
            sd = new ServiceDispatcher(c, context, handler, flags);

            if (map == null) {
                map = new ArrayMap<ServiceConnection, LoadedApk.ServiceDispatcher>();
                mServices.put(context, map);
            }

            map.put(c, sd);
        }
    }
}

這樣，在執行ServiceDispatcher的connected方法時，就會調用到ServiceConnection的 onServiceConnected，完成綁定ServiceConnection的觸發。

public void doConnected(ComponentName name, IBinder service)
{
    if (old != null) {
        mConnection.onServiceDisconnected(name);
    }

    // If there is a new service, it is now connected.
    if (service != null) {
        mConnection.onServiceConnected(name, service);
    }
}

至此，就執行完了bindService的主要過程。