学步园

1.我们先来看一下IServiceManager.h

class IServiceManager : public IInterface
{
public:
    DECLARE_META_INTERFACE(ServiceManager);

    /**
     * Retrieve an existing service, blocking for a few seconds
     * if it doesn't yet exist.
     */
    virtual sp<IBinder>         getService( const String16& name) const = 0;

    /**
     * Retrieve an existing service, non-blocking.
     */
    virtual sp<IBinder>         checkService( const String16& name) const = 0;

    /**
     * Register a service.
     */
    virtual status_t            addService( const String16& name,
                                            const sp<IBinder>& service) = 0;

    /**
     * Return list of all existing services.
     */
    virtual Vector<String16>    listServices() = 0;

    enum {
        GET_SERVICE_TRANSACTION = IBinder::FIRST_CALL_TRANSACTION,
        CHECK_SERVICE_TRANSACTION,
        ADD_SERVICE_TRANSACTION,
        LIST_SERVICES_TRANSACTION,
    };
};

sp<IServiceManager> defaultServiceManager();

IServiceManager.h文件中定义了一个类IServiceManager，这个类继承了IInterface接口。

而defaultServiceManager()只是类外部的一个函数。

我们在到IServiceManager.cpp文件中看一下defaultServiceManager()函数的实现：

sp<IServiceManager> defaultServiceManager()
{
    if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
    
    {
        AutoMutex _l(gDefaultServiceManagerLock);
        if (gDefaultServiceManager == NULL) {
            gDefaultServiceManager = interface_cast<IServiceManager>(
                ProcessState::self()->getContextObject(NULL));
        }
    }
    
    return gDefaultServiceManager;
}