path is frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

help to start the GraphicsAllocatorService, SurfaceFlinger service, SurfaceComposerAIDL service, DisplayService, etc

int main(int, char**) {
    signal(SIGPIPE, SIG_IGN);

    hardware::configureRpcThreadpool(1 /* maxThreads */, false /* callerWillJoin */);

    startGraphicsAllocatorService();

    /*
     thread pool and schedule policy related settings
    */

    // initialize before clients can connect
    flinger->init();

    // publish surface flinger
    sp<IServiceManager> sm(defaultServiceManager());
    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false,
                   IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL | IServiceManager::DUMP_FLAG_PROTO);

    // publish gui::ISurfaceComposer, the new AIDL interface
    sp<SurfaceComposerAIDL> composerAIDL = new SurfaceComposerAIDL(flinger);
    sm->addService(String16("SurfaceFlingerAIDL"), composerAIDL, false,
                   IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL | IServiceManager::DUMP_FLAG_PROTO);

    startDisplayService(); // dependency on SF getting registered above

    if (SurfaceFlinger::setSchedFifo(true) != NO_ERROR) {
        ALOGW("Couldn't set to SCHED_FIFO: %s", strerror(errno));
    }

    // run surface flinger in this thread
    flinger->run();

    return 0;
}

• ComposerServiceAIDL::getComposerService()

  /*static*/ sp<gui::ISurfaceComposer> ComposerServiceAIDL::getComposerService() {
      ComposerServiceAIDL& instance = ComposerServiceAIDL::getInstance();
      std::scoped_lock lock(instance.mMutex);
      if (instance.mComposerService == nullptr) {
          if (ComposerServiceAIDL::getInstance().connectLocked()) {
              ALOGD("ComposerServiceAIDL reconnected");
          }
      }
      return instance.mComposerService;
  }
  

• ComposerService::ComposerService()

  const String16 name("SurfaceFlinger");
  mComposerService = waitForService<ISurfaceComposer>(name);
  

• SurfaceComposerClient

  class DefaultComposerClient: public Singleton<DefaultComposerClient> {
      ...
  };
  ANDROID_SINGLETON_STATIC_INSTANCE(DefaultComposerClient);
  
  sp<SurfaceComposerClient> SurfaceComposerClient::getDefault() {
      return DefaultComposerClient::getComposerClient();
  }
  

• SurfaceComposerClient::getPhysicalDisplayIds()

  std::vector<PhysicalDisplayId> SurfaceComposerClient::getPhysicalDisplayIds() {
    std::vector<int64_t> displayIds;
    std::vector<PhysicalDisplayId> physicalDisplayIds;
    binder::Status status =
            ComposerServiceAIDL::getComposerService()->getPhysicalDisplayIds(&displayIds);
    if (status.isOk()) {
        physicalDisplayIds.reserve(displayIds.size());
        for (auto item : displayIds) {
            auto id = DisplayId::fromValue<PhysicalDisplayId>(static_cast<uint64_t>(item));
            physicalDisplayIds.push_back(*id);
        }
    }
    return physicalDisplayIds;
  }
  

• SurfaceComposerClient::getPrimaryPhysicalDisplayId/getInternalDisplayId, etc

• frameworks/base/core/jni/android_view_SurfaceControl.cpp nativeGetPhysicalDisplayIds
• frameworks/base/cmds/bootanimation/BootAnimation.cpp BootAnimation::readyToRun()/BootAnimation::parseOrientationProperty
• frameworks/native/services/automotive/display/AutomotiveDisplayProxyService.cpp AutomotiveDisplayProxyService::getDisplayIdList
• packages/services/Car/cpp/displayproxy/src/CarDisplayProxy.cpp CarDisplayProxy::getDisplayIdList