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接前一篇文章：Chromium源码由浅入深（三）

上回书结尾提到content/browser/gpu/gpu_internals_ui.cc的OnGpuInfoUpdate函数，本回对于这个函数的上下文进行深入分析。为了便于理解，再次贴出源码，如下：

void GpuMessageHandler::OnGpuInfoUpdate() {// Get GPU Info.const gpu::GPUInfo gpu_info = GpuDataManagerImpl::GetInstance()->GetGPUInfo();const gfx::GpuExtraInfo gpu_extra_info =GpuDataManagerImpl::GetInstance()->GetGpuExtraInfo();base::Value::Dict gpu_info_val = GetGpuInfo();// Add in blocklisting featuresbase::Value::Dict feature_status;feature_status.Set("featureStatus", GetFeatureStatus());feature_status.Set("problems", GetProblems());base::Value::List workarounds;for (const auto& workaround : GetDriverBugWorkarounds())workarounds.Append(workaround);feature_status.Set("workarounds", std::move(workarounds));gpu_info_val.Set("featureStatus", std::move(feature_status));if (!GpuDataManagerImpl::GetInstance()->IsGpuProcessUsingHardwareGpu()) {const gpu::GPUInfo gpu_info_for_hardware_gpu =GpuDataManagerImpl::GetInstance()->GetGPUInfoForHardwareGpu();if (gpu_info_for_hardware_gpu.IsInitialized()) {base::Value::Dict feature_status_for_hardware_gpu;feature_status_for_hardware_gpu.Set("featureStatus",GetFeatureStatusForHardwareGpu());feature_status_for_hardware_gpu.Set("problems",GetProblemsForHardwareGpu());base::Value::List workarounds_for_hardware_gpu;for (const auto& workaround : GetDriverBugWorkaroundsForHardwareGpu())workarounds_for_hardware_gpu.Append(workaround);feature_status_for_hardware_gpu.Set("workarounds", std::move(workarounds_for_hardware_gpu));gpu_info_val.Set("featureStatusForHardwareGpu",std::move(feature_status_for_hardware_gpu));const gpu::GpuFeatureInfo gpu_feature_info_for_hardware_gpu =GpuDataManagerImpl::GetInstance()->GetGpuFeatureInfoForHardwareGpu();base::Value::List gpu_info_for_hardware_gpu_val = GetBasicGpuInfo(gpu_info_for_hardware_gpu, gpu_feature_info_for_hardware_gpu,gfx::GpuExtraInfo{});gpu_info_val.Set("basicInfoForHardwareGpu",std::move(gpu_info_for_hardware_gpu_val));}}gpu_info_val.Set("compositorInfo", CompositorInfo());gpu_info_val.Set("gpuMemoryBufferInfo", GpuMemoryBufferInfo(gpu_extra_info));gpu_info_val.Set("displayInfo", GetDisplayInfo());gpu_info_val.Set("videoAcceleratorsInfo", GetVideoAcceleratorsInfo());gpu_info_val.Set("ANGLEFeatures", GetANGLEFeatures());gpu_info_val.Set("devicePerfInfo", GetDevicePerfInfo());gpu_info_val.Set("dawnInfo", GetDawnInfo());// Send GPU Info to javascript.web_ui()->CallJavascriptFunctionUnsafe("browserBridge.onGpuInfoUpdate",std::move(gpu_info_val));
}

重点关注以下代码片段：

 // Get GPU Info.const gpu::GPUInfo gpu_info = GpuDataManagerImpl::GetInstance()->GetGPUInfo();const gfx::GpuExtraInfo gpu_extra_info =GpuDataManagerImpl::GetInstance()->GetGpuExtraInfo();base::Value::Dict gpu_info_val = GetGpuInfo();

先来分析第一句：

const gpu::GPUInfo gpu_info = GpuDataManagerImpl::GetInstance()->GetGPUInfo();

对应的函数在content/browser/gpu/gpu_data_manager_impl.cc中，代码如下：

gpu::GPUInfo GpuDataManagerImpl::GetGPUInfo() {base::AutoLock auto_lock(lock_);return private_->GetGPUInfo();
}

可见，该函数只是加了锁，实际的工作则是交给了private_->GetGPUInfo()。

private_是GpuDataManagerImpl类中的成员变量，其定义在content/browser/gpu/gpu_data_manager_impl.h中，如下：

 std::unique_ptr<GpuDataManagerImplPrivate> private_ GUARDED_BY(lock_)

也就是说private_->GetGPUInfo()实际调用的是GpuDataManagerImplPrivate类中的函数，在content/browser/gpu/gpu_data_manager_impl_private.h中，代码如下：

gpu::GPUInfo GpuDataManagerImplPrivate::GetGPUInfo() const {return gpu_info_;
}

这里只是得到gpu_info_的值，那么它是在哪里被设置（改变）的？

gpu_info_是GpuDataManagerImplPrivate类的成员变量，也是在content/browser/gpu/gpu_data_manager_impl_private.h中定义，如下：

  gpu::GPUInfo gpu_info_;

而对于gpu_info_的赋值则是在content/browser/gpu/gpu_data_manager_impl_private.cc的oid GpuDataManagerImplPrivate::UpdateGpuInfo函数（准确地说应该叫方法）中，代码如下：

void GpuDataManagerImplPrivate::UpdateGpuInfo(const gpu::GPUInfo& gpu_info,const absl::optional<gpu::GPUInfo>& gpu_info_for_hardware_gpu) {
#if BUILDFLAG(IS_WIN)// If GPU process crashes and launches again, GPUInfo will be sent back from// the new GPU process again, and may overwrite the DX12, Vulkan, DxDiagNode// info we already collected. This is to make sure it doesn't happen.gpu::DxDiagNode dx_diagnostics = gpu_info_.dx_diagnostics;uint32_t d3d12_feature_level = gpu_info_.d3d12_feature_level;uint32_t vulkan_version = gpu_info_.vulkan_version;
#endifgpu_info_ = gpu_info;base::UmaHistogramCustomMicrosecondsTimes("GPU.GPUInitializationTime.V3", gpu_info_.initialization_time,base::Milliseconds(5), base::Seconds(5), 50);UMA_HISTOGRAM_EXACT_LINEAR("GPU.GpuCount", gpu_info_.GpuCount(), 10);RecordDiscreteGpuHistograms(gpu_info_);
#if BUILDFLAG(IS_WIN)if (!dx_diagnostics.IsEmpty()) {gpu_info_.dx_diagnostics = dx_diagnostics;}if (d3d12_feature_level != 0) {gpu_info_.d3d12_feature_level = d3d12_feature_level;}if (vulkan_version != 0) {gpu_info_.vulkan_version = vulkan_version;}
#endif  // BUILDFLAG(IS_WIN)bool needs_to_update_gpu_info_for_hardware_gpu =!gpu_info_for_hardware_gpu_.IsInitialized();if (!needs_to_update_gpu_info_for_hardware_gpu &&!gpu_info_.UsesSwiftShader()) {// On multi-GPU system, when switching to a different GPU, we want to reset// GPUInfo for hardware GPU, because we want to know on which GPU Chrome// crashes multiple times and falls back to SwiftShader.const gpu::GPUInfo::GPUDevice& active_gpu = gpu_info_.active_gpu();const gpu::GPUInfo::GPUDevice& cached_active_gpu =gpu_info_for_hardware_gpu_.active_gpu();
#if BUILDFLAG(IS_WIN)if (active_gpu.luid.HighPart != cached_active_gpu.luid.HighPart &&active_gpu.luid.LowPart != cached_active_gpu.luid.LowPart) {needs_to_update_gpu_info_for_hardware_gpu = true;}
#elseif (active_gpu.vendor_id != cached_active_gpu.vendor_id ||active_gpu.device_id != cached_active_gpu.device_id) {needs_to_update_gpu_info_for_hardware_gpu = true;}
#endif  // BUILDFLAG(IS_WIN)}if (needs_to_update_gpu_info_for_hardware_gpu) {if (gpu_info_for_hardware_gpu.has_value()) {DCHECK(gpu_info_for_hardware_gpu->IsInitialized());bool valid_info = true;if (gpu_info_for_hardware_gpu->UsesSwiftShader()) {valid_info = false;} else if (gpu_info_for_hardware_gpu->gl_renderer.empty() &&gpu_info_for_hardware_gpu->active_gpu().vendor_id == 0u) {valid_info = false;}if (valid_info)gpu_info_for_hardware_gpu_ = gpu_info_for_hardware_gpu.value();} else {if (!gpu_info_.UsesSwiftShader())gpu_info_for_hardware_gpu_ = gpu_info_;}}GetContentClient()->SetGpuInfo(gpu_info_);NotifyGpuInfoUpdate();
}

那么又是在哪里调用的GpuDataManagerImplPrivate::UpdateGpuInfo()？

在Chromium源码中搜索，共有几处，而真正匹配的只有一处，在content/browser/gpu/gpu_data_manager_impl.cc中，代码如下：

void GpuDataManagerImpl::UpdateGpuInfo(const gpu::GPUInfo& gpu_info,const absl::optional<gpu::GPUInfo>& gpu_info_for_hardware_gpu) {base::AutoLock auto_lock(lock_);private_->UpdateGpuInfo(gpu_info, gpu_info_for_hardware_gpu);
}

这就又回到了GpuDataManagerImpl类中。那么又是在哪里调用的GpuDataManagerImpl::UpdateGpuInfo()？

经过搜索定位，是在content/browser/gpu/gpu_process_host.cc中。但一共有两处都调用了这个函数。

• 第一处 GpuProcessHost::DidInitialize()中调用

代码如下：

void GpuProcessHost::DidInitialize(const gpu::GPUInfo& gpu_info,const gpu::GpuFeatureInfo& gpu_feature_info,const absl::optional<gpu::GPUInfo>& gpu_info_for_hardware_gpu,const absl::optional<gpu::GpuFeatureInfo>&gpu_feature_info_for_hardware_gpu,const gfx::GpuExtraInfo& gpu_extra_info) {if (GetGpuCrashCount() > 0) {LOG(WARNING) << "Reinitialized the GPU process after a crash. The reported ""initialization time was "<< gpu_info.initialization_time.InMilliseconds() << " ms";}if (kind_ != GPU_PROCESS_KIND_INFO_COLLECTION) {auto* gpu_data_manager = GpuDataManagerImpl::GetInstance();// Update GpuFeatureInfo first, because UpdateGpuInfo() will notify all// listeners.gpu_data_manager->UpdateGpuFeatureInfo(gpu_feature_info,gpu_feature_info_for_hardware_gpu);gpu_data_manager->UpdateGpuInfo(gpu_info, gpu_info_for_hardware_gpu);gpu_data_manager->UpdateGpuExtraInfo(gpu_extra_info);}#if BUILDFLAG(IS_ANDROID)// Android may kill the GPU process to free memory, especially when the app// is the background, so Android cannot have a hard limit on GPU starts.// Reset crash count on Android when context creation succeeds, but only if no// fallback option is available.if (!GpuDataManagerImpl::GetInstance()->CanFallback())recent_crash_count_ = 0;
#endif
}

• 第二处 GpuProcessHost::DidUpdateGPUInfo()中调用

代码如下：

void GpuProcessHost::DidUpdateGPUInfo(const gpu::GPUInfo& gpu_info) {GpuDataManagerImpl::GetInstance()->UpdateGpuInfo(gpu_info, absl::nullopt);
}

分别对以上两个函数（方法）进行搜索，搜索其被调用的地方，最终定位到实际上是在同一文件中，代码还挨着。是在components/viz/service/gl/gpu_service_impl.cc中，代码如下：

void GpuServiceImpl::UpdateGPUInfoGL() {DCHECK(main_runner_->BelongsToCurrentThread());gpu::CollectGraphicsInfoGL(&gpu_info_, GetContextState()->display());gpu_host_->DidUpdateGPUInfo(gpu_info_);
}void GpuServiceImpl::InitializeWithHost(mojo::PendingRemote<mojom::GpuHost> pending_gpu_host,gpu::GpuProcessActivityFlags activity_flags,scoped_refptr<gl::GLSurface> default_offscreen_surface,gpu::SyncPointManager* sync_point_manager,gpu::SharedImageManager* shared_image_manager,gpu::Scheduler* scheduler,base::WaitableEvent* shutdown_event) {DCHECK(main_runner_->BelongsToCurrentThread());mojo::Remote<mojom::GpuHost> gpu_host(std::move(pending_gpu_host));gpu_host->DidInitialize(gpu_info_, gpu_feature_info_,gpu_info_for_hardware_gpu_,gpu_feature_info_for_hardware_gpu_, gpu_extra_info_);gpu_host_ = mojo::SharedRemote<mojom::GpuHost>(gpu_host.Unbind(), io_runner_);if (!in_host_process()) {// The global callback is reset from the dtor. So Unretained() here is safe.// Note that the callback can be called from any thread. Consequently, the// callback cannot use a WeakPtr.GetLogMessageManager()->InstallPostInitializeLogHandler(base::BindRepeating(&GpuServiceImpl::RecordLogMessage, base::Unretained(this)));}if (!sync_point_manager) {owned_sync_point_manager_ = std::make_unique<gpu::SyncPointManager>();sync_point_manager = owned_sync_point_manager_.get();}if (!shared_image_manager) {// When using real buffers for testing overlay configurations, we need// access to SharedImageManager on the viz thread to obtain the buffer// corresponding to a mailbox.const bool display_context_on_another_thread =features::IsDrDcEnabled() && !gpu_driver_bug_workarounds_.disable_drdc;bool thread_safe_manager = display_context_on_another_thread;// Raw draw needs to access shared image backing on the compositor thread.thread_safe_manager |= features::IsUsingRawDraw();
#if BUILDFLAG(IS_OZONE)thread_safe_manager |= features::ShouldUseRealBuffersForPageFlipTest();
#endifowned_shared_image_manager_ = std::make_unique<gpu::SharedImageManager>(thread_safe_manager, display_context_on_another_thread);shared_image_manager = owned_shared_image_manager_.get();
#if BUILDFLAG(IS_OZONE)} else {// With this feature enabled, we don't expect to receive an external// SharedImageManager.DCHECK(!features::ShouldUseRealBuffersForPageFlipTest());
#endif}shutdown_event_ = shutdown_event;if (!shutdown_event_) {owned_shutdown_event_ = std::make_unique<base::WaitableEvent>(base::WaitableEvent::ResetPolicy::MANUAL,base::WaitableEvent::InitialState::NOT_SIGNALED);shutdown_event_ = owned_shutdown_event_.get();}if (scheduler) {scheduler_ = scheduler;} else {owned_scheduler_ =std::make_unique<gpu::Scheduler>(sync_point_manager, gpu_preferences_);scheduler_ = owned_scheduler_.get();}// Defer creation of the render thread. This is to prevent it from handling// IPC messages before the sandbox has been enabled and all other necessary// initialization has succeeded.gpu_channel_manager_ = std::make_unique<gpu::GpuChannelManager>(gpu_preferences_, this, watchdog_thread_.get(), main_runner_, io_runner_,scheduler_, sync_point_manager, shared_image_manager,gpu_memory_buffer_factory_.get(), gpu_feature_info_,std::move(activity_flags), std::move(default_offscreen_surface),image_decode_accelerator_worker_.get(), vulkan_context_provider(),metal_context_provider_.get(), dawn_context_provider());media_gpu_channel_manager_ = std::make_unique<media::MediaGpuChannelManager>(gpu_channel_manager_.get());// Create and Initialize compositor gpu thread.compositor_gpu_thread_ = CompositorGpuThread::Create(gpu_channel_manager_.get(),
#if BUILDFLAG(ENABLE_VULKAN)vulkan_implementation_,vulkan_context_provider_ ? vulkan_context_provider_->GetDeviceQueue(): nullptr,
#elsenullptr, nullptr,
#endifgpu_channel_manager_->default_offscreen_surface()? gpu_channel_manager_->default_offscreen_surface()->GetGLDisplay(): nullptr,!!watchdog_thread_);
}

欲知后事如何，且看下回分解。