From e4526ed7236a68c6ed31bf93f28fad24910e24d6 Mon Sep 17 00:00:00 2001
From: benstevens48 <ben@nebstone.co.uk>
Date: Wed, 17 Feb 2021 19:47:30 +0000
Subject: [PATCH] add thread safety using call_once

---
 winrt/lib/images/CanvasBitmap.cpp | 5 +++--
 winrt/lib/images/CanvasImage.cpp  | 5 ++---
 winrt/lib/images/CanvasImage.h    | 1 +
 winrt/lib/images/WicAdapter.h     | 8 ++++----
 4 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/winrt/lib/images/CanvasBitmap.cpp b/winrt/lib/images/CanvasBitmap.cpp
index 38aaefa5a..c93b1586a 100644
--- a/winrt/lib/images/CanvasBitmap.cpp
+++ b/winrt/lib/images/CanvasBitmap.cpp
@@ -272,8 +272,9 @@ namespace ABI { namespace Microsoft { namespace Graphics { namespace Canvas
 
     WicBitmapSource DefaultBitmapAdapter::CreateWicBitmapSource(ICanvasDevice* device, IStream* fileStream, bool tryEnableIndexing)
     {
+        auto factory = m_wicAdapter->GetFactory();
         ComPtr<IWICBitmapDecoder> wicBitmapDecoder;
-        ThrowIfFailed(m_wicAdapter->GetFactory()->CreateDecoderFromStream(
+        ThrowIfFailed(factory->CreateDecoderFromStream(
             fileStream,
             nullptr,
             WICDecodeMetadataCacheOnDemand,
@@ -310,7 +311,7 @@ namespace ABI { namespace Microsoft { namespace Graphics { namespace Canvas
         auto transformOptions = GetTransformOptionsFromPhotoOrientation(orientation);
 
         ComPtr<IWICFormatConverter> wicFormatConverter;
-        ThrowIfFailed(m_wicAdapter->GetFactory()->CreateFormatConverter(&wicFormatConverter));
+        ThrowIfFailed(factory->CreateFormatConverter(&wicFormatConverter));
 
         auto targetPixelFormat = GUID_WICPixelFormat32bppPBGRA;
 
diff --git a/winrt/lib/images/CanvasImage.cpp b/winrt/lib/images/CanvasImage.cpp
index 88f63ac75..bef76494f 100644
--- a/winrt/lib/images/CanvasImage.cpp
+++ b/winrt/lib/images/CanvasImage.cpp
@@ -406,12 +406,11 @@ namespace ABI { namespace Microsoft { namespace Graphics { namespace Canvas
 
     ComPtr<IWICImagingFactory2> const& DefaultCanvasImageAdapter::GetFactory()
     {
-        if (!m_wicAdapter)
-        {
+        std::call_once(m_initWicAdapterFlag, [this] {
             // Hold on to the wic adapter so it doesn't keep getting destroyed
             // and recreated.
             m_wicAdapter = WicAdapter::GetInstance();
-        }
+        });
 
         return m_wicAdapter->GetFactory();
     }
diff --git a/winrt/lib/images/CanvasImage.h b/winrt/lib/images/CanvasImage.h
index 2933009ac..7e4cf9362 100644
--- a/winrt/lib/images/CanvasImage.h
+++ b/winrt/lib/images/CanvasImage.h
@@ -94,6 +94,7 @@ namespace ABI { namespace Microsoft { namespace Graphics { namespace Canvas
     class DefaultCanvasImageAdapter : public CanvasImageAdapter
     {
         std::shared_ptr<WicAdapter> m_wicAdapter;
+        std::once_flag m_initWicAdapterFlag;
         
     public:
         virtual ComPtr<IAsyncAction> RunAsync(std::function<void()>&& fn) override;
diff --git a/winrt/lib/images/WicAdapter.h b/winrt/lib/images/WicAdapter.h
index 3abc345fd..2a511ab2e 100644
--- a/winrt/lib/images/WicAdapter.h
+++ b/winrt/lib/images/WicAdapter.h
@@ -21,6 +21,7 @@ class WicAdapter : public Singleton<WicAdapter, DefaultWicAdapter>
 class DefaultWicAdapter : public WicAdapter
 {
     ComPtr<IWICImagingFactory2> m_wicFactory;
+    std::once_flag m_initFactoryFlag;
 
 public:
     DefaultWicAdapter()
@@ -29,15 +30,14 @@ class DefaultWicAdapter : public WicAdapter
 
     virtual ComPtr<IWICImagingFactory2> const& GetFactory() override
     {
-        if (!m_wicFactory)
-        {
+        std::call_once(m_initFactoryFlag, [this] {
             ThrowIfFailed(
                 CoCreateInstance(
                     CLSID_WICImagingFactory,
                     nullptr,
                     CLSCTX_INPROC_SERVER,
-                    IID_PPV_ARGS(&m_wicFactory)));        
-        }
+                    IID_PPV_ARGS(&m_wicFactory)));
+        });
 
         return m_wicFactory;
     }