From 33b485767f584bef006049ed3beb792325190830 Mon Sep 17 00:00:00 2001
From: nvsickle <nvsickle@amazon.com>
Date: Tue, 20 Apr 2021 11:49:59 -0700
Subject: [PATCH] Address reviewer feedback, make FFont initialization state an
 atomic state machine

---
 .../AtomLyIntegration/AtomFont/FFont.h        |  9 +++++--
 .../AtomFont/Code/Source/FFont.cpp            | 24 ++++++++-----------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/Gems/AtomLyIntegration/AtomFont/Code/Include/AtomLyIntegration/AtomFont/FFont.h b/Gems/AtomLyIntegration/AtomFont/Code/Include/AtomLyIntegration/AtomFont/FFont.h
index 91fc0834ec..8e60cc2055 100644
--- a/Gems/AtomLyIntegration/AtomFont/Code/Include/AtomLyIntegration/AtomFont/FFont.h
+++ b/Gems/AtomLyIntegration/AtomFont/Code/Include/AtomLyIntegration/AtomFont/FFont.h
@@ -301,8 +301,13 @@ namespace AZ
         AtomFont* m_atomFont = nullptr;
 
         bool m_fontTexDirty = false;
-        bool m_fontInitialized = false;
-        AZStd::atomic_bool m_fontInitializing = false;
+        enum class InitializationState : AZ::u8
+        {
+            Uninitialized,
+            Initializing,
+            Initialized
+        };
+        AZStd::atomic<InitializationState> m_fontInitializationState = InitializationState::Uninitialized;
 
         FontEffects m_effects;
 
diff --git a/Gems/AtomLyIntegration/AtomFont/Code/Source/FFont.cpp b/Gems/AtomLyIntegration/AtomFont/Code/Source/FFont.cpp
index edbf148940..20879876e7 100644
--- a/Gems/AtomLyIntegration/AtomFont/Code/Source/FFont.cpp
+++ b/Gems/AtomLyIntegration/AtomFont/Code/Source/FFont.cpp
@@ -101,19 +101,16 @@ AZ::RPI::WindowContextSharedPtr AZ::FFont::GetDefaultWindowContext() const
 
 bool AZ::FFont::InitFont()
 {
-    if (m_fontInitialized)
+    auto initializationState = InitializationState::Uninitialized;
+    // Do an atomic transition to Initializing if we're in the Uninitialized state.
+    // Otherwise, check the current state.
+    // If we're Initialized, there's no more work to be done, return true to indicate we're good to go.
+    // If we're Initializing (on another thread), return false to let the consumer know it's not safe for us to be used yet.
+    if (!m_fontInitializationState.compare_exchange_strong(initializationState, InitializationState::Initializing))
     {
-        return true;
+        return initializationState == InitializationState::Initialized;
     }
 
-    // If we're being initialized in another thread, abort.
-    if (m_fontInitializing)
-    {
-        return false;
-    }
-
-    m_fontInitializing = true;
-
     // Create and initialize DynamicDrawContext for font draw
     AZ::RPI::Ptr<AZ::RPI::DynamicDrawContext> dynamicDraw = m_atomFont->GetOrCreateDynamicDrawForScene(GetDefaultViewportContext()->GetRenderScene().get());
 
@@ -136,8 +133,7 @@ bool AZ::FFont::InitFont()
     m_vertexCount = 0;
     m_indexCount = 0;
 
-    m_fontInitialized = true;
-    m_fontInitializing = false;
+    m_fontInitializationState = InitializationState::Initialized;
     return true;
 }
 
@@ -1522,7 +1518,7 @@ bool AZ::FFont::UpdateTexture()
 {
     using namespace AZ;
 
-    if (!m_fontInitialized || !m_fontImage)
+    if (m_fontInitializationState != InitializationState::Initialized || !m_fontImage)
     {
         return false;
     }
@@ -1590,7 +1586,7 @@ void AZ::FFont::Prepare(const char* str, bool updateTexture, const AtomFont::Gly
     const bool rerenderGlyphs = m_sizeBehavior == SizeBehavior::Rerender;
     const AtomFont::GlyphSize usedGlyphSize = rerenderGlyphs ? glyphSize : AtomFont::defaultGlyphSize;
     bool texUpdateNeeded = m_fontTexture->PreCacheString(str, nullptr, m_sizeRatio, usedGlyphSize, m_fontHintParams) == 1 || m_fontTexDirty;
-    if (m_fontInitialized && updateTexture && texUpdateNeeded && m_fontImage)
+    if (m_fontInitializationState == InitializationState::Initialized && updateTexture && texUpdateNeeded && m_fontImage)
     {
         UpdateTexture();
         m_fontTexDirty = false;