From 0f9002d724e94d0776b5c5d2dca9f9a71934b1ef Mon Sep 17 00:00:00 2001
From: Brad Davis <bdavis@saintandreas.org>
Date: Mon, 1 May 2017 14:13:59 -0700
Subject: [PATCH] Prevent possible crash in texture buffering thread

---
 libraries/gpu-gl/src/gpu/gl/GLTexture.cpp | 10 +++++++++-
 libraries/gpu-gl/src/gpu/gl/GLTexture.h   |  4 +++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/libraries/gpu-gl/src/gpu/gl/GLTexture.cpp b/libraries/gpu-gl/src/gpu/gl/GLTexture.cpp
index 7f075a1698..e85e74ce73 100644
--- a/libraries/gpu-gl/src/gpu/gl/GLTexture.cpp
+++ b/libraries/gpu-gl/src/gpu/gl/GLTexture.cpp
@@ -150,6 +150,7 @@ GLExternalTexture::~GLExternalTexture() {
 // Variable sized textures
 using MemoryPressureState = GLVariableAllocationSupport::MemoryPressureState;
 using WorkQueue = GLVariableAllocationSupport::WorkQueue;
+using TransferJobPointer = GLVariableAllocationSupport::TransferJobPointer;
 
 std::list<TextureWeakPointer> GLVariableAllocationSupport::_memoryManagedTextures;
 MemoryPressureState GLVariableAllocationSupport::_memoryPressureState { MemoryPressureState::Idle };
@@ -159,6 +160,7 @@ WorkQueue GLVariableAllocationSupport::_transferQueue;
 WorkQueue GLVariableAllocationSupport::_promoteQueue;
 WorkQueue GLVariableAllocationSupport::_demoteQueue;
 TexturePointer GLVariableAllocationSupport::_currentTransferTexture;
+TransferJobPointer GLVariableAllocationSupport::_currentTransferJob;
 size_t GLVariableAllocationSupport::_frameTexturesCreated { 0 };
 
 #define OVERSUBSCRIBED_PRESSURE_VALUE 0.95f
@@ -553,9 +555,15 @@ void GLVariableAllocationSupport::executeNextTransfer(const TexturePointer& curr
     if (!_pendingTransfers.empty()) {
         // Keeping hold of a strong pointer during the transfer ensures that the transfer thread cannot try to access a destroyed texture
         _currentTransferTexture = currentTexture;
-        if (_pendingTransfers.front()->tryTransfer()) {
+        // Keeping hold of a strong pointer to the transfer job ensures that if the pending transfer queue is rebuilt, the transfer job
+        // doesn't leave scope, causing a crash in the buffering thread
+        _currentTransferJob = _pendingTransfers.front();
+        // transfer jobs use asynchronous buffering of the texture data because it may involve disk IO, so we execute a try here to determine if the buffering 
+        // is complete
+        if (_currentTransferJob->tryTransfer()) {
             _pendingTransfers.pop();
             _currentTransferTexture.reset();
+            _currentTransferJob.reset();
         }
     }
 }
diff --git a/libraries/gpu-gl/src/gpu/gl/GLTexture.h b/libraries/gpu-gl/src/gpu/gl/GLTexture.h
index e0b8a63a99..2603b36b21 100644
--- a/libraries/gpu-gl/src/gpu/gl/GLTexture.h
+++ b/libraries/gpu-gl/src/gpu/gl/GLTexture.h
@@ -86,7 +86,8 @@ public:
         void transfer();
     };
 
-    using TransferQueue = std::queue<std::unique_ptr<TransferJob>>;
+    using TransferJobPointer = std::shared_ptr<TransferJob>;
+    using TransferQueue = std::queue<TransferJobPointer>;
     static MemoryPressureState _memoryPressureState;
 
 public:
@@ -100,6 +101,7 @@ protected:
     static WorkQueue _promoteQueue;
     static WorkQueue _demoteQueue;
     static TexturePointer _currentTransferTexture;
+    static TransferJobPointer _currentTransferJob;
     static const uvec3 INITIAL_MIP_TRANSFER_DIMENSIONS;
     static const uvec3 MAX_TRANSFER_DIMENSIONS;
     static const size_t MAX_TRANSFER_SIZE;