From 89ba94902aa09a10ad52f5f9eeb330c96e23b2ac Mon Sep 17 00:00:00 2001
From: Jason Simmons <jason-simmons@users.noreply.github.com>
Date: Wed, 25 Jun 2025 15:20:14 -0700
Subject: [PATCH] [Impeller] Make ContextVK hash values globally unique
 (#171119)

ContextVK had been using a thread-local counter to assign the value
returned by GetHash. But CommandPoolRecyclerVK was using these values as
keys in a process-wide global map.

If two engine instances using different task runner threads both created
a ContextVK, then the thread-local counter could cause both contexts to
share the same hash. So when
CommandPoolRecyclerVK::DestroyThreadLocalPools destroys the pools
associated with the first context's hash, it will also incorrectly
destroy the second context's pools.

Fixes https://github.com/flutter/flutter/issues/170141
---
 .../renderer/backend/vulkan/context_vk.cc        |  6 ++----
 .../backend/vulkan/context_vk_unittests.cc       | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk.cc b/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk.cc
index a9a42ad35a5..d75db4942bb 100644
--- a/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk.cc
+++ b/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk.cc
@@ -119,11 +119,9 @@ size_t ContextVK::ChooseThreadCountForWorkers(size_t hardware_concurrency) {
 }
 
 namespace {
-thread_local uint64_t tls_context_count = 0;
+std::atomic_uint64_t context_count = 0;
 uint64_t CalculateHash(void* ptr) {
-  // You could make a context once per nanosecond for 584 years on one thread
-  // before this overflows.
-  return ++tls_context_count;
+  return context_count.fetch_add(1);
 }
 }  // namespace
 
diff --git a/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk_unittests.cc b/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk_unittests.cc
index 3de93ec63e5..61c0d2bee16 100644
--- a/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk_unittests.cc
+++ b/engine/src/flutter/impeller/renderer/backend/vulkan/context_vk_unittests.cc
@@ -392,5 +392,21 @@ TEST(ContextVKTest, AHBSwapchainCapabilitiesCanBeMissing) {
 
 }  // namespace impeller
 
+TEST(ContextVKTest, HashIsUniqueAcrossThreads) {
+  uint64_t hash1, hash2;
+  std::thread thread1([&]() {
+    auto context = MockVulkanContextBuilder().Build();
+    hash1 = context->GetHash();
+  });
+  std::thread thread2([&]() {
+    auto context = MockVulkanContextBuilder().Build();
+    hash2 = context->GetHash();
+  });
+  thread1.join();
+  thread2.join();
+
+  EXPECT_NE(hash1, hash2);
+}
+
 }  // namespace testing
 }  // namespace impeller