From 6e278bf21683329448e58019c8262fba06c6d985 Mon Sep 17 00:00:00 2001
From: gaaclarke <30870216+gaaclarke@users.noreply.github.com>
Date: Mon, 2 Dec 2024 09:41:25 -0800
Subject: [PATCH] switched reactor to absl::flat_hash_map
 (flutter/engine#56845)

We don't need consistent pointers anymore since we are avoiding deleting
objects to minimize time in the writer lock

related pr with benchmarks: https://github.com/flutter/engine/pull/56844

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making or feature I am
adding, or the PR is [test-exempt]. See [testing the engine] for
instructions on writing and running engine tests.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I signed the [CLA].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#overview
[Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene
[test-exempt]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[C++, Objective-C, Java style guides]:
https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style
[testing the engine]:
https://github.com/flutter/flutter/wiki/Testing-the-engine
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#handling-breaking-changes
[Discord]: https://github.com/flutter/flutter/wiki/Chat
---
 .../flutter/impeller/renderer/backend/gles/BUILD.gn   |  1 +
 .../impeller/renderer/backend/gles/reactor_gles.h     | 11 +++++------
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/engine/src/flutter/impeller/renderer/backend/gles/BUILD.gn b/engine/src/flutter/impeller/renderer/backend/gles/BUILD.gn
index bede7318a3..f0b53263a4 100644
--- a/engine/src/flutter/impeller/renderer/backend/gles/BUILD.gn
+++ b/engine/src/flutter/impeller/renderer/backend/gles/BUILD.gn
@@ -104,5 +104,6 @@ impeller_component("gles") {
     "../../:renderer",
     "../../../shader_archive",
     "//flutter/fml",
+    "//flutter/third_party/abseil-cpp/absl/container:flat_hash_map",
   ]
 }
diff --git a/engine/src/flutter/impeller/renderer/backend/gles/reactor_gles.h b/engine/src/flutter/impeller/renderer/backend/gles/reactor_gles.h
index 881e2a9086..09dc092097 100644
--- a/engine/src/flutter/impeller/renderer/backend/gles/reactor_gles.h
+++ b/engine/src/flutter/impeller/renderer/backend/gles/reactor_gles.h
@@ -9,6 +9,7 @@
 #include <memory>
 #include <vector>
 
+#include "flutter/third_party/abseil-cpp/absl/container/flat_hash_map.h"
 #include "fml/closure.h"
 #include "impeller/base/thread.h"
 #include "impeller/renderer/backend/gles/handle_gles.h"
@@ -276,12 +277,10 @@ class ReactorGLES {
   std::map<std::thread::id, std::vector<Operation>> ops_ IPLR_GUARDED_BY(
       ops_mutex_);
 
-  // Make sure the container is one where erasing items during iteration doesn't
-  // invalidate other iterators.
-  using LiveHandles = std::unordered_map<const HandleGLES,
-                                         LiveHandle,
-                                         HandleGLES::Hash,
-                                         HandleGLES::Equal>;
+  using LiveHandles = absl::flat_hash_map<const HandleGLES,
+                                          LiveHandle,
+                                          HandleGLES::Hash,
+                                          HandleGLES::Equal>;
   mutable RWMutex handles_mutex_;
   LiveHandles handles_ IPLR_GUARDED_BY(handles_mutex_);
   int32_t handles_to_collect_count_ IPLR_GUARDED_BY(handles_mutex_) = 0;