set old_gen_heap_size to half of available memory on iOS (#20472)

ci/licenses_golden/licenses_flutter

@@ -19,6 +19,7 @@ FILE: ../../../flutter/assets/directory_asset_bundle.cc
 FILE: ../../../flutter/assets/directory_asset_bundle.h
 FILE: ../../../flutter/benchmarking/benchmarking.cc
 FILE: ../../../flutter/benchmarking/benchmarking.h
+FILE: ../../../flutter/common/constants.h
 FILE: ../../../flutter/common/exported_symbols.sym
 FILE: ../../../flutter/common/settings.cc
 FILE: ../../../flutter/common/settings.h

common/constants.h

@@ -0,0 +1,7 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+namespace flutter {
+constexpr double kMegaByteSizeInBytes = (1 << 20);
+}  // namespace flutter

flow/raster_cache.cc

@@ -6,6 +6,7 @@
 
 #include <vector>
 
+#include "flutter/common/constants.h"
 #include "flutter/flow/layers/layer.h"
 #include "flutter/flow/paint_utils.h"
 #include "flutter/fml/logging.h"
@@ -298,12 +299,11 @@ void RasterCache::SetCheckboardCacheImages(bool checkerboard) {
 
 void RasterCache::TraceStatsToTimeline() const {
 #if !FLUTTER_RELEASE
-  constexpr double kMegaBytes = (1 << 20);
   FML_TRACE_COUNTER("flutter", "RasterCache", reinterpret_cast<int64_t>(this),
                     "LayerCount", layer_cache_.size(), "LayerMBytes",
-                    EstimateLayerCacheByteSize() / kMegaBytes, "PictureCount",
-                    picture_cache_.size(), "PictureMBytes",
-                    EstimatePictureCacheByteSize() / kMegaBytes);
+                    EstimateLayerCacheByteSize() / kMegaByteSizeInBytes,
+                    "PictureCount", picture_cache_.size(), "PictureMBytes",
+                    EstimatePictureCacheByteSize() / kMegaByteSizeInBytes);
 
 #endif  // !FLUTTER_RELEASE
 }

shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm

@@ -6,6 +6,7 @@
 
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h"
 
+#include "flutter/common/constants.h"
 #include "flutter/common/task_runners.h"
 #include "flutter/fml/mapping.h"
 #include "flutter/fml/message_loop.h"
@@ -151,6 +152,16 @@ static flutter::Settings DefaultSettingsForProcess(NSBundle* bundle = nil) {
       make_mapping_callback(kPlatformStrongDill, kPlatformStrongDillSize);
 #endif  // FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG
 
+  // If we even support setting this e.g. from the command line or the plist,
+  // we should let the user override it.
+  // Otherwise, we want to set this to a value that will avoid having the OS
+  // kill us. On most iOS devices, that happens somewhere near half
+  // the available memory.
+  // The VM expects this value to be in megabytes.
+  if (settings.old_gen_heap_size <= 0) {
+    settings.old_gen_heap_size = std::round([NSProcessInfo processInfo].physicalMemory * .48 /
+                                            flutter::kMegaByteSizeInBytes);
+  }
   return settings;
 }
 

shell/platform/darwin/ios/framework/Source/FlutterDartProjectTest.mm

@@ -2,8 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#import <OCMock/OCMock.h>
 #import <XCTest/XCTest.h>
 
+#include "flutter/common/constants.h"
+#include "flutter/shell/platform/darwin/common/framework/Headers/FlutterMacros.h"
 #import "flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h"
 
 FLUTTER_ASSERT_ARC
@@ -19,6 +22,13 @@ FLUTTER_ASSERT_ARC
 - (void)tearDown {
 }
 
+- (void)testOldGenHeapSizeSetting {
+  FlutterDartProject* project = [[FlutterDartProject alloc] init];
+  int64_t old_gen_heap_size =
+      std::round([NSProcessInfo processInfo].physicalMemory * .48 / flutter::kMegaByteSizeInBytes);
+  XCTAssertEqual(project.settings.old_gen_heap_size, old_gen_heap_size);
+}
+
 - (void)testMainBundleSettingsAreCorrectlyParsed {
   NSBundle* mainBundle = [NSBundle mainBundle];
   NSDictionary* appTransportSecurity =