Optimize font handling on iOS (#31764)

Summary:
Few issues I saw when profiling RNTester:
- Repeatedly calling `-lowercaseString` during `weightOfFont` causes a TON of extra memory traffic, for no reason.
- `NSCache` is thread-safe, so no need for a mutex.
- Using `stringWithFormat:` for the cache key is slow. Use `NSValue` to store the data directly instead.
- Calling `-fontDescriptor` in `isItalicFont` and `isCondensedFont` is overly expensive and unnecessary.
- `+fontNamesForFamilyName:` is insanely expensive. Wrap it in a cache.

Unscientific test on RNTester iPhone 11 Pro, memory & time. Before:
<img width="1656" alt="Screen Shot 2021-06-23 at 7 40 06 AM" src="https://user-images.githubusercontent.com/2466893/123092882-f4f55100-d3f8-11eb-906f-d25086049a18.png">
<img width="1656" alt="Screen Shot 2021-06-23 at 7 41 30 AM" src="https://user-images.githubusercontent.com/2466893/123092886-f6267e00-d3f8-11eb-89f6-cfd2cae9f7b6.png">

After:
<img width="1455" alt="Screen Shot 2021-06-23 at 9 02 54 AM" src="https://user-images.githubusercontent.com/2466893/123101899-7d2c2400-d402-11eb-97f8-2ee97ee69ec4.png">
<img width="1455" alt="Screen Shot 2021-06-23 at 8 59 44 AM" src="https://user-images.githubusercontent.com/2466893/123101892-7bfaf700-d402-11eb-9a10-def46b37b87f.png">

Changelog:
[iOS][Changed] - Optimized font handling

Pull Request resolved: #31764

Reviewed By: appden

Differential Revision: D30241725

Pulled By: yungsters

fbshipit-source-id: 342e4f6e5492926acd2afc7d645e6878846369fc

Author: Adlai-Holler

BUCK

@@ -376,6 +376,7 @@ rn_xplat_cxx_library2(
         "$SDKROOT/System/Library/Frameworks/CFNetwork.framework",
         "$SDKROOT/System/Library/Frameworks/CoreGraphics.framework",
         "$SDKROOT/System/Library/Frameworks/CoreLocation.framework",
+        "$SDKROOT/System/Library/Frameworks/CoreText.framework",
         "$SDKROOT/System/Library/Frameworks/Foundation.framework",
         "$SDKROOT/System/Library/Frameworks/MapKit.framework",
         "$SDKROOT/System/Library/Frameworks/QuartzCore.framework",

React/Views/RCTFont.mm

@@ -11,18 +11,16 @@
 
 #import <CoreText/CoreText.h>
 
-#import <mutex>
-
 typedef CGFloat RCTFontWeight;
 static RCTFontWeight weightOfFont(UIFont *font)
 {
-  static NSArray *fontNames;
-  static NSArray *fontWeights;
+  static NSArray<NSString *> *weightSuffixes;
+  static NSArray<NSNumber *> *fontWeights;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
     // We use two arrays instead of one map because
     // the order is important for suffix matching.
-    fontNames = @[
+    weightSuffixes = @[
       @"normal",
       @"ultralight",
       @"thin",
@@ -54,28 +52,29 @@ static RCTFontWeight weightOfFont(UIFont *font)
     ];
   });
 
-  for (NSInteger i = 0; i < 0 || i < (unsigned)fontNames.count; i++) {
-    if ([font.fontName.lowercaseString hasSuffix:fontNames[i]]) {
-      return (RCTFontWeight)[fontWeights[i] doubleValue];
+  NSString *fontName = font.fontName;
+  NSInteger i = 0;
+  for (NSString *suffix in weightSuffixes) {
+    // CFStringFind is much faster than any variant of rangeOfString: because it does not use a locale.
+    auto options = kCFCompareCaseInsensitive | kCFCompareAnchored | kCFCompareBackwards;
+    if (CFStringFind((CFStringRef)fontName, (CFStringRef)suffix, options).location != kCFNotFound) {
+      return (RCTFontWeight)fontWeights[i].doubleValue;
     }
+    i++;
   }
 
-  NSDictionary *traits = [font.fontDescriptor objectForKey:UIFontDescriptorTraitsAttribute];
+  auto traits = (__bridge_transfer NSDictionary *)CTFontCopyTraits((CTFontRef)font);
   return (RCTFontWeight)[traits[UIFontWeightTrait] doubleValue];
 }
 
 static BOOL isItalicFont(UIFont *font)
 {
-  NSDictionary *traits = [font.fontDescriptor objectForKey:UIFontDescriptorTraitsAttribute];
-  UIFontDescriptorSymbolicTraits symbolicTraits = [traits[UIFontSymbolicTrait] unsignedIntValue];
-  return (symbolicTraits & UIFontDescriptorTraitItalic) != 0;
+  return (CTFontGetSymbolicTraits((CTFontRef)font) & kCTFontTraitItalic) != 0;
 }
 
 static BOOL isCondensedFont(UIFont *font)
 {
-  NSDictionary *traits = [font.fontDescriptor objectForKey:UIFontDescriptorTraitsAttribute];
-  UIFontDescriptorSymbolicTraits symbolicTraits = [traits[UIFontSymbolicTrait] unsignedIntValue];
-  return (symbolicTraits & UIFontDescriptorTraitCondensed) != 0;
+  return (CTFontGetSymbolicTraits((CTFontRef)font) & kCTFontTraitCondensed) != 0;
 }
 
 static RCTFontHandler defaultFontHandler;
@@ -130,18 +129,16 @@ static inline BOOL CompareFontWeights(UIFontWeight firstWeight, UIFontWeight sec
 
 static UIFont *cachedSystemFont(CGFloat size, RCTFontWeight weight)
 {
-  static NSCache *fontCache;
-  static std::mutex *fontCacheMutex = new std::mutex;
-
-  NSString *cacheKey = [NSString stringWithFormat:@"%.1f/%.2f", size, weight];
-  UIFont *font;
-  {
-    std::lock_guard<std::mutex> lock(*fontCacheMutex);
-    if (!fontCache) {
-      fontCache = [NSCache new];
-    }
-    font = [fontCache objectForKey:cacheKey];
-  }
+  static NSCache<NSValue *, UIFont *> *fontCache = [NSCache new];
+
+  struct __attribute__((__packed__)) CacheKey {
+    CGFloat size;
+    RCTFontWeight weight;
+  };
+
+  CacheKey key{size, weight};
+  NSValue *cacheKey = [[NSValue alloc] initWithBytes:&key objCType:@encode(CacheKey)];
+  UIFont *font = [fontCache objectForKey:cacheKey];
 
   if (!font) {
     if (defaultFontHandler) {
@@ -151,15 +148,36 @@ static inline BOOL CompareFontWeights(UIFontWeight firstWeight, UIFontWeight sec
       font = [UIFont systemFontOfSize:size weight:weight];
     }
 
-    {
-      std::lock_guard<std::mutex> lock(*fontCacheMutex);
-      [fontCache setObject:font forKey:cacheKey];
-    }
+    [fontCache setObject:font forKey:cacheKey];
   }
 
   return font;
 }
 
+// Caching wrapper around expensive +[UIFont fontNamesForFamilyName:]
+static NSArray<NSString *> *fontNamesForFamilyName(NSString *familyName)
+{
+  static NSCache<NSString *, NSArray<NSString *> *> *cache;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    cache = [NSCache new];
+    [NSNotificationCenter.defaultCenter
+        addObserverForName:(NSNotificationName)kCTFontManagerRegisteredFontsChangedNotification
+                    object:nil
+                     queue:nil
+                usingBlock:^(NSNotification *) {
+                  [cache removeAllObjects];
+                }];
+  });
+
+  auto names = [cache objectForKey:familyName];
+  if (!names) {
+    names = [UIFont fontNamesForFamilyName:familyName];
+    [cache setObject:names forKey:familyName];
+  }
+  return names;
+}
+
 @implementation RCTConvert (RCTFont)
 
 + (UIFont *)UIFont:(id)json
@@ -315,7 +333,7 @@ + (UIFont *)updateFont:(UIFont *)font
 
   // Gracefully handle being given a font name rather than font family, for
   // example: "Helvetica Light Oblique" rather than just "Helvetica".
-  if (!didFindFont && [UIFont fontNamesForFamilyName:familyName].count == 0) {
+  if (!didFindFont && fontNamesForFamilyName(familyName).count == 0) {
     font = [UIFont fontWithName:familyName size:fontSize];
     if (font) {
       // It's actually a font name, not a font family name,
@@ -339,7 +357,8 @@ + (UIFont *)updateFont:(UIFont *)font
 
   // Get the closest font that matches the given weight for the fontFamily
   CGFloat closestWeight = INFINITY;
-  for (NSString *name in [UIFont fontNamesForFamilyName:familyName]) {
+  NSArray<NSString *> *names = fontNamesForFamilyName(familyName);
+  for (NSString *name in names) {
     UIFont *match = [UIFont fontWithName:name size:fontSize];
     if (isItalic == isItalicFont(match) && isCondensed == isCondensedFont(match)) {
       CGFloat testWeight = weightOfFont(match);
@@ -352,11 +371,8 @@ + (UIFont *)updateFont:(UIFont *)font
 
   // If we still don't have a match at least return the first font in the fontFamily
   // This is to support built-in font Zapfino and other custom single font families like Impact
-  if (!font) {
-    NSArray *names = [UIFont fontNamesForFamilyName:familyName];
-    if (names.count > 0) {
-      font = [UIFont fontWithName:names[0] size:fontSize];
-    }
+  if (!font && names.count > 0) {
+    font = [UIFont fontWithName:names[0] size:fontSize];
   }
 
   // Apply font variants to font object

packages/rn-tester/RNTesterUnitTests/RCTFontTests.m

@@ -20,7 +20,7 @@ @implementation RCTFontTests
 // will be different objects, but the same font, so this macro now explicitly
 // checks that fontName (which includes the style) and pointSize are equal.
 #define RCTAssertEqualFonts(font1, font2) { \
-  XCTAssertTrue([font1.fontName isEqualToString:font2.fontName]); \
+  XCTAssertEqualObjects(font1.fontName, font2.fontName); \
   XCTAssertEqual(font1.pointSize,font2.pointSize); \
 }