Attempt to fix unreproducible crasher by replacing NSMapTable with our own weak reference collection.

Author: Mallory Paine

FastImageCache/FICImageTable.m

@@ -12,6 +12,7 @@
 #import "FICImageTableChunk.h"
 #import "FICImageTableEntry.h"
 #import "FICUtilities.h"
+#import "FICWeakReference.h"
 
 #import "FICImageCache+FICErrorLogging.h"
 
@@ -49,7 +50,7 @@ @interface FICImageTable () {
     size_t _chunkLength;
     NSInteger _chunkCount;
 
-    NSMapTable *_chunkMapTable;
+    NSMutableDictionary *_chunkDictionary;
     NSMutableArray *_recentChunks;
     NSRecursiveLock *_lock;
 
@@ -137,7 +138,7 @@ - (instancetype)initWithFormat:(FICImageFormat *)imageFormat {
         _imageRowLength = (NSInteger)FICByteAlignForCoreAnimation(pixelSize.width * bytesPerPixel);
         _imageLength = _imageRowLength * (NSInteger)pixelSize.height;
 
-        _chunkMapTable = [NSMapTable mapTableWithKeyOptions:NSMapTableStrongMemory valueOptions:NSMapTableWeakMemory];
+        _chunkDictionary = [[NSMutableDictionary alloc] init];
 
         _indexMap = [[NSMutableDictionary alloc] init];
         _occupiedIndexes = [[NSMutableIndexSet alloc] init];
@@ -198,16 +199,26 @@ - (void)dealloc {
 #pragma mark - Working with Chunks
 
 - (FICImageTableChunk *)_cachedChunkAtIndex:(NSInteger)index {
-    FICImageTableChunk *cachedChunk = [_chunkMapTable objectForKey:@(index)];
+    FICImageTableChunk *cachedChunk = nil;
+    NSNumber *indexNumber = @(index);
+    FICWeakReference *chunkReference = [_chunkDictionary objectForKey:indexNumber];
+    
+    if (chunkReference) {
+        cachedChunk = [chunkReference object];
+        if (!cachedChunk) {
+            [_chunkDictionary removeObjectForKey:indexNumber];
+        }
+    }
 
     return cachedChunk;
 }
 
 - (void)_setChunk:(FICImageTableChunk *)chunk index:(NSInteger)index {
+    NSNumber *indexNumber = @(index);
     if (chunk != nil) {
-        [_chunkMapTable setObject:chunk forKey:@(index)];
+        [_chunkDictionary setObject:[[FICWeakReference alloc] initWithObject:chunk] forKey:indexNumber];
     } else {
-        [_chunkMapTable removeObjectForKey:@(index)];
+        [_chunkDictionary removeObjectForKey:indexNumber];
     }
 }
 

FastImageCache/FICWeakReference.h

@@ -0,0 +1,17 @@
+//
+//  FICWeakReference.h
+//  FastImageCache
+//
+//  Copyright (c) 2014 Path, Inc.
+//  See LICENSE for full license agreement.
+//
+
+#import "FICImports.h"
+
+@interface FICWeakReference : NSObject
+
+- (instancetype)initWithObject:(id)object;
+
+@property(nonatomic, weak) id object;
+
+@end

FastImageCache/FICWeakReference.m

@@ -0,0 +1,20 @@
+//
+//  FICWeakReference.m
+//  FastImageCache
+//
+//  Copyright (c) 2014 Path, Inc.
+//  See LICENSE for full license agreement.
+//
+
+#import "FICWeakReference.h"
+
+@implementation FICWeakReference
+
+- (instancetype)initWithObject:(id)object {
+    if (self = [super init]) {
+        _object = object;
+    }
+    return self;
+}
+
+@end

FastImageCacheDemo/FastImageCacheDemo.xcodeproj/project.pbxproj

@@ -20,6 +20,7 @@
 		2E1BC90117C57CDF00836A7E /* FICDViewController.m in Sources */ = {isa = PBXBuildFile; fileRef = 2E1BC8FD17C57CD300836A7E /* FICDViewController.m */; };
 		2E64541017FF24C0001D0531 /* FICDTableView.m in Sources */ = {isa = PBXBuildFile; fileRef = 2E64540F17FF24C0001D0531 /* FICDTableView.m */; };
 		2EA7994417B2A10200684B86 /* main.m in Sources */ = {isa = PBXBuildFile; fileRef = 2EA7993F17B2A10200684B86 /* main.m */; };
+		31F9BA0418822719009630D0 /* FICWeakReference.m in Sources */ = {isa = PBXBuildFile; fileRef = 31F9BA0318822719009630D0 /* FICWeakReference.m */; };
 		EB171332181F089F00EB0E24 /* CoreImage.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = EB171331181F089F00EB0E24 /* CoreImage.framework */; };
 		EB642D8017DCB1750013D644 /* FICDFullscreenPhotoDisplayController.m in Sources */ = {isa = PBXBuildFile; fileRef = EB642D7F17DCB1750013D644 /* FICDFullscreenPhotoDisplayController.m */; };
 		EB6BD53818079DAB00D762CE /* CoreGraphics.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = EB6BD53718079DAB00D762CE /* CoreGraphics.framework */; };
@@ -56,6 +57,8 @@
 		2E64540E17FF24C0001D0531 /* FICDTableView.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = FICDTableView.h; sourceTree = "<group>"; };
 		2E64540F17FF24C0001D0531 /* FICDTableView.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = FICDTableView.m; sourceTree = "<group>"; };
 		2EA7993F17B2A10200684B86 /* main.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = main.m; sourceTree = "<group>"; };
+		31F9BA0218822719009630D0 /* FICWeakReference.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = FICWeakReference.h; sourceTree = "<group>"; };
+		31F9BA0318822719009630D0 /* FICWeakReference.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = FICWeakReference.m; sourceTree = "<group>"; };
 		EB171331181F089F00EB0E24 /* CoreImage.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = CoreImage.framework; path = System/Library/Frameworks/CoreImage.framework; sourceTree = SDKROOT; };
 		EB642D3717DC9C690013D644 /* FastImageCacheDemo-Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; path = "FastImageCacheDemo-Info.plist"; sourceTree = "<group>"; };
 		EB642D7E17DCB1750013D644 /* FICDFullscreenPhotoDisplayController.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = FICDFullscreenPhotoDisplayController.h; sourceTree = "<group>"; };
@@ -145,6 +148,8 @@
 				EB6BD53918079E2D00D762CE /* FICImports.h */,
 				2E1BC8ED17C57C4700836A7E /* FICUtilities.h */,
 				2E1BC8EE17C57C4700836A7E /* FICUtilities.m */,
+				31F9BA0218822719009630D0 /* FICWeakReference.h */,
+				31F9BA0318822719009630D0 /* FICWeakReference.m */,
 			);
 			name = FastImageCache;
 			path = ../FastImageCache;
@@ -243,6 +248,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				31F9BA0418822719009630D0 /* FICWeakReference.m in Sources */,
 				2EA7994417B2A10200684B86 /* main.m in Sources */,
 				2E1BC8F017C57C4700836A7E /* FICImageCache.m in Sources */,
 				2E1BC8F117C57C4700836A7E /* FICImageFormat.m in Sources */,