为什么这个简单的NSWindow创建代码会在ARC下关闭时触发自动释放池崩溃？

Question

我遇到了关机时自动释放池崩溃的问题,我已经减少到下面的小测试用例,只是创建一个窗口然后关闭它.如果崩溃,崩溃就会消失-fobjc-arc旗帜被拿走,.在OS X 10.8.2,Clang 4.1(421.11.66)上运行.我希望有更深入了解ARC的人可以告诉我这里发生了什么 - 在节目上运行zombie对象,它是NSWindow对象被释放太多次,或者保留不够,但是我以为ARC是为了照顾这一切？

堆栈跟踪是:

0   libobjc.A.dylib                 0x00007fff8fad4f5e objc_release + 14
1   libobjc.A.dylib                 0x00007fff8fad4230 (anonymous namespace)::AutoreleasePoolPage::pop(void*) + 464
2   com.apple.CoreFoundation        0x00007fff99d22342 _CFAutoreleasePoolPop + 34
3   com.apple.Foundation            0x00007fff936e84fa -[NSAutoreleasePool drain] + 154
4   com.apple.Foundation            0x00007fff936effa0 _NSAppleEventManagerGenericHandler + 125
5   com.apple.AE                    0x00007fff93a5ab48 aeDispatchAppleEvent(AEDesc const*, AEDesc*, unsigned int, unsigned char*) + 307
6   com.apple.AE                    0x00007fff93a5a9a9 dispatchEventAndSendReply(AEDesc const*, AEDesc*) + 37
7   com.apple.AE                    0x00007fff93a5a869 aeProcessAppleEvent + 318
8   com.apple.HIToolbox             0x00007fff8d0c18e9 AEProcessAppleEvent + 100
9   com.apple.AppKit                0x00007fff8e95c916 _DPSNextEvent + 1456
10  com.apple.AppKit                0x00007fff8e95bed2 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 128
11  com.apple.AppKit                0x00007fff8e953283 -[NSApplication run] + 517
12  Test                            0x00000001070e1d68 main + 152 (Test.mm:31)
13  libdyld.dylib                   0x00007fff8e10c7e1 start + 1

测试用例的代码是:

// Tested with `clang++ -fobjc-arc -g Test.mm -framework Cocoa -o Test && ./Test`

#import <Cocoa/Cocoa.h>

@interface MyApplication : NSApplication
@end
@implementation MyApplication
- (void) applicationDidFinishLaunching: (NSNotification *) note
{
    NSWindow * window = [[NSWindow alloc] initWithContentRect: NSMakeRect(100, 100, 100, 100)
                        styleMask: NSTitledWindowMask backing: NSBackingStoreBuffered defer: YES];

    [window close];

    [super stop: self];
}
@end

int main()
{
    @autoreleasepool
    {
        const ProcessSerialNumber psn = { 0, kCurrentProcess };
        TransformProcessType(&psn, kProcessTransformToForegroundApplication);
        SetFrontProcess(&psn);

        [MyApplication sharedApplication];
        [NSApp setDelegate: NSApp];

        [NSApp run];
    }

    return 0;
}

Answer 1

使用Instruments的Zombies配置文件显示,NSWindow对象通过调用放入自动释放池close:.一旦applicationDidFinishLaunching:完成并且销毁NSWindow实例,ARC正确地以引用计数为零结束.但是,自动释放池仍然知道现在已经不存在的NSWindow实例,然后尝试在关闭时释放它,导致崩溃.

在ARC下管理的自动释放对象似乎是一个坏主意,除非自动释放池保持对其对象的弱引用归零,这似乎不是在这里做的.

通过添加告诉窗口不要自动释放,可以防止这个问题[window setReleasedWhenClosed: NO];.