Question

情况:

我需要将一个目标- C 对象传递给一个非同步的CPI, 作为不透明引用( evue/code> ), 稍后将传递到我提供的回调功能。调回后会调用该对象上的方法。代码需要当着垃圾收集的面工作, 对象不能是我对CPIP的呼叫和我的回调之间的GC d 。



NSGarbageColector 类提供 dcode > disableColector Forpointer: 和 enable Colector Forpointer:  标记和未将对象标记为不可收集根的标记方法。


" 强 " 问: 

我无法从 Docs 和 Web 中找到的就是 如果对  disable Colector Forpointer:  的调用被计数, 并且必须用同样数量的  enable Colector Forpointer:  调用来平衡。 如果这是  not  the case, 每个对象都标为root 或不是, 调用  enable Colector Forpointer:  在我的调用中可能会清除由其它代码设置的现有根旗, 导致收集对象, 即使它应该被收集!

我所看到的替代办法是使用 CFrest  和 CFRelease  - 这些是否安全用于我自己的  NSBject  子类?我以前只用过这些功能用于免费访问的CF物体。

提供证据的答案的受益点。 我看到 disable Colector Forpointer:  在所有地方推荐, 没有提到这一安全方面 。

<强 > 注: 


I have to support garbage collection as this code will be used by a PrefPane for System Preferences. The 64-bit version of a PrefPane must use garbage collection. So using ARC or manual refcounting is not an option.
The C API is one of Apple s (IOKit) so I have no control over it either.

Answer 1

我想我找到了答案。垃圾收集器的源代码似乎不存在, 但信头文件声明 < code> NSGarbage Colector 的界面, < code> NSGarbage Colector.h 包含以下内容: < code> Foundation. framework

// references outside the heap, globals, and the stack, e.g. unscanned memory, malloc memory, must be tracked by the collector
- (void)disableCollectorForPointer:(void *)ptr;     // this pointer will not be collected...
- (void)enableCollectorForPointer:(void *)ptr;      // ...until this (stacking) call is made

请注意“ 坚固” 的“ 堆积” < / 坚固” 评论 - 我想这意味着电话确实被计数了? 更多的证据仍然令人欢迎!

<强> 更新:

我决定用一个小测试程序来测试我的假设(“强力”格克布里奇特.m

#import <Foundation/Foundation.h>

@interface PJGarbageCollectionTest : NSObject
@end

@implementation PJGarbageCollectionTest

- (id)init
{
    self = [super init];
    if (!self) return nil;
    NSLog(@"%@ -init", self);
    return self;
}

- (void)finalize
{
    NSLog(@"%@ -finalize", self);
    [super finalize];
}

@end

static void* ext_ptr1 = NULL;
static void* ext_ptr2 = NULL;

static void create()
{
    PJGarbageCollectionTest* test = [[PJGarbageCollectionTest alloc] init];
    [[NSGarbageCollector defaultCollector] disableCollectorForPointer:test];
    ext_ptr1 = test;
    [[NSGarbageCollector defaultCollector] disableCollectorForPointer:test];
    ext_ptr2 = test;
}

static void killref(void** ext_ptr)
{
    [[NSGarbageCollector defaultCollector] enableCollectorForPointer:*ext_ptr];
    *ext_ptr = NULL;
}


int main()
{
    NSLog(@"collector: %@", [NSGarbageCollector defaultCollector]);
    create();
    NSLog(@"Collecting with 2 external references");
    [[NSGarbageCollector defaultCollector] collectExhaustively];
    killref(&ext_ptr1);
    NSLog(@"Collecting with 1 external reference");
    [[NSGarbageCollector defaultCollector] collectExhaustively];
    killref(&ext_ptr2);
    NSLog(@"Collecting with 0 external references");
    [[NSGarbageCollector defaultCollector] collectExhaustively];
    return 0;
}

以 gcc -fobjc-gc- only -g -Wall -Wextra -ObjC gcbridgetest.m -Framework Foundation -o gcbridgetest 编译,以 ./gcbridgetest 运行,它提供以下输出,确认启用/禁用聚合器Forpointer:电话确实被计数 :

2012-06-12 16:08:08.278 gcbridgetest[29712:903] collector: <NSGarbageCollector: 0x20000f420>
2012-06-12 16:08:08.281 gcbridgetest[29712:903] <PJGarbageCollectionTest: 0x20000ee60> -init
2012-06-12 16:08:08.284 gcbridgetest[29712:903] Collecting with 2 external references
2012-06-12 16:08:08.285 gcbridgetest[29712:903] Collecting with 1 external reference
2012-06-12 16:08:08.286 gcbridgetest[29712:903] Collecting with 0 external references
2012-06-12 16:08:08.286 gcbridgetest[29712:903] <PJGarbageCollectionTest: 0x20000ee60> -finalize

友情链接