ARC中的Objective-C泄漏中的递归块 [英] Recursive Blocks in Objective-C leaking in ARC

问题描述

所以我正在使用递归块.我了解要递归的块，必须在其前面加上__block关键字，并且必须将其复制以便将其放在堆中.但是，当我这样做时，它在Instruments中显示为泄漏.有人知道我为什么或如何解决这个问题吗?

So I'm using recursive blocks. I understand that for a block to be recursive it needs to be preceded by the __block keyword, and it must be copied so it can be put on the heap. However, when I do this, it is showing up as a leak in Instruments. Does anybody know why or how I can get around it?

请注意下面的代码中，我引用了很多其他块，但是它们都不是递归的.

Please note in the code below I've got references to a lot of other blocks, but none of them are recursive.

__block NSDecimalNumber *(^ProcessElementStack)(LinkedList *, NSString *) = [^NSDecimalNumber *(LinkedList *cformula, NSString *function){
        LinkedList *list = [[LinkedList alloc] init];
        NSDictionary *dict;
        FormulaType type;
        while (cformula.count > 0) {
            dict = cformula.pop;
            type = [[dict objectForKey:@"type"] intValue];
            if (type == formulaOperandOpenParen || type == formulaListOperand || type == formulaOpenParen) [list add:ProcessElementStack(cformula, [dict objectForKey:@"name"])];
            else if (type == formulaField || type == formulaConstant) [list add:NumberForDict(dict)];
            else if (type == formulaOperand) [list add:[dict objectForKey:@"name"]];
            else if (type == formulaCloseParen) {
                if (function){
                    if ([function isEqualToString:@"AVG("]) return Average(list);
                    if ([function isEqualToString:@"MIN("]) return Minimum(list);
                    if ([function isEqualToString:@"MAX("]) return Maximum(list);
                    if ([function isEqualToString:@"SQRT("]) return SquareRoot(list);
                    if ([function isEqualToString:@"ABS("]) return EvaluateStack(list).absoluteValue;
                    return EvaluateStack(list);
                } else break;
            }
        }
        return EvaluateStack(list);
    } copy];
    NSDecimalNumber *number = ProcessElementStack([formula copy], nil); 

更新 因此，在我自己的研究中，我发现问题显然与该模块使用的其他模块的引用有关.如果我做这样简单的事情，它不会泄漏:

UPDATE So in my own research I've discovered that the problem apparently does have to do with the references to the other blocks this block uses. If I do something simple like this, it doesn't leak:

 __block void (^LeakingBlock)(int) = [^(int i){
        i++;
        if (i < 100) LeakingBlock(i);
    } copy];
    LeakingBlock(1);

但是，如果我在其中添加另一个块，则会泄漏:

However, if I add a another block in this, it does leak:

void (^Log)(int) = ^(int i){
   NSLog(@"log sub %i", i);
};

__block void (^LeakingBlock)(int) = [^(int i){
    Log(i);
    i++;
    if (i < 100) LeakingBlock(i);
} copy];
LeakingBlock(1);

我已经尝试将__block关键字用于Log()，还尝试复制它，但是它仍然泄漏.有什么想法吗?

I've tried using the __block keyword for Log() and also tried copying it, but it still leaks. Any ideas?

更新2 我找到了一种防止泄漏的方法，但是有点麻烦.如果我将传入的块转换为弱ID，然后将弱ID转换回为块类型，则可以防止泄漏.

UPDATE 2 I found a way to prevent the leak, but it's a bit onerous. If I convert the passed in block to a weak id, and then cast the weak id back into a the block type, I can prevent the leak.

void (^Log)(int) = ^(int i){
    NSLog(@"log sub %i", i);
};

__weak id WeakLogID = Log;

__block void (^LeakingBlock)(int) = [^(int i){
    void (^WeakLog)(int) = WeakLogID;
    WeakLog(i);
    if (i < 100) LeakingBlock(++i);
} copy];
LeakingBlock(1);

肯定有更好的方法吗?

推荐答案

好吧，我自己找到了答案...但是要感谢那些尝试提供帮助的人.

Ok, I found the answer on my own...but thanks to those who tried to help.

如果要在递归块中引用/使用其他块，则必须将它们作为弱变量传递.当然，__weak仅适用于块指针类型，因此必须首先对它们进行typedef.这是最终的解决方案:

If you're referencing/using other blocks in a recursive block, you must pass them in as weak variables. Of course, __weak only applies to block pointer types, so you must typedef them first. Here's the final solution:

    typedef void (^IntBlock)(int);

    IntBlock __weak Log = ^(int i){
        NSLog(@"log sub %i", i);
    };

    __block void (^LeakingBlock)(int) = ^(int i){
        Log(i);
        if (i < 100) LeakingBlock(++i);
    };
    LeakingBlock(1);

上面的代码没有泄漏.

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