CODEWITHSUNDEEP
objective-cmemory-managementautomatic-ref-countingnsdata
Atri Robot
Atri Robot

Reputation: 93

NSMutableData not releasing memory automatically

I am writing on a iOS program and I have a memory leak. I reproduce it on macOS, which I don't know how to solve it. It is very simple.

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        system("top -l 1 | grep LEAK"); // baseline
        NSMutableData* dataobj = [NSMutableData dataWithLength:DATA_SIZE];
        system("top -l 1 | grep LEAK"); // baseline + 8 bytes
        memset([dataobj mutableBytes], 1, DATA_SIZE);
        system("top -l 1 | grep LEAK"); // baseline + DATA_SIZE
        dataobj = nil;
        system("top -l 1 | grep LEAK"); // baseline + DATA_SIZE
    }
    return 0;
}

In the end, I am expecting memory usage at baseline again, but it is not. Waiting for 10 seconds still the same result. I believe it must be something wrong with my understanding of ARC or NSData.

Thank everyone who takes a look at it in advance.

Upvotes: 2

Views: 327

Answers (1)

clemens
clemens

Reputation: 17721

You're creating your data with:

NSMutableData* dataobj = [NSMutableData dataWithLength:DATA_SIZE];

Due to the Memory Management Policy you're not an owner of this object, and it is placed in the Autorelease Pool. Since you're code is completely embedded in an @autoreleasepool { ... }, it can't detect a deallocation of the data, because it is kept by this pool.

You're code doesn't contain a leak, and the operating system is responsible for the cleaning. This generally makes the success of your experiment very questionable. Finally, I would like to endorse Amin's comment: You're using the wrong methods. You should use Instruments instead.

Upvotes: 1

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