Re: ARC issue
Re: ARC issue
- Subject: Re: ARC issue
- From: Bob Cromwell <email@hidden>
- Date: Wed, 07 Nov 2012 21:45:59 +0800
According to ARC documentation, out parameter will be changed to auto release one:
NSError ** error will be auto changed to NSError * __autorelease * error.
So It's expected behavior that crash happens. An article about this here http://blog.pioneeringsoftware.co.uk/2012/03/06/out-parameters-when-arcing
On 2012-11-7, at 下午9:05, Andreas Grosam wrote:
> Xcode 4.5.1, ARC enabled.
>
> I've this C++ member function, for a testing environment (gtest):
>
>
> NSDictionary* fetchUser(NSNumber* ID, NSError** error)
> {
> id user = nil;
> //@autoreleasepool // crashes when @autoreleasepool is enabled
> {
> id data = ...; // response body of a HTTP Response (NSData) or NSError object, never nil.
> if ([data isKindOfClass:[NSData class]]) {
> user = [NSJSONSerialization JSONObjectWithData:data
> options:0
> error:error];
> }
> else if (error) {
> *error = data;
> }
> } // autoreleasepool
> return user;
> }
>
>
>
> The problem here is, if the autorelease pool is **enabled**, I get a crash in the caller's code:
> NSError* err = nil;
> NSDictionary* deletedUser = this->fetchUser(userID, &err);
> EXPECT_TRUE(deletedUser == nil); <== the crash occurs **before** this statement, but **after** the return statement of the function fetch user.
>
> The debugger does not show a stack frame to confirm this, though.
>
> libobjc.A.dylib`objc_msgSend:
> 0x7fff86b2fe80: testq %rdi, %rdi
> 0x7fff86b2fe83: je 0x7fff86b2feb0 ; objc_msgSend + 48
> 0x7fff86b2fe85: testb $1, %dil
> 0x7fff86b2fe89: jne 0x7fff86b2fec7 ; objc_msgSend + 71
> 0x7fff86b2fe8c: movq (%rdi), %r11
> 0x7fff86b2fe8f: pushq %rax
> ==> 0x7fff86b2fe90: movq 16(%r11), %r10 // Thread 1: EXC_BAD_ACCESS (code=13, address=0x0)
> 0x7fff86b2fe94: movl %esi, x
> 0x7fff86b2fe96: andl (%r10), x
> 0x7fff86b2fe99: movq 16(%r10,%rax,8), %r11
> 0x7fff86b2fe9e: incl x
> 0x7fff86b2fea0: testq %r11, %r11
> 0x7fff86b2fea3: je 0x7fff86b2fedb ; objc_msgSend + 91
> ...
>
> There is no stack frame.
>
>
> This has something to do with the error parameter. If I pass nil for the error parameter, the crash does not occur anymore.
>
>
> Any hints?
>
>
> Thanks in advance!
>
> Andreas
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