Crash in FoundationResponse.GetResponseText()

[gaearon]

I can't isolate the issue yet, but I have FoundationResponse.GetResponseText() crashing my process in some cases:

mono-rt:   at <unknown> <0xffffffff>
mono-rt:   at (wrapper managed-to-native) System.Runtime.InteropServices.Marshal.copy_from_unmanaged (intptr,int,System.Array,int) <IL 0x00024, 0xffffffff>
mono-rt:   at System.Runtime.InteropServices.Marshal.Copy (intptr,byte[],int,int) [0x00000] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.Runtime.InteropServices/Marshal.cs:146
mono-rt:   at System.IO.UnmanagedMemoryStream.Read (byte[],int,int) [0x0010b] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.IO/UnmanagedMemoryStream.cs:206
mono-rt:   at System.IO.StreamReader.ReadBuffer () [0x0000e] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.IO/StreamReader.cs:392
mono-rt:   at System.IO.StreamReader.ReadToEnd () [0x0002c] in /Developer/MonoTouch/Source/mono/mcs/class/corlib/System.IO/StreamReader.cs:580
mono-rt:   at Xamarin.Auth.Response.GetResponseText () [0x00046] in /Users/dan/Documents/Projects/stampsy-ipad/external/Xamarin.Social/Xamarin.Auth/src/Xamarin.Auth/Response.cs:93
mono-rt:   at Stampsy.Social.ServiceManager.GetResponseJson (System.Threading.Tasks.Task`1<Xamarin.Auth.Response>) [0x00074] in /Users/dan/Documents/Projects/stampsy-ipad/external/sociopath/libs/Stampsy.Social/Services/ServiceManager.cs:101
mono-rt:   at Stampsy.Social.ServiceManager/<ParsePageAsync>c__AnonStorey15`1.<>m__2C (System.Threading.Tasks.Task`1<Xamarin.Auth.Response>) [0x00008] in /Users/dan/Documents/Projects/stampsy-ipad/external/sociopath/libs/Stampsy.Social/Services/ServiceManager.cs:129

[gaearon]

This seems to happen when large NSData is passed to FoundationResponse constructor.
In my case, its length was 498430.

I'll see why the data is so large, but still the crash is weird, is the memory being freed too soon?

[ermau]

I'll see why the data is so large, but still the crash is weird, is the memory being freed too soon?

Looks like a possibility, I don't see anything holding on to a reference of the NSData.

[gaearon]

Would it be better to hold on to NSData or to pin it and store GCHandle? I suppose without pinning, its address could change, no? Or does it not matter because its Bytes point to native memory GC can't move anyway? Thanks.

[ermau]

Probably simpler to just hold on to the NSData, as you said the Bytes is going to be unmanaged memory. Really the construction of the new stream could be moved to GetResponseStream if we hold on to the NSData as well.

[gaearon]

I see. Should I dispose of both stream and NSData in Dispose, or just NSData? Do I need to put Dispose calls inside if (disposing)?

[ermau]

Do I need to put Dispose calls inside if (disposing)?

Yes, NSObject has its own finalizer and the execution order of finalizers is not guaranteed.

[ermau]

The real question is why @praeclarum special cases NSMutableData? AsStream() automatically keeps a reference to the NSData.

[gaearon]

@ermau

But FoundationResponse's base class is Response, not NSObject. It just follows the same convention. It also frees its own field (HttpWebResponse response) without doing this check.

[ermau]

But FoundationResponse's base class is Response, not NSObject.

NSData's base class is NSObject.

It also frees its own field (HttpWebResponse response) without doing this check.

True, that doesn't make it correct unfortunately. I'll have to fix that.