Bug 13671 - CGImageDestination leaks the Handle, creating a memory leak
Summary: CGImageDestination leaks the Handle, creating a memory leak
Alias: None
Product: iOS
Classification: Xamarin
Component: Xamarin.iOS.dll ()
Version: 6.4.0
Hardware: PC Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2013-07-31 21:28 UTC by Adrian Gallero
Modified: 2013-08-01 08:13 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Adrian Gallero 2013-07-31 21:28:13 UTC
CGImageDestination.FromData and CGImageDestination.FromURL never dispose the internal CGImageDestination handle.

Steps to reproduce:
1)Create a new single view iOS app, add a button.
2)In the event handle write:
       partial void test(NSObject sender)
            using (NSData data = NSData.FromArray(new byte[] { 0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00, 0x80, 0x00, 0x00, 
                0x05, 0x04, 0x04, 0x00 ,0x00, 0x00, 0x2C, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x02, 0x02, 0x44, 0x01, 0x00, 0x3B}))
                for (int i = 0; i < 100000; i++)
                    using (MonoTouch.ImageIO.CGImageDestination imgDest = MonoTouch.ImageIO.CGImageDestination.FromData(data, "public.png", 1))
            GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);

3) Look at the memory usage in instrument, the CGImage handles are never released.

Proposed fix:
FromData and FromURL call new CGImageDestination(p):

public static CGImageDestination FromData (NSData data, string typeIdentifier, int imageCount, CGImageDestinationOptions options)

			var ret = p == IntPtr.Zero ? null : new CGImageDestination (p);
			if (dict != null)
				dict.Dispose ();
			return ret;

but the constructor for CGImageDestination(p) is:

// invoked by marshallers
		internal CGImageDestination (IntPtr handle) : this (handle, false)
			this.handle = handle;
Which calls the constructor with "owns = false", so the handle is retained. By the way, the line this.handle = handle is redundant, since this(handle, false) will assign the handle anyway.

So the correct thing to do is to call the constructor with "owns = true":

var ret = p == IntPtr.Zero ? null : new CGImageDestination (p, true);

This is the way it is called in CGImageSource too.
Comment 1 Adrian Gallero 2013-07-31 21:29:55 UTC
Just a note, this is a *big* memory leak, since the CGImageDestination not freeing will mean the full CGImages are not freed either. For big images this can create a crash very soon.

This is a critical bug for me (and for everyone using CGImageDestination)
Comment 2 Rolf Bjarne Kvinge [MSFT] 2013-08-01 08:13:54 UTC
Fixed. This fix will be included in 6.4.2.

maccore/master: 36fbaec3bfe670044f91931ff7c625735c0fa8ff
monotouch/master-3.0: 73e151d9f521f826c3f98f114aa8752924db65f2
monotouch/monotouch-6.4-series: be06e3f33e1a9d82797b1d1b1b961de17ac68c77