Bug 13670 - System.IO.Compression.DeflateStream finalizer leaks native memory.
Summary: System.IO.Compression.DeflateStream finalizer leaks native memory.
Alias: None
Product: Class Libraries
Classification: Mono
Component: System ()
Version: master
Hardware: PC Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Marek Safar
Depends on:
Reported: 2013-07-31 19:12 UTC by Adrian Gallero
Modified: 2013-08-08 04:31 UTC (History)
2 users (show)

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

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Description Adrian Gallero 2013-07-31 19:12:52 UTC
If for any reason you don't dispose a DeflateStream, the finalizer will fail to release all the native memory.

Steps to reproduce:

1) In a new iOS single view application, drop a button and use the following event handler:
 partial void test(NSObject sender)
            for (int i = 0; i < 100000; i++) 
            using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
                new System.IO.Compression.DeflateStream(ms, System.IO.Compression.CompressionMode.Decompress);
            GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);

2)Deploy to a device (Tested here with iPhone 5). Note that the emulator leaks too, but it will take more time to crash because it has much more memory available.

Expected results:
It works

Actual results:
It crashes. In the emulator, it doesn't crash but memory usage goes over 2 gb.

If you run it under Instruments there are a lot of z_stream leaks that aren't returned to the system.

Looking at the implementation, the issue seems to be that CloseZStream is only called if disposing. It should also be called form the finalizer, or the z_stream member won't be released: 

		protected override void Dispose (bool disposing)
			if (disposing && !disposed) {
				disposed = true;
				IntPtr zz = z_stream;
				z_stream = IntPtr.Zero;
				int res = 0;
				if (zz != IntPtr.Zero)
					res = CloseZStream (zz); // This will Flush() the remaining output if any
Comment 1 Marek Safar 2013-08-08 04:31:41 UTC
Fixed. However the finalizer may not run before OOM is reach therefore you need to Dispose the object manually to get reliable behaviour.