[System] Fix DeflateStream crash with high concurrency on Read/Write/Close (#5994)

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=56727

mcs/class/System/System.IO.Compression/DeflateStream.cs

@@ -332,7 +332,7 @@ namespace System.IO.Compression
 		UnmanagedReadOrWrite feeder; // This will be passed to unmanaged code and used there
 
 		Stream base_stream;
-		IntPtr z_stream;
+		SafeDeflateStreamHandle z_stream;
 		GCHandle data;
 		bool disposed;
 		byte [] io_buffer;
@@ -347,7 +347,7 @@ namespace System.IO.Compression
 			dsn.data = GCHandle.Alloc (dsn);
 			dsn.feeder = mode == CompressionMode.Compress ? new UnmanagedReadOrWrite (UnmanagedWrite) : new UnmanagedReadOrWrite (UnmanagedRead);
 			dsn.z_stream = CreateZStream (mode, gzip, dsn.feeder, GCHandle.ToIntPtr (dsn.data));
-			if (dsn.z_stream == IntPtr.Zero) {
+			if (dsn.z_stream.IsInvalid) {
 				dsn.Dispose (true);
 				return null;
 			}
@@ -369,10 +369,7 @@ namespace System.IO.Compression
 			
 				io_buffer = null;
 			
-				IntPtr zz = z_stream;
-				z_stream = IntPtr.Zero;
-				if (zz != IntPtr.Zero)
-					CloseZStream (zz); // This will Flush() the remaining output if any
+				z_stream.Dispose();
 			}
 
 			if (data.IsAllocated) {
@@ -498,21 +495,21 @@ namespace System.IO.Compression
 
 #if !ORBIS
 		[DllImport (LIBNAME, CallingConvention=CallingConvention.Cdecl)]
-		static extern IntPtr CreateZStream (CompressionMode compress, bool gzip, UnmanagedReadOrWrite feeder, IntPtr data);
+		static extern SafeDeflateStreamHandle CreateZStream (CompressionMode compress, bool gzip, UnmanagedReadOrWrite feeder, IntPtr data);
 
 		[DllImport (LIBNAME, CallingConvention=CallingConvention.Cdecl)]
 		static extern int CloseZStream (IntPtr stream);
 
 		[DllImport (LIBNAME, CallingConvention=CallingConvention.Cdecl)]
-		static extern int Flush (IntPtr stream);
+		static extern int Flush (SafeDeflateStreamHandle stream);
 
 		[DllImport (LIBNAME, CallingConvention=CallingConvention.Cdecl)]
-		static extern int ReadZStream (IntPtr stream, IntPtr buffer, int length);
+		static extern int ReadZStream (SafeDeflateStreamHandle stream, IntPtr buffer, int length);
 
 		[DllImport (LIBNAME, CallingConvention=CallingConvention.Cdecl)]
-		static extern int WriteZStream (IntPtr stream, IntPtr buffer, int length);
+		static extern int WriteZStream (SafeDeflateStreamHandle stream, IntPtr buffer, int length);
 #else
-		static IntPtr CreateZStream (CompressionMode compress, bool gzip, UnmanagedReadOrWrite feeder, IntPtr data)
+		static SafeDeflateStreamHandle CreateZStream (CompressionMode compress, bool gzip, UnmanagedReadOrWrite feeder, IntPtr data)
 		{
 			throw new PlatformNotSupportedException ();
 		}
@@ -522,22 +519,39 @@ namespace System.IO.Compression
 			throw new PlatformNotSupportedException ();
 		}
 
-		static int Flush (IntPtr stream)
+		static int Flush (SafeDeflateStreamHandle stream)
 		{
 			throw new PlatformNotSupportedException ();
 		}
 
-		static int ReadZStream (IntPtr stream, IntPtr buffer, int length)
+		static int ReadZStream (SafeDeflateStreamHandle stream, IntPtr buffer, int length)
 		{
 			throw new PlatformNotSupportedException ();
 		}
 
-		static int WriteZStream (IntPtr stream, IntPtr buffer, int length)
+		static int WriteZStream (SafeDeflateStreamHandle stream, IntPtr buffer, int length)
 		{
 			throw new PlatformNotSupportedException ();
 		}
 #endif
 
+		sealed class SafeDeflateStreamHandle : SafeHandle
+		{
+			public override bool IsInvalid
+			{
+				get { return handle == IntPtr.Zero; }
+			}
+
+			private SafeDeflateStreamHandle() : base(IntPtr.Zero, true)
+			{
+			}
+
+			override protected bool ReleaseHandle()
+			{
+				DeflateStreamNative.CloseZStream(handle);
+				return true;
+			}
+		}
 	}
 }