Add ability to enable Read Sharing when Writing to files

examples/ReadFromUri/ReadFromUri.cs

@@ -136,6 +136,11 @@ public FileAbstraction (string file)
 
 	public Stream WriteStream => new FileStream (Name, FileMode.Open);
 
+	public bool ReadShareWhenWriting {
+		get => throw new NotSupportedException ();
+		set => throw new NotSupportedException ();
+	}
+
 	public void CloseStream (Stream stream)
 	{
 		stream.Close ();

src/TaglibSharp.Tests/FileFormats/Id3BothFormatTest.cs

@@ -1,4 +1,6 @@
 using NUnit.Framework;
+using System.Threading;
+using System.Threading.Tasks;
 using TagLib;
 
 namespace TaglibSharp.Tests.FileFormats
@@ -133,5 +135,43 @@ public void TestCreateId3Tags ()
 			file = File.Create (tempFile);
 			Assert.AreEqual (TagTypes.Id3v1 | TagTypes.Id3v2, file.TagTypes);
 		}
+
+		[Test]
+		public async Task TestReadShareWhenWriting ()
+		{
+			// Simulate having another thread open the file and begin playing it (by
+			// keeping it open) until we tell it to stop playback and close the file.
+			SemaphoreSlim playbackStarted = new SemaphoreSlim (0);
+			SemaphoreSlim stopPlayback = new SemaphoreSlim (0);
+			_ = Task.Run (async () => {
+				using (var fileToPlay = System.IO.File.Open (tmp_file, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.ReadWrite)) {
+					playbackStarted.Release();
+					await stopPlayback.WaitAsync();
+				}
+			});
+
+			// Wait until playback in the other thread has begun.
+			await playbackStarted.WaitAsync();
+
+			// Now that the file is in use, ensure writing to it leads to an IOException
+			// due to the AudioFile's write stream not being shared for reading.
+			Assert.Catch (typeof (System.IO.IOException), () => {
+				var file = File.Create (tmp_file);
+				file.RemoveTags (TagTypes.AllTags);
+				file.Save ();
+			});
+
+			// Now try writing again, but this time explicitly mark the write
+			// stream as being shared for reading.  Ensure no exception occurs.
+			Assert.DoesNotThrow (() => {
+				var file = File.Create (tmp_file);
+				file.FileAbstraction.ReadShareWhenWriting = true;
+				file.RemoveTags (TagTypes.AllTags);
+				file.Save ();
+			});
+
+			// Finally, tell the other thread it can now "stop" playback and close the file.
+			stopPlayback.Release();
+		}
 	}
 }

src/TaglibSharp.Tests/Helpers.cs

@@ -78,6 +78,11 @@ public MemoryFileAbstraction (int maxSize, byte[] data)
 
 		public Stream WriteStream => stream;
 
+		public bool ReadShareWhenWriting {
+			get => throw new NotSupportedException ();
+			set => throw new NotSupportedException ();
+		}
+
 		public void CloseStream (Stream stream)
 		{
 			// This causes a stackoverflow

src/TaglibSharp/File.cs

@@ -189,6 +189,12 @@ public enum AccessMode
 		/// </summary>
 		List<string> corruption_reasons;
 
+		/// <summary>
+		///    Specifies whether the file should be readable by other
+		///    threads while being written to by the thread that opened it.
+		/// </summary>
+		public bool read_share_when_writing;
+
 		#endregion
 
 
@@ -1621,7 +1627,15 @@ public LocalFileAbstraction (string path)
 			/// </value>
 			public Stream WriteStream => System.IO.File.Open (Name,
 				FileMode.Open,
-				FileAccess.ReadWrite);
+				FileAccess.ReadWrite,
+				ReadShareWhenWriting ? FileShare.Read : FileShare.None);
+
+			/// <summary>
+			///    Gets or sets a value indicating whether the file should
+			///    be readable by other threads while being written to by
+			///    the thread that opened it.
+			/// </summary>
+			public bool ReadShareWhenWriting { get; set; }
 
 			/// <summary>
 			///    Closes a stream created by the current instance.
@@ -1793,6 +1807,19 @@ public interface IFileAbstraction
 			/// </remarks>
 			Stream WriteStream { get; }
 
+			/// <summary>
+			///    Gets or sets a value indicating whether the file
+			///    should be readable by other threads while being
+			///    written to by the thread that opened it.
+			/// </summary>
+			/// <remarks>
+			///    This property is useful when editing ID3 tags of
+			///    MP3 files.  In particular, setting it to true
+			///    ensures you can listen to a song in one application
+			///    while simultaneously editing its ID3 tags in another.
+			/// </remarks>
+			bool ReadShareWhenWriting { get; set; }
+
 			/// <summary>
 			///    Closes a stream originating from the current
 			///    instance.

src/TaglibSharp/Tiff/Rw2/IFDReader.cs

@@ -21,6 +21,7 @@
 // USA
 //
 
+using System;
 using System.IO;
 using TagLib.IFD;
 
@@ -133,5 +134,10 @@ public void CloseStream (Stream stream)
 		public Stream WriteStream {
 			get { return ReadStream; }
 		}
+
+		public bool ReadShareWhenWriting {
+			get => throw new NotSupportedException ();
+			set => throw new NotSupportedException ();
+		}
 	}
 }