Getting file permission on read while using MMF - file-io

Question

I have two processes. One writing in a memory mapped file using .NET 4 MemoryMappedFiles and the other reading the file using FileStream in .NET 3.5 (MONO). Everything works fine when I get the permission, no problem reading or writing the file. The problem is to obtain a permission.
Writing MMF (the Writer):
MemoryMappedFile.CreateFromFile
(filenameToMap, FileMode.Create, "Something",
Marshal.SizeOf(objectToMap), MemoryMappedFileAccess.ReadWrite);
Reading MMF (the Reader):
new FileStream(filenameToMap, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.ReadWrite);
First I start the Writer, then the Reader.
I tested it using this naive approach:
while (true)
{
try
{
new FileStream(mapPath + "map.mp", FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.ReadWrite);
break;
}
catch { }
}
After roughly 10 seconds, the Reader usually gets permission and everything runs smooth. If I would catch the exception, it would throw:
IOException: Sharing violation on path
C:\path at
System.IO.FileStream..ctor
(System.String path, FileMode mode,
FileAccess access, FileShare share,
Int32 bufferSize, Boolean anonymous,
FileOptions options) [0x00000] in
:0
Any idea why these two processes don't share the file properly from beginning?