private static IBinaryDataAccessor OpenAutodetectFormat(string filename, IFileSystem fileSystem)
{
var fileLength = fileSystem.GetFileLength(filename);
// First try a byte array
// It's the fastest, but has the biggest memory footprint
// We might not be able to fit a large file into memory, and I don't know how to open a 2GB or larger file in memory,
// so we may have to fall back onto something else
if (fileLength < int.MaxValue)
{
try
{
return(new InMemoryBinaryDataAccessor(fileSystem.ReadAllBytes(filename)));
}
catch (OutOfMemoryException)
{
}
}
// Next, try a memory mapped file system
// Its speed is comparable to a byte array, but slightly slower (difference may be bigger since the InMemoryBinaryDataAccessor is the only one to support Span and Memory, which I have not yet seen the speed of first-hand)
// This method might not be available depending on whether or not we have a real file system at our disposal
// In the future, this may need to be feature-switchable, since we can't resize this file without disposing of it first
if (fileSystem is IMemoryMappableFileSystem memoryMappableFileSystem)
{
var memoryMappedFile = memoryMappableFileSystem.OpenMemoryMappedFile(filename);
var accessor = new MemoryMappedFileDataAccessor(memoryMappedFile, fileLength);
try
{
// Sometimes we might not have enough memory.
// When that happens, we get an IOException saying something "There are not enough memory resources available"
if (memoryMappedFile.CreateViewAccessor().Capacity > -1) // Compare the capacity to -1 just to see if we get an IOException
{
return(accessor);
}
}
catch (IOException)
{
// We can't use a MemoryMapped file.
// Streams are more reliable anyway; just slower.
}
}
// If all else fails, we can use a stream.
// It's the slowest since it is not thread-safe, and the StreamBinaryDataAccessor has to use appropriate locking
return(new StreamBinaryDataAccessor(fileSystem.OpenFile(filename)));
}
public BinaryFile(MemoryMappedFile memoryMappedFile, int fileLength)
{
Accessor = new MemoryMappedFileDataAccessor(memoryMappedFile, fileLength);
}
