/// <summary> Construct from a read-only file. </summary>
/// <remarks>
/// Used when recovering files written by a previous program
/// instance from their locations.
/// </remarks>
public BlockFile(IFileMemory file, uint fileId)
{
_pinner = new Pinner();
_file = file ?? throw new ArgumentNullException(nameof(file));
FileId = fileId;
_flags = new AppendList <ReadFlag>();
var offset = 0L;
while (offset < _file.Length)
{
var block = AtOffset(offset);
ref var header = ref block.Header;
if (header.Rank != _flags.Count || header.ContentLength < 0 ||
header.ContentLength + BlockHeader.Size > _file.Length)
{
// The header of the block appears broken. Do not include
// it in the list, and stop scanning (since we don't know
// how far to jump ahead).
break;
}
var thisOffset = offset;
_flags.Append(ReadFlag.Triggered(() => VerifyAtOffset(thisOffset)));
offset += block.RelativeOffsetToNextBlock;
}
/// <summary>
/// Attempts to schedule a write of the specified length into the file.
/// </summary>
/// <returns>
/// A valid block address representing the location where the written
/// block will be found, or a 'None' address if the file does not
/// currently have enough room for this.
/// </returns>
/// <remarks>
/// The provided writer will be invoked at some point in the future.
///
/// Thread-safe.
/// </remarks>
public BlockAddress TryScheduleWrite(
uint realm,
Hash hash,
int length,
WithSpan.ReadWrite writer)
{
if (length < 0)
{
throw new ArgumentException($"Negative length: {length}", nameof(length));
}
int rank;
long offset;
lock (_syncRoot)
{
offset = _offset;
_offset = BlockAddress.Ceiling(offset + BlockHeader.Size + length);
if (_offset > _file.Length)
{
// Since this file is about to be flushed and closed,
// because it's "full enough", we prevent additional writes.
_offset = _file.Length;
return(BlockAddress.None);
}
rank = _flags.Count;
_flags.Append(ReadFlag.Triggered(() => PerformWrite(offset, writer)));
}
// We touched '_offset' and '_flags' in the critical section, the remaining
// work on the actual byte span can be done without mutex.
var span = _file.AsMemory(offset, BlockHeader.Size).Span;
ref var header = ref MemoryMarshal.Cast <byte, BlockHeader>(span)[0];