/// <summary>
/// Calls <paramref name="onBlock"/> on the contents of the block at
/// address <paramref name="address"/>.
/// </summary>
/// <remarks>
/// If the block has pending work (such as validating contents, or
/// writing them out), that pending work is performed before the call.
///
/// Fully thread-safe.
///
/// Function <paramref name="onBlock"/> should endeavour to return
/// quickly, as the provided span is pinned, for all intents and
/// purposes, until it does.
/// </remarks>
/// <returns>
/// True of the block could be extracted and passed to <paramref name="onBlock"/>.
/// This may fail if the file is being unpinned, or if the block does not
/// have the expected realm/hash, or if it is corrupted, or if the address has
/// somehow expired.
///
/// The out argument contains the return value of <paramref name="onBlock"/>.
/// </returns>
/// <see cref="BlockFile.TryWithBlockAtAddress"/>
public bool TryWithBlockAtAddress <T>(
BlockAddress address,
uint realm,
Hash hash,
WithSpan.ReadOnlyReturns <T> onBlock,
out T result)
{
if (address.IsNone())
{
result = default;
return(false);
}
// BlockAddress.File() is 1..1023 but our array is zero-indexed.
var fid = address.File() - 1;
var file = _readFiles[fid];
if (file == null)
{
result = default;
return(false);
}
return(file.TryWithBlockAtAddress(
address,
realm,
hash,
onBlock,
out result));
}
/// <summary>
/// Calls <paramref name="reader"/> on the block represented by the
/// realm and hash.
/// </summary>
/// <exception cref="MissingBlockException">
/// If the block is not present in the scratch space, or was corrupted
/// and failed a checksum check.
/// </exception>
public T Read <T>(uint realm, Hash hash, WithSpan.ReadOnlyReturns <T> reader)
{
var addr = _index.Get(realm, hash);
try
{
if (_wheel.TryWithBlockAtAddress(addr, realm, hash, reader, out var result))
{
return(result);
}
}
// 'MissingBlock' and 'ChecksumFailed', if they happen inside, should
// converted to a 'MissingBlock' and ensure that the broken block is
// removed.
catch (MissingBlockException) {}
catch (CheckSumFailedException) {}
_index.Remove(realm, hash, addr);
throw new MissingBlockException(realm, hash);
}
