/// <summary>Add a value to a counter in one atomic operation</summary>
/// <param name="transaction"></param>
/// <param name="counterKey">Key of the counter, relative to the list's subspace</param>
/// <param name="value">Value that will be added</param>
/// <remarks>This operation will not cause the current transaction to conflict. It may create conflicts for transactions that would read the value of the counter.</remarks>
public void Add([NotNull] IFdbTransaction transaction, [NotNull] TKey counterKey, long value)
{
if (transaction == null)
{
throw new ArgumentNullException(nameof(transaction));
}
if (counterKey == null)
{
throw new ArgumentNullException(nameof(counterKey));
}
//REVIEW: we could no-op if value == 0 but this may change conflict behaviour for other transactions...
transaction.AtomicAdd64(this.Location.Keys[counterKey], value);
}
public async Task EraseAsync(IFdbTransaction trans, Slice key)
{
if (trans == null)
{
throw new ArgumentNullException(nameof(trans));
}
if (!(await ContainsAsync(trans, key).ConfigureAwait(false)))
{
return;
}
for (int level = 0; level < MAX_LEVELS; level++)
{
// This could be optimized with hash
var k = this.Subspace.Encode(level, key);
var c = await trans.GetAsync(k).ConfigureAwait(false);
if (c.HasValue)
{
trans.Clear(k);
}
if (level == 0)
{
continue;
}
var prevKey = await GetPreviousNodeAsync(trans, level, key);
Contract.Assert(prevKey != key);
long countChange = -1;
if (c.HasValue)
{
countChange += DecodeCount(c);
}
trans.AtomicAdd64(this.Subspace.Encode(level, prevKey), countChange);
}
}
/// <summary>Returns a 64-bit integer that
/// 1) has never and will never be returned by another call to this
/// method on the same subspace
/// 2) is nearly as short as possible given the above
/// </summary>
public async Task <long> AllocateAsync([NotNull] IFdbTransaction trans)
{
if (trans == null)
{
throw new ArgumentNullException(nameof(trans));
}
// find the current window size, by reading the last entry in the 'counters' subspace
long start = 0, count = 0;
var kv = await trans
.Snapshot
.GetRange(this.Counters.Keys.ToRange())
.LastOrDefaultAsync();
if (kv.Key.IsPresent)
{
start = this.Counters.Keys.Decode <long>(kv.Key);
count = kv.Value.ToInt64();
}
// check if the window is full
int window = GetWindowSize(start);
if ((count + 1) * 2 >= window)
{ // advance the window
if (FdbDirectoryLayer.AnnotateTransactions)
{
trans.Annotate("Advance allocator window size to {0} starting at {1}", window, start + window);
}
trans.ClearRange(this.Counters.GetPrefix(), this.Counters.Keys.Encode(start) + FdbKey.MinValue);
start += window;
count = 0;
trans.ClearRange(this.Recent.GetPrefix(), this.Recent.Keys.Encode(start));
}
// Increment the allocation count for the current window
trans.AtomicAdd64(this.Counters.Keys.Encode(start), 1);
// As of the snapshot being read from, the window is less than half
// full, so this should be expected to take 2 tries. Under high
// contention (and when the window advances), there is an additional
// subsequent risk of conflict for this transaction.
while (true)
{
// Find a random free slot in the current window...
long candidate;
lock (m_rnd)
{
candidate = start + m_rnd.Next(window);
}
// test if the key is used
var key = this.Recent.Keys.Encode(candidate);
var value = await trans.GetAsync(key).ConfigureAwait(false);
if (value.IsNull)
{ // free slot
// mark as used
trans.Set(key, Slice.Empty);
if (FdbDirectoryLayer.AnnotateTransactions)
{
trans.Annotate("Allocated prefix {0} from window [{1}..{2}] ({3} used)", candidate, start, start + window - 1, count + 1);
}
return(candidate);
}
// no luck this time, try again...
}
}
public static async Task <long> AllocateAsync(IFdbTransaction trans, ITypedKeySubspace <int, long> subspace, Random rng)
{
Contract.NotNull(trans);
// find the current window size, by reading the last entry in the 'counters' subspace
long start = 0, count = 0;
var kv = await trans
.Snapshot
.GetRange(subspace.EncodePartialRange(COUNTERS))
.LastOrDefaultAsync();
if (kv.Key.Count != 0)
{
start = subspace.DecodeLast(kv.Key);
count = kv.Value.ToInt64();
}
// check if the window is full
int window = GetWindowSize(start);
if ((count + 1) * 2 >= window)
{ // advance the window
if (FdbDirectoryLayer.AnnotateTransactions)
{
trans.Annotate("Advance allocator window size to {0} starting at {1}", window, start + window);
}
trans.ClearRange(subspace[COUNTERS, 0], subspace[COUNTERS, start + 1]);
start += window;
count = 0;
trans.ClearRange(subspace[RECENT, 0], subspace[RECENT, start]);
}
// Increment the allocation count for the current window
trans.AtomicAdd64(subspace[COUNTERS, start], 1);
// As of the snapshot being read from, the window is less than half
// full, so this should be expected to take 2 tries. Under high
// contention (and when the window advances), there is an additional
// subsequent risk of conflict for this transaction.
while (true)
{
// Find a random free slot in the current window...
long candidate;
lock (rng)
{
candidate = start + rng.Next(window);
}
// test if the key is used
var key = subspace[RECENT, candidate];
var value = await trans.GetAsync(key).ConfigureAwait(false);
if (value.IsNull)
{ // free slot
// mark as used
trans.Set(key, Slice.Empty);
if (FdbDirectoryLayer.AnnotateTransactions)
{
trans.Annotate("Allocated prefix {0} from window [{1}..{2}] ({3} used)", candidate, start, start + window - 1, count + 1);
}
return(candidate);
}
// no luck this time, try again...
}
}
