/// <summary>
/// create a new table-lock
/// </summary>
/// <param name="ctx"></param>
/// <returns></returns>
private LockEntry CreateTabLock(ref LockContext ctx)
{
if (!TabLocks.TryGetValue(ctx.Index, out var list))
{
list = new LinkedList <LockEntry>();
TabLocks[ctx.Index] = list;;
}
var tx = ctx.Transaction;
var entry = new LockEntry(ctx.Page, ctx.Flags, ctx.RecordCount);
if (entry.IsWaiting)
{
tx.WaitLock = entry;
}
list.AddLast(entry);
tx.Locks.AddLast(entry);
entry.GNode = list.Last;
entry.TNode = tx.Locks.Last;
entry.Index = ctx.Index;
entry.Transaction = ctx.Transaction;
entry.Thread = Thread.CurrentThread.ManagedThreadId;
return(entry);
}
/// <summary>
/// check current transaction has held the table's lock >=ctx-lock-level and not been in wait state
/// </summary>
/// <param name="ctx"></param>
/// <returns></returns>
private bool IsHeldTabLock(ref LockContext ctx, out LockEntry entry)
{
var locks = TabLocks.GetValueOrDefault(ctx.Index);
if (locks == null)
{
entry = null;
return(false);
}
for (var node = locks.First; node != null; node = node.Next)
{
var lockEntry = node.Value;
if (lockEntry.Transaction != ctx.Transaction)
{
continue;
}
if (lockEntry.IsExclusive || !ctx.Flags.IsExclusive())
{
entry = lockEntry;
return(true);
}
}
entry = null;
return(false);
}
/// <summary>
/// is other's transaction has held the table's lock and conflict with the ctx-lock
/// </summary>
/// <param name="ctx"></param>
/// <returns></returns>
private bool IsOthersHeldOrWaitConflictTabLock(Transaction tx, TableIndex index, LockFlags flags, LockEntry endEntry = null)
{
var locks = TabLocks.GetValueOrDefault(index);
if (locks == null)
{
return(false);
}
for (var node = locks.First; node != null; node = node.Next)
{
var entry = node.Value;
if (entry == endEntry)
{
break;
}
if (entry.Transaction == tx)
{
continue;
}
if (entry.IsExclusive || flags.IsExclusive())
{
return(true);
}
}
return(false);
}
/// <summary>
/// lock a table
/// </summary>
/// <param name="ctx"></param>
/// <param name="entry"></param>
/// <returns></returns>
public DBResult LockTab(ref LockContext ctx, out LockEntry entry)
{
var locks = TabLocks.GetValueOrDefault(ctx.Index);
if (locks == null || locks.Count == 0)
{
entry = CreateTabLock(ref ctx);
return(DBResult.Success);
}
if (IsHeldTabLock(ref ctx, out entry))
{
return(DBResult.Success);
}
if (IsOthersHeldOrWaitConflictTabLock(ctx.Transaction, ctx.Index, ctx.Flags))
{
ctx.Flags |= LockFlags.Waiting;
return(CreateTabLockForWait(ref ctx, out entry));
}
entry = CreateTabLock(ref ctx);
return(DBResult.Success);
}
internal LockEntry FindFirstTabLockEntry(TableIndex index)
{
return(TabLocks.TryGetValue(index, out var list) ? list.First.Value : null);
}
