/// <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);
}