public async Task <LeaseResponse> TryAcquireLeaseAsync(AcquireLeaseRequest acquireLeaseRequest)
{
using (var conn = await ConnectionHelper.GetOpenConnectionAsync(this.connectionString))
{
var transaction = conn.BeginTransaction(IsolationLevel.Serializable);
var command = conn.CreateCommand();
command.Transaction = transaction;
try
{
// obtain lock on the record blocking other nodes until the transaction is committed
command.CommandText = "UPDATE ResourceGroups SET LockedByClient = @ClientId WHERE ResourceGroup = @ResourceGroup";
command.Parameters.AddWithValue("@ClientId", acquireLeaseRequest.ClientId);
command.Parameters.Add("@ResourceGroup", SqlDbType.VarChar, 100).Value = acquireLeaseRequest.ResourceGroup;
await command.ExecuteNonQueryAsync();
// get the resource group (TODO, use OUTPUT on UPDATE query instead of another query)
command.Parameters.Clear();
command.CommandText = @"SELECT [ResourceGroup]
,[CoordinatorId]
,[LastCoordinatorRenewal]
,[CoordinatorServer]
,[LockedByClient]
,[FencingToken]
,[LeaseExpirySeconds]
,[HeartbeatSeconds]
,GETUTCDATE() AS [TimeNow]
FROM [RBR].[ResourceGroups]
WHERE ResourceGroup = @ResourceGroup";
command.Parameters.Add("@ResourceGroup", SqlDbType.VarChar, 100).Value = acquireLeaseRequest.ResourceGroup;
ResourceGroup rg = null;
using (var reader = await command.ExecuteReaderAsync())
{
if (await reader.ReadAsync())
{
rg = new ResourceGroup()
{
Name = acquireLeaseRequest.ResourceGroup,
CoordinatorId = GetGuidFromNullableGuid(reader, "CoordinatorId"),
CoordinatorServer = GetStringFromNullableGuid(reader, "CoordinatorServer"),
LastCoordinatorRenewal = GetDateTimeFromNullable(reader, "LastCoordinatorRenewal"),
TimeNow = (DateTime)reader["TimeNow"],
LockedByClientId = GetGuidFromNullableGuid(reader, "LockedByClient"),
FencingToken = (int)reader["FencingToken"],
LeaseExpirySeconds = (int)reader["LeaseExpirySeconds"],
HeartbeatSeconds = (int)reader["HeartbeatSeconds"]
};
}
}
if (rg == null)
{
return new LeaseResponse()
{
Result = LeaseResult.NoLease, Lease = new Lease()
{
ExpiryPeriod = TimeSpan.FromMinutes(1), HeartbeatPeriod = TimeSpan.FromSeconds(25)
}
}
}
;
// determine the response, if the CoordinatorId is empty or expired then grant, else deny
var response = new LeaseResponse();
response.Lease = new Lease();
if (rg.CoordinatorId == Guid.Empty || (rg.TimeNow - rg.LastCoordinatorRenewal).TotalSeconds > rg.LeaseExpirySeconds)
{
response.Lease.ResourceGroup = acquireLeaseRequest.ResourceGroup;
response.Lease.ClientId = acquireLeaseRequest.ClientId;
response.Lease.ExpiryPeriod = TimeSpan.FromSeconds(rg.LeaseExpirySeconds);
response.Lease.HeartbeatPeriod = TimeSpan.FromSeconds(rg.HeartbeatSeconds);
response.Lease.FencingToken = ++rg.FencingToken;
response.Result = LeaseResult.Granted;
command.Parameters.Clear();
command.CommandText = @"UPDATE [RBR].[ResourceGroups]
SET [CoordinatorId] = @ClientId
,[LastCoordinatorRenewal] = GETUTCDATE()
,[CoordinatorServer] = @Server
,[FencingToken] = @FencingToken
WHERE ResourceGroup = @ResourceGroup";
command.Parameters.AddWithValue("@ClientId", acquireLeaseRequest.ClientId);
command.Parameters.AddWithValue("@FencingToken", response.Lease.FencingToken);
command.Parameters.Add("@Server", SqlDbType.NVarChar, 500).Value = Environment.MachineName;
command.Parameters.Add("@ResourceGroup", SqlDbType.VarChar, 100).Value = acquireLeaseRequest.ResourceGroup;
await command.ExecuteNonQueryAsync();
}
else
{
response.Lease.ExpiryPeriod = TimeSpan.FromSeconds(rg.LeaseExpirySeconds);
response.Lease.HeartbeatPeriod = TimeSpan.FromSeconds(rg.HeartbeatSeconds);
response.Result = LeaseResult.Denied;
}
transaction.Commit();
return(response);
}
catch (SqlException ex)
{
try
{
this.logger.Error("Rolling back lease acquisition: ", ex);
transaction.Rollback();
}
catch (Exception rex)
{
this.logger.Error("Rollback of lease acquisition failed: ", rex);
}
return(new LeaseResponse()
{
Result = TransientErrorDetector.IsTransient(ex) ? LeaseResult.TransientError : LeaseResult.Error,
Message = "Lease acquisition failure",
Exception = ex
});
}
}
}
public async Task <LeaseResponse> TryRenewLeaseAsync(RenewLeaseRequest renewLeaseRequest)
{
using (var conn = await ConnectionHelper.GetOpenConnectionAsync(this.connectionString))
{
var transaction = conn.BeginTransaction(IsolationLevel.Serializable);
var command = conn.CreateCommand();
command.Transaction = transaction;
try
{
// obtain lock on the record blocking other nodes until the transaction is committed
command.CommandText = "UPDATE ResourceGroups SET LockedByClient = @ClientId WHERE ResourceGroup = @ResourceGroup";
command.Parameters.AddWithValue("@ClientId", renewLeaseRequest.ClientId);
command.Parameters.Add("@ResourceGroup", SqlDbType.VarChar, 100).Value = renewLeaseRequest.ResourceGroup;
await command.ExecuteNonQueryAsync();
// get the resource group
command.Parameters.Clear();
command.CommandText = @"SELECT [ResourceGroup]
,[CoordinatorId]
,[LastCoordinatorRenewal]
,[CoordinatorServer]
,[LockedByClient]
,[FencingToken]
,[LeaseExpirySeconds]
,[HeartbeatSeconds]
,GETUTCDATE() AS [TimeNow]
FROM [RBR].[ResourceGroups]
WHERE ResourceGroup = @ResourceGroup";
command.Parameters.Add("@ResourceGroup", SqlDbType.VarChar, 100).Value = renewLeaseRequest.ResourceGroup;
ResourceGroup rg = null;
using (var reader = await command.ExecuteReaderAsync())
{
if (await reader.ReadAsync())
{
rg = new ResourceGroup()
{
Name = renewLeaseRequest.ResourceGroup,
CoordinatorId = GetGuidFromNullableGuid(reader, "CoordinatorId"),
CoordinatorServer = GetStringFromNullableGuid(reader, "CoordinatorServer"),
LastCoordinatorRenewal = GetDateTimeFromNullable(reader, "LastCoordinatorRenewal"),
TimeNow = (DateTime)reader["TimeNow"],
LockedByClientId = GetGuidFromNullableGuid(reader, "LockedByClient"),
FencingToken = (int)reader["FencingToken"],
LeaseExpirySeconds = (int)reader["LeaseExpirySeconds"],
HeartbeatSeconds = (int)reader["HeartbeatSeconds"]
};
}
}
if (rg == null)
{
return new LeaseResponse()
{
Result = LeaseResult.NoLease
}
}
;
// determine the response, if the CoordinatorId matches the current client id and the fencing token is the same then grant, else deny
var response = new LeaseResponse();
response.Lease = new Lease();
if (!rg.CoordinatorId.Equals(renewLeaseRequest.ClientId) || rg.FencingToken > renewLeaseRequest.FencingToken)
{
return new LeaseResponse()
{
Result = LeaseResult.Denied
}
}
;
if ((rg.TimeNow - rg.LastCoordinatorRenewal).TotalSeconds <= rg.LeaseExpirySeconds)
{
response.Lease.ResourceGroup = renewLeaseRequest.ResourceGroup;
response.Lease.ClientId = renewLeaseRequest.ClientId;
response.Lease.ExpiryPeriod = TimeSpan.FromSeconds(rg.LeaseExpirySeconds);
response.Lease.HeartbeatPeriod = TimeSpan.FromSeconds(rg.HeartbeatSeconds);
response.Lease.FencingToken = rg.FencingToken;
response.Result = LeaseResult.Granted;
command.Parameters.Clear();
command.CommandText = @"UPDATE [RBR].[ResourceGroups]
SET [LastCoordinatorRenewal] = GETUTCDATE()
WHERE ResourceGroup = @ResourceGroup";
command.Parameters.Add("@ResourceGroup", SqlDbType.VarChar, 100).Value = renewLeaseRequest.ResourceGroup;
await command.ExecuteNonQueryAsync();
}
else
{
response.Result = LeaseResult.Denied;
}
transaction.Commit();
return(response);
}
catch (Exception ex)
{
try
{
this.logger.Error("Rolling back lease renewal: ", ex);
transaction.Rollback();
}
catch (Exception rex)
{
this.logger.Error("Rollback of lease renewal failed: ", rex);
}
return(new LeaseResponse()
{
Result = LeaseResult.Error,
Message = ex.ToString(),
Exception = ex
});
}
}
}