/// <summary>
/// Attempts to acquire the lock synchronously. Usage:
/// <code>
/// using (var handle = myLock.TryAcquire(...))
/// {
/// if (handle != null) { /* we have the lock! */ }
/// }
/// // dispose releases the lock if we took it
/// </code>
/// </summary>
/// <param name="lock"></param>
/// <param name="timeout">How long to wait before giving up on acquiring the lock. Defaults to 0</param>
/// <returns>An <see cref="IDisposable"/> "handle" which can be used to release the lock, or null if the lock was not taken</returns>
public LockAcquisitionResult TryAcquire(string @lock, TimeSpan timeout = default(TimeSpan))
{
// synchronous mode
var timeoutMillis = timeout.ToInt32Timeout();
// calculate safe lock name
var lockName = ToSafeLockName(@lock, MaxLockNameLength, s => s);
DbConnection acquireConnection = null;
var cleanup = true;
try
{
acquireConnection = GetConnection();
if (_connectionString != null)
{
acquireConnection.Open();
}
else if (acquireConnection == null)
{
throw new InvalidOperationException("The transaction had been disposed");
}
else if (acquireConnection.State != ConnectionState.Open)
{
throw new InvalidOperationException("The connection is not open");
}
var checkCommand = SqlHelpers.CreateCheckLockAvailabilityCommand(acquireConnection, timeoutMillis, lockName);
var exists = (int)checkCommand.ExecuteScalar() > 0;
if (exists)
{
return(LockAcquisitionResult.Fail);
}
var id = Guid.NewGuid();
SqlParameter insertReturnValue;
using (var insertCommand = SqlHelpers.CreateInsertApplicationLockCommand(acquireConnection, id,
timeoutMillis, lockName, Utc, out insertReturnValue))
{
insertCommand.ExecuteNonQuery();
}
var ret = (int)insertReturnValue.Value;
cleanup = ret == 0;
var success = ret == 0;
var owner = string.Empty;
if (success)
{
// hash owner
owner = _encryptor.Encrypt(id.ToString());
// check no duplicates.
var checkDuplicateCommand = SqlHelpers.CreateCheckLockAvailabilityCommand(acquireConnection, timeoutMillis, lockName);
var duplicatesExist = (int)checkDuplicateCommand.ExecuteScalar() > 1;
if (duplicatesExist)
{
// delete current lock
ReleaseLock(lockName, owner);
return(LockAcquisitionResult.Fail);
}
}
return(new LockAcquisitionResult
{
Success = success,
LockOwner = owner
});
}
catch
{
// in case we fail to create lock scope or something
cleanup = true;
throw;
}
finally
{
if (cleanup)
{
Cleanup(acquireConnection);
}
}
}