ACS2 - Parallel Execution Standard¶

ACS2 is used to provide information for parallel execution of transactions.

Interface¶

A contract that inherits ACS2 only needs to implement one method:

Methods¶

Method Name	Request Type	Response Type	Description
GetResourceInfo	aelf.Transaction	acs2.ResourceInfo	Gets the resource information that the transaction execution depends on.

Types¶

acs2.ResourceInfo¶

Field	Type	Description	Label
write_paths	aelf.ScopedStatePath	The state path that depends on when writing.	repeated
read_paths	aelf.ScopedStatePath	The state path that depends on when reading.	repeated
non_parallelizable	bool	Whether the transaction is not executed in parallel.

aelf.Address¶

Field	Type	Description	Label
value	bytes

aelf.BinaryMerkleTree¶

Field	Type	Description	Label
nodes	Hash	The leaf nodes.	repeated
root	Hash	The root node hash.
leaf_count	int32	The count of leaf node.

aelf.Hash¶

Field	Type	Description	Label
value	bytes

aelf.LogEvent¶

Field	Type	Description	Label
address	Address	The contract address.
name	string	The name of the log event.
indexed	bytes	The indexed data, used to calculate bloom.	repeated
non_indexed	bytes	The non indexed data.

aelf.MerklePath¶

Field	Type	Description	Label
merkle_path_nodes	MerklePathNode	The merkle path nodes.	repeated

aelf.MerklePathNode¶

Field	Type	Description	Label
hash	Hash	The node hash.
is_left_child_node	bool	Whether it is a left child node.

aelf.SInt32Value¶

Field	Type	Description	Label
value	sint32

aelf.SInt64Value¶

Field	Type	Description	Label
value	sint64

aelf.ScopedStatePath¶

Field	Type	Description	Label
address	Address	The scope address, which will be the contract address.
path	StatePath	The path of contract state.

aelf.SmartContractRegistration¶

Field	Type	Description
category	sint32	The category of contract code(0: C#).
code	bytes	The byte array of the contract code.
code_hash	Hash	The hash of the contract code.
is_system_contract	bool	Whether it is a system contract.
version	int32	The version of the current contract.

aelf.StatePath¶

Field	Type	Description	Label
parts	string	The partial path of the state path.	repeated

aelf.Transaction¶

Field	Type	Description
from	Address	The address of the sender of the transaction.
to	Address	The address of the contract when calling a contract.
ref_block_number	int64	The height of the referenced block hash.
ref_block_prefix	bytes	The first four bytes of the referenced block hash.
method_name	string	The name of a method in the smart contract at the To address.
params	bytes	The parameters to pass to the smart contract method.
signature	bytes	When signing a transaction it’s actually a subset of the fields: from/to and the target method as well as the parameter that were given. It also contains the reference block number and prefix.

aelf.TransactionExecutingStateSet¶

Field	Type	Description	Label
writes	TransactionExecutingStateSet.WritesEntry	The changed states.	repeated
reads	TransactionExecutingStateSet.ReadsEntry	The read states.	repeated
deletes	TransactionExecutingStateSet.DeletesEntry	The deleted states.	repeated

aelf.TransactionExecutingStateSet.DeletesEntry¶

Field	Type	Description	Label
key	string
value	bool

aelf.TransactionExecutingStateSet.ReadsEntry¶

Field	Type	Description	Label
key	string
value	bool

aelf.TransactionExecutingStateSet.WritesEntry¶

Field	Type	Description	Label
key	string
value	bytes

aelf.TransactionResult¶

Field	Type	Description	Label
transaction_id	Hash	The transaction id.
status	TransactionResultStatus	The transaction result status.
logs	LogEvent	The log events.	repeated
bloom	bytes	Bloom filter for transaction logs. A transaction log event can be defined in the contract and stored in the bloom filter after the transaction is executed. Through this filter, we can quickly search for and determine whether a log exists in the transaction result.
return_value	bytes	The return value of the transaction execution.
block_number	int64	The height of the block hat packages the transaction.
block_hash	Hash	The hash of the block hat packages the transaction.
error	string	Failed execution error message.

aelf.TransactionResultStatus¶

Name	Number	Description
NOT_EXISTED	0	The execution result of the transaction does not exist.
PENDING	1	The transaction is in the transaction pool waiting to be packaged.
FAILED	2	Transaction execution failed.
MINED	3	The transaction was successfully executed and successfully packaged into a block.
CONFLICT	4	When executed in parallel, there are conflicts with other transactions.
PENDING_VALIDATION	5	The transaction is waiting for validation.
NODE_VALIDATION_FAILED	6	Transaction validation failed.

Usage¶

AElf uses the key-value database to store data. For the data generated during the contract execution, a mechanism called State Path is used to determine the key of the data.

For example Token contract defines a property,

public MappedState<Address, string, long> Balances { get; set; }

it can be used to access, modify balance.

Assuming that the address of the Token contract is Nmjj7noTpMqZ522j76SDsFLhiKkThv1u3d4TxqJMD8v89tWmE. If you want to know the balance of the address 2EM5uV6bSJh6xJfZTUa1pZpYsYcCUAdPvZvFUJzMDJEx3rbioz, you can directly use this key to access redis / ssdb to get its value.

Nmjj7noTpMqZ522j76SDsFLhiKkThv1u3d4TxqJMD8v89tWmE/Balances/2EM5uV6bSJh6xJfZTUa1pZpYsYcCUAdPvZvFUJzMDJEx3rbioz/ELF

On AElf, the implementation of parallel transaction execution is also based on the key , developers need to provide a method may access to the StatePath, then the corresponding transactions will be properly grouped before executing: if the two methods do not access the same StatePath, then you can safely place them in different groups.

Attention: The transaction will be canceled and labeled to “can not be groupped” when the StatePath mismatchs the method.

If you are interested in the logic, you can view the code ITransactionGrouper, as well as IParallelTransactionExecutingService .

Implementation¶

Token contract, as an example, the core logic of method Transfer is to modify the balance of address. It accesses the balances property mentioned above twice.

At this point, we need to notify ITransactionGrouper via the GetResourceInfo method of the key of the ELF balance of address A and address B:

var args = TransferInput.Parser.ParseFrom(txn.Params);
var resourceInfo = new ResourceInfo
{
    Paths =
    {
        GetPath(nameof(TokenContractState.Balances), txn.From.ToString(), args.Symbol),
        GetPath(nameof(TokenContractState.Balances), args.To.ToString(), args.Symbol),
    }
};
return resourceInfo;

The GetPath forms a ScopedStatePath from several pieces of data that make up the key:

private ScopedStatePath GetPath(params string[] parts)
{
    return new ScopedStatePath
    {
        Address = Context.Self,
        Path = new StatePath
        {
            Parts =
            {
                parts
            }
        }
    }
}

Test¶

You can construct two transactions, and the transactions are passed directly to an implementation instance of ITransactionGrouper, and the GroupAsync method is used to see whether the two transactions are parallel.

We prepare two stubs that implement the ACS2 contract with different addresses to simulate the Transfer:

var keyPair1 = SampleECKeyPairs.KeyPairs[0];
var acs2DemoContractStub1 = GetACS2DemoContractStub(keyPair1);
var keyPair2 = SampleECKeyPairs.KeyPairs[1];
var acs2DemoContractStub2 = GetACS2DemoContractStub(keyPair2);

Then take out some services and data needed for testing from Application:

var transactionGrouper = Application.ServiceProvider.GetRequiredService<ITransactionGrouper>();
var blockchainService = Application.ServiceProvider.GetRequiredService<IBlockchainService>();
var chain = await blockchainService.GetChainAsync();

Finally, check it via transactionGrouper:

// Situation can be parallel executed.
{
    var groupedTransactions = await transactionGrouper.GroupAsync(new ChainContext
    {
        BlockHash = chain.BestChainHash,
        BlockHeight = chain.BestChainHeight
    }, new List<Transaction>
    {
        acs2DemoContractStub1.TransferCredits.GetTransaction(new TransferCreditsInput
        {
            To = Address.FromPublicKey(SampleECKeyPairs.KeyPairs[2].PublicKey),
            Symbol = "ELF",
            Amount = 1
        }),
        acs2DemoContractStub2.TransferCredits.GetTransaction(new TransferCreditsInput
        {
            To = Address.FromPublicKey(SampleECKeyPairs.KeyPairs[3].PublicKey),
            Symbol = "ELF",
            Amount = 1
        }),
    });
    groupedTransactions.Parallelizables.Count.ShouldBe(2);
}
// Situation cannot.
{
    var groupedTransactions = await transactionGrouper.GroupAsync(new ChainContext
    {
        BlockHash = chain.BestChainHash,
        BlockHeight = chain.BestChainHeight
    }, new List<Transaction>
    {
        acs2DemoContractStub1.TransferCredits.GetTransaction(new TransferCreditsInput
        {
            To = Address.FromPublicKey(SampleECKeyPairs.KeyPairs[2].PublicKey),
            Symbol = "ELF",
            Amount = 1
        }),
        acs2DemoContractStub2.TransferCredits.GetTransaction(new TransferCreditsInput
        {
            To = Address.FromPublicKey(SampleECKeyPairs.KeyPairs[2].PublicKey),
            Symbol = "ELF",
            Amount = 1
        }),
    });
    groupedTransactions.Parallelizables.Count.ShouldBe(1);
}

Example¶

You can refer to the implementation of the MultiToken contract for GetResourceInfo. Noting that for the ResourceInfo provided by the method Transfer, you need to consider charging a transaction fee in addition to the two keys mentioned in this article.