Run Times

The Algorand Virtual Machine has two run-time (execution) modes:

  • Logic Signature (or Stateless) mode: executes Logic Signatures,

  • Application (or Stateful) mode: executes Smart Contracts.

For further details about the execution modes, refer to the AVM normative specification.

Each mode differs in opcode availability, Ledger resources accessibility, program sizes, and computational budget.

AVM Run-Time

Logic Signature Mode

The following diagram shows the general flow when a Logic Signature is executed, starting from a transaction message reception in the Network Layer, going through the AVM for program execution, and all the way up to the transaction approval and subsequent push into the Transaction Pool, to be added to an upcoming block’s payset.

sequenceDiagram
    Network->>TxHandler: Incoming message
    TxHandler->>+MessageCache: Check for<br/>duplicate message
    MessageCache->>-TxHandler: returns
    TxHandler->>+RateLimiter: Rate Limit Check
    RateLimiter->>-TxHandler: returns
    TxHandler->>+SigVerifier: Verify LogicSig
    SigVerifier->>+AVM: Run LogicSig
    AVM->>-SigVerifier: returns
    SigVerifier->>-TxHandler: returns
    TxHandler->>+TxPool: Push verified tx to pool

Application Mode

The following diagram shows the execution path of a transaction containing a call to an Application. Note that code execution is done in a different pipeline; applications being stateful, a full block context is needed to evaluate their correctness, and so code execution happens at block evaluation time.

For further details on the block evaluation stage, see the Ledger non-normative specifications.

sequenceDiagram
    BlockEvaluator->>+TxGroup: Eval group
    TxGroup->>+Tx: Eval transaction
    Tx->>+AVM: Application call
    AVM->>-Tx: returns
    Tx->>-TxGroup: returns
    TxGroup->>-BlockEvaluator: returns

A special way of executing an application is the internal cross-application call, (itxn_begin opcode).

Note that the beginning of this flow is the same as in a regular application call, as this constitutes a subcase of an Application mode call.

sequenceDiagram
    BlockEvaluator->>+TxGroup: Eval group
    TxGroup->>+Tx: Eval transaction
    Tx->>+AVM: Application call
    AVM->>+InternalTxGroup: itxn_begin
    InternalTxGroup->>+InternalTx: Process each<br/>transaction
    InternalTx->>+AVM: Process ApplicationCall transaction
    AVM->>-InternalTx: returns
    InternalTx->>-InternalTxGroup: returns
    InternalTxGroup->>-AVM: returns
    AVM->>-Tx: returns
    Tx->>-TxGroup: returns
    TxGroup->>-BlockEvaluator: returns