Here is my sample code, whether the contract to contract calls in setName function is synchronous or asynchronous?

Question

pragma solidity ^0.4.22;

contract Testing {


    function setName(bytes32 firstName , bytes32 lastName) public  returns(bool) {
        Sample _test = new Sample(firstName);
        _test.addLastName(firstName, lastName);
        return true;
    }
}

contract Sample {

    address a;

    bytes32 firstName;

    bytes32 lastName;

    constructor(bytes32 _firstName) public {
        firstName = _firstName;
    }

    modifier onlyBy(bytes32 _firstName) {
        require(
            firstName == _firstName,
            "Error"
        );
        _;
    }

    function addLastName(bytes32 firstName, bytes32 _name) public onlyBy(firstName) returns(bool) {
        lastName = _name;
        return true;
    }
}


I am getting this error


(node:12667) UnhandledPromiseRejectionWarning: Error: Transaction has been reverted by the EVM:

    {
       "blockHash":"0xe709d446057c70ba4928424a71e072aa0b144461ceea0fc535849cd05c7b1cda",
       "blockNumber":4301,
       "contractAddress":null,
       "cumulativeGasUsed":62775,
       "from":"0x112fda795ce61992653b8775597a9152ee776e4c",
       "gasUsed":62775,
       "logsBloom":"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
       "status":false,
       "to":"0x41e864e68ecebe2fd69cea1eed49b5fc516e9af9",
       "transactionHash":"0x33b3921491631d4e2d35a3887858f21a3c02b2dd552b624bb243e2c33f6c4e86",
       "transactionIndex":0,
       "events":{

       }
    }

Answer 1

PREMISE

As already said, the EVM execute fully deterministically and sequentially.

ANSWER

You get the exception from javascript because the execution runs out of gas. You can guess that because the gas used is the same amount of "gasLimit". This means that either you allocate too low gas or alternatively, you use too much gas for the execution. I propend for the latter because each time you call test you are deploying a new contract in the network with

Sample _test = new Sample(firstName);.

When you call new under the hood it uses a CREATE instruction. It costs 32000 gas. In addition, you have also to pay 200 gas for each byte stored on the blockchain, i.e. the persistent code of the contract. In addition you pay for the executed instructions and for the memory used during the execution. Moreover, the intrinsic cost for a transaction is 21000 units of gas. You also pay 4 gas units for each input byte that is 0 and 68 gas units for each input byte that is not equal to 0.

So let's sum up the amount of gas used:

21000 + |input_price| + 32000 + |o|*200 + |amount of gas for the rest of execution| Where |o| is the size of the code that will persist on the blockchain.

You can easily see that 62775, is too low to grant the whole execution.

Answer 2

All smart contracts in Ethereum are executed synchronously - that includes external/contract-to-contract calls!

If your transaction calls a contract that itself calls 5 other contracts, those calls will all be executed before any other transactions (from other users) are executed.

So, if your transaction is the first transaction included in a block, all the results of your transaction will occur before the execution of any of the other transactions in that block start.