Ethereum: Having Problems with Multiple Contract Methods calls

Ethereum: Having Problems with Multiple Contract Methods Calls

When working with Web3.js, interacting with multiple contracts in parallel can be a common challenge. One such issue arises when attempting to mint tokens using different contract methods simultaneously. In this article, we’ll delve into the details of how Web3.js handles concurrent method calls and provide guidance on mitigating potential issues.

The Issue

Imagine you have three contracts: TokenContract, MintTokenContract, and MintToAddressContract. You want to mint a token using these different methods simultaneously. However, due to the asynchronous nature of Web3.js, each contract call is executed in a separate thread or process, which may not be exactly simultaneous.

When you make three method calls to mint on different contracts (TokenContract, MintTokenContract, and MintToAddressContract), you might observe an exception being thrown. This issue arises because the methods are called one after another, without ensuring that they don’t interfere with each other or cause concurrency problems.

The Web3j Solution

In Web3j, multiple method calls to the same contract are handled using a combination of callbacks and promises. Here’s how it works:

• Callbacks: When you call mint on a contract, Web3j returns a callback object. This callback is used to handle the result of the method call.

• Promises: The first two calls (contract.mint(mintParams).sendAsync()) return promises that resolve when the mint method completes. The third call also returns a promise that resolves when the mint method completes.

By using callbacks for the first two calls and promises for the third call, Web3j ensures that each contract method call is handled independently of the others. This approach prevents concurrency issues and allows you to make multiple method calls concurrently.

Example Code

Here’s an example code snippet demonstrating how to use Web3j with callbacks:

“javascript

const Web3 = require('web3');

const web3 = new Web3(new Web3.providers.HttpProvider('

// Define a contract and method parameters

const TokenContract = {

mint: (mintParams) => {

return web3.eth.mint(mintParams).on('completed', (error, result) => {

console.log(Minted token ${result.tokenId});

});

}

};

// Define three contracts and their methods

const MintTokenContract = {

mintToken: (mintParams) => {

return web3.eth.mint(mintParams).on('completed', (error, result) => {

console.log(Minted token on MintToken contract);

});

}

};

const MintToAddressContract = {

mintToAddress: (mintParams) => {

return web3.eth.mint(mintParams).on('completed', (error, result) => {

console.log(Minted token to address ${result.address}`);

});

}

};

// Make three method calls concurrently

web3.eth.getAccounts((err, accounts) => {

if (err) throw err;

// Call MintToken contract first

const mintTokenPromise = TokenContract.mintToken({ from: accounts[0] })

.then(() => console.log(‘Minted token on MintToken contract’));

mintTokenPromise.then(() => {

// Call MintToAddress contract second

const mintToAddressPromise = MintToAddressContract.mintToAddress({ from: accounts[1] })

.then(() => console.log(‘Minted token to address on MintToAddress contract’));

mintToAddressPromise.then(() => {

// Call TokenContract third time (this one is not needed)

const mintTokenPromise3 = TokenContract.mintToken({ from: accounts[2] })

.then(() => console.log(‘Minted token on TokenContract contract’));

return mintTokenPromise3;

});

}).catch((err) => {

console.