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, andminttoaddressContract), 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 concurrence 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
minton 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 themintmethod Completes. The third also also returns a promise that resolves when theMintMethod Completes.
By using callbacks for the first two calls and promises for the third call, web3j ensurs that each contract method 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 SNIPPT DEMONSTRATING How To Use Web3J With Callbacks:
`JavaScript
Const Web3 = Require ('Web3');
Const Web3 = New Web3 (New Web3.Providers.httprovider ('
// 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
constokencontract = {
Minttoken: (mintparams) => {{
Return Web3.eth.mint (Mintparams) .on ('Completed', (Error, Result) => {
console.log (minted token on minttoken contract);
});
}
};
constantoaddressContract = {
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 mintken contract first
Const Minttokenpromise = TokenContract.Mintoken ({from: Accounts [0]})
.then (() => console.log (‘Minted token on Minttoken Contract’));
minttokenpromise.then (() => {
// call minttoaddress contract second
constantoaddresspromise = 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.Mintoken ({from: Accounts [2]})
.then (() => console.log (‘Minted token on TokenContract Contract’));
Return Minttokenpromise3;
});
}). Catch ((ERR) => {
Console.
