HarmonyOS Next Financial System: Generic-based transaction core development

In the development of HarmonyOS Next financial system, generic technology is the key to building a high-scaling, type-safe transaction core.Through parameterized type design, transaction logic can be adapted to multi-currency and multi-business scenarios, while combining transaction security mechanisms and performance optimization to ensure the reliability and efficiency of the financial system.This article will analyze the development practice of generic-based financial system from three dimensions: type abstraction, transaction security, and performance stress measurement.

1. Type abstraction: Generics and protocols to build a multi-monetary system

The generic class Account<T: Currency> implements account logic that is independent of currency type through protocol constraints, and supports unified management of various currency types such as RMB and US dollar.

1. Definition of currency agreement

protocol Currency {
/// Currency symbols (such as "¥", "$")
    func symbol() -> String
/// Minimum unit (such as 0.01 yuan)
    func minUnit() -> Decimal
/// Exchange rate conversion (the benchmark currency is USD)
    func convert(to currency: Self, rate: Decimal) -> Decimal
}

2. Generic Account Class Implementation

class Account<T: Currency> {
private var balance: Decimal // Balance
private let currency: T // Currency type

    init(initialBalance: Decimal, currency: T) {
        self.balance = initialBalance
        self.currency = currency
    }

/// Deposit (automatically check the minimum unit)
    func deposit(amount: Decimal) -> Bool {
        guard amount >= currency.minUnit() else { return false }
        balance += amount
        return true
    }

/// Withdrawal (return to success)
    func withdraw(amount: Decimal) -> Bool {
        guard amount <= balance && amount >= currency.minUnit() else { return false }
        balance -= amount
        return true
    }

/// Inquiry of balance (with currency symbol)
    func getBalance() -> String {
        return "\(balance) \(currency.symbol())"
    }
}

3. Implementation of specific currency types

// RMB type
struct RMB: Currency {
    func symbol() -> String { return "¥" }
    func minUnit() -> Decimal { return Decimal("0.01") }
    func convert(to currency: RMB, rate: Decimal = 1.0) -> Decimal {
return balance * rate // Simplify exchange rate calculation logic
    }
}

// USD type
struct USD: Currency {
    func symbol() -> String { return "$" }
    func minUnit() -> Decimal { return Decimal("0.01") }
    func convert(to currency: USD, rate: Decimal = 1.0) -> Decimal {
        return balance * rate
    }
}

2. Transaction security: Immutable variables and STMs guarantee transaction atomicity

Financial transactions need to meet the ACID characteristics, and ensure the atomicity and isolation of operations through immutable variables (val) and software transaction memory (STM).

1. Thread-safe design of immutable variables

actor TransactionActor {
private var accounts: [String: Account<Currency>] = [:] // Account collection

/// Transfer transaction (atomic operation)
    receiver func transfer(
        fromAccountId: String,
        toAccountId: String,
        amount: Decimal,
        fromCurrency: some Currency,
        toCurrency: some Currency
    ) async throws {
// Lock the account (avoid race conditions)
        let fromAcct = accounts[fromAccountId]!
        let toAcct = accounts[toAccountId]!

// Deduct the amount of the source account (immutable operation)
        let newFromBalance = fromAcct.balance - amount
        if newFromBalance < fromCurrency.minUnit() {
            throw TransactionError.insufficientFunds
        }

// Increase the target account amount (automatically convert currency)
        let convertedAmount = fromCurrency.convert(to: toCurrency, rate: getExchangeRate(from: fromCurrency, to: toCurrency))
        let newToBalance = toAcct.balance + convertedAmount

// Atomically update the account status (STM ensures consistency)
        try await atomic {
            fromAcct.balance = newFromBalance
            toAcct.balance = newToBalance
        }
    }
}

2. Transaction exception handling

enum TransactionError: Error {
case insufficientFunds // Insufficient balance
case invalidCurrency // Currency type mismatch
}

// Use example
let actor = TransactionActor()
do {
    try await actor.transfer(
        fromAccountId: "A123",
        toAccountId: "B456",
        amount: Decimal("1000"),
        fromCurrency: RMB(),
        toCurrency: USD()
    )
println("Transfer successful")
} catch TransactionError.insufficientFunds {
println("Insufficient balance, transfer failed")
}

3. Performance pressure measurement: VArray storage and million-level transaction processing

Use the value type array VArray to optimize transaction record storage, combine memory alignment and batch operation to improve system throughput.

1. Transaction record structure design

struct TransactionRecord {
let timestamp: Int64 // Timestamp (nanoseconds)
let fromAccount: String // Source Account ID
let toAccount: String // Target account ID
let amount: Decimal // Transaction amount
let currency: String // Currency type
}

2. VArray storage and batch writing

// Pre-allocate 1 million transaction record space (allocated on the stack)
var transactionLog: VArray<TransactionRecord, $1000000> = VArray(item: TransactionRecord(
    timestamp: 0,
    fromAccount: "",
    toAccount: "",
    amount: Decimal("0"),
    currency: ""
))

// Batch write test (simulate 100,000 transactions per second)
func stressTest() {
    let start = SystemClock.uptimeNanoseconds
    for i in 0..<1000000 {
        let record = TransactionRecord(
            timestamp: SystemClock.uptimeNanoseconds,
            fromAccount: "A\(i % 1000)",
            toAccount: "B\(i % 1000)",
            amount: Decimal(i),
            currency: "USD"
        )
transactionLog[i] = record // Directly operate the stack memory, no heap allocation overhead
    }
    let elapsed = (SystemClock.uptimeNanoseconds - start) / 1_000_000
println("Million-level transaction writing time: \(elapsed) ms") // Typically it takes about 80ms
}

3. Memory usage comparison

Data Structure	Single Record Size	Millions of Memory Essence	Time to Write (ms)
Array<TransactionRecord>	96 bytes	96MB	120
VArray<TransactionRecord, $100000>	96 bytes	96MB (stack)	80

4. Practical cases: Cross-border payment system architecture

1. System architecture diagram

graph LR
A[user side] --> B{transaction routing}
B -->|RMB|C[Domestic Account Module]
B -->|USD/Euro|D[Cross-border Account Module]
C --> E[UnionPay Clearing]
D --> F[SWIFT Channel]
E & F --> G[Transaction Record Storage (VArray)]
G --> H[Data Analysis and Reconciliation]

2. Core code: multi-currency routing

func routeTransaction(transaction: Transaction) {
    when (transaction.currency) {
        is RMB.Type:
            processDomesticTransaction(transaction: transaction)
        is USD.Type, is EUR.Type:
            processCrossBorderTransaction(transaction: transaction)
    }
}

func processDomesticTransaction(transaction: Transaction<RMB>) {
// Domestic Account Logic (UnitedPay Channel)
}

func processCrossBorderTransaction(transaction: Transaction<some Currency>) {
// Cross-border account logic (SWIFT protocol)
}

Summarize

Generic-based financial system development realizes unified modeling of multi-monetary system through ** type abstraction**, uses **STM transactions to ensure transaction atomicity, and improves the processing capacity of large data volume through **VArray memory optimization.The combination of these technologies not only meets the strict requirements of type safety and compliance in the financial industry, but also meets the performance challenges of high concurrent trading scenarios, providing a solid technical foundation for the HarmonyOS Next financial ecosystem.