DatabaseService.kt

import kotlinx.coroutines.*
import java.util.concurrent.Executors
class DatabaseService {
    // Custom dispatcher with limited threads matching DB connection pool
    private val dbDispatcher = Executors.newFixedThreadPool(5).asCoroutineDispatcher()
    
    data class QueryResult(val data: List<String>)
    
    suspend fun executeQuery(query: String): QueryResult = withContext(dbDispatcher) {
        println("Executing '$query' on ${Thread.currentThread().name}")
        delay(200) // Simulate query execution
        QueryResult(listOf("result1", "result2"))
    }
    
    suspend fun executeBatchQueries(queries: List<String>): List<QueryResult> = coroutineScope {
        queries.map { query ->
            async { executeQuery(query) }
        }.awaitAll()
    }
    
    fun shutdown() {
        dbDispatcher.close()
    }
}
fun main() = runBlocking {
    val dbService = DatabaseService()
    
    try {
        val queries = List(20) { "SELECT * FROM table WHERE id = $it" }
        
        val time = measureTimeMillis {
            val results = dbService.executeBatchQueries(queries)
            println("Executed ${results.size} queries")
        }
        
        println("Time: $time ms (limited by 5 DB connections)")
        
    } finally {
        dbService.shutdown()
    }
}