```rust use mobc::Pool; use std::str::FromStr; use std::time::Instant; use mobcpostgres::PgConnectionManager; use tokiopostgres::Config; use tokio_postgres::NoTls;
async fn main() { let config = Config::fromstr("postgres://user:passwd@localhost:5432").unwrap(); let manager = PgConnectionManager::new(config, NoTls); let pool = Pool::builder().maxopen(20).build(manager); const MAX: usize = 5000;
let now = Instant::now();
let (tx, mut rx) = tokio::sync::mpsc::channel::<usize>(16);
for i in 0..MAX {
let pool = pool.clone();
let mut tx_c = tx.clone();
tokio::spawn(async move {
let client = pool.get().await.unwrap();
let rows = client.query("SELECT 1 + 2", &[]).await.unwrap();
let value: i32 = rows[0].get(0);
assert_eq!(value, 3);
tx_c.send(i).await.unwrap();
});
}
for _ in 0..MAX {
rx.recv().await.unwrap();
}
println!("cost: {:?}", now.elapsed());
} ```