feat(runner): implement concurrent benchmark execution

- Add tokio::Semaphore for bounded parallelism
- Split benchmark into sequential warmup and parallel measured phases
- Refactor to spawn_benchmark_tasks() and spawn_single_iteration()
- Add write_results() to aggregate and output records
- Use u32 for CLI arguments (iters, warmup, concurrency, payload_bytes)

runner/src/main.rs

@@ -30,7 +30,7 @@ use std::{
     sync::Arc,
     time::Instant,
 };
-use tokio::net::TcpStream;
+use tokio::{net::TcpStream, sync::Semaphore, task::JoinHandle};
 use tokio_rustls::TlsConnector;
 
 /// TLS benchmark runner.
@@ -47,19 +47,19 @@ struct Args {
 
     /// Payload size in bytes to request from server.
     #[arg(long, default_value = "1024")]
-    payload_bytes: u64,
+    payload_bytes: u32,
 
     /// Number of benchmark iterations (excluding warmup).
     #[arg(long, default_value = "100")]
-    iters: u64,
+    iters: u32,
 
     /// Number of warmup iterations (not recorded).
     #[arg(long, default_value = "10")]
-    warmup: u64,
+    warmup: u32,
 
     /// Number of concurrent connections.
     #[arg(long, default_value = "1")]
-    concurrency: u64,
+    concurrency: u32,
 
     /// Output file for NDJSON records (stdout if not specified).
     #[arg(long)]
@@ -146,7 +146,7 @@ fn build_tls_config(mode: KeyExchangeMode) -> miette::Result<Arc<ClientConfig>>
 #[allow(clippy::cast_possible_truncation)] // nanoseconds won't overflow u64 for reasonable durations
 async fn run_iteration(
     server: SocketAddr,
-    payload_bytes: u64,
+    payload_bytes: u32,
     tls_connector: &TlsConnector,
     server_name: &ServerName<'static>,
 ) -> miette::Result<IterationResult> {
@@ -165,15 +165,15 @@ async fn run_iteration(
 
     let handshake_ns = start.elapsed().as_nanos() as u64;
 
-    // Send request
+        // Send request
-    write_request(&mut tls_stream, payload_bytes)
+        write_request(&mut tls_stream, u64::from(payload_bytes))
-        .await
+            .await
-        .map_err(|e| miette!("write request failed: {e}"))?;
+            .map_err(|e| miette!("write request failed: {e}"))?;
 
-    // Read response
+        // Read response
-    read_payload(&mut tls_stream, payload_bytes)
+        read_payload(&mut tls_stream, u64::from(payload_bytes))
-        .await
+            .await
-        .map_err(|e| miette!("read payload failed: {e}"))?;
+            .map_err(|e| miette!("read payload failed: {e}"))?;
 
     let ttlb_ns = start.elapsed().as_nanos() as u64;
 
@@ -188,8 +188,6 @@ async fn run_benchmark(
     tls_connector: TlsConnector,
     server_name: ServerName<'static>,
 ) -> miette::Result<()> {
-    let total_iters = args.warmup + args.iters;
-
     // Open output file or use stdout
     let mut output: Box<dyn Write + Send> = match &args.out {
         Some(path) => {
@@ -206,34 +204,22 @@ async fn run_benchmark(
     );
     eprintln!();
 
-    // TODO: Implement concurrency
+    for _ in 0..args.warmup {
-    for i in 0..total_iters {
+        run_iteration(
-        let is_warmup = i < args.warmup;
-
-        let result = run_iteration(
             args.server,
             args.payload_bytes,
             &tls_connector,
             &server_name,
         )
         .await?;
-
-        if !is_warmup {
-            let record = BenchRecord {
-                iteration: i - args.warmup,
-                mode: args.mode,
-                payload_bytes: args.payload_bytes,
-                handshake_ns: result.handshake_ns,
-                ttlb_ns: result.ttlb_ns,
-            };
-
-            writeln!(output, "{record}").map_err(|e| miette!("failed to write record: {e}"))?;
-        }
-
-        if is_warmup && i == args.warmup.saturating_sub(1) {
-            eprintln!("Warmup complete.");
-        }
     }
+    eprintln!("Warmup complete.");
+
+    #[allow(clippy::cast_possible_truncation)] // concurrency is limited to reasonable values
+    let semaphore = Arc::new(Semaphore::new(args.concurrency as usize));
+    let tasks = spawn_benchmark_tasks(&args, &semaphore, &tls_connector, &server_name);
+
+    write_results(&mut output, tasks).await?;
 
     output
         .flush()
@@ -243,6 +229,78 @@ async fn run_benchmark(
     Ok(())
 }
 
+type ReturnHandle = JoinHandle<(IterationResult, Option<BenchRecord>)>;
+
+fn spawn_benchmark_tasks(
+    args: &Args,
+    semaphore: &Arc<Semaphore>,
+    tls_connector: &TlsConnector,
+    server_name: &ServerName<'static>,
+) -> Vec<ReturnHandle> {
+    let server = args.server;
+    let payload_bytes = args.payload_bytes;
+    let mode = args.mode;
+
+    (0..args.iters)
+        .map(|i| {
+            spawn_single_iteration(
+                i,
+                payload_bytes,
+                mode,
+                server,
+                semaphore.clone(),
+                tls_connector.clone(),
+                server_name.clone(),
+            )
+        })
+        .collect()
+}
+
+#[allow(clippy::too_many_arguments)]
+fn spawn_single_iteration(
+    i: u32,
+    payload_bytes: u32,
+    mode: KeyExchangeMode,
+    server: SocketAddr,
+    semaphore: Arc<Semaphore>,
+    tls_connector: TlsConnector,
+    server_name: ServerName<'static>,
+) -> ReturnHandle {
+    tokio::spawn(async move {
+        let _permit = semaphore
+            .acquire()
+            .await
+            .expect("semaphore should not be closed");
+
+        let result = run_iteration(server, payload_bytes, &tls_connector, &server_name)
+            .await
+            .expect("iteration should not fail");
+
+        let record = BenchRecord {
+            iteration: u64::from(i),
+            mode,
+            payload_bytes: u64::from(payload_bytes),
+            handshake_ns: result.handshake_ns,
+            ttlb_ns: result.ttlb_ns,
+        };
+
+        (result, Some(record))
+    })
+}
+
+async fn write_results(
+    output: &mut Box<dyn Write + Send>,
+    tasks: Vec<ReturnHandle>,
+) -> miette::Result<()> {
+    for task in tasks {
+        let (_result, record) = task.await.expect("task should not panic");
+        if let Some(record) = record {
+            writeln!(output, "{record}").map_err(|e| miette!("failed to write record: {e}"))?;
+        }
+    }
+    Ok(())
+}
+
 #[tokio::main]
 async fn main() -> miette::Result<()> {
     let args = Args::parse();