⚡ Bolt: parallelize session destruction

.jules/bolt.md

@@ -1,3 +1,5 @@
-## 2025-05-15 - [Sequential session destruction in SDKs]
-**Learning:** All Copilot SDKs (Node.js, Python, Go, .NET) were initially implementing session destruction sequentially during client shutdown. This leads to a linear increase in shutdown time as the number of active sessions grows, especially when individual destructions involve retries and backoff.
-**Action:** Parallelize session cleanup using language-specific concurrency primitives (e.g., `Promise.all` in Node.js, `asyncio.gather` in Python, `Task.WhenAll` in .NET, or WaitGroups/Channels in Go) to ensure shutdown time remains constant and minimal.
+# Bolt's Performance Journal
+
+## 2025-05-15 - Parallel Session Destruction
+**Learning:** Sequential session destruction during client shutdown is a significant bottleneck when multiple sessions are active, as each destruction involves a JSON-RPC request over IPC/Network. Parallelizing this across all SDKs (Go, .NET, Python) brings them to parity with the Node.js implementation and significantly reduces shutdown latency.
+**Action:** Always prefer parallel execution for independent I/O-bound cleanup tasks during client shutdown.

dotnet/src/Client.cs

@@ -3,6 +3,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 using Microsoft.Extensions.AI;
+using System.Linq;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using StreamJsonRpc;
@@ -210,25 +211,42 @@ async Task<Connection> StartCoreAsync(CancellationToken ct)
     /// </example>
     public async Task StopAsync()
     {
-        var errors = new List<Exception>();
+        // Destroy all active sessions in parallel to speed up shutdown.
+        // This reduces StopAsync() time from O(N*T) to O(T) where N is the number of sessions.
+        var errors = new ConcurrentBag<Exception>();
 
-        foreach (var session in _sessions.Values.ToArray())
+        var sessionTasks = _sessions.Values.ToArray().Select(async session =>
         {
-            try
-            {
-                await session.DisposeAsync();
-            }
-            catch (Exception ex)
+            for (int attempt = 1; attempt <= 3; attempt++)
             {
-                errors.Add(new Exception($"Failed to destroy session {session.SessionId}: {ex.Message}", ex));
+                try
+                {
+                    await session.DisposeAsync();
+                    return; // Success
+                }
+                catch (Exception ex)
+                {
+                    if (attempt == 3)
+                    {
+                        errors.Add(new Exception($"Failed to destroy session {session.SessionId} after 3 attempts: {ex.Message}", ex));
+                    }
+                    else
+                    {
+                        // Exponential backoff: 100ms, 200ms
+                        await Task.Delay(100 * attempt);
+                    }
+                }
             }
-        }
+        });
+
+        await Task.WhenAll(sessionTasks);
 
         _sessions.Clear();
-        await CleanupConnectionAsync(errors);
+        var errorList = errors.ToList();
+        await CleanupConnectionAsync(errorList);
         _connectionTask = null;
 
-        ThrowErrors(errors);
+        ThrowErrors(errorList);
     }
 
     /// <summary>

go/client.go

@@ -294,10 +294,38 @@ func (c *Client) Stop() error {
 	}
 	c.sessionsMux.Unlock()
 
+	// Destroy all active sessions in parallel to speed up shutdown.
+	// This reduces Stop() time from O(N*T) to O(T) where N is the number of sessions.
+	var wg sync.WaitGroup
+	errsChan := make(chan error, len(sessions))
+
 	for _, session := range sessions {
-		if err := session.Destroy(); err != nil {
-			errs = append(errs, fmt.Errorf("failed to destroy session %s: %w", session.SessionID, err))
-		}
+		wg.Add(1)
+		go func(s *Session) {
+			defer wg.Done()
+			var lastErr error
+			for attempt := 1; attempt <= 3; attempt++ {
+				if err := s.Destroy(); err != nil {
+					lastErr = err
+					if attempt < 3 {
+						// Exponential backoff: 100ms, 200ms
+						time.Sleep(time.Duration(100*attempt) * time.Millisecond)
+					}
+				} else {
+					lastErr = nil
+					break
+				}
+			}
+			if lastErr != nil {
+				errsChan <- fmt.Errorf("failed to destroy session %s after 3 attempts: %w", s.SessionID, lastErr)
+			}
+		}(session)
+	}
+
+	wg.Wait()
+	close(errsChan)
+	for err := range errsChan {
+		errs = append(errs, err)
 	}
 
 	c.sessionsMux.Lock()

python/copilot/client.py

@@ -313,13 +313,34 @@ async def stop(self) -> list["StopError"]:
             sessions_to_destroy = list(self._sessions.values())
             self._sessions.clear()
 
-        for session in sessions_to_destroy:
-            try:
-                await session.destroy()
-            except Exception as e:
-                errors.append(
-                    StopError(message=f"Failed to destroy session {session.session_id}: {e}")
+        # Destroy all active sessions in parallel to speed up shutdown.
+        # This reduces stop() time from O(N*T) to O(T) where N is the number of sessions.
+        async def destroy_with_retry(session: CopilotSession) -> Optional[StopError]:
+            last_error = None
+            for attempt in range(1, 4):
+                try:
+                    await session.destroy()
+                    return None
+                except Exception as e:
+                    last_error = e
+                    if attempt < 3:
+                        # Exponential backoff: 100ms, 200ms
+                        await asyncio.sleep(0.1 * attempt)
+            return StopError(
+                message=(
+                    f"Failed to destroy session {session.session_id} after 3 attempts: {last_error}"
                 )
+            )
+
+        if sessions_to_destroy:
+            results = await asyncio.gather(
+                *[destroy_with_retry(s) for s in sessions_to_destroy], return_exceptions=True
+            )
+            for res in results:
+                if isinstance(res, StopError):
+                    errors.append(res)
+                elif isinstance(res, Exception):
+                    errors.append(StopError(message=str(res)))
 
         # Close client
         if self._client: