Return the stored profile from concurrent CreateProfile calls

Keybinding.Test/ProfileCreateConcurrencyTests.cs

@@ -0,0 +1,49 @@
+// Copyright (c) 2023-2026 ktsu-dev contributors
+
+namespace ktsu.Keybinding.Test;
+
+using ktsu.Keybinding.Core.Models;
+using ktsu.Keybinding.Core.Services;
+
+[TestClass]
+public class ProfileCreateConcurrencyTests
+{
+	private const int ThreadCount = 8;
+	private const int Trials = 500;
+
+	public TestContext TestContext { get; set; } = null!;
+
+	[TestMethod]
+	public void CreateProfile_CalledConcurrentlyForOneId_ReturnsTheStoredProfileToEveryCaller()
+	{
+		for (int trial = 0; trial < Trials; trial++)
+		{
+			ProfileManager profiles = new();
+			Profile[] returned = new Profile[ThreadCount];
+			using Barrier barrier = new(ThreadCount);
+
+			Thread[] threads = [.. Enumerable.Range(0, ThreadCount).Select(i => new Thread(() =>
+			{
+				barrier.SignalAndWait(TestContext.CancellationToken);
+				returned[i] = profiles.CreateProfile("p", "P");
+			}))];
+
+			foreach (Thread thread in threads)
+			{
+				thread.Start();
+			}
+
+			foreach (Thread thread in threads)
+			{
+				thread.Join();
+			}
+
+			Profile? stored = profiles.GetProfile("p");
+			Assert.IsNotNull(stored);
+			for (int i = 0; i < ThreadCount; i++)
+			{
+				Assert.AreSame(stored, returned[i], $"Trial {trial}: caller {i} got a Profile that was never stored, so its bindings would be lost.");
+			}
+		}
+	}
+}

Keybinding/Services/ProfileManager.cs

@@ -32,7 +32,7 @@
 	{
 		if (string.IsNullOrWhiteSpace(id))
 		{
 			throw new ArgumentException("Profile ID cannot be null or whitespace", nameof(id));
 		}
 
 		if (string.IsNullOrWhiteSpace(name))
@@ -42,16 +42,10 @@
 
 		string normalizedId = id.Trim();
 
-		// Return existing profile if it already exists
-		if (_profiles.TryGetValue(normalizedId, out Profile? existingProfile))
-		{
-			return existingProfile;
-		}
-
-		// Create new profile
-		Profile newProfile = new(normalizedId, name.Trim(), description);
-		_profiles.TryAdd(normalizedId, newProfile);
-		return newProfile;
+		// Return the existing profile, or store a new one, in one atomic step: a separate lookup
+		// and add let two concurrent callers each return their own Profile while only one of
+		// them was stored (ktsu-dev/Keybinding#112)
+		return _profiles.GetOrAdd(normalizedId, key => new Profile(key, name.Trim(), description));
 	}
 
 	/// <inheritdoc/>
@@ -79,7 +73,7 @@
 	{
 		return string.IsNullOrWhiteSpace(profileId)
 			? throw new ArgumentException("Profile ID cannot be null or whitespace", nameof(profileId))
 			: _profiles.TryGetValue(profileId.Trim(), out Profile? profile) ? profile : null;
 	}
 
 	/// <inheritdoc/>