Ensure watched projects are not built in parallel to avoid file locking issues

src/Microsoft.Tye.Hosting/Model/Application.cs

@@ -3,10 +3,12 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Threading.Tasks;
 
 namespace Microsoft.Tye.Hosting.Model
 {
@@ -25,6 +27,9 @@ public Application(FileInfo source, Dictionary<string, Service> services)
 
         public Dictionary<string, Service> Services { get; }
 
+        internal ConcurrentDictionary<string, TaskCompletionSource<ProcessResult>> OngoingBuildProjectProcesses { get; }
+            = new ConcurrentDictionary<string, TaskCompletionSource<ProcessResult>>();
+
         public Dictionary<object, object> Items { get; } = new Dictionary<object, object>();
 
         public string? Network { get; set; }

src/Microsoft.Tye.Hosting/ProcessRunner.cs

@@ -359,9 +359,28 @@ async Task RunApplicationAsync(IEnumerable<(int ExternalPort, int Port, string?
                             },
                             Build = async () =>
                             {
-                                if (service.Description.RunInfo is ProjectRunInfo)
+                                if (service.Description.RunInfo is ProjectRunInfo projectRunInfo)
                                 {
+                                    var projectFile = projectRunInfo.ProjectFile.FullName;
+                                    var newProcess = new TaskCompletionSource<ProcessResult>();
+                                    var ongoingProcess = application.OngoingBuildProjectProcesses.GetOrAdd(projectFile, newProcess);
+
+                                    if (ongoingProcess != newProcess)
+                                    {
+                                        _logger.LogDebug($"[{replica}] A build has already been triggered for project {projectFile}");
+                                        return (await ongoingProcess.Task).ExitCode;
+                                    }
+
+                                    _logger.LogDebug($"[{replica}] Building project {projectFile}");
                                     var buildResult = await ProcessUtil.RunAsync("dotnet", $"build \"{service.Status.ProjectFilePath}\" /nologo", throwOnError: false, workingDirectory: application.ContextDirectory);
+                                    _logger.LogDebug($"[{replica}] Finished Building project {projectFile}");
+
+                                    ongoingProcess.SetResult(buildResult);
+
+                                    // Cannot remove a specific KVP until net5.0. Workaround is to cast to ICollection<KVP<>>
+                                    ICollection<KeyValuePair<string, TaskCompletionSource<ProcessResult>>> projectProcesses = application.OngoingBuildProjectProcesses;
+                                    projectProcesses.Remove(KeyValuePair.Create(projectFile, ongoingProcess));
+
                                     if (buildResult.ExitCode != 0)
                                     {
                                         _logger.LogInformation("Building projects failed with exit code {ExitCode}: \r\n" + buildResult.StandardOutput, buildResult.ExitCode);

src/Microsoft.Tye.Hosting/Watch/DotNetWatcher.cs

@@ -88,7 +88,7 @@ public async Task WatchAsync(ProcessSpec processSpec, IFileSetFactory fileSetFac
                     if (finishedTask == processTask)
                     {
                         // Now wait for a file to change before restarting process
-                        await fileSetWatcher.GetChangedFileAsync(cancellationToken, () => _logger.LogWarning("Waiting for a file to change before restarting dotnet..."));
+                        await fileSetWatcher.GetChangedFileAsync(cancellationToken, () => _logger.LogWarning("watch: {Replica} Waiting for a file to change before restarting dotnet...", replica));
                     }
 
                     if (!string.IsNullOrEmpty(fileSetTask.Result))
@@ -112,7 +112,8 @@ public async Task WatchAsync(ProcessSpec processSpec, IFileSetFactory fileSetFac
                                 // Build failed, keep retrying builds until successful build. 
                             }
 
-                            await fileSetWatcher.GetChangedFileAsync(cancellationToken, () => _logger.LogWarning("Waiting for a file to change before restarting dotnet..."));
+                            // Now wait for a file to change before restarting process
+                            await fileSetWatcher.GetChangedFileAsync(cancellationToken, () => _logger.LogWarning("watch: {Replica} Waiting for a file to change before restarting dotnet...", replica));
                         }
                     }
                 }