Add Workflow.RunTaskAsync and Workflow.WhenAllAsync (#313)

Fixes #303

Author: cretz

README.md

@@ -688,7 +688,8 @@ use `TaskScheduler.Default` implicitly (and some analyzers even encourage this).
 with .NET tasks inside of workflows:
 
 * Do not use `Task.Run` - this uses the default scheduler and puts work on the thread pool.
-  * Use `Task.Factory.StartNew` or instantiate the `Task` and run `Task.Start` on it.
+  * Use `Workflow.RunTaskAsync` instead.
+  * Can also use `Task.Factory.StartNew` with current scheduler or instantiate the `Task` and run `Task.Start` on it.
 * Do not use `Task.ConfigureAwait(false)` - this will not use the current context.
   * If you must use `Task.ConfigureAwait`, use `Task.ConfigureAwait(true)`.
   * There is no significant performance benefit to `Task.ConfigureAwait` in workflows anyways due to how the scheduler
@@ -701,6 +702,10 @@ with .NET tasks inside of workflows:
   * Use `Workflow.WhenAnyAsync` instead.
   * Technically this only applies to an enumerable set of tasks with results or more than 2 tasks with results. Other
     uses are safe. See [this issue](https://github.com/dotnet/runtime/issues/87481).
+* Do not use `Task.WhenAll`
+  * Use `Workflow.WhenAllAsync` instead.
+  * Technically `Task.WhenAll` is currently deterministic in .NET and safe, but it is better to use the wrapper to be
+    sure.
 * Do not use `System.Threading.Semaphore` or `System.Threading.SemaphoreSlim` or `System.Threading.Mutex`.
   * Use `Temporalio.Workflows.Semaphore` or `Temporalio.Workflows.Mutex` instead.
   * _Technically_ `SemaphoreSlim` does work if only the async form of `WaitAsync` is used without no timeouts and

src/Temporalio/Workflows/Workflow.cs

@@ -1021,6 +1021,39 @@ public static Guid NewGuid()
         /// </remarks>
         public static bool Patched(string patchId) => Context.Patch(patchId, deprecated: false);
 
+        /// <summary>
+        /// Workflow-safe form of <see cref="Task.Run(Func{Task}, CancellationToken)" />.
+        /// </summary>
+        /// <param name="function">The work to execute asynchronously.</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the work
+        /// if it has not yet started. Defaults to <see cref="CancellationToken"/>.</param>
+        /// <returns>A task for the running task (but not necessarily the task that is returned
+        /// from the function).</returns>
+        public static Task RunTaskAsync(
+            Func<Task> function, CancellationToken? cancellationToken = null) =>
+            Task.Factory.StartNew(
+                function,
+                cancellationToken ?? CancellationToken,
+                TaskCreationOptions.None,
+                TaskScheduler.Current).Unwrap();
+
+        /// <summary>
+        /// Workflow-safe form of <see cref="Task.Run{TResult}(Func{TResult}, CancellationToken)" />.
+        /// </summary>
+        /// <typeparam name="TResult">The type of the result returned by the task.</typeparam>
+        /// <param name="function">The work to execute asynchronously.</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the work
+        /// if it has not yet started. Defaults to <see cref="CancellationToken"/>.</param>
+        /// <returns>A task for the running task (but not necessarily the task that is returned
+        /// from the function).</returns>
+        public static Task<TResult> RunTaskAsync<TResult>(
+            Func<Task<TResult>> function, CancellationToken? cancellationToken = null) =>
+            Task.Factory.StartNew(
+                function,
+                cancellationToken ?? CancellationToken,
+                TaskCreationOptions.None,
+                TaskScheduler.Current).Unwrap();
+
         /// <summary>
         /// Start a child workflow via lambda invoking the run method.
         /// </summary>
@@ -1220,6 +1253,44 @@ public static async Task<Task<TResult>> WhenAnyAsync<TResult>(IEnumerable<Task<T
             return (Task<TResult>)task;
         }
 
+        /// <summary>
+        /// Workflow-safe form of <see cref="Task.WhenAll(IEnumerable{Task})" /> (which just calls
+        /// the standard library call currently because it is already safe).
+        /// </summary>
+        /// <param name="tasks">The tasks to wait on for completion.</param>
+        /// <returns>A task that represents the completion of all of the supplied tasks.</returns>
+        public static Task WhenAllAsync(IEnumerable<Task> tasks) =>
+            Task.WhenAll(tasks);
+
+        /// <summary>
+        /// Workflow-safe form of <see cref="Task.WhenAll(Task[])" /> (which just calls the standard
+        /// library call currently because it is already safe).
+        /// </summary>
+        /// <param name="tasks">The tasks to wait on for completion.</param>
+        /// <returns>A task that represents the completion of all of the supplied tasks.</returns>
+        public static Task WhenAllAsync(params Task[] tasks) =>
+            Task.WhenAll(tasks);
+
+        /// <summary>
+        /// Workflow-safe form of <see cref="Task.WhenAll{TResult}(IEnumerable{Task{TResult}})" />
+        /// (which just calls the standard library call currently because it is already safe).
+        /// </summary>
+        /// <typeparam name="TResult">The type of the completed task..</typeparam>
+        /// <param name="tasks">The tasks to wait on for completion.</param>
+        /// <returns>A task that represents the completion of all of the supplied tasks.</returns>
+        public static Task<TResult[]> WhenAllAsync<TResult>(IEnumerable<Task<TResult>> tasks) =>
+            Task.WhenAll(tasks);
+
+        /// <summary>
+        /// Workflow-safe form of <see cref="Task.WhenAll{TResult}(Task{TResult}[])" /> (which just
+        /// calls the standard library call currently because it is already safe).
+        /// </summary>
+        /// <typeparam name="TResult">The type of the completed task..</typeparam>
+        /// <param name="tasks">The tasks to wait on for completion.</param>
+        /// <returns>A task that represents the completion of all of the supplied tasks.</returns>
+        public static Task<TResult[]> WhenAllAsync<TResult>(params Task<TResult>[] tasks) =>
+            Task.WhenAll(tasks);
+
         /// <summary>
         /// Unsafe calls that can be made in a workflow.
         /// </summary>

tests/Temporalio.Tests/Worker/WorkflowWorkerTests.cs

@@ -242,6 +242,15 @@ public async Task<string> RunAsync(Scenario scenario)
                 case Scenario.WorkflowWhenAnyWithResultThreeParam:
                     return await await Workflow.WhenAnyAsync(
                         Task.FromResult("done"), Task.FromResult("done"), Task.FromResult("done"));
+                case Scenario.WorkflowWhenAll:
+                    return string.Join(string.Empty, await Workflow.WhenAllAsync(
+                        Task.FromResult("do"), Task.FromResult("ne")));
+                case Scenario.WorkflowRunTask:
+                    return await Workflow.RunTaskAsync(async () => "done");
+                case Scenario.WorkflowRunTaskAfterTaskStart:
+                    var runTaskStart = new Task<string>(() => "done");
+                    runTaskStart.Start();
+                    return await Workflow.RunTaskAsync(() => runTaskStart);
             }
             throw new InvalidOperationException("Unexpected completion");
         }
@@ -266,6 +275,9 @@ public enum Scenario
             // https://github.com/dotnet/runtime/issues/87481
             TaskWhenAnyWithResultTwoParam,
             WorkflowWhenAnyWithResultThreeParam,
+            WorkflowWhenAll,
+            WorkflowRunTask,
+            WorkflowRunTaskAfterTaskStart,
         }
     }
 
@@ -325,6 +337,9 @@ Task AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario scenario) =>
         await AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario.TaskContinueWith);
         await AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario.TaskWhenAnyWithResultTwoParam);
         await AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario.WorkflowWhenAnyWithResultThreeParam);
+        await AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario.WorkflowWhenAll);
+        await AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario.WorkflowRunTask);
+        await AssertScenarioSucceeds(StandardLibraryCallsWorkflow.Scenario.WorkflowRunTaskAfterTaskStart);
     }
 
     [Workflow]