OutputCompletionSource

.changes/unreleased/Improvements-385.yaml

@@ -0,0 +1,6 @@
+component: sdk
+kind: Improvements
+body: Add `DeferredOutput` for resolving some output/input cycles
+time: 2024-11-19T08:28:36.110409Z
+custom:
+  PR: "385"

sdk/Pulumi.Tests/Core/OutputTests.cs

@@ -918,6 +918,38 @@ public Task FormatBraceSyntax() => RunInNormal(async () =>
                 Assert.False(data.IsSecret);
                 Assert.Equal("{ pip pip", data.Value);
             });
+
+
+            [Fact]
+            public Task DeferredOutput()
+                => RunInNormal(async () =>
+                {
+                    var defO = new DeferredOutput<int>();
+                    var o1 = CreateOutput(0, isKnown: true);
+
+                    Assert.False(defO.Output.DataTask.IsCompleted);
+                    defO.Resolve(o1);
+
+                    var data = await defO.Output.DataTask.ConfigureAwait(false);
+                    Assert.True(data.IsKnown);
+                    Assert.Equal(0, data.Value);
+                });
+
+            [Fact]
+            public Task DeferredOutputOnlySetOnce()
+                => RunInNormal(async () =>
+                {
+                    var defO = new DeferredOutput<int>();
+                    var o1 = CreateOutput(0, isKnown: true);
+                    defO.Resolve(o1);
+
+                    var o2 = CreateOutput(1, isKnown: true);
+                    Assert.Throws<System.InvalidOperationException>(() => defO.Resolve(o2));
+
+                    var data = await defO.Output.DataTask.ConfigureAwait(false);
+                    Assert.True(data.IsKnown);
+                    Assert.Equal(0, data.Value);
+                });
         }
     }
 }

sdk/Pulumi/Core/Output.cs

@@ -707,4 +707,54 @@ public override string ToString()
             return message;
         }
     }
+
+    /// <summary>
+    /// Represents the producer side of an <see cref="Output{T}"/> value, providing access to the consumer side through
+    /// the Output property.
+    /// </summary>
+    public sealed class DeferredOutput<T>
+    {
+        private int _set = 0;
+        private readonly TaskCompletionSource<OutputData<T>> _tcs = new TaskCompletionSource<OutputData<T>>();
+
+        /// <summary>
+        /// The <see cref="Output{T}"/> that represents the consumer side of this <see cref="DeferredOutput{T}"/>.
+        /// </summary>
+        public Output<T> Output { get; }
+
+        public DeferredOutput()
+        {
+            Output = new Output<T>(_tcs.Task);
+        }
+
+        /// <summary>
+        /// Resolves the value of the <see cref="Output{T}"/> represented by this <see
+        /// cref="DeferredOutput{T}"/> to the same eventually resolved result as the provided <see
+        /// cref="Output{T}"/>.
+        /// </summary>
+        public void Resolve(Output<T> output)
+        {
+            // Multithread safe check to ensure the DeferredOutput can only be set once.
+            if (System.Threading.Interlocked.Exchange(ref _set, 1) == 1)
+            {
+                throw new InvalidOperationException("DeferredOutput can only be resolved once.");
+            }
+
+            output.DataTask.ContinueWith(t =>
+            {
+                if (t.IsFaulted)
+                {
+                    _tcs.SetException(t.Exception!);
+                }
+                else if (t.IsCanceled)
+                {
+                    _tcs.SetCanceled();
+                }
+                else
+                {
+                    _tcs.SetResult(t.Result);
+                }
+            });
+        }
+    }
 }

sdk/Pulumi/Pulumi.xml

@@ -779,6 +779,24 @@
              then).
              </summary>
         </member>
+        <member name="T:Pulumi.DeferredOutput`1">
+            <summary>
+            Represents the producer side of an <see cref="T:Pulumi.Output`1"/> value, providing access to the consumer side through
+            the Output property.
+            </summary>
+        </member>
+        <member name="P:Pulumi.DeferredOutput`1.Output">
+            <summary>
+            The <see cref="T:Pulumi.Output`1"/> that represents the consumer side of this <see cref="T:Pulumi.DeferredOutput`1"/>.
+            </summary>
+        </member>
+        <member name="M:Pulumi.DeferredOutput`1.Resolve(Pulumi.Output{`0})">
+            <summary>
+            Resolves the value of the <see cref="T:Pulumi.Output`1"/> represented by this <see
+            cref="T:Pulumi.DeferredOutput`1"/> to the same eventually resolved result as the provided <see
+            cref="T:Pulumi.Output`1"/>.
+            </summary>
+        </member>
         <member name="T:Pulumi.OutputExtensions">
             <summary>
             Extension methods for <see cref="T:Pulumi.Output`1"/>.