Add StandardInput/Output/Error SafeFileHandle properties and LeaveHandlesOpen to ProcessStartInfo by Copilot · Pull Request #125848 · dotnet/runtime

Copilot · 2026-03-20T17:57:11Z

Description

Adds three new SafeFileHandle? properties and a LeaveHandlesOpen property to ProcessStartInfo that allow passing file handles directly to child processes, bypassing the RedirectStandard* pipe-based mechanism.

var psi = new ProcessStartInfo("grep") { ArgumentList = { "test" } };
SafeFileHandle.CreateAnonymousPipe(out SafeFileHandle readPipe, out SafeFileHandle writePipe);
psi.StandardInput = readPipe;
psi.StandardOutput = File.OpenHandle("output.txt", FileMode.Create, FileAccess.Write);
Process.Start(psi);

By default, Process.Start disposes the standard handles after starting the child process. Set LeaveHandlesOpen to true to keep them open for the caller to manage.

Changes

ProcessStartInfo.cs: New StandardInput, StandardOutput, StandardError auto-properties (SafeFileHandle?) with XML docs. Remarks document that handles do not need to be inheritable (the runtime handles that), and list typical APIs (SafeFileHandle.CreateAnonymousPipe, File.OpenHandle, File.OpenNullHandle, Console.OpenStandardInputHandle/OpenStandardOutputHandle/OpenStandardErrorHandle), interaction with LeaveHandlesOpen, and constraints. New LeaveHandlesOpen property (bool, default false) controlling whether handles are disposed after process start.
ref/System.Diagnostics.Process.cs: Public API surface additions for StandardInput, StandardOutput, StandardError, and LeaveHandlesOpen
Process.cs validation: When any StandardX handle is set, UseShellExecute must be false and the corresponding RedirectStandardX must also be false. Reuses existing SR.CantRedirectStreams error message for the UseShellExecute check.
Process.cs pipe creation: New handles take priority over default stdin/stdout/stderr inheritance. Handles are always disposed after starting the child process unless LeaveHandlesOpen is true.
Strings.resx: New error string CantSetHandleAndRedirect
ProcessHandlesTests.cs: Tests for pipe redirection, inherited handles, piping, and validation error cases

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…artInfo Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

adamsitnik · 2026-03-20T17:57:55Z

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs

+            {
+                if (startInfo.UseShellExecute)
+                {
+                    throw new InvalidOperationException(SR.CantUseHandlesWithShellExecute);


Let's re-use existing error message:

Suggested change

throw new InvalidOperationException(SR.CantUseHandlesWithShellExecute);

throw new InvalidOperationException(SR.CantRedirectStreams);

Done in 60844f3 — now reuses SR.CantRedirectStreams and removed the unused CantUseHandlesWithShellExecute string from Strings.resx.

dotnet-policy-service · 2026-03-20T18:06:09Z

Tagging subscribers to this area: @dotnet/area-system-diagnostics-process
See info in area-owners.md if you want to be subscribed.

stephentoub · 2026-03-20T19:38:21Z

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.cs

+        /// When set, the handle is passed directly to the child process and <see cref="RedirectStandardInput"/> must be <see langword="false"/>.
+        /// </summary>
+        /// <value>A <see cref="SafeFileHandle"/> to use as the standard input handle of the child process, or <see langword="null"/> to use the default behavior.</value>
+        public SafeFileHandle? StandardInput { get; set; }


Are there any requirements around its inheritability that should be called out in the docs?

Maybe add some XML comments remarks around when this would be used, what APIs it might typically used in conjunction with, etc.?

Added <remarks> sections to all three properties in 60844f3 covering: inheritability requirement, typical APIs to use (SafeFileHandle.CreateAnonymousPipe, File.OpenHandle), interaction with the new LeaveHandlesOpen property, and constraints (RedirectStandard* / UseShellExecute).

adamsitnik

@copilot please address all the feedback

src/libraries/System.Diagnostics.Process/ref/System.Diagnostics.Process.cs

adamsitnik · 2026-03-20T22:23:41Z

src/libraries/System.Diagnostics.Process/tests/ProcessHandlesTests.cs

+            using SafeFileHandle inputHandle = Console.OpenStandardInputHandle();
+            using SafeFileHandle outputHandle = Console.OpenStandardOutputHandle();
+            using SafeFileHandle errorHandle = Console.OpenStandardErrorHandle();
+
+            startInfo.StandardInput = inputHandle;
+            startInfo.StandardOutput = outputHandle;
+            startInfo.StandardError = errorHandle;


Let the new property dispose all these handles for us.

Suggested change

using SafeFileHandle inputHandle = Console.OpenStandardInputHandle();

using SafeFileHandle outputHandle = Console.OpenStandardOutputHandle();

using SafeFileHandle errorHandle = Console.OpenStandardErrorHandle();

startInfo.StandardInput = inputHandle;

startInfo.StandardOutput = outputHandle;

startInfo.StandardError = errorHandle;

startInfo.StandardInput = Console.OpenStandardInputHandle();

startInfo.StandardOutput = Console.OpenStandardOutputHandle();

startInfo.StandardError = Console.OpenStandardErrorHandle();

Done in 60844f3 — removed the using statements; handles are now disposed by Process.Start since LeaveHandlesOpen defaults to false.

…pen property, improve XML docs Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/9f61c68e-edfd-42e9-b86b-bfb9ee7d8946

adamsitnik

@copilot address my feedback

adamsitnik · 2026-03-20T23:23:37Z

src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.cs

+        /// </summary>
+        /// <remarks>
+        /// <para>
+        /// The handle must be inheritable. Use <see cref="SafeFileHandle.CreateAnonymousPipe"/> to create a pair of


It should not be inheritable, because other process may inherit it by accident before we get here.

Also, do mention File.OpenNullHandle and Console.OpenSatndardInputHandle API

Updated in c8b8723 — the docs now state the handle does not need to be inheritable (runtime handles that). Also added mentions of File.OpenNullHandle and Console.OpenStandardInputHandle / OpenStandardOutputHandle / OpenStandardErrorHandle for each respective property.

adamsitnik · 2026-03-20T23:24:12Z

src/libraries/System.Diagnostics.Process/tests/ProcessHandlesTests.cs

+                using Process process = Process.Start(startInfo)!;
+
+                // Close the parent copy of the child handle, so the pipe will signal EOF when the child exits
+                writePipe.Close();


Not needed anymore

Removed in c8b8723 — Process.Start closes it now since LeaveHandlesOpen defaults to false.

adamsitnik · 2026-03-20T23:24:52Z

src/libraries/System.Diagnostics.Process/tests/ProcessHandlesTests.cs

+
+                // Close the parent copy of the child handles, so the pipes will signal EOF when the child exits
+                outputWrite.Close();
+                errorWrite.Close();


Not needed anymore

Removed in c8b8723.

…ullHandle/OpenStandard*Handle APIs, remove redundant Close() calls Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/29b43a66-dcf9-47b0-95df-28d834129305

Copilot AI and others added 3 commits March 20, 2026 17:30

Add StandardInput/Output/Error SafeFileHandle properties to ProcessSt…

419d7ab

…artInfo Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Remove unrelated files from commit

18995de

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Address code review: fix pipe handle cleanup in tests

d40cf18

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI assigned Copilot and adamsitnik Mar 20, 2026

Copilot created this pull request from a session on behalf of adamsitnik March 20, 2026 17:57 View session

adamsitnik reviewed Mar 20, 2026

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github-actions bot added the area-System.Diagnostics.Process label Mar 20, 2026

adamsitnik added the NO-REVIEW Experimental/testing PR, do NOT review it label Mar 20, 2026

stephentoub reviewed Mar 20, 2026

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adamsitnik reviewed Mar 20, 2026

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Copilot started work on behalf of adamsitnik March 20, 2026 22:28 View session

Address review feedback: reuse CantRedirectStreams, add LeaveHandlesO…

60844f3

…pen property, improve XML docs Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/9f61c68e-edfd-42e9-b86b-bfb9ee7d8946

Copilot AI changed the title ~~Add StandardInput/Output/Error SafeFileHandle properties to ProcessStartInfo~~ Add StandardInput/Output/Error SafeFileHandle properties and LeaveHandlesOpen to ProcessStartInfo Mar 20, 2026

Copilot AI requested a review from adamsitnik March 20, 2026 23:00

Copilot finished work on behalf of adamsitnik March 20, 2026 23:00

adamsitnik reviewed Mar 20, 2026

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Copilot started work on behalf of adamsitnik March 20, 2026 23:26 View session

Copilot AI requested a review from adamsitnik March 20, 2026 23:52

Copilot finished work on behalf of adamsitnik March 20, 2026 23:52

build-analysis bot mentioned this pull request Mar 21, 2026

Assertion failure in ConnectAsync_WithBuffer_Succeeds on Android/MacCatalyst/tvOS (Mono/CoreCLR/NativeAOT) #125825

Open

	throw new InvalidOperationException(SR.CantUseHandlesWithShellExecute);
	throw new InvalidOperationException(SR.CantRedirectStreams);

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Copilot AI commented Mar 20, 2026 •

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