Add Process.StartAndForget APIs for fire-and-forget process launching by Copilot · Pull Request #126078 · dotnet/runtime

Copilot · 2026-03-25T08:04:36Z

Adds two new static methods to Process for scenarios where you want to launch a process, get its PID, and immediately release all resources without waiting for it to exit.

Description

New APIs (Process.Scenarios.cs):

Process.StartAndForget(ProcessStartInfo) — validates no stream redirection is configured (redirected streams must be drained to prevent deadlocks, incompatible with fire-and-forget), starts the process, captures the PID, disposes the Process instance, and returns the PID.
Process.StartAndForget(string fileName, IList<string>? arguments = null) — builds a ProcessStartInfo and delegates to the ProcessStartInfo overload above.

// Before: resource leak unless caller explicitly disposes
Process p = Process.Start("myapp", args);
int pid = p.Id;
p.Dispose(); // easy to forget

// After: idiomatic, guaranteed cleanup
int pid = Process.StartAndForget("myapp", args);

Redirection guard — throws InvalidOperationException if any RedirectStandardInput/Output/Error flag is set, with a message explaining the deadlock risk.

Supporting changes:

Reference assembly updated with both signatures, including the // this needs to come after the ios attribute due to limitations in the platform analyzer comment on [SupportedOSPlatformAttribute("maccatalyst")], consistent with other Start overloads in the file
New string resource StartAndForget_RedirectNotSupported in Strings.resx
Process.Scenarios.cs added to System.Diagnostics.Process.csproj
Tests in StartAndForget.cs:
- Happy paths (both overloads) merged into a single [ConditionalTheory] parameterized by bool useProcessStartInfo, with explicit Kill()/WaitForExit() cleanup in try/finally
- ArgumentNullException tests use AssertExtensions.Throws to verify parameter names ("startInfo" and "fileName")
- InvalidOperationException for each redirect flag combination via [Theory]
- Null-arguments test is a plain [Fact] (no RemoteExecutor dependency) that passes null directly; uses hostname on Windows and ls on Unix (hostname is not available on Android or Azure Linux)

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Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/095d096c-d5d9-4ad1-b5f2-45fbadf30315

dotnet-policy-service · 2026-03-25T08:25:02Z

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adamsitnik

@copilot address my feedback

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

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

Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/942ffa7e-9504-40eb-9a58-9c4b6ceee3c1

adamsitnik

@copilot address my feedback

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

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adamsitnik

@copilot address my feedback

adamsitnik · 2026-03-25T13:00:44Z

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

+        public void StartAndForget_WithNullArguments_StartsProcess()
+        {
+            // hostname is available on all platforms and requires no arguments
+            int pid = Process.StartAndForget("hostname", null);


This test fails on Azure Linux:

System.Diagnostics.Tests.StartAndForgetTests.StartAndForget_WithNullArguments_StartsProcess [FAIL] System.ComponentModel.Win32Exception : An error occurred trying to start process 'hostname' with working directory '/root/helix/work/workitem/e'. No such file or directory Stack Trace: /_/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs(561,0): at System.Diagnostics.Process.ForkAndExecProcess(ProcessStartInfo startInfo, String resolvedFilename, String[] argv, String[] envp, String cwd, Boolean setCredentials, UInt32 userId, UInt32 groupId, UInt32[] groups, Int32& stdinFd, Int32& stdoutFd, Int32& stderrFd, Boolean usesTerminal, Boolean throwOnNoExec) /_/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Unix.cs(456,0): at System.Diagnostics.Process.StartCore(ProcessStartInfo startInfo) /_/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.cs(1284,0): at System.Diagnostics.Process.Start() /_/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Scenarios.cs(53,0): at System.Diagnostics.Process.StartAndForget(ProcessStartInfo startInfo) /_/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Scenarios.cs(98,0): at System.Diagnostics.Process.StartAndForget(String fileName, IList`1 arguments) /_/src/libraries/System.Diagnostics.Process/tests/StartAndForget.cs(40,0): at System.Diagnostics.Tests.StartAndForgetTests.StartAndForget_WithNullArguments_StartsProcess() /_/src/mono/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.Mono.cs(22,0): at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args) /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(57,0): at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

@copilot use "hostname" on Windows and "ls" on other OSes

Suggested change

int pid = Process.StartAndForget("hostname", null);

// hostname is not available on Android or Azure Linux.

// ls is available on every Unix.

int pid = Process.StartAndForget(OperatingSystem.IsWindows() ? "hostname" : "ls", null);

Fixed in bff4ded — applied the suggestion exactly: hostname on Windows, ls on Unix.

stephentoub · 2026-03-25T12:58:09Z

src/libraries/System.Diagnostics.Process/src/Resources/Strings.resx

    <value>Invalid performance counter data with type '{0}'.</value>
  </data>
+  <data name="StartAndForget_RedirectNotSupported" xml:space="preserve">
+    <value>Stream redirection is not supported by StartAndForget. Redirected streams must be drained to avoid deadlocks, which is incompatible with fire-and-forget semantics.</value>


What would someone be trying to do with stream redirection? I wonder if it makes sense to nudge folks towards setting StandardXxHandle here, possible to OpenNullHandle?

stephentoub · 2026-03-25T12:59:00Z

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

+            using Process process = new Process();
+            process.StartInfo = startInfo;
+            process.Start();
+            return process.Id;


Wouldn't we want to use the SafeProcessHandle.Start functionality here?

Wouldn't we want to use the SafeProcessHandle.Start functionality here?

Yes, as soon as we have SafeProcessHandle.Start, this API should use it instead of Process.

And FWIW I want to expose it as soon as #125848 gets merged (just move it from Process.StartCore as is to SafeProcessHandle.Start

stephentoub · 2026-03-25T13:01:32Z

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

+                foreach (string argument in arguments)
+                {
+                    startInfo.ArgumentList.Add(argument);
+                }


@eiriktsarpalis / @tannergooding, this kind of loop comes up all the time. We should really have an AddRange for IList. We've held off on adding it as an extension method because of the possibility of instead adding it as a DIM, and decisions there have been blocked on the whole I{ReadOnly}List consolidation, but it'd be a shame if we delayed getting AddRange even further. Can we come up with a decision for how to add AddRange regardless of the I{ReadOnly}List decision?

stephentoub · 2026-03-25T13:03:13Z

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

+
+            if (startInfo.RedirectStandardInput || startInfo.RedirectStandardOutput || startInfo.RedirectStandardError)
+            {
+                throw new InvalidOperationException(SR.StartAndForget_RedirectNotSupported);


Do we need to throw? Presumably if redirection is set, the user is really just asking for it to not go to the default stdin / stdout / stderr? In which case, we could make these convenient by just setting these up to be null handles, handling the disposal of those, etc.?

My take is following: so far, RedirectStandardX always meant "I want to interact with the X". With the new APIs, the users will be allowed to make it explicit (info.StandardXHandle = File.OpenNullHandle()); So I would prefer not to choose any deafult other than pipe when RedirectStandardX is set to true

I would prefer to throw for RedirectStandardX here, but I am supportive of setting all standard handles to NUL by default.

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Add Process.StartAndForget APIs for fire-and-forget scenarios

ad79bd9

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Copilot AI assigned Copilot and adamsitnik Mar 25, 2026

Copilot created this pull request from a session on behalf of adamsitnik March 25, 2026 08:04 View session

github-actions bot added the area-System.Diagnostics.Process label Mar 25, 2026

adamsitnik reviewed Mar 25, 2026

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Copilot started work on behalf of adamsitnik March 25, 2026 08:50 View session

Address review feedback on StartAndForget tests and ref file

0f8be81

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Copilot AI requested a review from adamsitnik March 25, 2026 09:19

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src/libraries/System.Diagnostics.Process/tests/StartAndForget.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of adamsitnik March 25, 2026 10:02 View session

Fix StartAndForget_WithNullArguments_StartsProcess to actually pass null

9be6c1c

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Copilot AI requested a review from adamsitnik March 25, 2026 10:28

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stephentoub reviewed Mar 25, 2026

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Fix StartAndForget_WithNullArguments test: use hostname on Windows, l…

bff4ded

…s on Unix Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com> Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/a8a7e105-927e-424f-986b-434912ec8a8e

Copilot AI requested a review from adamsitnik March 25, 2026 13:28

Copilot finished work on behalf of adamsitnik March 25, 2026 13:28

-            int pid = Process.StartAndForget("hostname", null);
+            // hostname is not available on Android or Azure Linux.
+            // ls is available on every Unix.
+            int pid = Process.StartAndForget(OperatingSystem.IsWindows() ? "hostname" : "ls", null);

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