Add macOS support for StartSuspended via POSIX_SPAWN_START_SUSPENDED by Copilot · Pull Request #129570 · dotnet/runtime

Copilot · 2026-06-18T10:44:37Z

Extends ProcessStartInfo.StartSuspended and SafeProcessHandle.Resume() to macOS using POSIX_SPAWN_START_SUSPENDED. Approved API: #94127 (comment)

Changes

API surface: Added [SupportedOSPlatform("macos")] to StartSuspended and Resume() in ref and src
Managed → native interop: Interop.Sys.ForkAndExecProcess managed wrapper now accepts ProcessStartInfo directly (instead of individual bool parameters) and extracts StartDetached, KillOnParentExit, and StartSuspended internally
Native (pal_process.c): Set POSIX_SPAWN_START_SUSPENDED flag in the macOS posix_spawn path when startSuspended is true; returns ENOTSUP in the fork() path when startSuspended is true to prevent silent behavior differences when credentials force the fork path on macOS
Native (pal_process_wasi.c): Updated WASI stub signature to include startSuspended parameter
Resume on Unix: ResumeCore calls SignalCore(PosixSignal.SIGCONT); shared Resume() throws PlatformNotSupportedException on unsupported OS; Resume() no longer prohibits multiple calls — OS errors are surfaced directly as Win32Exception
Validation: ProcessStartInfo.Validate() throws PlatformNotSupportedException when StartSuspended=true on non-Windows/non-macOS platforms; throws InvalidOperationException for UseShellExecute incompatibility on supported platforms
XML docs: Updated Resume() docs to remove the "can only be called once" restriction and document per-platform behavior
Tests: Extended StartSuspendedTests from TestPlatforms.Windows to TestPlatforms.Windows | TestPlatforms.OSX; Resume_OnNonSuspendedProcess test (Windows-only) now expects Win32Exception from the OS instead of InvalidOperationException; non-supported OS test verifies PlatformNotSupportedException

Usage

Process process = new()
{
    StartInfo =
    {
        FileName = "/usr/bin/some-app",
        StartSuspended = true, // now works on macOS
    }
};

using SafeProcessHandle handle = SafeProcessHandle.Start(process.StartInfo);
// process is suspended, configure it as needed...
handle.Resume(); // sends SIGCONT on macOS
ProcessExitStatus status = handle.WaitForExit();

…and Resume via SIGCONT Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

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

adamsitnik

@copilot please address my feedback

…plify ResumeCore, update WASI stub, fix tests Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot · 2026-06-18T11:32:27Z

@copilot please address my feedback

All feedback addressed in commit 3e2d0d6:

Passed ProcessStartInfo to Interop.Sys.ForkAndExecProcess instead of individual parameters
Simplified ResumeCore to just SignalCore(PosixSignal.SIGCONT), removed _startedSuspended field
Added platform check in shared Resume() to throw PlatformNotSupportedException on unsupported OS
Updated pal_process_wasi.c stub with startSuspended parameter
Fixed comment in fork() path (removed Catalyst mention)
Removed double-resume test, made Resume_OnNonSuspendedProcess Windows-specific, fixed non-supported OS test to expect PlatformNotSupportedException

All 635 tests pass with 0 failures.

adamsitnik

@copilot address my feedback

…idate() before ResumeCore Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot · 2026-06-18T11:58:09Z

@copilot address my feedback

Both changes applied in the latest commit: reformatted the ForkAndExecProcess call to the preferred style and added Validate() before ResumeCore().

adamsitnik

@copilot address my feedback and run the tests locally before pushing the changes

adamsitnik · 2026-06-18T16:44:39Z

/azp list

azure-pipelines · 2026-06-18T16:44:45Z

CI/CD Pipelines for this repository: runtime-coreclr outerloop runtime-coreclr jitstress runtime-coreclr jitstressregs runtime-coreclr jitstress2-jitstressregs runtime-coreclr gcstress0x3-gcstress0xc runtime-coreclr gcstress-extra runtime-coreclr r2r-extra runtime-coreclr jitstress-isas-x86 runtime-coreclr jitstress-isas-arm runtime-coreclr jitstressregs-x86 runtime-coreclr libraries-jitstressregs runtime-coreclr libraries-jitstress2-jitstressregs runtime-coreclr r2r runtime-coreclr runincontext runtime-coreclr crossgen2 runtime-libraries-coreclr outerloop runtime-libraries-coreclr outerloop-windows runtime-libraries-coreclr outerloop-linux runtime-libraries-coreclr outerloop-osx runtime runtime-libraries enterprise-linux runtime-libraries stress-http runtime-libraries stress-ssl runtime-dev-innerloop runtime-coreclr crossgen2 outerloop coreclr-release-outerloop-nightly runtime-coreclr crossgen2-composite runtime-jit-experimental runtime-coreclr libraries-jitstress dotnet-linker-tests runtime-coreclr ilasm runtime-coreclr crossgen2-composite gcstress runtime-coreclr pgo runtime-coreclr libraries-pgo Antigen runtime-community Fuzzlyn runtime-coreclr superpmi-replay runtime-wasm runtime-coreclr superpmi-diffs runtime-coreclr superpmi-asmdiffs-checked-release runtime-extra-platforms jit-cfg runtime-wasm-perf runtime-llvm runtime-cet runtime-coreclr jitstress-random runtime-coreclr libraries-jitstress-random runtime-wasm-non-libtests runtime-android runtime-androidemulator runtime-ioslike runtime-ioslikesimulator runtime-linuxbionic runtime-maccatalyst runtime-coreclr pgostress runtime-coreclr jitstress-isas-avx512 runtime-libraries-mono outerloop runtime-sanitized runtime-wasm-dbgtests runtime-wasm-optional runtime-nativeaot-outerloop runtime-coreclr superpmi-collect-test runtime-diagnostics runtime-interpreter runtime-report-green runtime-coreclr hardware-intrinsics runtime-libraries-interpreter runtime-libraries stress-http-pr runtime-libraries stress-ssl-pr hardware-intrinsics-arm64

adamsitnik · 2026-06-18T16:45:22Z

/azp run runtime-maccatalyst

azure-pipelines · 2026-06-18T16:45:39Z

Azure Pipelines successfully started running 1 pipeline(s).

adamsitnik

LGTM

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

src/libraries/System.Diagnostics.Process/tests/StartSuspendedTests.cs:66

The test suite no longer validates Resume()’s documented error behavior on macOS: the “Resume called twice” test was removed entirely, and Resume_OnNonSuspendedProcess_ThrowsInvalidOperationException is now Windows-only. Given the public XML docs for SafeProcessHandle.Resume() say it throws when the process wasn’t started suspended or has already been resumed, we should keep coverage for these cases on macOS once the implementation enforces the same contract there.

        [ConditionalFact]
        [PlatformSpecific(TestPlatforms.Windows)]
        public void Resume_OnNonSuspendedProcess_ThrowsInvalidOperationException()
        {
            Process process = CreateProcess(static () => RemoteExecutor.SuccessExitCode);

            using SafeProcessHandle processHandle = SafeProcessHandle.Start(process.StartInfo);

            Assert.Throws<InvalidOperationException>(() => processHandle.Resume());

            processHandle.WaitForExitOrKillOnTimeout(TimeSpan.FromMilliseconds(WaitInMS));
        }

adamsitnik · 2026-06-22T13:54:58Z

+            if ((OperatingSystem.IsWindows() || OperatingSystem.IsMacOS()) && StartSuspended && UseShellExecute)
            {
                throw new InvalidOperationException(SR.StartSuspendedNotCompatible);
            }


@copilot apply this suggestion

Applied in the latest commit. ProcessStartInfo.Validate() now throws PlatformNotSupportedException when StartSuspended=true on non-Windows/non-macOS platforms, before checking the UseShellExecute incompatibility.

adamsitnik

@copilot please address my feedback

adamsitnik · 2026-06-22T13:54:58Z

+            if ((OperatingSystem.IsWindows() || OperatingSystem.IsMacOS()) && StartSuspended && UseShellExecute)
            {
                throw new InvalidOperationException(SR.StartSuspendedNotCompatible);
            }


@copilot apply this suggestion

…nded on unsupported OS, update Resume() docs and Windows impl, return error in fork() path Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot · 2026-06-22T14:43:44Z

@copilot please address my feedback

All three items addressed in the latest commit:

ProcessStartInfo.cs: Throws PlatformNotSupportedException when StartSuspended=true on non-Windows/non-macOS platforms
SafeProcessHandle.cs XML docs: Updated to remove "can only be called once" restriction; Resume() now documents that OS errors are surfaced via Win32Exception
pal_process.c fork() path: Returns ENOTSUP when startSuspended=true to prevent silent behavior differences when credentials force the fork() path on macOS

adamsitnik

@copilot address my feedback

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

Copilot · 2026-06-22T15:41:40Z

@copilot address my feedback

Addressed in the latest commit — ResumeCore keeps the _mainThreadHandle null check (throws InvalidOperationException) but no longer disposes the handle after first resume.

Copilot AI and others added 2 commits June 18, 2026 10:21

Add macOS support for StartSuspended via POSIX_SPAWN_START_SUSPENDED …

73d80c1

…and Resume via SIGCONT Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Address code review feedback: improve comments for clarity

0ae0148

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

Copilot AI self-assigned this Jun 18, 2026

Copilot AI review requested due to automatic review settings June 18, 2026 10:44

Copilot AI assigned adamsitnik Jun 18, 2026

Copilot AI removed the request for review from Copilot June 18, 2026 10:44

Copilot created this pull request from a session on behalf of adamsitnik June 18, 2026 10:45 View session

Copilot AI requested a review from adamsitnik June 18, 2026 10:45

Copilot finished work on behalf of adamsitnik June 18, 2026 10:45

adamsitnik reviewed Jun 18, 2026

View reviewed changes

adamsitnik added this to the 11.0.0 milestone Jun 18, 2026

adamsitnik added the area-System.Diagnostics.Process label Jun 18, 2026

Copilot started work on behalf of adamsitnik June 18, 2026 11:04 View session

adamsitnik linked an issue Jun 18, 2026 that may be closed by this pull request

[API Proposal]: ProcessStartInfo.CreateSuspended, Process.Resume #94127

Open

Address PR feedback: pass ProcessStartInfo to ForkAndExecProcess, sim…

d81838f

…plify ResumeCore, update WASI stub, fix tests Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot June 18, 2026 11:31

Copilot finished work on behalf of adamsitnik June 18, 2026 11:33

Copilot AI requested a review from adamsitnik June 18, 2026 11:33

adamsitnik reviewed Jun 18, 2026

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Comment thread src/libraries/Common/src/Interop/Unix/System.Native/Interop.ForkAndExecProcess.cs Outdated

Comment thread src/libraries/System.Diagnostics.Process/src/Microsoft/Win32/SafeHandles/SafeProcessHandle.cs

Copilot started work on behalf of adamsitnik June 18, 2026 11:53 View session

Address review feedback: reformat ForkAndExecProcess call and add Val…

22bc942

…idate() before ResumeCore Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot June 18, 2026 11:58

Copilot finished work on behalf of adamsitnik June 18, 2026 11:58

Copilot AI requested a review from adamsitnik June 18, 2026 11:58

adamsitnik reviewed Jun 18, 2026

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Comment thread src/libraries/System.Diagnostics.Process/tests/StartSuspendedTests.cs Outdated

Copilot started work on behalf of adamsitnik June 18, 2026 12:17 View session

adamsitnik approved these changes Jun 18, 2026

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adamsitnik requested review from sebastienros and wfurt June 18, 2026 18:23

Merge branch 'main' into copilot/start-suspended-for-macos

2afce6c

build-analysis Bot mentioned this pull request Jun 22, 2026

Intermittent build failure in AfterSourceBuild: "Could not write state file" #76488

Open

adamsitnik requested a review from Copilot June 22, 2026 12:00

Copilot started reviewing on behalf of adamsitnik June 22, 2026 12:01 View session

Copilot AI reviewed Jun 22, 2026

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adamsitnik reviewed Jun 22, 2026

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Copilot started work on behalf of adamsitnik June 22, 2026 13:56 View session

Address review feedback: PlatformNotSupportedException for StartSuspe…

f3ca01d

…nded on unsupported OS, update Resume() docs and Windows impl, return error in fork() path Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot finished work on behalf of adamsitnik June 22, 2026 14:44

Copilot AI requested a review from adamsitnik June 22, 2026 14:44

adamsitnik reviewed Jun 22, 2026

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Comment thread ...ries/System.Diagnostics.Process/src/Microsoft/Win32/SafeHandles/SafeProcessHandle.Windows.cs

Copilot started work on behalf of adamsitnik June 22, 2026 15:30 View session

Restore _mainThreadHandle null check in ResumeCore without closing ha…

11f6e6b

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

Copilot AI requested review from Copilot and removed request for Copilot June 22, 2026 15:41

Copilot AI requested a review from adamsitnik June 22, 2026 15:42

Copilot finished work on behalf of adamsitnik June 22, 2026 15:42

build-analysis Bot mentioned this pull request Jun 22, 2026

[browser] Wasm.Build.Tests timeout - Timed out after 10s waiting for 'WASM EXIT' #116697

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