Add Linux and Android support for ProcessStartInfo.KillOnParentExit using prctl(PR_SET_PDEATHSIG) by Copilot · Pull Request #127112 · dotnet/runtime

Copilot · 2026-04-18T21:57:23Z

Description

Adds Linux and Android support for ProcessStartInfo.KillOnParentExit using prctl(PR_SET_PDEATHSIG). Since PR_SET_PDEATHSIG fires when the calling thread exits (not the process), a dedicated long-lived thread is used to perform fork+exec so the signal is only delivered when the process exits.

Key design decisions

Dedicated thread: EnsurePDeathSigThread lazily starts a detached thread that lives for the process lifetime. The thread-start check uses a plain bool protected by the mutex (no atomics needed since the check is always done under the mutex).
Mutex/condvar synchronization: Callers submit a PDeathSigForkRequest struct to the dedicated thread via a shared pointer, protected by a mutex. Callers wait for s_pdeathsig_request == NULL before submitting to prevent overwriting a pending request, and each request has a per-request done flag to avoid lost-wakeup issues.
Orphan detection: After prctl(PR_SET_PDEATHSIG) in the child, a getppid() check detects if the parent died between fork and prctl, since PR_SET_PDEATHSIG will not deliver the signal in that case.
KillOnParentExit passed unconditionally: The managed code passes KillOnParentExit to the native shim unconditionally; the native side handles unsupported platforms as a no-op via HAVE_PR_SET_PDEATHSIG.
Android support: PR_SET_PDEATHSIG is available on Android, so [SupportedOSPlatform("android")] is added alongside [SupportedOSPlatform("linux")].

…R_SET_PDEATHSIG) Implements PR_SET_PDEATHSIG-based KillOnParentExit on Linux using a dedicated long-lived thread to ensure the death signal fires on process exit, not thread exit. Changes: - Add HAVE_PR_SET_PDEATHSIG cmake check and config - Add killOnParentExit parameter to SystemNative_ForkAndExecProcess - Implement dedicated pdeathsig thread with mutex/condvar synchronization - Call prctl(PR_SET_PDEATHSIG, SIGKILL) in child after fork - Pass KillOnParentExit through managed interop layer - Add [SupportedOSPlatform("linux")] to ref and impl - Enable KillOnParentExitTests on Linux Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/85b53068-8457-4ee3-bdbf-4339fc5a007e Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

…necessary prctl in thread, improve getppid comment Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/85b53068-8457-4ee3-bdbf-4339fc5a007e Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

adamsitnik · 2026-04-19T10:58:54Z

@copilot fix following build failure:


FAILED: libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o 
  /usr/bin/gcc-15 -DBUILDENV_CHECKED=1 -DDEBUG -DDISABLE_CONTRACTS -DHAS_CONSOLE_SIGNALS -DHOST_64BIT -DHOST_AMD64 -DHOST_UNIX -DPALEXPORT=EXTERN_C -DTARGET_64BIT -DTARGET_AMD64 -DTARGET_LINUX -DTARGET_UNIX -DURTBLDENV_FRIENDLY=Checked -D_DBG -D_DEBUG -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 -I/__w/1/s/artifacts/obj/coreclr/linux.x64.Checked/libs-native/System.Native -I/__w/1/s/src/native/libs/System.Native -I/__w/1/s/src/native -I/__w/1/s/src/native/inc -std=gnu99 -Wno-declaration-after-statement -D_GNU_SOURCE -std=gnu11 -fPIC -O2 -Wall -g -fno-omit-frame-pointer -fno-strict-overflow -fno-strict-aliasing -fstack-protector-strong -Werror -Wno-unused-variable -Wno-unused-value -Wno-unused-function -Wno-tautological-compare -Wno-unknown-pragmas -Wimplicit-fallthrough -Wno-unused-but-set-variable -ffp-contract=off -Wno-uninitialized -Wno-strict-aliasing -Wno-array-bounds -Wno-stringop-truncation -fsigned-char -fvisibility=hidden -ffunction-sections -I/__w/1/s/src/native/libs/Common -I/__w/1/s/artifacts/obj/coreclr/linux.x64.Checked/libs-native/Common -MD -MT libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o -MF libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o.d -o libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o -c /__w/1/s/src/native/libs/System.Native/pal_process.c
  /__w/1/s/src/native/libs/System.Native/pal_process.c: In function ‘PDeathSigThreadFunc’:
  /__w/1/s/src/native/libs/System.Native/pal_process.c:411:1: error: no return statement in function returning non-void [-Werror=return-type]
    411 | }
        | ^
  cc1: all warnings being treated as errors

Add return NULL after infinite while(1) loop to satisfy GCC's -Werror=return-type, with clang pragma to suppress -Wunreachable-code-return. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/2659e9ab-8d2c-48d8-a7af-d5356d056e46 Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot · 2026-04-19T11:03:25Z

@copilot fix following build failure:

'''log...

Fixed in dc2712a. Added return NULL; after the infinite while(1) loop to satisfy GCC's -Werror=return-type, with a clang pragma to suppress -Wunreachable-code-return (which was the original reason the return was removed).

adamsitnik

@copilot fix the WASM build

  FAILED: libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o 
  /__w/1/s/src/mono/browser/emsdk/emscripten/emcc -DCOMPILER_SUPPORTS_W_RESERVED_IDENTIFIER -DDISABLE_CONTRACTS -DGEN_PINVOKE=1 -DHOST_32BIT=1 -DHOST_BROWSER -DHOST_UNIX -DHOST_WASM -DNDEBUG -DTARGET_32BIT -DTARGET_BROWSER -DTARGET_UNIX -DTARGET_WASM -DTARGET_WASM32 -DURTBLDENV_FRIENDLY=Retail -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 -I/__w/1/s/artifacts/obj/coreclr/browser.wasm.Release/libs-native/System.Native -I/__w/1/s/src/native/libs/System.Native -I/__w/1/s/src/native -I/__w/1/s/src/native/inc -std=gnu99 -Wno-declaration-after-statement -Wno-pre-c11-compat -O3 -DNDEBUG -std=gnu11 -fwasm-exceptions -mbulk-memory -msimd128 -O3 -Wall -Wno-null-conversion -glldb -Wno-unused-parameter -Wno-alloca -Wno-implicit-int-float-conversion -fno-omit-frame-pointer -fno-strict-overflow -fno-strict-aliasing -Werror -Wno-unused-variable -Wno-unused-value -Wno-unused-function -Wno-tautological-compare -Wno-unknown-pragmas -Wimplicit-fallthrough -Wno-unused-but-set-variable -ffp-contract=off -Wno-unknown-warning-option -ferror-limit=4096 -Wno-unused-private-field -Wno-constant-logical-operand -Wno-pragma-pack -Wno-incompatible-ms-struct -Wno-reserved-identifier -Wno-unsafe-buffer-usage -Wno-single-bit-bitfield-constant-conversion -Wno-cast-function-type-strict -Wno-switch-default -fsigned-char -fvisibility=hidden -ffunction-sections -I/__w/1/s/src/native/libs/Common -I/__w/1/s/artifacts/obj/coreclr/browser.wasm.Release/libs-native/Common -Oz -Weverything -Wno-format-nonliteral -Wno-disabled-macro-expansion -Wno-padded -Wno-empty-translation-unit -Wno-cast-align -Wno-typedef-redefinition -Wno-thread-safety-analysis -Wno-c11-extensions -Wno-pre-c11-compat -MD -MT libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o -MF libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o.d -o libs-native/System.Native/CMakeFiles/System.Native-Static.dir/pal_process.c.o -c /__w/1/s/src/native/libs/System.Native/pal_process.c
  /__w/1/s/src/native/libs/System.Native/pal_process.c:537:12: error: call to undeclared function 'ForkAndExecProcessInternal'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    537 |     return ForkAndExecProcessInternal(
        |            ^
  /__w/1/s/src/native/libs/System.Native/pal_process.c:544:16: error: static declaration of 'ForkAndExecProcessInternal' follows non-static declaration
    544 | static int32_t ForkAndExecProcessInternal(
        |                ^
  /__w/1/s/src/native/libs/System.Native/pal_process.c:537:12: note: previous implicit declaration is here
    537 |     return ForkAndExecProcessInternal(
        |            ^
  2 errors generated.

Move ForkAndExecProcessInternal forward declaration outside #if HAVE_PR_SET_PDEATHSIG so it's visible on all platforms (fixes WASM build). Simplify return NULL in PDeathSigThreadFunc by removing pragma guards. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/0261d155-fd8a-43c3-80bc-9085dec73b97 Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot · 2026-04-19T11:44:47Z

@copilot fix the WASM build

'''log...

Fixed in 3723cc4. The ForkAndExecProcessInternal forward declaration was inside the #if HAVE_PR_SET_PDEATHSIG block, so on WASM (where it's 0) it wasn't visible. Moved the forward declaration before the #if block so it's always available.

…ndroid support Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/7d461b6e-4e3b-451c-b496-397402d75d53 Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

adamsitnik · 2026-05-03T20:18:15Z

/azp run runtime-android runtime-androidemulator

azure-pipelines · 2026-05-03T20:18:21Z

No pipelines are associated with this pull request.

adamsitnik · 2026-05-03T20:18:31Z

/azp run runtime-android

azure-pipelines · 2026-05-03T20:18:40Z

Azure Pipelines successfully started running 1 pipeline(s).

adamsitnik

LGTM, we just need to update one XML doc sentence

Co-authored-by: Adam Sitnik <adam.sitnik@gmail.com>

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

tmds

lgtm, I left some suggestions.

… call under mutex; update orphan-check comment Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/4461470f-ca8e-45c7-b43a-5462587db7d2 Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/d9dfd77d-8e4a-4f81-be02-e37aa63b1e6c Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

Copilot AI and others added 2 commits April 18, 2026 21:45

Copilot AI assigned Copilot and adamsitnik Apr 18, 2026

Copilot AI requested review from Copilot and removed request for Copilot April 18, 2026 21:57

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github-actions Bot added the area-System.Diagnostics.Process label Apr 18, 2026

This was referenced Apr 19, 2026

System.Net.NameResolution.Tests DNS failures: Name or service not known #126641

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Libraries .NET 4.8.1 build failing #127007

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System.DirectoryServices.Protocols.LdapException : The LDAP server is unavailable. #127070

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Copilot started work on behalf of adamsitnik May 3, 2026 19:59 View session

Pass startInfo.KillOnParentExit unconditionally to native shim, add A…

86046de

…ndroid support Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/7d461b6e-4e3b-451c-b496-397402d75d53 Co-authored-by: adamsitnik <6011991+adamsitnik@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot May 3, 2026 20:08

Copilot AI changed the title ~~Add Linux support for ProcessStartInfo.KillOnParentExit using prctl(PR_SET_PDEATHSIG)~~ Add Linux and Android support for ProcessStartInfo.KillOnParentExit using prctl(PR_SET_PDEATHSIG) May 3, 2026

Copilot finished work on behalf of adamsitnik May 3, 2026 20:09

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adamsitnik requested a review from jkotas May 3, 2026 22:14

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build-analysis Bot mentioned this pull request May 4, 2026

browser-wasm linux Release LibraryTests queues timing out #117974

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Comment thread src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.cs Outdated

Apply suggestions from code review

632091e

Co-authored-by: Adam Sitnik <adam.sitnik@gmail.com>

Copilot AI review requested due to automatic review settings May 4, 2026 07:23

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Merge branch 'main' into copilot/extend-kill-on-parent-exit-linux

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adamsitnik enabled auto-merge (squash) May 4, 2026 07:25

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

Comment thread src/native/libs/System.Native/pal_process.c

tmds reviewed May 4, 2026

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Comment thread src/native/libs/System.Native/pal_process.c Outdated

adamsitnik mentioned this pull request May 4, 2026

Run Process tests in parallel #127698

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Comment thread src/native/libs/System.Native/pal_process.c Outdated

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jkotas reviewed May 4, 2026

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Comment thread src/native/libs/System.Native/pal_process.c Outdated

Change s_pdeathsig_thread_started type from int to bool

715c83c

Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/d9dfd77d-8e4a-4f81-be02-e37aa63b1e6c Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>

build-analysis Bot mentioned this pull request May 4, 2026

Checkout failure: "Git fetch failed with exit code 128" dotnet/arcade#9009

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[main] Source code updates from dotnet/runtime dotnet/dotnet#6423

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Copilot AI commented Apr 18, 2026 •

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