bugfix/guard_page_and_ex_handle by Copilot · Pull Request #13 · Melnytskyi/fast_task

Copilot · 2026-05-18T15:28:30Z

Review new PR comment and identify actionable review threads to address
Inspect current code and run existing build/tests to establish baseline
Implement fixes for scheduler abort_tasks behavior and executing_tasks accounting
Implement guard-page-safe stack clearing on Linux/Windows reuse paths
Fix CMake source-dir include path and validate FAST_TASK_GUARD_PAGE_COUNT input
Add/adjust tests for abort_tasks=true queued-task shutdown behavior
Run targeted tests, then final validation (including parallel validation)
Fix stack allocation to always reserve size + guard_page_size (new comment)
Validate and push fix

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/57e0a87f-741a-4a2b-b21f-6a61b611b899 Co-authored-by: Melnytskyi <[email protected]>

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/47d0fa60-d990-4aa9-95a7-48d5b37d8a91 Co-authored-by: Melnytskyi <[email protected]>

- Add fast_task::stack_overflow exception to include/exceptions.hpp - Implement Linux x86_64 SIGSEGV handler in light_stack.cpp: * Install per-thread alternate signal stack + process-wide sigaction * On guard-page fault: mprotect to RW, set up return address from [RBP+8] so the DWARF unwind chain is intact, redirect RIP to __stack_overflow_raise * Restore PROT_NONE on guard page when recycling stacks (unlimited/limited_buffer) - Add CMake fallback to valgrind stub headers when system valgrind not installed - Add tests/stackfull/test_stackfull_guard.cpp (4 tests, all pass) Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/7235f5d5-bf5b-4d9b-860b-d2d013dbcf4e Co-authored-by: Melnytskyi <[email protected]>

- Check mprotect() return value in signal handler; fall back to old handler on failure - Validate RBP is within valid (non-guard) stack bounds before dereferencing [RBP+8] - Check sigaltstack() return value; free alt-stack memory on failure - Discard stack in unlimited_buffer/limited_buffer if mprotect(PROT_NONE) fails Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/7235f5d5-bf5b-4d9b-860b-d2d013dbcf4e Co-authored-by: Melnytskyi <[email protected]>

…ow recovery - Add FAST_TASK_GUARD_PAGE_COUNT cmake option (default 1); passes FT_GUARD_PAGE_COUNT to the library so guard page size is configurable at build time; 0 disables mprotect - Remove stack_overflow exception type from exceptions.hpp - Linux light_stack: remove SIGSEGV handler machinery (handler, alt-stack, sigaction); make __install_signal_handler_mem a no-op; drive guard_page_size from FT_GUARD_PAGE_COUNT; guard mprotect(PROT_NONE) in create_stack with #if FT_GUARD_PAGE_COUNT > 0; remove mprotect restoration from unlimited_buffer / limited_buffer - Windows light_stack: drive guard_page_size from FT_GUARD_PAGE_COUNT; guard PAGE_GUARD commit with #if FT_GUARD_PAGE_COUNT > 0 - test_stackfull_guard: remove stack-overflow tests; keep 2 exception-callback tests Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/463eb9a4-b8be-4088-becb-33ec6fdfbd0e Co-authored-by: Melnytskyi <[email protected]>

Copilot

Pull request overview

This PR simplifies stack guard handling by moving away from stack-overflow recovery and adds configurable guard-page sizing, Valgrind header fallbacks, exception-callback coverage, and an abort option for closing bind-only executors.

Changes:

Adds FAST_TASK_GUARD_PAGE_COUNT and applies guard-page sizing on Linux/Windows stacks.
Adds bundled minimal Valgrind header stubs for builds without system Valgrind headers.
Adds exception callback tests and extends bind-only executor close API with abort_tasks.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
`CMakeLists.txt`	Adds guard-page count definition and Valgrind stub include fallback.
`include/task/scheduler.hpp`	Extends `close_bind_only_executor` with `abort_tasks`.
`src/tasks/_internal.hpp`	Stores binded executor abort-on-close state.
`src/tasks/classes/task/scheduler.cpp`	Propagates abort-on-close state while closing bind-only executors.
`src/tasks/scheduler.cpp`	Handles in-place exception callbacks and aborts queued binded tasks on close.
`src/tasks/util/light_stack.cpp`	Applies configurable guard-page behavior and removes Linux signal-handler recovery.
`tests/stackfull/CMakeLists.txt`	Registers the new stackfull guard test target.
`tests/stackfull/test_stackfull_guard.cpp`	Adds portable exception-callback and RAII unwinding tests.
`third_party/valgrind-stubs/valgrind/memcheck.h`	Adds minimal Memcheck no-op macros.
`third_party/valgrind-stubs/valgrind/valgrind.h`	Adds minimal Valgrind no-op macros.

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Melnytskyi · 2026-05-18T15:38:10Z

@copilot apply changes based on the comments in this thread

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/1508b0a8-36ab-4951-93df-4db9191e6658 Co-authored-by: Melnytskyi <[email protected]>

Copilot · 2026-05-18T15:51:11Z

@copilot apply changes based on the comments in this thread

Implemented the requested review-thread fixes in commits c2a5790 and b4c6989: abort-on-close now correctly handles queued bind-worker tasks (without rescheduling when aborting), aborted tasks now mark completed and decrement glob.executing_tasks, guard-page stack clearing skips protected ranges safely on Linux/Windows, FAST_TASK_GUARD_PAGE_COUNT is validated as a non-negative integer, Valgrind stub include uses CMAKE_CURRENT_SOURCE_DIR, and a bind-executor test now covers close_bind_only_executor(id, true) with queued tasks plus shutdown/await behavior.

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Melnytskyi · 2026-05-18T16:37:43Z

@copilot change the stack allocation to allocate size + guard_pages_size instead of just size to keep the behavior as expected regardless of the library configuration (big guard page setting could set whole stack as guard page and the coroutine couldn't start)

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/c5f400fb-8b0b-4f7e-8b0d-1be09730581f Co-authored-by: Melnytskyi <[email protected]>

Copilot · 2026-05-18T16:48:39Z

@copilot change the stack allocation to allocate size + guard_pages_size instead of just size to keep the behavior as expected regardless of the library configuration (big guard page...

Fixed in commit 3be6541. Both the Windows and Linux allocate() functions now compute size__ = ((size + guard_page_size + page_size - 1) / page_size) * page_size — exactly size + guard_page_size (page-aligned) — removing the old (pages + 1) * page_size formula that added a spurious extra page. The usable portion of every allocated stack is now exactly the requested size regardless of FT_GUARD_PAGE_COUNT.

Copilot

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 7 comments.

Copilot AI and others added 5 commits May 18, 2026 00:47

Complete TODOs in scheduler.cpp and light_stack.cpp

dc9b44d

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/57e0a87f-741a-4a2b-b21f-6a61b611b899 Co-authored-by: Melnytskyi <[email protected]>

Move on_exception call outside catch block in in_place_run to avoid UB

6d6b368

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/47d0fa60-d990-4aa9-95a7-48d5b37d8a91 Co-authored-by: Melnytskyi <[email protected]>

Copilot AI assigned Copilot and Melnytskyi May 18, 2026

Copilot created this pull request from a session on behalf of Melnytskyi May 18, 2026 15:28 View session

Melnytskyi changed the title ~~Guard pages as fast-fail with configurable count; remove overflow-recovery machinery~~ bugfix/guard_page_and_ex_handle May 18, 2026

Melnytskyi requested a review from Copilot May 18, 2026 15:29

Copilot started reviewing on behalf of Melnytskyi May 18, 2026 15:30 View session

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Copilot started work on behalf of Melnytskyi May 18, 2026 15:38 View session

Copilot AI and others added 2 commits May 18, 2026 15:47

Fix abort_tasks close path, guard-page clearing, and config validation

c2a5790

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/1508b0a8-36ab-4951-93df-4db9191e6658 Co-authored-by: Melnytskyi <[email protected]>

Refine abort-close test determinism and guard-page clear safety

b4c6989

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Copilot finished work on behalf of Melnytskyi May 18, 2026 15:51

Copilot AI requested a review from Melnytskyi May 18, 2026 15:51

Copilot started work on behalf of Melnytskyi May 18, 2026 16:37 View session

fix: allocate size + guard_page_size to preserve usable stack size

3be6541

Agent-Logs-Url: https://github.com/Melnytskyi/fast_task/sessions/c5f400fb-8b0b-4f7e-8b0d-1be09730581f Co-authored-by: Melnytskyi <[email protected]>

Copilot finished work on behalf of Melnytskyi May 18, 2026 16:49

Melnytskyi approved these changes May 18, 2026

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Melnytskyi marked this pull request as ready for review May 18, 2026 16:53

Melnytskyi requested a review from Copilot May 18, 2026 16:53

Copilot started reviewing on behalf of Melnytskyi May 18, 2026 16:53 View session

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Melnytskyi merged commit fcde43f into main May 18, 2026
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Melnytskyi deleted the copilot/complete-todos-in-scheduler-and-light-stack-again branch May 18, 2026 17:07

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