posix: implement POSIX semaphore interfaces by oI0ck · Pull Request #457 · phoenix-rtos/libphoenix

oI0ck · 2026-01-29T18:07:09Z

TASK: RTOS-1407

Description

This PR introduces implementation of POSIX standard semaphore interfaces.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

Already covered by automatic testing.
New test added: posix: add posix directory and semaphore tests phoenix-rtos-tests#448
Tested by hand on: ia32-generic-qemu

Checklist:

My change requires a change to the documentation.
I have updated the documentation accordingly.
I have added tests to cover my changes.
All new and existing linter checks and tests passed.
My changes generate no new compilation warnings for any of the targets.

Special treatment

This PR needs additional PRs to work (list the PRs, preferably in merge-order).
posixsrv: implement named semaphore server phoenix-rtos-posixsrv#27
libc: add sem_* family functions documentation phoenix-rtos-doc#252
I will merge this PR by myself when appropriate.

gemini-code-assist · 2026-01-29T18:07:28Z

Summary of Changes

Hello @oI0ck, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces comprehensive support for POSIX standard semaphore interfaces within the libphoenix library. It enables developers to use both named and unnamed semaphores for synchronization, integrating with the posixsrv for named semaphore management and extending the core sys/threads functionality for unnamed semaphores. This significantly enhances the concurrency primitives available in the Phoenix-RTOS environment.

Highlights

POSIX Semaphore API: Implemented the full suite of POSIX semaphore functions, including sem_open, sem_close, sem_unlink, sem_init, sem_destroy, sem_wait, sem_trywait, sem_timedwait, sem_post, and sem_getvalue.
Named and Unnamed Semaphores: The implementation distinguishes between named semaphores (managed via inter-process communication with posixsrv) and unnamed semaphores (managed internally).
Core Semaphore Operations: Introduced semaphoreTryDown and semaphoreCount functions in the underlying sys/threads.h and sys/semaphore.c to support the POSIX API.
Messaging Integration: Named semaphores utilize msgSend and ioctl calls to communicate with a posixsrv for their operations, defining specific IOCTL commands (SEM_UP, SEM_DOWN, SEM_DOWN_TRY, SEM_DOWN_TIMEOUT).

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Code Review

This PR introduces POSIX semaphore implementation. The changes are extensive, adding new headers and implementation files for named and unnamed semaphores. The overall structure is good, but I've found several critical issues in the implementation, including race conditions, incorrect logic leading to deadlocks, and potential memory corruption. There are also some areas where the code can be simplified and made more robust. Please address the critical issues before merging.

github-actions · 2026-01-29T18:26:09Z

Unit Test Results

14 250 tests +520 13 389 ✅ +518 58m 31s ⏱️ + 1m 59s
790 suites + 10 859 💤 ± 0
1 files ± 0 2 ❌ + 2

For more details on these failures, see this check.

Results for commit 63ca129. ± Comparison against base commit 9bffcee.

♻️ This comment has been updated with latest results.

datadog-phoenix-rtos · 2026-06-22T09:19:25Z

⚠️ Warnings

🚦 3 Pipeline jobs failed

ci | call-ci / build (armv7a9-zynq7000-zedboard)

ci | call-ci / build (armv7m7-imxrt106x-evk)

ci | call-ci / tests-summary

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 057606b | Docs | Give us feedback!}

oI0ck · 2026-06-22T12:14:50Z

This is currently blocked by:

oI0ck · 2026-06-30T12:35:39Z

CI shows problems with this change, I'm converting it to a draft until I am sure that it is in mergable state.

ziemleszcz · 2026-09-02T09:46:39Z

Please rebase thsi PR and resolve conficts.

No functional change. TASK: RTOS-1407

TASK: RTOS-1407

semaphoreUp() incremented the counter unconditionally, so a semaphore posted SEM_VALUE_MAX times wrapped silently. POSIX requires sem_post() to fail with EOVERFLOW instead, so report -EOVERFLOW and leave the value untouched. semaphoreCreate() accepted any initial value. Reject one above the limit, and a NULL semaphore. TASK: RTOS-1407

sem_getvalue() and sem_trywait() need a way to read the counter and to take the semaphore without blocking. Add the two primitives they are built on. Both take the internal mutex with mutexLock() rather than mutexTry(): contention on it is an implementation detail, not a property of the semaphore, so letting it surface would make semaphoreCount() report a spurious 0 and semaphoreTryDown() fail while the semaphore is free. TASK: RTOS-1407 Assisted-by: claude-opus-5

semaphoreDown() takes a relative timeout, resolves it against the monotonic clock and waits on the condvar's own clock. sem_timedwait() is specified in terms of an absolute CLOCK_REALTIME deadline, which that interface cannot express without the caller converting between clock domains by hand. Add semaphoreDownAtClock(), which passes the deadline and the clock straight to condClockWait() and lets the kernel resolve both. A deadline that has already passed comes back as -ETIME before the caller is parked, so the value is still checked first and an available semaphore is still taken. The one value the kernel cannot express is 0, which it reads as "no deadline", so the epoch is turned into -ETIME here. PH_CLOCK_RELATIVE is rejected: the retry loop hands the same value to every condClockWait() call, which would restart a relative timeout after each wakeup. TASK: RTOS-1407 Assisted-by: claude-opus-5

Add the POSIX semaphore API. Unnamed semaphores are backed directly by libphoenix's semaphore_t. Named ones live in posixsrv, which exposes each of them as a device node under /dev/posix/sem/. A named sem_t holds an open descriptor on that node rather, so operations travel as ordinary ioctl() calls and the kernel drops the server-side reference when the process exits. The descriptor is opened O_CLOEXEC, giving the POSIX requirement that named semaphores are closed across a successful exec(). TASK: RTOS-1407 Assisted-by: claude-opus-5

semaphoreUp() signalled only on the 0 -> 1 transition, assuming that a positive value meant there were no waiters. This is incorrect. Track the number of waiters and signal whenever a waiter is present. TASK: RTOS-1407

adamgreloch · 2026-10-02T16:46:08Z

+		err = condClockWait(s->cond, s->mutex, deadline, clock);
+		--s->waiters;
+	} while ((err == 0) || (err == -EINTR));
+
+	mutexUnlock(s->mutex);


condClockWait may return with lock not held

adamgreloch · 2026-10-02T16:47:57Z

+/* not required by POSIX, but ensures that
+ * sem_getvalue() does not return an overflowed value.
+ */


Suggested change

/* not required by POSIX, but ensures that

* sem_getvalue() does not return an overflowed value.

*/

/*

* not required by POSIX, but ensures that

* sem_getvalue() does not return an overflowed value.

*/

oI0ck requested a review from Darchiv January 29, 2026 18:07

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oI0ck mentioned this pull request Jan 29, 2026

posix: add posix directory and semaphore tests phoenix-rtos/phoenix-rtos-tests#448

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oI0ck force-pushed the michal.lach/sem branch from ba94ea8 to da0f0fd Compare January 29, 2026 18:10

oI0ck marked this pull request as draft January 29, 2026 18:37

oI0ck force-pushed the michal.lach/sem branch from da0f0fd to b6d1928 Compare February 2, 2026 01:07

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oI0ck force-pushed the michal.lach/sem branch from b6d1928 to 20f142f Compare February 2, 2026 01:10

oI0ck marked this pull request as ready for review February 2, 2026 16:06

julianuziemblo reviewed Feb 3, 2026

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oI0ck force-pushed the michal.lach/sem branch 2 times, most recently from cf48092 to f3710e3 Compare February 10, 2026 13:19

oI0ck force-pushed the michal.lach/sem branch from 239fd04 to 706ff80 Compare May 29, 2026 15:51

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oI0ck force-pushed the michal.lach/sem branch from 706ff80 to c6a2d17 Compare June 22, 2026 09:18

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oI0ck force-pushed the michal.lach/sem branch 2 times, most recently from 23e321c to 057606b Compare June 22, 2026 09:24

oI0ck force-pushed the michal.lach/sem branch from 057606b to 8b13146 Compare June 30, 2026 12:19

oI0ck marked this pull request as draft June 30, 2026 12:35

oI0ck force-pushed the michal.lach/sem branch 3 times, most recently from 070fbcb to 67a05ba Compare June 30, 2026 17:32

oI0ck force-pushed the michal.lach/sem branch from 67a05ba to 75a25a1 Compare July 20, 2026 23:10

oI0ck force-pushed the michal.lach/sem branch from 74bdc2c to c0eed79 Compare July 28, 2026 10:49

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Comment thread include/phoenix/semaphore.h

oI0ck force-pushed the michal.lach/sem branch 3 times, most recently from 0fcb1c0 to 78ea982 Compare July 29, 2026 12:28

oI0ck requested review from Darchiv, julianuziemblo and ziemleszcz July 29, 2026 16:01

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oI0ck force-pushed the michal.lach/sem branch 2 times, most recently from 657275d to 169a290 Compare July 31, 2026 15:26

oI0ck requested a review from ziemleszcz July 31, 2026 15:28

oI0ck force-pushed the michal.lach/sem branch from 169a290 to e24eb57 Compare September 21, 2026 12:28

ziemleszcz force-pushed the michal.lach/sem branch from e24eb57 to 2daeb8f Compare September 25, 2026 11:44

ziemleszcz self-assigned this Sep 25, 2026

ziemleszcz requested a review from a team September 25, 2026 15:01

include: replace %LICENSE% with SPDX identifiers

cccf220

No functional change. TASK: RTOS-1407

ziemleszcz force-pushed the michal.lach/sem branch from 2daeb8f to 5df6063 Compare October 1, 2026 10:32

adamgreloch reviewed Oct 2, 2026

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Comment thread posix/sem.c

oI0ck and others added 7 commits October 2, 2026 13:25

include/assert: add C/C++ compatible static_assert macro

acc1845

TASK: RTOS-1407

limits: add semaphore specific POSIX limits

3c44fd6

TASK: RTOS-1407

semaphores: fix lost wakeup in semaphoreUp()

63ca129

semaphoreUp() signalled only on the 0 -> 1 transition, assuming that a positive value meant there were no waiters. This is incorrect. Track the number of waiters and signal whenever a waiter is present. TASK: RTOS-1407

ziemleszcz force-pushed the michal.lach/sem branch from 5df6063 to 63ca129 Compare October 2, 2026 11:50

adamgreloch reviewed Oct 2, 2026

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oI0ck commented Jan 29, 2026 • edited by ziemleszcz Loading Uh oh! There was an error while loading. Please reload this page.

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Description

Types of changes

How Has This Been Tested?

Checklist:

Special treatment

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gemini-code-assist Bot commented Jan 29, 2026

Summary of Changes

Highlights

Footnotes

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Code Review

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Unit Test Results

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⚠️ Warnings

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oI0ck commented Jun 22, 2026

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adamgreloch Oct 2, 2026

oI0ck commented Jan 29, 2026 •

edited by ziemleszcz

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