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

oI0ck · 2026-01-29T18:07:09Z

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

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.

gemini-code-assist · 2026-01-29T18:09:53Z

+					memset(path, 0, sizeof(path));
+					strcpy(path, SEMAPHORE_PATH);
+					strcpy(path + strlen(SEMAPHORE_PATH), dent->d_name);


Using multiple strcpy calls to build a path can be fragile and inefficient. Using snprintf is a safer and more readable way to construct file paths, as it protects against buffer overflows.

snprintf(path, sizeof(path), "%s%s", SEMAPHORE_PATH, dent->d_name);

hm yeah, why not snprintf?

I think that it is not worth to have the overhead of parsing the format string when just cating two strings together (ironic to consider this overhead but allocate PATH_MAX on the stack XD).

Though, there is a bug in here because dent->d_name can be PATH_MAX and a path of such length will cause a OOB write here.

I'll change this concatenation to use strlcpy in the next revision.

github-actions · 2026-01-29T18:26:09Z

Unit Test Results

10 935 tests 10 256 ✅ 55m 50s ⏱️
690 suites 670 💤
1 files 9 ❌

For more details on these failures, see this check.

Results for commit 67a05ba.

♻️ This comment has been updated with latest results.

julianuziemblo · 2026-02-03T13:44:09Z

+
+#define SEM_FAILED ((sem_t *)0xDAAB0000)
+
+typedef struct _sem_t {


_sem_t identifier is not used anywhere. If it's not required by POSIX - remove it.

julianuziemblo · 2026-02-03T13:48:14Z

+#define SEMAPHORE_PATH      ("/dev/posix/sem/")
+#define SEMCTL_PATH         ("/dev/posix/semctl")


nitpick: we don't seem to use parenthesis to define string in macros as they interfere with string concatenation by the compiler (we couldn't, for example, write code like const char *path = SEMAPHORE_PATH "my_sem" in the client).

Darchiv · 2026-06-17T18:29:30Z

+#define SEMCTL_PATH         ("/dev/posix/semctl")
+#define SEMAPHORE_MAX_COUNT (128)
+#define SEMAPHORE_NAME_MAX  (NAME_MAX - sizeof(SEMAPHORE_PATH) - 1)
+#define SEM_VALUE_MAX       INT_MAX


I think this should be defined per-architecture in libphoenix/include/arch/*/limits.h (like NAME_MAX). It can be just #define SEM_VALUE_MAX INT_MAX, but the important part is that the definition should be available via limits.h.

Is SEMAPHORE_MAX_COUNT used anywhere? Is should be SEM_NSEMS_MAX and defined in limits.h like in the point above. Please actually enforce the limit. Note that _POSIX_SEM_NSEMS_MAX == 256 which is the minimum value for this limit.

See sysconf(). You could implement _SC_SEM_VALUE_MAX and _SC_SEM_NSEMS_MAX.

Also, this is a good place to static-assert SEM_VALUE_MAX with _POSIX_SEM_VALUE_MAX and SEM_NSEMS_MAX with _POSIX_SEM_NSEMS_MAX in case someone changes limits.h incorrectly. Maybe also check whether the limit does not exceed the semaphore value type size (unsigned int).

Darchiv · 2026-06-17T18:39:19Z

+		else {
+		}
+
+		sem = (sem_t *)malloc(sizeof(*sem));


Type cast redundant

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:

JIRA: RTOS-1088

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.

JIRA: RTOS-1088

Up until C23, C used _Static_assert for compile time assertions. C23 changed it to static_assert, to match C++ keyword. Since we can include some of our headers in C++ source, this static assertions should be portable between C++ and C source.

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

github-actions Bot reviewed Jan 29, 2026

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Comment thread include/semaphore.h

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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12 tasks

gemini-code-assist Bot reviewed Jan 29, 2026

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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

github-actions Bot reviewed Feb 2, 2026

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Comment thread include/semaphore.h Outdated

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

View reviewed changes

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

Darchiv reviewed Jun 17, 2026

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

github-actions Bot reviewed Jun 22, 2026

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Comment thread include/sys/semaphore.h Outdated

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

semaphores: add semaphoreTryDown and semaphoreCount functions

bb5961f

JIRA: RTOS-1088

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 2 times, most recently from 0615ab7 to 070fbcb Compare June 30, 2026 17:30

posix: implement sem_* family functions

8880205

JIRA: RTOS-1088

oI0ck added 2 commits June 30, 2026 19:31

limits: add semaphore specific POSIX limits

67a05ba

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


		#define SEM_FAILED ((sem_t *)0xDAAB0000)

		typedef struct _sem_t {

		#define SEMAPHORE_PATH ("/dev/posix/sem/")
		#define SEMCTL_PATH ("/dev/posix/semctl")

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Description

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⚠️ Warnings

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