posix: implement POSIX semaphore interfaces

include/assert.h

@@ -25,6 +25,16 @@
 extern "C" {
 #endif
 
+/*
+ * We want to be able to include our headers in C++ source and it uses a different
+ * keyword for static assertions, the same goes for C from C23 onwards
+ */
+#if defined(__cplusplus) || __STDC_VERSION__ == 202311L
+#define STATIC_ASSERT static_assert
+#else
+#define STATIC_ASSERT _Static_assert
+#endif
+
 
 #ifndef NDEBUG
 #define assert(__expr) \

include/limits.h

@@ -5,8 +5,8 @@
  *
  * limits.h
  *
- * Copyright 2019 Phoenix Systems
- * Author: Andrzej Glowinski
+ * Copyright 2019, 2026 Phoenix Systems
+ * Author: Andrzej Glowinski, Michal Lach
  *
  * This file is part of Phoenix-RTOS.
  *
@@ -36,4 +36,7 @@
 
 #include <posix/limits.h>
 
+#define SEM_VALUE_MAX INT_MAX
+#define SEM_NSEMS_MAX _POSIX_SEM_NSEMS_MAX
+
 #endif

include/semaphore.h

@@ -0,0 +1,61 @@
+/*
+ * Phoenix-RTOS
+ *
+ * libphoenix
+ *
+ * POSIX implementation - semaphores
+ *
+ * Copyright 2026 Phoenix Systems
+ * Author: Michal Lach
+ *
+ * This file is part of Phoenix-RTOS.
+ *
+ * %LICENSE%
+ */
+
+#include <time.h>
+#include <limits.h>
+#include <sys/threads.h>
+#include <sys/semaphore.h>
+
+#define SEM_FAILED ((sem_t *)0xDAAB0000)
+
+typedef struct _sem_t {
+	/* clang-format off */
+	enum { smNamed, smUnnamed } type;
+	/* clang-format on */
+
+	union {
+		semaphore_t unnamed;
+		oid_t named;
+	};
+} sem_t;
+
+extern int sem_wait(sem_t *sem);
+
+
+extern int sem_trywait(sem_t *sem);
+
+
+extern int sem_timedwait(sem_t *restrict sem, const struct timespec *restrict abs_timeout);
+
+
+extern int sem_getvalue(sem_t *restrict sem, int *restrict value);
+
+
+extern int sem_post(sem_t *sem);
+
+
+extern int sem_close(sem_t *sem);
+
+
+extern sem_t *sem_open(const char *name, int oflag, ... /* mode_t mode, unsigned int value */);
+
+
+extern int sem_unlink(const char *name);
+
+
+extern int sem_destroy(sem_t *sem);
+
+
+extern int sem_init(sem_t *sem, int pshared, unsigned int value);

include/sys/semaphore.h

@@ -0,0 +1,29 @@
+/*
+ * Phoenix-RTOS
+ *
+ * libphoenix
+ *
+ * POSIX implementation - semaphores
+ *
+ * Copyright 2026 Phoenix Systems
+ * Author: Michal Lach
+ *
+ * This file is part of Phoenix-RTOS.
+ *
+ * %LICENSE%
+ */
+
+#include <assert.h>
+#include <limits.h>
+#include <sys/ioctl.h>
+
+#define SEMAPHORE_PATH "/dev/posix/sem/"
+#define SEMCTL_PATH    "/dev/posix/semctl"
+
+STATIC_ASSERT(SEM_VALUE_MAX >= _POSIX_SEM_VALUE_MAX, "SEM_VALUE_MAX shall be greater or equal to _POSIX_SEM_VALUE_MAX");
+STATIC_ASSERT(SEM_NSEMS_MAX >= _POSIX_SEM_NSEMS_MAX, "SEM_NSEMS_MAX shall be greater or equal to _POSIX_SEM_NSEMS_MAX");
+
+#define SEM_UP           _IO('s', 0x1)
+#define SEM_DOWN         _IO('s', 0x2)
+#define SEM_DOWN_TRY     _IO('s', 0x3)
+#define SEM_DOWN_TIMEOUT _IOW('s', 0x4, time_t)

include/sys/threads.h

@@ -5,8 +5,8 @@
  *
  * sys/threads
  *
- * Copyright 2017, 2018 Phoenix Systems
- * Author: Pawel Pisarczyk, Aleksander Kaminski
+ * Copyright 2017, 2018, 2026 Phoenix Systems
+ * Author: Pawel Pisarczyk, Aleksander Kaminski, Michal Lach
  *
  * This file is part of Phoenix-RTOS.
  *
@@ -16,6 +16,8 @@
 #ifndef _LIBPHOENIX_SYS_THREADS_H_
 #define _LIBPHOENIX_SYS_THREADS_H_
 
+#include <assert.h>
+#include <limits.h>
 #include <sys/types.h>
 #include <sys/rb.h>
 #include <stddef.h>
@@ -36,6 +38,9 @@ typedef struct {
 } semaphore_t;
 
 
+STATIC_ASSERT(SEM_VALUE_MAX <= UINT_MAX, "The maximum semaphore value SEM_VALUE_MAX shall be less or equal to the maximum possible value of its container");
+
+
 struct __errno_t {
 	rbnode_t linkage;
 	int tid;
@@ -113,12 +118,18 @@ extern int semaphoreCreate(semaphore_t *s, unsigned int v);
 extern int semaphoreDown(semaphore_t *s, time_t timeout);
 
 
+extern int semaphoreTryDown(semaphore_t *s);
+
+
 extern int semaphoreUp(semaphore_t *s);
 
 
 extern int semaphoreDone(semaphore_t *s);
 
 
+extern int semaphoreCount(semaphore_t *s);
+
+
 extern int phCondCreate(handle_t *h, const struct condAttr *attr);
 
 

include/unistd.h

@@ -44,12 +44,14 @@ extern "C" {
 #define X_OK (1 << 0)
 
 
-#define _SC_OPEN_MAX   0
-#define _SC_IOV_MAX    1
-#define _SC_ATEXIT_MAX 2
-#define _SC_CLK_TCK    3
-#define _SC_PAGESIZE   4
-#define _SC_PAGE_SIZE  _SC_PAGESIZE /* spec. 1170 compatibility */
+#define _SC_OPEN_MAX      0
+#define _SC_IOV_MAX       1
+#define _SC_ATEXIT_MAX    2
+#define _SC_CLK_TCK       3
+#define _SC_PAGESIZE      4
+#define _SC_SEM_VALUE_MAX 5
+#define _SC_SEM_NSEMS_MAX 6
+#define _SC_PAGE_SIZE     _SC_PAGESIZE /* spec. 1170 compatibility */
 
 #define _POSIX_NO_TRUNC             1
 #define _POSIX_ASYNC_IO             -1 /* Async IO not implemented. */

posix/Makefile

@@ -5,4 +5,4 @@
 # Author: Pawel Pisarczyk
 #
 
-OBJS += $(addprefix $(PREFIX_O)posix/, stubs.o utils.o idtree.o)
+OBJS += $(addprefix $(PREFIX_O)posix/, stubs.o utils.o idtree.o sem.o)