pthread: Implemented POSIX unnamed semaphore

components/pthread/include/semaphore.h

@@ -0,0 +1,73 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <time.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef unsigned int sem_t;
+
+/**
+ * This is the maximum value to which any POSIX semaphore can count on ESP chips.
+ */
+#define SEM_VALUE_MAX 0x7FFF
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ *
+ * Must NOT be called if threads are still blocked on semaphore!
+ */
+int sem_destroy(sem_t *sem);
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ *
+ * Note that on ESP chips, pshared is ignored. Semaphores can always be shared between FreeRTOS tasks.
+ */
+int sem_init(sem_t *sem, int pshared, unsigned value);
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ *
+ * Note that, unlike specified in POSIX, this implementation returns -1 and sets errno to
+ * EAGAIN if the semaphore can not be unlocked (posted) due to its value being SEM_VALUE_MAX.
+ */
+int sem_post(sem_t *sem);
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ *
+ * Note the following three deviations/issues originating from the underlying FreeRTOS implementation:
+ * * The time value passed by abstime will be rounded up to the next FreeRTOS tick.
+ * * The actual timeout will happen after the tick the time was rounded to
+ *   and before the following tick.
+ * * It is possible, though unlikely, that the task is preempted directly after the timeout calculation,
+ *   delaying timeout of the following blocking operating system call by the duration of the preemption.
+ */
+int sem_timedwait(sem_t * restrict semaphore, const struct timespec *restrict abstime);
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ */
+int sem_trywait(sem_t *sem);
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ */
+int sem_wait(sem_t *sem);
+
+/**
+ * This is a POSIX function, please refer to the POSIX specification for a detailed description.
+ */
+int sem_getvalue(sem_t *restrict sem, int *restrict sval);
+
+#ifdef __cplusplus
+}
+#endif