[components/libc/posix]add comments for barrier APIs.

Author: GorrayLi

components/libc/posix/pthreads/pthread_barrier.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2006-2021, RT-Thread Development Team
+ * Copyright (c) 2006-2024 RT-Thread Development Team
  *
  * SPDX-License-Identifier: Apache-2.0
  *
@@ -51,6 +51,31 @@ int pthread_barrierattr_setpshared(pthread_barrierattr_t *attr, int pshared)
 }
 RTM_EXPORT(pthread_barrierattr_setpshared);
 
+/**
+ * @brief Destroys a barrier object.
+ *
+ * The `pthread_barrier_destroy` function releases any resources associated
+ * with the specified barrier object. After a barrier has been destroyed,
+ * it cannot be used again unless it is reinitialized using `pthread_barrier_init`.
+ *
+ * @param[in] barrier
+ * A pointer to an initialized `pthread_barrier_t` object to be destroyed.
+ *
+ * @return
+ * - `0` on success.
+ * - `EINVAL` if the `barrier` is invalid or uninitialized.
+ * - `EBUSY` if there are threads currently blocked on the barrier.
+ *
+ * @note
+ * - Ensure that no threads are blocked on the barrier before calling this function.
+ * - Attempting to destroy a barrier that is still in use results in undefined behavior.
+ *
+ * @warning
+ * Destroying a barrier without ensuring it is no longer in use can lead to
+ * resource leaks or undefined program behavior.
+ *
+ * @see pthread_barrier_init, pthread_barrier_wait
+ */
 int pthread_barrier_destroy(pthread_barrier_t *barrier)
 {
     rt_err_t result;
@@ -64,6 +89,38 @@ int pthread_barrier_destroy(pthread_barrier_t *barrier)
 }
 RTM_EXPORT(pthread_barrier_destroy);
 
+/**
+ * @brief Initializes a barrier for synchronizing threads.
+ *
+ * The `pthread_barrier_init` function initializes a barrier object
+ * that allows a specified number of threads to synchronize at a barrier point.
+ * Each thread waits at the barrier until the required number of threads have called
+ * `pthread_barrier_wait`.
+ *
+ * @param[out] barrier
+ * A pointer to the `pthread_barrier_t` object to be initialized.
+ * This object must not already be initialized.
+ *
+ * @param[in] attr
+ * A pointer to a `pthread_barrierattr_t` object that specifies
+ * attributes for the barrier (e.g., process-shared or process-private).
+ * If NULL, the default attributes are used.
+ *
+ * @param[in] count
+ * The number of threads that must call `pthread_barrier_wait`
+ * before any of them successfully return from the barrier.
+ *
+ * @return
+ * - `0` on success.
+ * - `EINVAL` if the `count` is zero or `barrier` is invalid.
+ *
+ * @note The barrier must be destroyed using `pthread_barrier_destroy`
+ * when it is no longer needed.
+ *
+ * @warning If `count` is set to zero, the behavior is undefined.
+ *
+ * @see pthread_barrier_wait, pthread_barrier_destroy
+ */
 int pthread_barrier_init(pthread_barrier_t           *barrier,
                          const pthread_barrierattr_t *attr,
                          unsigned                     count)
@@ -83,6 +140,33 @@ int pthread_barrier_init(pthread_barrier_t           *barrier,
 }
 RTM_EXPORT(pthread_barrier_init);
 
+/**
+ * @brief Synchronizes threads at a barrier.
+ *
+ * The `pthread_barrier_wait` function blocks the calling thread at the specified
+ * barrier until the required number of threads have reached the barrier. Once
+ * the required number of threads have called this function, all threads are
+ * unblocked and can proceed.
+ *
+ * @param[in] barrier
+ * A pointer to an initialized `pthread_barrier_t` object representing the barrier
+ * at which threads will synchronize.
+ *
+ * @return
+ * - `0` for all threads except one.
+ * - `EINVAL` - The `barrier` is invalid or uninitialized.
+ *
+ * @note
+ * - All threads participating in the barrier must call `pthread_barrier_wait`
+ *   before any of them are released.
+ *
+ * @warning
+ * Ensure that the number of threads specified during the barrier's initialization
+ * matches the number of threads calling this function, otherwise the program
+ * may hang indefinitely.
+ *
+ * @see pthread_barrier_init, pthread_barrier_destroy
+ */
 int pthread_barrier_wait(pthread_barrier_t *barrier)
 {
     rt_err_t result;