kernel: thread: k_thread_foreach_unlocked: Implement

Implement thread foreach processing with limited locking
to allow threads processing that may take more time but allows
missing some threads processing when the thread list is modified.

Signed-off-by: Radoslaw Koppel <radoslaw.koppel@nordicsemi.no>

include/kernel.h

@@ -644,15 +644,45 @@ typedef void (*k_thread_user_cb_t)(const struct k_thread *thread,
  * @param user_data Pointer to user data.
  *
  * @note CONFIG_THREAD_MONITOR must be set for this function
- * to be effective. Also this API uses irq_lock to protect the
+ * to be effective.
- * _kernel.threads list which means creation of new threads and
+ * @note This API uses @ref k_spin_lock to protect the _kernel.threads
- * terminations of existing threads are blocked until this
+ * list which means creation of new threads and terminations of existing
- * API returns.
+ * threads are blocked until this API returns.
  *
  * @return N/A
  */
 extern void k_thread_foreach(k_thread_user_cb_t user_cb, void *user_data);
 
+/**
+ * @brief Iterate over all the threads in the system without locking.
+ *
+ * This routine works exactly the same like @ref k_thread_foreach
+ * but unlocks interrupts when user_cb is executed.
+ *
+ * @param user_cb Pointer to the user callback function.
+ * @param user_data Pointer to user data.
+ *
+ * @note CONFIG_THREAD_MONITOR must be set for this function
+ * to be effective.
+ * @note This API uses @ref k_spin_lock only when accessing the _kernel.threads
+ * queue elements. It unlocks it during user callback function processing.
+ * If a new task is created when this @c foreach function is in progress,
+ * the added new task would not be included in the enumeration.
+ * If a task is aborted during this enumeration, there would be a race here
+ * and there is a possibility that this aborted task would be included in the
+ * enumeration.
+ * @note If the task is aborted and the memory occupied by its @c k_thread
+ * structure is reused when this @c k_thread_foreach_unlocked is in progress
+ * it might even lead to the system behave unstable.
+ * This function may never return, as it would follow some @c next task
+ * pointers treating given pointer as a pointer to the k_thread structure
+ * while it is something different right now.
+ * Do not reuse the memory that was occupied by k_thread structure of aborted
+ * task if it was aborted after this function was called in any context.
+ */
+extern void k_thread_foreach_unlocked(
+	k_thread_user_cb_t user_cb, void *user_data);
+
 /** @} */
 
 /**

kernel/thread.c

@@ -55,6 +55,24 @@ void k_thread_foreach(k_thread_user_cb_t user_cb, void *user_data)
 #endif
 }
 
+void k_thread_foreach_unlocked(k_thread_user_cb_t user_cb, void *user_data)
+{
+#if defined(CONFIG_THREAD_MONITOR)
+	struct k_thread *thread;
+	k_spinlock_key_t key;
+
+	__ASSERT(user_cb != NULL, "user_cb can not be NULL");
+
+	key = k_spin_lock(&lock);
+	for (thread = _kernel.threads; thread; thread = thread->next_thread) {
+		k_spin_unlock(&lock, key);
+		user_cb(thread, user_data);
+		key = k_spin_lock(&lock);
+	}
+	k_spin_unlock(&lock, key);
+#endif
+}
+
 bool k_is_in_isr(void)
 {
 	return arch_is_in_isr();