lib: os: add heap event listener

* add generic heap event listener module that can be used
  for notifying an application of heap-related events
* use the listener module in newlib libc hooks
* add a unit test

Signed-off-by: Damian Krolik <damian.krolik@nordicsemi.no>

include/sys/heap_listener.h

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2021 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_SYS_HEAP_LISTENER_H
+#define ZEPHYR_INCLUDE_SYS_HEAP_LISTENER_H
+
+#include <stdint.h>
+#include <sys/slist.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+struct heap_listener {
+	/** Singly linked list node */
+	sys_snode_t node;
+
+	/**
+	 * Identifier of the heap whose events are listened.
+	 *
+	 * It can be a heap pointer, if the heap is represented as an object,
+	 * or 0 in the case of the global libc heap.
+	 */
+	uintptr_t heap_id;
+
+	/** Function called when the listened heap is resized */
+	void (*resize_cb)(void *old_heap_end, void *new_heap_end);
+};
+
+/**
+ * @brief Register heap event listener
+ *
+ * Add the listener to the global list of heap listeners that can be notified by
+ * different heap implementations upon certain events related to the heap usage.
+ *
+ * @param listener Pointer to the heap_listener object
+ */
+void heap_listener_register(struct heap_listener *listener);
+
+/**
+ * @brief Unregister heap event listener
+ *
+ * Remove the listener from the global list of heap listeners that can be
+ * notified by different heap implementations upon certain events related to the
+ * heap usage.
+ *
+ * @param listener Pointer to the heap_listener object
+ */
+void heap_listener_unregister(struct heap_listener *listener);
+
+/**
+ * @brief Notify listeners of heap resize event
+ *
+ * Notify registered heap event listeners with matching heap identifier that the
+ * heap has been resized.
+ *
+ * @param heap_id Heap identifier
+ * @param old_heap_end Address of the heap end before the change
+ * @param new_heap_end Address of the heap end after the change
+ */
+void heap_listener_notify_resize(uintptr_t heap_id, void *old_heap_end, void *new_heap_end);
+
+/**
+ * @brief Construct heap identifier from heap pointer
+ *
+ * Construct a heap identifer from a pointer to the heap object, such as
+ * sys_heap.
+ *
+ * @param heap_pointer Pointer to the heap object
+ */
+#define HEAP_ID_FROM_POINTER(heap_pointer) ((uintptr_t)heap_pointer)
+
+/**
+ * @brief Libc heap identifier
+ *
+ * Identifier of the global libc heap.
+ */
+#define HEAP_ID_LIBC ((uintptr_t)0)
+
+/**
+ * @brief Define heap event listener object
+ *
+ * Sample usage:
+ * @code
+ * void on_heap_resized(void *old_heap_end, void *new_heap_end)
+ * {
+ *   LOG_INF("Libc heap end moved from %p to %p", old_heap_end, new_heap_end);
+ * }
+ *
+ * HEAP_LISTENER_DEFINE(my_listener, HEAP_ID_LIBC, on_heap_resized);
+ * @endcode
+ *
+ * @param name		Name of the heap event listener object
+ * @param _heap_id	Identifier of the heap to be listened
+ * @param _resize_cb	Function to be called when the listened heap is resized
+ */
+#define HEAP_LISTENER_DEFINE(name, _heap_id, _resize_cb) \
+	struct heap_listener name = { .heap_id = _heap_id, .resize_cb = _resize_cb }
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_SYS_HEAP_LISTENER_H */