array: introduce an array collection storing elements very efficiently

Currently we use the very versatile linked-list collection to store elements
with variable count. This is fine, but very inefficient: Due to the many
methods in the linked list, on 64-bit platforms an empty list alone is more
than 200 bytes. As we currently have about 50 lists per IKE_SA/CHILD_SA pair,
this takes up to 10KB just for managing the empty lists. This is about the
half of memory used by an IKE_SA/CHILD_SA pair, and obviously way too much.

The new array type is not an object, but a collection of functions on an
abstract type.

The following lists are per IKE_SA and should be considered for a replacement
with more efficient arrays (this uses load-testers on-demand created dynamic
configurations, other scenarios have different lists):

14 -> ike_sa_create() @ src/libcharon/sa/ike_sa.c:2198
10 -> auth_cfg_create() @ src/libstrongswan/credentials/auth_cfg.c:1088
 6 -> task_manager_v2_create() @ src/libcharon/sa/ikev2/task_manager_v2.c:1505
 6 -> proposal_create() @ src/libcharon/config/proposal.c:592
 5 -> peer_cfg_create() @ src/libcharon/config/peer_cfg.c:657
 4 -> child_sa_create() @ src/libcharon/sa/child_sa.c:1090
 2 -> child_cfg_create() @ src/libcharon/config/child_cfg.c:536
 1 -> ike_cfg_create() @ src/libcharon/config/ike_cfg.c:330
 1 -> put_connected_peers() @ src/libcharon/sa/ike_sa_manager.c:854

src/libstrongswan/collections/array.h

@@ -0,0 +1,194 @@
+/*
+ * Copyright (C) 2013 Martin Willi
+ * Copyright (C) 2013 revosec AG
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+/**
+ * @defgroup array array
+ * @{ @ingroup collections
+ */
+
+#ifndef ARRAY_H_
+#define ARRAY_H_
+
+#include <collections/enumerator.h>
+
+/**
+ * Variable sized array with fixed size elements.
+ *
+ * An array is a primitive object with associated functions to avoid the
+ * overhead of an object with methods. It is efficient in memory usage, but
+ * less effecient than a linked list in manipulating elements.
+ */
+typedef struct array_t array_t;
+
+typedef enum array_idx_t array_idx_t;
+
+/**
+ * Special array index values for insert/remove.
+ */
+enum array_idx_t {
+	ARRAY_HEAD = 0,
+	ARRAY_TAIL = -1,
+};
+
+/**
+ * Callback function invoked for each array element.
+ *
+ * Data is a pointer to the array element. If this is a pointer based array,
+ * (esize is zero), data is the pointer itself.
+ *
+ * @param data			pointer to array data, or the pointer itself
+ * @param idx			array index
+ * @param user			user data passed with callback
+ */
+typedef void (*array_callback_t)(void *data, int idx, void *user);
+
+/**
+ * Create a array instance.
+ *
+ * Elements get tight packed to each other. If any alignment is required, pass
+ * appropriate padding to each element. The reserved space does not affect
+ * array_count(), but just preallocates buffer space.
+ *
+ * @param esize			element size for this array, use 0 for a pointer array
+ * @param reserve		number of items to allocate space for
+ * @return				array instance
+ */
+array_t *array_create(u_int esize, u_int8_t reserve);
+
+/**
+ * Get the number of elements currently in the array.
+ *
+ * @return				number of elements
+ */
+int array_count(array_t *array);
+
+/**
+ * Compress an array, remove unused head/tail space.
+ *
+ * @param array			array to compress, or NULL
+ */
+void array_compress(array_t *array);
+
+/**
+ * Create an enumerator over an array.
+ *
+ * The enumerater enumerates directly over the array element (pass a pointer to
+ * element types), unless the array is pointer based. If zero is passed as
+ * element size during construction, the enumerator enumerates over the
+ * deferenced pointer values.
+ *
+ * @param array			array to create enumerator for, or NULL
+ * @return				enumerator, over elements or pointers
+ */
+enumerator_t* array_create_enumerator(array_t *array);
+
+/**
+ * Remove an element at enumerator position.
+ *
+ * @param array			array to remove element in
+ * @param enumerator	enumerator position, from array_create_enumerator()
+ */
+void array_remove_at(array_t *array, enumerator_t *enumerator);
+
+/**
+ * Insert an element to an array.
+ *
+ * If the array is pointer based (esize = 0), the pointer itself is appended.
+ * Otherwise the element gets copied from the pointer.
+ * The idx must be either within array_count() or one above to append the item.
+ * Passing -1 has the same effect as passing array_count(), i.e. appends the
+ * item. It is always valid to pass idx 0 to prepend the item.
+ *
+ * @param array			array to append element to
+ * @param idx			index to insert item at
+ * @param data			pointer to array element to copy
+ */
+void array_insert(array_t *array, int idx, void *data);
+
+/**
+ * Create an pointer based array if it does not exist, insert pointer.
+ *
+ * This is a convenience function for insert a pointer and implicitly
+ * create a pointer based array if array is NULL. Array is set the the newly
+ * created array, if any.
+ *
+ * @param array			pointer to array reference, potentially NULL
+ * @param idx			index to insert item at
+ * @param ptr			pointer to append
+ */
+void array_insert_create(array_t **array, int idx, void *ptr);
+
+/**
+ * Insert all items from an enumerator to an array.
+ *
+ * @param array			array to add items to
+ * @param idx			index to insert each item with
+ * @param enumerator	enumerator over void*, gets destroyed
+ */
+void array_insert_enumerator(array_t *array, int idx, enumerator_t *enumerator);
+
+/**
+ * Remove an element from the array end.
+ *
+ * If data is given, the element is copied to that position.
+ *
+ * @param array			array to remove element from, or NULL
+ * @param data			data to copy element to, or NULL
+ * @return				TRUE if idx existed and item removed
+ */
+bool array_remove(array_t *array, int idx, void *data);
+
+/**
+ * Invoke a callback for all array members.
+ *
+ * @param array			array to traverse, or NULL
+ * @param cb			callback function to invoke each element with
+ * @param user			user data to pass to callback
+ */
+void array_invoke(array_t *array, array_callback_t cb, void *user);
+
+/**
+ * Invoke a method of each element defined with offset.
+ *
+ * @param array			array to traverse, or NULL
+ * @param offset		offset of element method, use offsetof()
+ */
+void array_invoke_offset(array_t *array, size_t offset);
+
+/**
+ * Destroy an array.
+ *
+ * @param array			array to destroy, or NULL
+ */
+void array_destroy(array_t *array);
+
+/**
+ * Destroy an array, call a function to clean up all elements.
+ *
+ * @param array			array to destroy, or NULL
+ * @param cb			callback function to free element data
+ * @param user			user data to pass to callback
+ */
+void array_destroy_function(array_t *array, array_callback_t cb, void *user);
+
+/**
+ * Destroy an array, call element method defined with offset.
+ *
+ * @param array			array to destroy, or NULL
+ * @param offset		offset of element method, use offsetof()
+ */
+void array_destroy_offset(array_t *array, size_t offset);
+
+#endif /** ARRAY_H_ @}*/