/** Memory pool for fixed size objects.
 *
 * This datastructure is based on a lock-less stack (lstack).
 *
 * @file
 * @author Steffen Vogel <post@steffenvogel.de>
 * @copyright 2014-2022, Institute for Automation of Complex Power Systems, EONERC
 * @license Apache 2.0
 *********************************************************************************/

#pragma once

#include <cstddef>
#include <sys/types.h>

#include <villas/queue.h>
#include <villas/common.hpp>
#include <villas/node/memory.hpp>

namespace villas {
namespace node {

/** A thread-safe memory pool */
struct Pool {
	enum State state;

	off_t  buffer_off; /**< Offset from the struct address to the underlying memory area */

	size_t len;		/**< Length of the underlying memory area */
	size_t blocksz;		/**< Length of a block in bytes */
	size_t alignment;	/**< Alignment of a block in bytes */

	struct CQueue queue; /**< The queue which is used to keep track of free blocks */
};

#define pool_buffer(p) ((char *) (p) + (p)->buffer_off)

/** Initiazlize a pool
 *
 * @param[inout] p The pool data structure.
 * @param[in] cnt The total number of blocks which are reserverd by this pool.
 * @param[in] blocksz The size in bytes per block.
 * @param[in] mem The type of memory which should be used for this pool.
 * @retval 0 The pool has been successfully initialized.
 * @retval <>0 There was an error during the pool initialization.
 */
int pool_init(struct Pool *p, size_t cnt, size_t blocksz, struct memory::Type *mem = memory::default_type) __attribute__ ((warn_unused_result));

/** Destroy and release memory used by pool. */
int pool_destroy(struct Pool *p) __attribute__ ((warn_unused_result));

/** Pop up to \p cnt values from the stack an place them in the array \p blocks.
 *
 * @return The number of blocks actually retrieved from the pool.
 *         This number can be smaller than the requested \p cnt blocks
 *         in case the pool currently holds less than \p cnt blocks.
 */
ssize_t pool_get_many(struct Pool *p, void *blocks[], size_t cnt);

/** Push \p cnt values which are giving by the array values to the stack. */
ssize_t pool_put_many(struct Pool *p, void *blocks[], size_t cnt);

/** Get a free memory block from pool. */
void * pool_get(struct Pool *p);

/** Release a memory block back to the pool. */
int pool_put(struct Pool *p, void *buf);

} /* namespace node */
} /* namespace villas */