hash.h

/*
 * Copyright 1993, 1995 Christopher Seiwald.
 *
 * This file is part of Jam - see jam.c for Copyright information.
 */

/*  This file is ALSO:
 *  Copyright 2022 René Ferdinand Rivera Morell
 *  Distributed under the Boost Software License, Version 1.0.
 *  (See accompanying file LICENSE.txt or
 * https://www.bfgroup.xyz/b2/LICENSE.txt)
 */

/*
 * hash.h - simple in-memory hashing routines
 */

#ifndef BOOST_JAM_HASH_H
#define BOOST_JAM_HASH_H

#include "config.h"

#include "mem.h"
#include "object.h"

#include <mutex>

/*
 * An opaque struct representing an item in the hash table. The first element of
 * every struct stored in the table must be an OBJECT * which is treated as the
 * key.
 */
typedef struct hashdata HASHDATA;

/*
 * hashinit() - initialize a hash table, returning a handle.
 *
 * Parameters:
 *   datalen - item size
 *   name    - used for debugging
 */
struct hash * hashinit(int32_t datalen, char const * name);

/*
 * hash_free() - free a hash table, given its handle
 */
void hash_free(struct hash *);
void hashdone(struct hash *);

typedef void (*hashenumerate_f)(void *, void *);

/*
 * hashenumerate() - call f(i, data) on each item, i in the hash table. The
 * enumeration order is unspecified.
 */
void hashenumerate(struct hash *, void (*f)(void *, void *), void * data);

template <typename T, typename D>
void hash_enumerate(struct hash * h, void (*f)(T *, D *), D * data)
{
	hashenumerate(h, reinterpret_cast<hashenumerate_f>(f), data);
}
template <typename T, typename D>
void hash_enumerate(struct hash * h, void (*f)(T *, D *))
{
	hashenumerate(h, reinterpret_cast<hashenumerate_f>(f), nullptr);
}

/*
 * hash_insert() - insert a new item in a hash table, or return an existing one.
 *
 * Preconditions:
 *   - hp must be a hash table created by hashinit()
 *   - key must be an object created by object_new()
 *
 * Postconditions:
 *   - if the key does not already exist in the hash table, *found == 0 and the
 *     result will be a pointer to an uninitialized item. The key of the new
 *     item must be set to a value equal to key before any further operations on
 *     the hash table except hashdone().
 *   - if the key is present then *found == 1 and the result is a pointer to the
 *     existing record.
 */
HASHDATA * hash_insert(struct hash *, OBJECT * key, int32_t * found);

/*
 * hash_find() - find a record in the table or NULL if none exists
 */
HASHDATA * hash_find(struct hash *, OBJECT * key);

struct hashstats
{
	int count;
	int num_items;
	int tab_size;
	int item_size;
	int sets;
	int num_hashes;
};

void hashstats_init(struct hashstats * stats);
void hashstats_add(struct hashstats * stats, struct hash *);
void hashstats_print(struct hashstats * stats, char const * name);

namespace b2 { namespace core {

template <typename T>
struct concurrent_hash
{
	using key_type = b2::value_ptr;
	using value_type = T;

	concurrent_hash(const char * debug_name)
	{
		table = hashinit(sizeof(value_type), debug_name);
	}

	~concurrent_hash() { reset(); }

	void reset()
	{
		std::lock_guard<std::mutex> guard(mutex);
		if (table != nullptr)
		{
			hashenumerate(table, concurrent_hash::destroy_at, nullptr);
			hashdone(table);
			table = nullptr;
		}
	}

	template <typename... Args>
	std::pair<value_type *, bool> get(b2::value_ptr key, Args... args)
	{
		int found = 0;
		std::lock_guard<std::mutex> guard(mutex);
		value_type * val
			= reinterpret_cast<value_type *>(hash_insert(table, key, &found));
		if (found == 0) b2::jam::ctor_ptr<value_type>(val, args...);
		return std::make_pair(val, found != 0);
	}

	template <typename F>
	void guarded(F f)
	{
		std::lock_guard<std::mutex> guard(mutex);
		f();
	}

	private:
	std::mutex mutex;
	hash * table = nullptr;

	static void destroy_at(void * p, void * _)
	{
		b2::jam::dtor_ptr(static_cast<value_type *>(p));
	}
};

}} // namespace b2::core

#endif