Cytoplasm/src/include/HashMap.h

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/*
* Copyright (C) 2022-2023 Jordan Bancino <@jordan:bancino.net>
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef CYTOPLASM_HASHMAP_H
#define CYTOPLASM_HASHMAP_H
/***
* @Nm HashMap
* @Nd A simple hash map implementation.
* @Dd October 11 2022
* @Xr Array Queue
*
* This is the public interface for Cytoplasm's hash map
* implementation. This hash map is designed to be simple,
* well-documented, and generally readable and understandable, yet also
* performant enough to be useful, because it is used extensively
* throughout the project.
* .Pp
* Fundamentally, this is an entirely generic map implementation. It
* can be used for many general purposes, but it is designed only to
* implement the features Cytoplasm needs to be functional. One
* example of a Cytoplasm-specific feature is that keys cannot be
* arbitrary data; they are NULL-terminated C strings.
*/
#include <stddef.h>
#include "Array.h"
/**
* These functions operate on an opaque structure, which the caller
* has no knowledge about.
*/
typedef struct HashMap HashMap;
/**
* Create a new hash map that is ready to be used with the rest of the
* functions defined here.
*/
extern HashMap * HashMapCreate(void);
/**
* Free the specified hash map such that it becomes invalid and any
* future use results in undefined behavior. Note that this function
* does not free the values stored in the hash map, but since it stores
* the keys internally, it will free the keys. You should use
* .Fn HashMapIterate
* to free the values stored in this map appropriately before calling
* this function.
*/
extern void HashMapFree(HashMap *);
/**
* Control the maximum load of the hash map before it is expanded.
* When the hash map reaches the given capacity, it is grown. You
* don't want to only grow hash maps when they are full, because that
* makes them perform very poorly. The maximum load value is a
* percentage of how full the hash map is, and it should be between
* 0 and 1, where 0 means that no elements will cause the map to be
* expanded, and 1 means that the hash map must be completely full
* before it is expanded. The default maximum load on a new hash map
* is 0.75, which should be good enough for most purposes, however,
* this function exists specifically so that the maximum load can be
* fine-tuned.
*/
extern void HashMapMaxLoadSet(HashMap *, float);
/**
* Use a custom hashing function with the given hash map. New hash
* maps have a sane hashing function that should work okay for most
* use cases, but if you have a better hashing function, it can be
* specified this way. Do not change the hash function after keys have
* been added; doing so results in undefined behavior. Only set a new
* hash function immediately after constructing a new hash map, before
* anything has been added to it.
* .Pp
* The hash function takes a pointer to a C string, and is expected
* to return a fairly unique numerical hash value which will be
* converted into an array index.
*/
extern void
HashMapFunctionSet(HashMap *, unsigned long (*) (const char *));
/**
* Set the given string key to the given value. Note that the key is
* copied into the hash map's own memory space, but the value is not.
* It is the caller's job to ensure that the value pointer remains
* valid for the life of the hash map, and are freed when no longer
* needed.
*/
extern void * HashMapSet(HashMap *, char *, void *);
/**
* Retrieve the value for the given key, or return NULL if no such
* key exists in the hash map.
*/
extern void * HashMapGet(HashMap *, const char *);
/**
* Remove a value specified by the given key from the hash map, and
* return it to the caller to deal with. This function returns NULL
* if no such key exists.
*/
extern void * HashMapDelete(HashMap *, const char *);
/**
* Iterate over all the keys and values of a hash map. This function
* works very similarly to
* .Xr getopt 3 ,
* where calls are repeatedly made in a while loop until there are no
* more items to go over. The difference is that this function does not
* rely on globals; it takes pointer pointers, and stores all
* necessary state inside the hash map itself.
* .Pp
* Note that this function is not thread-safe; two threads cannot be
* iterating over any given hash map at the same time, though they
* can each be iterating over different hash maps.
* .Pp
* This function can be tricky to use in some scenarios, as it
* continues where it left off on each call, until there are no more
* elements to go through in the hash map. If you are not iterating
* over the entire map in one go, and happen to break the loop, then
* the next time you attempt to iterate the hash map, you'll start
* somewhere in the middle, which is most likely not the intended
* behavior. Thus, it is always recommended to iterate over the entire
* hash map if you're going to use this function.
* .Pp
* Also note that the behavior of this function is undefined if
* insertions or deletions occur during the iteration. This
* functionality has not been tested, and will likely not work.
*/
extern bool HashMapIterate(HashMap *, char **, void **);
/**
* A reentrant version of
* .Fn HashMapIterate
* that allows the caller to overcome the flaws of that function by
* storing the cursor outside of the hash map structure itself. This
* allows multiple threads to iterate over the same hash map at the
* same time, and it allows the iteration to be halted midway through
* without causing any unintended side effects.
* .Pp
* The cursor should be initialized to 0 at the start of iteration.
*/
extern bool
HashMapIterateReentrant(HashMap *, char **, void **, size_t *);
/**
* Collect the string keys of a hash map and return them as an array.
* The returned array holds pointers to the strings stored in the
* hash map, so the strings should NOT be freed; it is sufficient to
* free the array itself. Likewise, once the hash map is freed, the
* array elements are invalid and the array should be freed.
*/
extern Array * HashMapKeys(HashMap *);
/**
* Collect the values of a hash map and return them as an array. The
* returned array holds the same pointers to the values as the hash
* map.
*/
extern Array * HashMapValues(HashMap *);
#endif /* CYTOPLASM_HASHMAP_H */