ucx: docs/src/features.md@9c097dabba2c (annotated)

docs/src/features.md@9c097dabba2c (annotated)

docs/src/features.md

Mon, 03 Jul 2023 18:37:19 +0200

author: Mike Becker <universe@uap-core.de>
date: Mon, 03 Jul 2023 18:37:19 +0200
changeset 731: 9c097dabba2c
parent 730: 9fecb2769d32
child 732: a3b5f27ad956
permissions: -rw-r--r--

add documentation for the lists

 ---
 title: UCX Features
 ---
 <div id="modules">
 ------------------------ -------------------------  -------------------  ---------------------------------
 [Allocator](#allocator)  [String](#string)          [Buffer](#buffer)    [Memory&nbsp;Pool](#memory-pool)
 [Iterator](#iterator)    [Collection](#collection)  [List](#list)        [Map](#map)
 [Utilities](#utilities)
 ------------------------ -------------------------  -------------------  ---------------------------------
 </div>
 ## Allocator
 *Header file:* [allocator.h](api/allocator_8h.html)
 The UCX allocator provides an interface for implementing an own memory allocation mechanism.
 Various function in UCX provide an additional alternative signature that takes an allocator as
 argument. A default allocator implementation using the stdlib memory management functions is
 available via the global symbol `cxDefaultAllocator`.
 If you want to define your own allocator, you need to initialize the `CxAllocator` structure
 with a pointer to an allocator class (containing function pointers for the memory management
 functions) and an optional pointer to an arbitrary memory region that can be used to store
 state information for the allocator. An example is shown below:
 ```c
 struct my_allocator_state {
     size_t total;
     size_t avail;
     char mem[];
 };
 static cx_allocator_class my_allocator_class = {
         my_malloc_impl,
         my_realloc_impl,   // all these functions are somewhere defined
         my_calloc_impl,
         my_free_impl
 };
 CxAllocator create_my_allocator(size_t n) {
     CxAllocator alloc;
     alloc.cl = &my_allocator_class;
     alloc.data = calloc(1, sizeof(struct my_allocator_state) + n);
     return alloc;
 }
 void free_my_allocator(CxAllocator *alloc) {
     free(alloc.data);
     free(alloc);
 }
 ```
 ## String
 *Header file:* [string.h](api/string_8h.html)
 UCX strings come in two variants: immutable (`cxstring`) and mutable (`cxmutstr`).
 The functions of UCX are designed to work with immutable strings by default but in situations where it is necessary,
 the API also provides alternative functions that work directly with mutable strings.
 Functions that change a string in-place are, of course, only accepting mutable strings.
 When you are using UCX functions, or defining your own functions, you are sometimes facing the "problem",
 that the function only accepts arguments of type `cxstring` but you only have a `cxmutstr` at hand.
 In this case you _should not_ introduce a wrapper function that accepts the `cxmutstr`,
 but instead you should use the `cx_strcast()` function to cast the argument to the correct type.
 In general, UCX strings are **not** necessarily zero-terminated. If a function guarantees to return zero-terminated
 string, it is explicitly mentioned in the documentation of the respective function.
 As a rule of thumb, you _should not_ pass the strings of a UCX string structure to another API without explicitly
 ensuring that the string is zero-terminated.
 ## Buffer
 *Header file:* [buffer.h](api/buffer_8h.html)
 Instances of this buffer implementation can be used to read from or write to memory like you would do with a stream.
 This allows the use of `cx_stream_copy()` (see [Utilities](#utilities)) to copy contents from one buffer to another,
 or from a file or network streams to the buffer and vice-versa.
 More features for convenient use of the buffer can be enabled, like automatic memory management and automatic
 resizing of the buffer space.
 Since UCX 3.0, the buffer also supports automatic flushing of contents to another stream (or buffer) as an alternative
 to automatically resizing the buffer space.
 Please refer to the API doc for the fields prefixed with `flush_` to learn more.
 ## Memory Pool
 *Header file:* [mempool.h](api/mempool_8h.html)
 A memory pool is providing an allocator implementation that automatically deallocates the memory upon its destruction.
 It also allows you to register destructor functions for the allocated memory, which are automatically called before
 the memory is deallocated.
 Additionally, you may also register _independent_ destructor functions within a pool in case some external library
 allocated memory for you, which should be destroyed together with this pool.
 Many UCX features support the use of an allocator.
 The [strings](#string), for instance, provide several functions suffixed with `_a` that allow specifying an allocator.
 You can use this to keep track of the memory occupied by dynamically allocated strings and cleanup everything with
 just a single call to `cxMempoolDestroy()`.
 The following code illustrates this on the example of reading a CSV file into memory.
 ```C
 #include <stdio.h>
 #include <cx/mempool.h>
 #include <cx/linked_list.h>
 #include <cx/string.h>
 #include <cx/buffer.h>
 #include <cx/utils.h>
 typedef struct {
     cxstring column_a;
     cxstring column_b;
     cxstring column_c;
 } CSVData;
 int main(void) {
     CxMempool* pool = cxBasicMempoolCreate(128);
     FILE *f = fopen("test.csv", "r");
     if (!f) {
         perror("Cannot open file");
         return 1;
     }
     // close the file automatically at pool destruction
     cxMempoolRegister(pool, f, (cx_destructor_func) fclose);
     // create a buffer using the memory pool for destruction
     CxBuffer *content = cxBufferCreate(NULL, 256, pool->allocator, CX_BUFFER_AUTO_EXTEND);
     // read the file into the buffer and turn it into a string
     cx_stream_copy(f, content, (cx_read_func) fread, (cx_write_func) cxBufferWrite);
     cxstring contentstr = cx_strn(content->space, content->size);
     // split the string into lines - use the mempool for allocating the target array
     cxstring* lines;
     size_t lc = cx_strsplit_a(pool->allocator, contentstr,
                               CX_STR("\n"), SIZE_MAX, &lines);
     // skip the header and parse the remaining data into a linked list
     // the nodes of the linked list shall also be allocated by the mempool
     CxList* datalist = cxLinkedListCreate(pool->allocator, NULL, sizeof(CSVData));
     for (size_t i = 1 ; i < lc ; i++) {
         if (lines[i].length == 0) continue;
         cxstring fields[3];
         size_t fc = cx_strsplit(lines[i], CX_STR(";"), 3, fields);
         if (fc != 3) {
             fprintf(stderr, "Syntax error in line %zu.\n", i);
             cxMempoolDestroy(pool);
             return 1;
         }
         CSVData* data = cxMalloc(pool->allocator, sizeof(CSVData));
         data->column_a = fields[0];
         data->column_b = fields[1];
         data->column_c = fields[2];
         cxListAdd(datalist, data);
     }
     // iterate through the list and output the data
     CxIterator iter = cxListIterator(datalist);
     cx_foreach(CSVData*, data, iter) {
         printf("Column A: %.*s | "
                "Column B: %.*s | "
                "Column C: %.*s\n",
                (int)data->column_a.length, data->column_a.ptr,
                (int)data->column_b.length, data->column_b.ptr,
                (int)data->column_c.length, data->column_c.ptr
         );
     }
     // cleanup everything, no manual free() needed
     cxMempoolDestroy(pool);
     return 0;
 }
 ```
 ## Iterator
 *Header file:* [iterator.h](api/iterator_8h.html)
 ## Collection
 *Header file:* [collection.h](api/collection_8h.html)
 Collections in UCX 3 have several common features.
 If you want to implement an own collection data type that uses the same features, you can use the
 `CX_COLLECTION_MEMBERS` macro at the beginning of your struct to roll out all members a usual UCX collection has.
 ```c
 struct my_fancy_collection_s {
     CX_COLLECTION_MEMBERS
     struct my_collection_data_s *data;
 };
 ```
 Based on this structure, this header provides some convenience macros for invoking the destructor functions
 that are part of the basic collection members.
 The idea of having destructor functions within a collection is that you can destroy the collection _and_ the
 contents with one single function call.
 When you are implementing a collection, you are responsible for invoking the destructors at the right places, e.g.
 when removing (and deleting) elements in the collection, clearing the collection, or - the most prominent case -
 destroying the collection.
 You can always look at the UCX list and map implementations if you need some inspiration.
 ## List
 *Header file:* [list.h](api/list_8h.html)
 This header defines a common interface for all list implementations, which is basically as simple as the following
 structure.
 ```c
 struct cx_list_s {
     CX_COLLECTION_MEMBERS       // size, capacity, etc.
     cx_list_class const *cl;    // The list class definition
 };
 ```
 The actual structure contains one more class pointer that is used when wrapping a list into a pointer aware list
 with `cxListStorePointers()`. What this means, is that - if you want to implement your own list structure - you
 only need to cover the case where the list is storing copies of your objects.
 UCX comes with two common list implementations (linked list and array list) that should cover most use cases.
 But if you feel the need to implement an own list, the only thing you need to do is to define a struct where
 `struct cx_list_s`, and set an appropriate list class that implements the functionality.
 It is strongly recommended that this class is shared among all instances of the same list type, because otherwise
 the `cxListCompare` function cannot use the optimized implementation of your class and will instead fall back to
 using iterators to compare the contents element-wise.
 ### Linked List
 *Header file:* [linked_list.h](api/linked__list_8h.html)
 On top of implementing the list interface, this header also defines several low-level functions that
 work with arbitrary structures.
 Low-level functions, in contrast to the high-level list interface, can easily be recognized by their snake-casing.
 The function `cx_linked_list_at`, for example, implements a similar functionality like `cxListAt`, but operates
 on arbitrary structures.
 The following snippet shows how it is used.
 All other low-level functions work similarly.
 ```c
 struct node {
     node *next;
     node *prev;
     int data;
 };
 const ptrdiff_t loc_prev = offsetof(struct node, prev);
 const ptrdiff_t loc_next = offsetof(struct node, next);
 const ptrdiff_t loc_data = offsetof(struct node, data);
 struct node a = {0}, b = {0}, c = {0}, d = {0};
 cx_linked_list_link(&a, &b, loc_prev, loc_next);
 cx_linked_list_link(&b, &c, loc_prev, loc_next);
 cx_linked_list_link(&c, &d, loc_prev, loc_next);
 cx_linked_list_at(&a, 0, loc_next, 2); // returns pointer to c
 ```
 ### Array List
 *Header file:* [array_list.h](api/array__list_8h.html)
 Since low-level array lists are just plain arrays, there is no need for such many low-level functions as for linked
 lists.
 However, there is one extremely powerful function that can be used for several complex tasks: `cx_array_copy`.
 The full signature is shown below:
 ```c
 enum cx_array_copy_result cx_array_copy(
         void **target,
         size_t *size,
         size_t *capacity,  // optional
         size_t index,
         void const *src,
         size_t elem_size,
         size_t elem_count,
         struct cx_array_reallocator_s *reallocator // optional
 );
 ```
 The `target` argument is a pointer to the target array pointer.
 The reason for this additional indirection is that - given that you provide a `reallocator` - this function writes
 back the pointer to the possibly reallocated array.
 THe next two arguments are pointers to the `size` and `capacity` of the target array.
 Tracking the capacity is optional.
 If you do not specify a pointer for the capacity, automatic reallocation of the array is entirely disabled (i.e. it
 does not make sense to specify a `reallocator` then).
 In this case, the function cannot copy more than `size-index` elements and if you try, it will return
 `CX_ARRAY_COPY_REALLOC_NOT_SUPPORTED` and do nothing.
 On a successful invocation, the function copies `elem_count` number of elements, each of size `elem_size` from
 `src` to `*target` and uses the `reallocator` to extend the array when necessary.
 Finally, the size, capacity, and the pointer to the array are all updated and the function returns
 `CX_ARRAY_COPY_SUCCESS`.
 The third, but extremely rare, return code is `CX_ARRAY_COPY_REALLOC_FAILED` and speaks for itself.
 A few things to note:
 * `*target` and `src` can point to the same memory region, effectively copying elements within the array with `memmove`
 * `*target` does not need to point to the start of the array, but `size` and `capacity` always start counting from the
   position, `*target` points to - in this scenario, specifying a `reallocator` is forbidden for obvious reasons
 * `index` does not need to be within size of the current array, if `capacity` is specified
 * `index` does not even need to be within the capacity of the array, if `reallocator` is specified
 ## Map
 *Header file:* [map.h](api/map_8h.html)
 ### Hash Map
 *Header file:* [hash_map.h](api/hash__map_8h.html)
 ## Utilities
 *Header file:* [utils.h](api/utils_8h.html)
 UCX provides some utilities for routine tasks. Most of them are simple macros, like e.g. the `cx_for_n()` macro,
 creating a `for` loop counting from zero to (n-1) which is extremely useful to traverse the indices of
 an array.
 But the most useful utilities are the *stream copy* functions, which provide a simple way to copy all - or a
 bounded amount of - data from one stream to another. Since the read/write functions of a UCX buffer are
 fully compatible with stream read/write functions, you can easily transfer data from file or network streams to
 a UCX buffer or vice-versa.
 The following example shows, how easy it is to read the contents of a file into a buffer:
 ```c
 FILE *inputfile = fopen(infilename, "r");
 if (inputfile) {
     CxBuffer fbuf;
     cxBufferInit(&fbuf, NULL, 4096, NULL, CX_BUFFER_AUTO_EXTEND);
     cx_stream_copy(inputfile, &fbuf,
                    (cx_read_func) fread,
                    (cx_write_func) cxBufferWrite);
     fclose(inputfile);
     // ... do something meaningful with the contents ...
     cxBufferDestroy(&fbuf);
 } else {
     perror("Error opening input file");
     if (fout != stdout) {
         fclose(fout);
     }
 }
 ```
 ### Printf Functions
 *Header file:* [printf.h](api/printf_8h.html)
 In this utility header you can find `printf()`-like functions that can write the formatted output to an arbitrary
 stream (or UCX buffer, resp.), or to memory allocated by an allocator within a single function call.
 With the help of these convenience functions, you do not need to `snprintf` your string to a temporary buffer anymore,
 plus you do not need to worry about too small buffer sizes, because the functions will automatically allocate enough
 memory to contain the entire formatted string.
 ### Compare Functions
 *Header file:* [compare.h](api/compare_8h.html)
 This header file contains a collection of compare functions for various data types.
 Their signatures are designed to be compatible with the `cx_compare_func` function pointer type.

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docs/src/features.md@9c097dabba2c (annotated)

docs/src/features.md