Sat, 01 Jul 2023 14:05:52 +0200
add mempool example
1 ---
2 title: UCX Features
3 ---
5 <div id="modules">
7 ------------------------ ------------------------- ------------------- ---------------------------------
8 [Allocator](#allocator) [String](#string) [Buffer](#buffer) [Memory Pool](#memory-pool)
9 [Iterator](#iterator) [Collection](#collection) [List](#list) [Map](#map)
10 [Utilities](#utilities)
11 ------------------------ ------------------------- ------------------- ---------------------------------
13 </div>
15 ## Allocator
17 *Header file:* [allocator.h](api/allocator_8h.html)
19 The UCX allocator provides an interface for implementing an own memory allocation mechanism.
20 Various function in UCX provide an additional alternative signature that takes an allocator as
21 argument. A default allocator implementation using the stdlib memory management functions is
22 available via the global symbol `cxDefaultAllocator`.
24 If you want to define your own allocator, you need to initialize the `CxAllocator` structure
25 with a pointer to an allocator class (containing function pointers for the memory management
26 functions) and an optional pointer to an arbitrary memory region that can be used to store
27 state information for the allocator. An example is shown below:
29 ```c
30 struct my_allocator_state {
31 size_t total;
32 size_t avail;
33 char mem[];
34 };
36 static cx_allocator_class my_allocator_class = {
37 my_malloc_impl,
38 my_realloc_impl, // all these functions are somewhere defined
39 my_calloc_impl,
40 my_free_impl
41 };
43 CxAllocator create_my_allocator(size_t n) {
44 CxAllocator alloc;
45 alloc.cl = &my_allocator_class;
46 alloc.data = calloc(1, sizeof(struct my_allocator_state) + n);
47 return alloc;
48 }
50 void free_my_allocator(CxAllocator *alloc) {
51 free(alloc.data);
52 free(alloc);
53 }
54 ```
56 ## String
58 *Header file:* [string.h](api/string_8h.html)
60 UCX strings come in two variants: immutable (`cxstring`) and mutable (`cxmutstr`).
61 The functions of UCX are designed to work with immutable strings by default but in situations where it is necessary,
62 the API also provides alternative functions that work directly with mutable strings.
63 Functions that change a string in-place are, of course, only accepting mutable strings.
65 When you are using UCX functions, or defining your own functions, you are sometimes facing the "problem",
66 that the function only accepts arguments of type `cxstring` but you only have a `cxmutstr` at hand.
67 In this case you _should not_ introduce a wrapper function that accepts the `cxmutstr`,
68 but instead you should use the `cx_strcast()` function to cast the argument to the correct type.
70 In general, UCX strings are **not** necessarily zero-terminated. If a function guarantees to return zero-terminated
71 string, it is explicitly mentioned in the documentation of the respective function.
72 As a rule of thumb, you _should not_ pass the strings of a UCX string structure to another API without explicitly
73 ensuring that the string is zero-terminated.
75 ## Buffer
77 *Header file:* [buffer.h](api/buffer_8h.html)
79 Instances of this buffer implementation can be used to read from or write to memory like you would do with a stream.
80 This allows the use of `cx_stream_copy()` (see [Utilities](#utilities)) to copy contents from one buffer to another,
81 or from a file or network streams to the buffer and vice-versa.
83 More features for convenient use of the buffer can be enabled, like automatic memory management and automatic
84 resizing of the buffer space.
86 Since UCX 3.0, the buffer also supports automatic flushing of contents to another stream (or buffer) as an alternative
87 to automatically resizing the buffer space.
88 Please refer to the API doc for the fields prefixed with `flush_` to learn more.
90 ## Memory Pool
92 *Header file:* [mempool.h](api/mempool_8h.html)
94 A memory pool is providing an allocator implementation that automatically deallocates the memory upon its destruction.
95 It also allows you to register destructor functions for the allocated memory, which are automatically called before
96 the memory is deallocated.
97 Additionally, you may also register _independent_ destructor functions within a pool in case some external library
98 allocated memory for you, which should be destroyed together with this pool.
100 Many UCX features support the use of an allocator.
101 The [strings](#string), for instance, provide several functions suffixed with `_a` that allow specifying an allocator.
102 You can use this to keep track of the memory occupied by dynamically allocated strings and cleanup everything with
103 just a single call to `cxMempoolDestroy()`.
105 The following code illustrates this on the example of reading a CSV file into memory.
106 ```C
107 #include <stdio.h>
108 #include <cx/mempool.h>
109 #include <cx/linked_list.h>
110 #include <cx/string.h>
111 #include <cx/buffer.h>
112 #include <cx/utils.h>
114 typedef struct {
115 cxstring column_a;
116 cxstring column_b;
117 cxstring column_c;
118 } CSVData;
120 int main(void) {
121 CxMempool* pool = cxBasicMempoolCreate(128);
123 FILE *f = fopen("test.csv", "r");
124 if (!f) {
125 perror("Cannot open file");
126 return 1;
127 }
128 // close the file automatically at pool destruction
129 cxMempoolRegister(pool, f, (cx_destructor_func) fclose);
131 // create a buffer using the memory pool for destruction
132 CxBuffer *content = cxBufferCreate(NULL, 256, pool->allocator, CX_BUFFER_AUTO_EXTEND);
134 // read the file into the buffer and turn it into a string
135 cx_stream_copy(f, content, (cx_read_func) fread, (cx_write_func) cxBufferWrite);
136 cxstring contentstr = cx_strn(content->space, content->size);
138 // split the string into lines - use the mempool for allocating the target array
139 cxstring* lines;
140 size_t lc = cx_strsplit_a(pool->allocator, contentstr,
141 CX_STR("\n"), SIZE_MAX, &lines);
143 // skip the header and parse the remaining data into a linked list
144 // the nodes of the linked list shall also be allocated by the mempool
145 CxList* datalist = cxLinkedListCreate(pool->allocator, NULL, sizeof(CSVData));
146 for (size_t i = 1 ; i < lc ; i++) {
147 if (lines[i].length == 0) continue;
148 cxstring fields[3];
149 size_t fc = cx_strsplit(lines[i], CX_STR(";"), 3, fields);
150 if (fc != 3) {
151 fprintf(stderr, "Syntax error in line %zu.\n", i);
152 cxMempoolDestroy(pool);
153 return 1;
154 }
155 CSVData* data = cxMalloc(pool->allocator, sizeof(CSVData));
156 data->column_a = fields[0];
157 data->column_b = fields[1];
158 data->column_c = fields[2];
159 cxListAdd(datalist, data);
160 }
162 // iterate through the list and output the data
163 CxIterator iter = cxListIterator(datalist);
164 cx_foreach(CSVData*, data, iter) {
165 printf("Column A: %.*s | "
166 "Column B: %.*s | "
167 "Column C: %.*s\n",
168 (int)data->column_a.length, data->column_a.ptr,
169 (int)data->column_b.length, data->column_b.ptr,
170 (int)data->column_c.length, data->column_c.ptr
171 );
172 }
174 // cleanup everything, no manual free() needed
175 cxMempoolDestroy(pool);
177 return 0;
178 }
179 ```
181 ## Iterator
183 *Header file:* [iterator.h](api/iterator_8h.html)
185 ## Collection
187 *Header file:* [collection.h](api/collection_8h.html)
189 ## List
191 *Header file:* [list.h](api/list_8h.html)
193 ### Linked List
195 *Header file:* [linked_list.h](api/linked__list_8h.html)
197 ### Array List
199 *Header file:* [array_list.h](api/array__list_8h.html)
201 ## Map
203 *Header file:* [map.h](api/map_8h.html)
205 ### Hash Map
207 *Header file:* [hash_map.h](api/hash__map_8h.html)
209 ## Utilities
211 *Header file:* [utils.h](api/utils_8h.html)
213 UCX provides some utilities for routine tasks. Most of them are simple macros, like e.g. the `cx_for_n()` macro,
214 creating a `for` loop counting from zero to (n-1) which is extremely useful to traverse the indices of
215 an array.
217 But the most useful utilities are the *stream copy* functions, which provide a simple way to copy all - or a
218 bounded amount of - data from one stream to another. Since the read/write functions of a UCX buffer are
219 fully compatible with stream read/write functions, you can easily transfer data from file or network streams to
220 a UCX buffer or vice-versa.
222 The following example shows, how easy it is to read the contents of a file into a buffer:
223 ```c
224 FILE *inputfile = fopen(infilename, "r");
225 if (inputfile) {
226 CxBuffer fbuf;
227 cxBufferInit(&fbuf, NULL, 4096, NULL, CX_BUFFER_AUTO_EXTEND);
228 cx_stream_copy(inputfile, &fbuf,
229 (cx_read_func) fread,
230 (cx_write_func) cxBufferWrite);
231 fclose(inputfile);
233 // ... do something meaningful with the contents ...
235 cxBufferDestroy(&fbuf);
236 } else {
237 perror("Error opening input file");
238 if (fout != stdout) {
239 fclose(fout);
240 }
241 }
242 ```
244 ### Printf Functions
246 *Header file:* [printf.h](api/printf_8h.html)
248 In this utility header you can find `printf()`-like functions that can write the formatted output to an arbitrary
249 stream (or UCX buffer, resp.), or to memory allocated by an allocator within a single function call.
250 With the help of these convenience functions, you do not need to `snprintf` your string to a temporary buffer anymore,
251 plus you do not need to worry about too small buffer sizes, because the functions will automatically allocate enough
252 memory to contain the entire formatted string.
254 ### Compare Functions
256 *Header file:* [compare.h](api/compare_8h.html)
258 This header file contains a collection of compare functions for various data types.
259 Their signatures are designed to be compatible with the `cx_compare_func` function pointer type.