1registry(3) C Library Functions registry(3)
2
6 registry - Store and back up key-value pairs.
7
9 This module provides support for storing key-value pairs in a table
10 known as a registry, backing up registries to Mnesia in an atomic man‐
11 ner, and later restoring the contents of a registry from Mnesia.
12
14 int ei_reg_close(reg)
15 Types:
17 ei_reg *reg;
19 A registry that has previously been created with ei_reg_open()
21 is closed, and all the objects it contains are freed.
22 reg is the registry to close.
24 Returns 0.
26 int ei_reg_delete(reg,key)
28 Types:
30 ei_reg *reg;
32 const char *key;
33 Deletes an object from the registry. The object is not removed
35 from the registry, it is only marked for later removal so that
36 on later backups to Mnesia, the corresponding object can be
37 removed from the Mnesia table as well. If another object is
38 later created with the same key, the object will be reused.
39 The object is removed from the registry after a call to
41 ei_reg_dump() or ei_reg_purge().
42 * reg is the registry containing key.
44 * key is the object to remove.
46 Returns 0 on success, otherwise -1.
48 int ei_reg_dump(fd,reg,mntab,flags)
50 Types:
52 int fd;
54 ei_reg *reg;
55 const char *mntab;
56 int flags;
57 Dumps the contents of a registry to a Mnesia table in an atomic
59 manner, that is, either all data or no data is updated. If any
60 errors are encountered while backing up the data, the entire
61 operation is aborted.
62 * fd is an open connection to Erlang. Mnesia 3.0 or later must
64 be running on the Erlang node.
65 * reg is the registry to back up.
67 * mntab is the name of the Mnesia table where the backed up
69 data is to be placed. If the table does not exist, it is
70 created automatically using configurable defaults. For
71 information about configuring this behavior, see Mnesia.
72 If flags is 0, the backup includes only those objects that have
74 been created, modified, or deleted since the last backup or
75 restore (that is, an incremental backup). After the backup, any
76 objects that were marked dirty are now clean, and any objects
77 that had been marked for deletion are deleted.
78 Alternatively, setting flags to EI_FORCE causes a full backup to
80 be done, and EI_NOPURGE causes the deleted objects to be left in
81 the registry afterwards. These can be bitwise OR'ed together if
82 both behaviors are desired. If EI_NOPURGE was specified,
83 ei_reg_purge() can be used to explicitly remove the deleted
84 items from the registry later.
85 Returns 0 on success, otherwise -1.
87 double ei_reg_getfval(reg,key)
89 Types:
91 ei_reg *reg;
93 const char *key;
94 Gets the value associated with key in the registry. The value
96 must be a floating point type.
97 * reg is the registry where the object will be looked up.
99 * key is the name of the object to look up.
101 On success, the function returns the value associated with key.
103 If the object is not found or if it is not a floating point
104 object, -1.0 is returned. To avoid problems with in-band error
105 reporting (that is, if you cannot distinguish between -1.0 and a
106 valid result), use the more general function ei_reg_getval()
107 instead.
108 int ei_reg_getival(reg,key)
110 Types:
112 ei_reg *reg;
114 const char *key;
115 Gets the value associated with key in the registry. The value
117 must be an integer.
118 * reg is the registry where the object will be looked up.
120 * key is the name of the object to look up.
122 On success, the function returns the value associated with key.
124 If the object is not found or if it is not an integer object, -1
125 is returned. To avoid problems with in-band error reporting
126 (that is, if you cannot distinguish between -1 and a valid
127 result), use the more general function ei_reg_getval() instead.
128 const void *ei_reg_getpval(reg,key,size)
130 Types:
132 ei_reg *reg;
134 const char *key;
135 int size;
136 Gets the value associated with key in the registry. The value
138 must be a binary (pointer) type.
139 * reg is the registry where the object will be looked up.
141 * key is the name of the object to look up.
143 * size is initialized to contain the length in bytes of the
145 object, if it is found.
146 On success, the function returns the value associated with key
148 and indicates its length in size. If the object is not found or
149 if it is not a binary object, NULL is returned. To avoid prob‐
150 lems with in-band error reporting (that is, if you cannot dis‐
151 tinguish between NULL and a valid result), use the more general
152 function ei_reg_getval() instead.
153 const char *ei_reg_getsval(reg,key)
155 Types:
157 ei_reg *reg;
159 const char *key;
160 Gets the value associated with key in the registry. The value
162 must be a string.
163 * reg is the registry where the object will be looked up.
165 * key is the name of the object to look up.
167 On success, the function returns the value associated with key.
169 If the object is not found or if it is not a string, NULL is
170 returned. To avoid problems with in-band error reporting (that
171 is, if you cannot distinguish between NULL and a valid result),
172 use the more general function ei_reg_getval() instead.
173 int ei_reg_getval(reg,key,flags,v,...)
175 Types:
177 ei_reg *reg;
179 const char *key;
180 int flags;
181 void *v (see below)
182 A general function for retrieving any kind of object from the
184 registry.
185 * reg is the registry where the object will be looked up.
187 * key is the name of the object to look up.
189 * flags indicates the type of object that you are looking for.
191 If flags is 0, any kind of object is returned. If flags is
192 EI_INT, EI_FLT, EI_STR, or EI_BIN, then only values of that
193 kind are returned.
194 The buffer pointed to by v must be large enough to hold the
196 return data, that is, it must be a pointer to one of int,
197 double, char*, or void*, respectively.
198 If flags is EI_BIN, a fifth argument int *size is required,
200 so that the size of the object can be returned.
201 On success, v (and size if the object is binary) is initialized
203 with the value associated with key, and the function returns
204 EI_INT, EI_FLT, EI_STR, or EI_BIN, indicating the type of
205 object. On failure, -1 is returned and the arguments are not
206 updated.
207 int ei_reg_markdirty(reg,key)
209 Types:
211 ei_reg *reg;
213 const char *key;
214 Marks a registry object as dirty. This ensures that it is
216 included in the next backup to Mnesia. Normally this operation
217 is not necessary, as all of the normal registry 'set' functions
218 do this automatically. However, if you have retrieved the value
219 of a string or binary object from the registry and modified the
220 contents, then the change is invisible to the registry and the
221 object is assumed to be unmodified. This function allows you to
222 make such modifications and then let the registry know about
223 them.
224 * reg is the registry containing the object.
226 * key is the name of the object to mark.
228 Returns 0 on success, otherwise -1.
230 ei_reg *ei_reg_open(size)
232 Types:
234 int size;
236 Opens (creates) a registry, which initially is empty. To close
238 the registry later, use ei_reg_close().
239 size is the approximate number of objects you intend to store in
241 the registry. As the registry uses a hash table with collision
242 chaining, no absolute upper limit exists on the number of
243 objects that can be stored in it. However, for reasons of effi‐
244 ciency, it is a good idea to choose a number that is appropriate
245 for your needs. To change the size later, use ei_reg_resize().
246 Notice that the number you provide is increased to the nearest
247 larger prime number.
248 Returns an empty registry on success, otherwise NULL.
250 int ei_reg_purge(reg)
252 Types:
254 ei_reg *reg;
256 Removes all objects marked for deletion. When objects are
258 deleted with ei_reg_delete() they are not removed from the reg‐
259 istry, only marked for later removal. On a later backup to Mne‐
260 sia, the objects can also be removed from the Mnesia table. If
261 you are not backing up to Mnesia, you may wish to remove the
262 objects manually with this function.
263 reg is a registry containing objects marked for deletion.
265 Returns 0 on success, otherwise -1.
267 int ei_reg_resize(reg,newsize)
269 Types:
271 ei_reg *reg;
273 int newsize;
274 Changes the size of a registry.
276 newsize is the new size to make the registry. The number is
278 increased to the nearest larger prime number.
279 On success, the registry is resized, all contents rehashed, and
281 0 is returned. On failure, the registry is left unchanged and -1
282 is returned.
283 int ei_reg_restore(fd,reg,mntab)
285 Types:
287 int fd;
289 ei_reg *reg;
290 const char *mntab;
291 The contents of a Mnesia table are read into the registry.
293 * fd is an open connection to Erlang. Mnesia 3.0 or later must
295 be running on the Erlang node.
296 * reg is the registry where the data is to be placed.
298 * mntab is the name of the Mnesia table to read data from.
300 Notice that only tables of a certain format can be restored,
302 that is, those that have been created and backed up to with
303 ei_reg_dump(). If the registry was not empty before the opera‐
304 tion, the contents of the table are added to the contents of the
305 registry. If the table contains objects with the same keys as
306 those already in the registry, the registry objects are over‐
307 written with the new values. If the registry contains objects
308 that were not in the table, they are unchanged by this opera‐
309 tion.
310 After the restore operation, the entire contents of the registry
312 is marked as unmodified. Notice that this includes any objects
313 that were modified before the restore and not overwritten by the
314 restore.
315 Returns 0 on success, otherwise -1.
317 int ei_reg_setfval(reg,key,f)
319 Types:
321 ei_reg *reg;
323 const char *key;
324 double f;
325 Creates a key-value pair with the specified key and floating
327 point value f. If an object already exists with the same key,
328 the new value replaces the old one. If the previous value was a
329 binary or string, it is freed with free().
330 * reg is the registry where the object is to be placed.
332 * key is the object name.
334 * f is the floating point value to assign.
336 Returns 0 on success, otherwise -1.
338 int ei_reg_setival(reg,key,i)
340 Types:
342 ei_reg *reg;
344 const char *key;
345 int i;
346 Creates a key-value pair with the specified key and integer
348 value i. If an object already exists with the same key, the new
349 value replaces the old one. If the previous value was a binary
350 or string, it is freed with free().
351 * reg is the registry where the object is to be placed.
353 * key is the object name.
355 * i is the integer value to assign.
357 Returns 0 on success, otherwise -1.
359 int ei_reg_setpval(reg,key,p,size)
361 Types:
363 ei_reg *reg;
365 const char *key;
366 const void *p;
367 int size;
368 Creates a key-value pair with the specified key whose "value" is
370 the binary object pointed to by p. If an object already exists
371 with the same key, the new value replaces the old one. If the
372 previous value was a binary or string, it is freed with free().
373 * reg is the registry where the object is to be placed.
375 * key is the object name.
377 * p is a pointer to the binary object. The object itself must
379 have been created through a single call to malloc() or a
380 similar function, so that the registry can later delete it
381 if necessary by calling free().
382 * size is the length in bytes of the binary object.
384 Returns 0 on success, otherwise -1.
386 int ei_reg_setsval(reg,key,s)
388 Types:
390 ei_reg *reg;
392 const char *key;
393 const char *s;
394 Creates a key-value pair with the specified key whose "value" is
396 the specified string s. If an object already exists with the
397 same key, the new value replaces the old one. If the previous
398 value was a binary or string, it is freed with free().
399 * reg is the registry where the object is to be placed.
401 * key is the object name.
403 * s is the string to assign. The string itself must have been
405 created through a single call to malloc() or similar a func‐
406 tion, so that the registry can later delete it if necessary
407 by calling free().
408 Returns 0 on success, otherwise -1.
410 int ei_reg_setval(reg,key,flags,v,...)
412 Types:
414 ei_reg *reg;
416 const char *key;
417 int flags;
418 v (see below)
419 Creates a key-value pair with the specified key whose value is
421 specified by v. If an object already exists with the same key,
422 the new value replaces the old one. If the previous value was a
423 binary or string, it is freed with free().
424 * reg is the registry where the object is to be placed.
426 * key is the object name.
428 * flags indicates the type of the object specified by v. Flags
430 must be one of EI_INT, EI_FLT, EI_STR, and EI_BIN, indicat‐
431 ing whether v is int, double, char*, or void*.
432 If flags is EI_BIN, a fifth argument size is required, indi‐
434 cating the size in bytes of the object pointed to by v.
435 If you wish to store an arbitrary pointer in the registry, spec‐
437 ify a size of 0. In this case, the object itself is not trans‐
438 ferred by an ei_reg_dump() operation, only the pointer value.
439 Returns 0 on success, otherwise -1.
441 int ei_reg_stat(reg,key,obuf)
443 Types:
445 ei_reg *reg;
447 const char *key;
448 struct ei_reg_stat *obuf;
449 Returns information about an object.
451 * reg is the registry containing the object.
453 * key is the object name.
455 * obuf is a pointer to an ei_reg_stat structure, defined as
457 follows:
458 struct ei_reg_stat {
460 int attr;
461 int size;
462 };
463 In attr the attributes of the object are stored as the logical
466 OR of its type (one of EI_INT, EI_FLT, EI_BIN, and EI_STR),
467 whether it is marked for deletion (EI_DELET), and whether it has
468 been modified since the last backup to Mnesia (EI_DIRTY).
469 Field size indicates the size in bytes required to store EI_STR
471 (including the terminating 0) and EI_BIN objects, or 0 for
472 EI_INT and EI_FLT.
473 Returns 0 and initializes obuf on success, otherwise -1.
475 int ei_reg_tabstat(reg,obuf)
477 Types:
479 ei_reg *reg;
481 struct ei_reg_tabstat *obuf;
482 Returns information about a registry. Using information returned
484 by this function, you can see whether the size of the registry
485 is suitable for the amount of data it contains.
486 * reg is the registry to return information about.
488 * obuf is a pointer to an ei_reg_tabstat structure, defined as
490 follows:
491 struct ei_reg_tabstat {
493 int size;
494 int nelem;
495 int npos;
496 int collisions;
497 };
498 Field size indicates the number of hash positions in the reg‐
501 istry. This is the number you provided when you created or last
502 resized the registry, rounded up to the nearest prime number.
503 * nelem indicates the number of elements stored in the reg‐
505 istry. It includes objects that are deleted but not purged.
506 * npos indicates the number of unique positions that are occu‐
508 pied in the registry.
509 * collisions indicates how many elements are sharing positions
511 in the registry.
512 On success, 0 is returned and obuf is initialized to contain ta‐
514 ble statistics, otherwise -1 is returned.
515Ericsson AB erl_interface 3.13 registry(3)