1umem_cache_create(3MALLMOeCm)ory Allocation Library Functuimoenms_cache_create(3MALLOC)
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6 umem_cache_create, umem_cache_destroy, umem_cache_alloc,
7 umem_cache_free - allocation cache manipulation
8
10 cc [ flag ... ] file... -lumem [ library ... ]
11 #include <umem.h>
12 umem_cache_t *umem_cache_create(char *debug_name, size_t bufsize,
14 size_t align, umem_constructor_t *constructor,
15 umem_destructor_t *destructor, umem_reclaim_t *reclaim,
16 void *callback_data, vmem_t *source, int cflags);
17 void umem_cache_destroy(umem_cache_t *cache);
20 void *umem_cache_alloc(umem_cache_t *cache, int flags);
23 void umem_cache_free(umem_cache_t *cache, void *buffer);
26
29 These functions create, destroy, and use an "object cache" An object
30 cache is a collection of buffers of a single size, with optional con‐
31 tent caching enabled by the use of callbacks (see Cache Callbacks).
32 Object caches are MT-Safe. Multiple allocations and freeing of memory
33 from different threads can proceed simultaneously. Object caches are
34 faster and use less space per buffer than malloc(3MALLOC) and
35 umem_alloc(3MALLOC). For more information about object caching, see
36 "The Slab Allocator: An Object-Caching Kernel Memory Allocator" and
37 "Magazines and vmem: Extending the Slab Allocator to Many CPUs and
38 Arbitrary Resources".
39 The umem_cache_create() function creates object caches. Once a cache
42 has been created, objects can be requested from and returned to the
43 cache using umem_cache_alloc() and umem_cache_free(), respectively. A
44 cache with no outstanding buffers can be destroyed with
45 umem_cache_destroy().
46 Creating and Destroying Caches
48 The umem_cache_create() function creates a cache of objects and takes
49 as arguments the following:
50 debug_name A human-readable name for debugging purposes.
52 bufsize The size, in bytes, of the buffers in this cache.
55 align The minimum alignment required for buffers in this
58 cache. This parameter must be a power of 2. If 0, it
59 is replaced with the minimum required alignment for
60 the current architecture.
61 constructor The callback to construct an object.
64 destructor The callback to destroy an object.
67 reclaim The callback to reclaim objects.
70 callback_data An opaque pointer passed to the callbacks.
73 source This parameter must be NULL.
76 cflags This parameter must be either 0 or UMC_NODEBUG. If
79 UMC_NODEBUG, all debugging features are disabled for
80 this cache. See umem_debug(3MALLOC).
81 Each cache can have up to three associated callbacks:
85 int constructor(void *buffer, void *callback_data, int flags);
87 void destructor(void *buffer, void *callback_data);
88 void reclaim(void *callback_data);
89 The callback_data argument is always equal to the value passed to
93 umem_cache_create(), thereby allowing a client to use the same callback
94 functions for multiple caches, but with customized behavior.
95 The reclaim callback is called when the umem function is requesting
98 more memory from the operating system. This callback can be used by
99 clients who retain objects longer than they are strictly needed (for
100 example, caching non-active state). A typical reclaim callback might
101 return to the cache ten per cent of the unneeded buffers.
102 The constructor and destructor callbacks enable the management of buf‐
105 fers with the constructed state. The constructor takes as arguments a
106 buffer with undefined contents, some callback data, and the flags to
107 use for any allocations. This callback should transform the buffer into
108 the constructed state.
109 The destructor callback takes as an argument a constructed object and
112 prepares it for return to the general pool of memory. The destructor
113 should undo any state that the constructor created. For debugging, the
114 destructor can also check that the buffer is in the constructed state,
115 to catch incorrectly freed buffers. See umem_debug(3MALLOC) for fur‐
116 ther information on debugging support.
117 The umem_cache_destroy() function destroys an object cache. If the
120 cache has any outstanding allocations, the behavior is undefined.
121 Allocating Objects
123 The umem_cache_alloc() function takes as arguments:
124 cache a cache pointer
126 flags flags that determine the behavior if umem_cache_alloc() is
129 unable to fulfill the allocation request
130 If successful, umem_cache_alloc() returns a pointer to the beginning of
134 an object of bufsize length.
135 There are three cases to consider:
138 o A new buffer needed to be allocated. If the cache was cre‐
140 ated with a constructor, it is applied to the buffer and the
141 resulting object is returned.
142 o The object cache was able to use a previously freed buffer.
144 If the cache was created with a constructor, the object is
145 returned unchanged from when it was freed.
146 o The allocation of a new buffer failed. The flags argument
148 determines the behavior:
149 UMEM_DEFAULT The umem_cache_alloc() function returns NULL
152 if the allocation fails.
153 UMEM_NOFAIL The umem_cache_alloc() function cannot
156 return NULL. A callback is used to determine
157 what action occurs. See umem_alloc(3MALLOC)
158 for more information.
159 Freeing Objects
163 The umem_cache_free() function takes as arguments:
164 cache a cache pointer
166 buf a pointer previously returned from umem_cache_alloc(). This
169 argument must not be NULL.
170 If the cache was created with a constructor callback, the object must
174 be returned to the constructed state before it is freed.
175 Undefined behavior results if an object is freed multiple times, if an
178 object is modified after it is freed, or if an object is freed to a
179 cache other than the one from which it was allocated.
180 Caches with Constructors
182 When a constructor callback is in use, there is essentially a contract
183 between the cache and its clients. The cache guarantees that all
184 objects returned from umem_cache_alloc() will be in the constructed
185 state, and the client guarantees that it will return the object to the
186 constructed state before handing it to umem_cache_free().
187
189 Upon failure, the umem_cache_create() function returns a null pointer.
190
192 The umem_cache_create() function will fail if:
193 EAGAIN There is not enough memory available to allocate the cache
195 data structure.
196 EINVAL The debug_name argument is NULL, the align argument is not a
199 power of two or is larger than the system pagesize, or the
200 bufsize argument is 0.
201 ENOMEM The libumem library could not be initialized, or the bufsize
204 argument is too large and its use would cause integer over‐
205 flow to occur.
206
209 Example 1 Use a fixed-size structure with no constructor callback.
210 #include <umem.h>
212 typedef struct my_obj {
214 long my_data1;
215 } my_obj_t;
216 /*
218 * my_objs can be freed at any time. The contents of
219 * my_data1 is undefined at allocation time.
220 */
221 umem_cache_t *my_obj_cache;
223 ...
225 my_obj_cache = umem_cache_create("my_obj", sizeof (my_obj_t),
226 0, NULL, NULL, NULL, NULL, NULL, 0);
227 ...
228 my_obj_t *cur = umem_cache_alloc(my_obj_cache, UMEM_DEFAULT);
229 ...
230 /* use cur */
231 ...
232 umem_cache_free(my_obj_cache, cur);
233 ...
234 Example 2 Use an object with a mutex.
237 #define _REENTRANT
239 #include <synch.h>
240 #include <umem.h>
241 typedef struct my_obj {
243 mutex_t my_mutex;
244 long my_data;
245 } my_obj_t;
246 /*
248 * my_objs can only be freed when my_mutex is unlocked.
249 */
250 int
251 my_obj_constructor(void *buf, void *ignored, int flags)
252 {
253 my_obj_t *myobj = buf;
254 (void) mutex_init(&my_obj->my_mutex, USYNC_THREAD, NULL);
256 return (0);
258 }
259 void
261 my_obj_destructor(void *buf, void *ignored)
262 {
263 my_obj_t *myobj = buf;
264 (void) mutex_destroy(&my_obj->my_mutex);
266 }
267 umem_cache_t *my_obj_cache;
269 ...
271 my_obj_cache = umem_cache_create("my_obj", sizeof (my_obj_t),
272 0, my_obj_constructor, my_obj_destructor, NULL, NULL,
273 NULL, 0);
274 ...
275 my_obj_t *cur = umem_cache_alloc(my_obj_cache, UMEM_DEFAULT);
276 cur->my_data = 0; /* cannot assume anything about my_data */
277 ...
278 umem_cache_free(my_obj_cache, cur);
279 ...
280 Example 3 Use a more complex object with a mutex.
283 #define _REENTRANT
285 #include <assert.h>
286 #include <synch.h>
287 #include <umem.h>
288 typedef struct my_obj {
290 mutex_t my_mutex;
291 cond_t my_cv;
292 struct bar *my_barlist;
293 unsigned my_refcount;
294 } my_obj_t;
295 /*
297 * my_objs can only be freed when my_barlist == NULL,
298 * my_refcount == 0, there are no waiters on my_cv, and
299 * my_mutex is unlocked.
300 */
301 int
303 my_obj_constructor(void *buf, void *ignored, int flags)
304 {
305 my_obj_t *myobj = buf;
306 (void) mutex_init(&my_obj->my_mutex, USYNC_THREAD, NULL);
308 (void) cond_init(&my_obj->my_cv, USYNC_THREAD, NULL);
309 myobj->my_barlist = NULL;
310 myobj->my_refcount = 0;
311 return (0);
313 }
314 void
316 my_obj_destructor(void *buf, void *ignored)
317 {
318 my_obj_t *myobj = buf;
319 assert(myobj->my_refcount == 0);
321 assert(myobj->my_barlist == NULL);
322 (void) cond_destroy(&my_obj->my_cv);
323 (void) mutex_destroy(&my_obj->my_mutex);
324 }
325 umem_cache_t *my_obj_cache;
327 ...
329 my_obj_cache = umem_cache_create("my_obj", sizeof (my_obj_t),
330 0, my_obj_constructor, my_obj_destructor, NULL, NULL,
331 NULL, 0);
332 ...
333 my_obj_t *cur = umem_cache_alloc(my_obj_cache, UMEM_DEFAULT);
334 ...
335 /* use cur */
336 ...
337 umem_cache_free(my_obj_cache, cur);
338 ...
339 Example 4 Use objects with a subordinate buffer while reusing call‐
342 backs.
343 #include assert.h>
345 #include umem.h>
346 typedef struct my_obj {
348 char *my_buffer;
349 size_t my_size;
350 } my_obj_t;
351 /*
353 * my_size and the my_buffer pointer should never be changed
354 */
355 int
357 my_obj_constructor(void *buf, void *arg, int flags)
358 {
359 size_t sz = (size_t)arg;
360 my_obj_t *myobj = buf;
362 if ((myobj->my_buffer = umem_alloc(sz, flags)) == NULL)
364 return (1);
365 my_size = sz;
367 return (0);
369 }
370 void
372 my_obj_destructor(void *buf, void *arg)
373 {
374 size_t sz = (size_t)arg;
375 my_obj_t *myobj = buf;
377 assert(sz == buf->my_size);
379 umem_free(myobj->my_buffer, sz);
380 }
381 ...
383 umem_cache_t *my_obj_4k_cache;
384 umem_cache_t *my_obj_8k_cache;
385 ...
386 my_obj_cache_4k = umem_cache_create("my_obj_4k", sizeof (my_obj_t),
387 0, my_obj_constructor, my_obj_destructor, NULL,
388 (void *)4096, NULL, 0);
389 my_obj_cache_8k = umem_cache_create("my_obj_8k", sizeof (my_obj_t),
391 0, my_obj_constructor, my_obj_destructor, NULL,
392 (void *)8192, NULL, 0);
393 ...
394 my_obj_t *my_obj_4k = umem_cache_alloc(my_obj_4k_cache,
395 UMEM_DEFAULT);
396 my_obj_t *my_obj_8k = umem_cache_alloc(my_obj_8k_cache,
397 UMEM_DEFAULT);
398 /* no assumptions should be made about the contents
399 of the buffers */
400 ...
401 /* make sure to return them to the correct cache */
402 umem_cache_free(my_obj_4k_cache, my_obj_4k);
403 umem_cache_free(my_obj_8k_cache, my_obj_8k);
404 ...
405 See the EXAMPLES section of umem_alloc(3MALLOC) for examples involving
409 the UMEM_NOFAIL flag.
410
412 See attributes(5) for descriptions of the following attributes:
413 ┌─────────────────────────────┬─────────────────────────────┐
418 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
419 ├─────────────────────────────┼─────────────────────────────┤
420 │Interface Stability │Committed │
421 ├─────────────────────────────┼─────────────────────────────┤
422 │MT-Level │MT-Safe │
423 └─────────────────────────────┴─────────────────────────────┘
424
426 setcontext(2), atexit(3C), libumem(3LIB), longjmp(3C), swapcontext(3C),
427 thr_exit(3C), umem_alloc(3MALLOC), umem_debug(3MALLOC), attributes(5)
428 Bonwick, Jeff, "The Slab Allocator: An Object-Caching Kernel Memory
431 Allocator", Proceedings of the Summer 1994 Usenix Conference.
432 Bonwick, Jeff and Jonathan Adams, "Magazines and vmem: Extending the
435 Slab Allocator to Many CPUs and Arbitrary Resources", Proceedings of
436 the Summer 2001 Usenix Conference.
437
439 Any of the following can cause undefined results:
440 o Destroying a cache that has outstanding allocated buffers.
442 o Using a cache after it has been destroyed.
444 o Calling umem_cache_free() on the same buffer multiple times.
446 o Passing a NULL pointer to umem_cache_free().
448 o Writing past the end of a buffer.
450 o Reading from or writing to a buffer after it has been freed.
452 o Performing UMEM_NOFAIL allocations from an atexit(3C) han‐
454 dler.
455 Per-cache callbacks can be called from a variety of contexts. The use
458 of functions that modify the active context, such as setcontext(2),
459 swapcontext(3C), and thr_exit(3C), or functions that are unsafe for use
460 in multithreaded applications, such as longjmp(3C) and siglongjmp(3C),
461 result in undefined behavior.
462 A constructor callback that performs allocations must pass its flags
465 argument unchanged to umem_alloc(3MALLOC) and umem_cache_alloc(). Any
466 allocations made with a different flags argument results in undefined
467 behavior. The constructor must correctly handle the failure of any
468 allocations it makes.
469
471 Object caches make the following guarantees about objects:
472 o If the cache has a constructor callback, it is applied to
474 every object before it is returned from umem_cache_alloc()
475 for the first time.
476 o If the cache has a constructor callback, an object passed to
478 umem_cache_free() and later returned from umem_cache_alloc()
479 is not modified between the two events.
480 o If the cache has a destructor, it is applied to all objects
482 before their underlying storage is returned.
483 No other guarantees are made. In particular, even if there are buffers
486 recently freed to the cache, umem_cache_alloc() can fail.
487SunOS 5.11 24 Mar 2008 umem_cache_create(3MALLOC)