Memory Allocation Library Functions umem_cache_create(3MALLOC)
NAME
umem_cache_create, umem_cache_destroy, umem_cache_alloc,
umem_cache_free - allocation cache manipulation
SYNOPSIS
cc [ flag ... ] file... -lumem [ library ... ]
#include
umem_cache_t *umem_cache_create(char *debug_name, size_t bufsize,
size_t align, umem_constructor_t *constructor,
umem_destructor_t *destructor, umem_reclaim_t *reclaim,
void *callback_data, vmem_t *source, int cflags);
void umem_cache_destroy(umem_cache_t *cache);
void *umem_cache_alloc(umem_cache_t *cache, int flags);
void umem_cache_free(umem_cache_t *cache, void *buffer);
DESCRIPTION
These functions create, destroy, and use an "object cache" An object cache is a collection of buffers of a single size,with optional content caching enabled by the use of call-
backs (see Cache Callbacks). Object caches are MT-Safe.
Multiple allocations and freeing of memory from differentthreads can proceed simultaneously. Object caches are fas-
ter and use less space per buffer than malloc(3MALLOC) andumem_alloc(3MALLOC). For more information about object
caching, see "The Slab Allocator: An Object-Caching Kernel
Memory Allocator" and "Magazines and vmem: Extending the Slab Allocator to Many CPUs and Arbitrary Resources".The umem_cache_create() function creates object caches. Once
a cache has been created, objects can be requested from andreturned to the cache using umem_cache_alloc() and
umem_cache_free(), respectively. A cache with no outstanding
buffers can be destroyed with umem_cache_destroy().
Creating and Destroying CachesThe umem_cache_create() function creates a cache of objects
and takes as arguments the following:debug_name A human-readable name for debugging pur-
poses.SunOS 5.11 Last change: 24 Mar 2008 1
Memory Allocation Library Functions umem_cache_create(3MALLOC)
bufsize The size, in bytes, of the buffers in this cache. align The minimum alignment required for buffers in this cache. This parameter must be a power of 2. If 0, it is replaced with the minimum required alignment for the current architecture. constructor The callback to construct an object. destructor The callback to destroy an object. reclaim The callback to reclaim objects.callback_data An opaque pointer passed to the callbacks.
source This parameter must be NULL. cflags This parameter must be either 0 orUMC_NODEBUG. If UMC_NODEBUG, all debugging
features are disabled for this cache. Seeumem_debug(3MALLOC).
Each cache can have up to three associated callbacks:int constructor(void *buffer, void *callback_data, int flags);
void destructor(void *buffer, void *callback_data);
void reclaim(void *callback_data);
The callback_data argument is always equal to the value
passed to umem_cache_create(), thereby allowing a client to
use the same callback functions for multiple caches, but with customized behavior. The reclaim callback is called when the umem function isrequesting more memory from the operating system. This call-
back can be used by clients who retain objects longer thanthey are strictly needed (for example, caching non-active
state). A typical reclaim callback might return to theSunOS 5.11 Last change: 24 Mar 2008 2
Memory Allocation Library Functions umem_cache_create(3MALLOC)
cache ten per cent of the unneeded buffers.The constructor and destructor callbacks enable the manage-
ment of buffers with the constructed state. The constructor takes as arguments a buffer with undefined contents, some callback data, and the flags to use for any allocations.This callback should transform the buffer into the con-
structed state. The destructor callback takes as an argument a constructed object and prepares it for return to the general pool ofmemory. The destructor should undo any state that the con-
structor created. For debugging, the destructor can also check that the buffer is in the constructed state, to catchincorrectly freed buffers. See umem_debug(3MALLOC) for
further information on debugging support.The umem_cache_destroy() function destroys an object cache.
If the cache has any outstanding allocations, the behavior is undefined. Allocating ObjectsThe umem_cache_alloc() function takes as arguments:
cache a cache pointer flags flags that determine the behavior ifumem_cache_alloc() is unable to fulfill the alloca-
tion requestIf successful, umem_cache_alloc() returns a pointer to the
beginning of an object of bufsize length. There are three cases to consider: o A new buffer needed to be allocated. If the cache was created with a constructor, it is applied to the buffer and the resulting object is returned. o The object cache was able to use a previously freedbuffer. If the cache was created with a construc-
tor, the object is returned unchanged from when it was freed. o The allocation of a new buffer failed. The flagsSunOS 5.11 Last change: 24 Mar 2008 3
Memory Allocation Library Functions umem_cache_create(3MALLOC)
argument determines the behavior:UMEM_DEFAULT The umem_cache_alloc() function
returns NULL if the allocation fails.UMEM_NOFAIL The umem_cache_alloc() function
cannot return NULL. A callback is used to determine what actionoccurs. See umem_alloc(3MALLOC) for
more information. Freeing ObjectsThe umem_cache_free() function takes as arguments:
cache a cache pointer buf a pointer previously returned fromumem_cache_alloc(). This argument must not be NULL.
If the cache was created with a constructor callback, the object must be returned to the constructed state before it is freed. Undefined behavior results if an object is freed multiple times, if an object is modified after it is freed, or if an object is freed to a cache other than the one from which it was allocated. Caches with Constructors When a constructor callback is in use, there is essentially a contract between the cache and its clients. The cacheguarantees that all objects returned from umem_cache_alloc()
will be in the constructed state, and the client guarantees that it will return the object to the constructed statebefore handing it to umem_cache_free().
RETURN VALUES
Upon failure, the umem_cache_create() function returns a
null pointer.ERRORS
The umem_cache_create() function will fail if:
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Memory Allocation Library Functions umem_cache_create(3MALLOC)
EAGAIN There is not enough memory available to allocate the cache data structure.EINVAL The debug_name argument is NULL, the align argu-
ment is not a power of two or is larger than the system pagesize, or the bufsize argument is 0. ENOMEM The libumem library could not be initialized, or the bufsize argument is too large and its use would cause integer overflow to occur.EXAMPLES
Example 1 Use a fixed-size structure with no constructor
callback.#include
typedef struct my_obj {
long my_data1;
} my_obj_t;
/** my_objs can be freed at any time. The contents of
* my_data1 is undefined at allocation time.
*/umem_cache_t *my_obj_cache;
...my_obj_cache = umem_cache_create("my_obj", sizeof (my_obj_t),
0, NULL, NULL, NULL, NULL, NULL, 0); ...my_obj_t *cur = umem_cache_alloc(my_obj_cache, UMEM_DEFAULT);
... /* use cur */ ...umem_cache_free(my_obj_cache, cur);
... Example 2 Use an object with a mutex.#define _REENTRANT
#include
#include
typedef struct my_obj {
mutex_t my_mutex;
long my_data;
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Memory Allocation Library Functions umem_cache_create(3MALLOC)
} my_obj_t;
/** my_objs can only be freed when my_mutex is unlocked.
*/ intmy_obj_constructor(void *buf, void *ignored, int flags)
{my_obj_t *myobj = buf;
(void) mutex_init(&my_obj->my_mutex, USYNC_THREAD, NULL);
return (0); } voidmy_obj_destructor(void *buf, void *ignored)
{my_obj_t *myobj = buf;
(void) mutex_destroy(&my_obj->my_mutex);
}umem_cache_t *my_obj_cache;
...my_obj_cache = umem_cache_create("my_obj", sizeof (my_obj_t),
0, my_obj_constructor, my_obj_destructor, NULL, NULL,
NULL, 0); ...my_obj_t *cur = umem_cache_alloc(my_obj_cache, UMEM_DEFAULT);
cur->my_data = 0; /* cannot assume anything about my_data */
...umem_cache_free(my_obj_cache, cur);
... Example 3 Use a more complex object with a mutex.#define _REENTRANT
#include
#include
#include
typedef struct my_obj {
mutex_t my_mutex;
cond_t my_cv;
struct bar *my_barlist;
unsigned my_refcount;
} my_obj_t;
/*SunOS 5.11 Last change: 24 Mar 2008 6
Memory Allocation Library Functions umem_cache_create(3MALLOC)
* my_objs can only be freed when my_barlist == NULL,
* my_refcount == 0, there are no waiters on my_cv, and
* my_mutex is unlocked.
*/ intmy_obj_constructor(void *buf, void *ignored, int flags)
{my_obj_t *myobj = buf;
(void) mutex_init(&my_obj->my_mutex, USYNC_THREAD, NULL);
(void) cond_init(&my_obj->my_cv, USYNC_THREAD, NULL);
myobj->my_barlist = NULL;
myobj->my_refcount = 0;
return (0); } voidmy_obj_destructor(void *buf, void *ignored)
{my_obj_t *myobj = buf;
assert(myobj->my_refcount == 0);
assert(myobj->my_barlist == NULL);
(void) cond_destroy(&my_obj->my_cv);
(void) mutex_destroy(&my_obj->my_mutex);
}umem_cache_t *my_obj_cache;
...my_obj_cache = umem_cache_create("my_obj", sizeof (my_obj_t),
0, my_obj_constructor, my_obj_destructor, NULL, NULL,
NULL, 0); ...my_obj_t *cur = umem_cache_alloc(my_obj_cache, UMEM_DEFAULT);
... /* use cur */ ...umem_cache_free(my_obj_cache, cur);
...Example 4 Use objects with a subordinate buffer while reus-
ing callbacks.#include assert.h>
#include umem.h>
typedef struct my_obj {
char *my_buffer;
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Memory Allocation Library Functions umem_cache_create(3MALLOC)
size_t my_size;
} my_obj_t;
/** my_size and the my_buffer pointer should never be changed
*/ intmy_obj_constructor(void *buf, void *arg, int flags)
{size_t sz = (size_t)arg;
my_obj_t *myobj = buf;
if ((myobj->my_buffer = umem_alloc(sz, flags)) == NULL)
return (1);my_size = sz;
return (0); } voidmy_obj_destructor(void *buf, void *arg)
{size_t sz = (size_t)arg;
my_obj_t *myobj = buf;
assert(sz == buf->my_size);
umem_free(myobj->my_buffer, sz);
} ...umem_cache_t *my_obj_4k_cache;
umem_cache_t *my_obj_8k_cache;
...my_obj_cache_4k = umem_cache_create("my_obj_4k", sizeof (my_obj_t),
0, my_obj_constructor, my_obj_destructor, NULL,
(void *)4096, NULL, 0);my_obj_cache_8k = umem_cache_create("my_obj_8k", sizeof (my_obj_t),
0, my_obj_constructor, my_obj_destructor, NULL,
(void *)8192, NULL, 0); ...my_obj_t *my_obj_4k = umem_cache_alloc(my_obj_4k_cache,
UMEM_DEFAULT);
my_obj_t *my_obj_8k = umem_cache_alloc(my_obj_8k_cache,
UMEM_DEFAULT);
/* no assumptions should be made about the contents of the buffers */ ...SunOS 5.11 Last change: 24 Mar 2008 8
Memory Allocation Library Functions umem_cache_create(3MALLOC)
/* make sure to return them to the correct cache */umem_cache_free(my_obj_4k_cache, my_obj_4k);
umem_cache_free(my_obj_8k_cache, my_obj_8k);
...See the EXAMPLES section of umem_alloc(3MALLOC) for examples
involving the UMEM_NOFAIL flag.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
SEE ALSO
setcontext(2), atexit(3C), libumem(3LIB), longjmp(3C),swapcontext(3C), thr_exit(3C), umem_alloc(3MALLOC),
umem_debug(3MALLOC), attributes(5)
Bonwick, Jeff, "The Slab Allocator: An Object-Caching Kernel
Memory Allocator", Proceedings of the Summer 1994 Usenix Conference. Bonwick, Jeff and Jonathan Adams, "Magazines and vmem: Extending the Slab Allocator to Many CPUs and ArbitraryResources", Proceedings of the Summer 2001 Usenix Confer-
ence. WARNINGS Any of the following can cause undefined results: o Destroying a cache that has outstanding allocated buffers. o Using a cache after it has been destroyed.o Calling umem_cache_free() on the same buffer multi-
ple times.SunOS 5.11 Last change: 24 Mar 2008 9
Memory Allocation Library Functions umem_cache_create(3MALLOC)
o Passing a NULL pointer to umem_cache_free().
o Writing past the end of a buffer. o Reading from or writing to a buffer after it has been freed.o Performing UMEM_NOFAIL allocations from an
atexit(3C) handler.Per-cache callbacks can be called from a variety of con-
texts. The use of functions that modify the active context,such as setcontext(2), swapcontext(3C), and thr_exit(3C), or
functions that are unsafe for use in multithreaded applica-
tions, such as longjmp(3C) and siglongjmp(3C), result in undefined behavior. A constructor callback that performs allocations must passits flags argument unchanged to umem_alloc(3MALLOC) and
umem_cache_alloc(). Any allocations made with a different
flags argument results in undefined behavior. The construc-
tor must correctly handle the failure of any allocations it makes. NOTES Object caches make the following guarantees about objects: o If the cache has a constructor callback, it is applied to every object before it is returned fromumem_cache_alloc() for the first time.
o If the cache has a constructor callback, an objectpassed to umem_cache_free() and later returned from
umem_cache_alloc() is not modified between the two
events. o If the cache has a destructor, it is applied to all objects before their underlying storage is returned. No other guarantees are made. In particular, even if thereare buffers recently freed to the cache, umem_cache_alloc()
can fail.SunOS 5.11 Last change: 24 Mar 2008 10