plucky (3) pmemobj_tx_xpublish.3.gz
NAME
pmemobj_reserve(), pmemobj_xreserve(), pmemobj_defer_free(), pmemobj_set_value(), pmemobj_publish(),
pmemobj_tx_publish(), pmemobj_tx_xpublish(), pmemobj_cancel(), POBJ_RESERVE_NEW(), POBJ_RESERVE_ALLOC(),
POBJ_XRESERVE_NEW(),POBJ_XRESERVE_ALLOC() - Delayed atomicity actions (EXPERIMENTAL)
SYNOPSIS
#include <libpmemobj.h>
PMEMoid pmemobj_reserve(PMEMobjpool *pop, struct pobj_action *act,
size_t size, uint64_t type_num); (EXPERIMENTAL)
PMEMoid pmemobj_xreserve(PMEMobjpool *pop, struct pobj_action *act,
size_t size, uint64_t type_num, uint64_t flags); (EXPERIMENTAL)
void pmemobj_defer_free(PMEMobjpool *pop, PMEMoid oid, struct pobj_action *act);
void pmemobj_set_value(PMEMobjpool *pop, struct pobj_action *act,
uint64_t *ptr, uint64_t value); (EXPERIMENTAL)
int pmemobj_publish(PMEMobjpool *pop, struct pobj_action *actv,
size_t actvcnt); (EXPERIMENTAL)
int pmemobj_tx_publish(struct pobj_action *actv, size_t actvcnt); (EXPERIMENTAL)
int pmemobj_tx_xpublish(struct pobj_action *actv, size_t actvcnt, uint64_t flags); (EXPERIMENTAL)
void pmemobj_cancel(PMEMobjpool *pop, struct pobj_action *actv,
size_t actvcnt); (EXPERIMENTAL)
POBJ_RESERVE_NEW(pop, t, act) (EXPERIMENTAL)
POBJ_RESERVE_ALLOC(pop, t, size, act) (EXPERIMENTAL)
POBJ_XRESERVE_NEW(pop, t, act, flags) (EXPERIMENTAL)
POBJ_XRESERVE_ALLOC(pop, t, size, act, flags) (EXPERIMENTAL)
DESCRIPTION
All of the functions described so far have an immediate effect on the persistent state of the pool, and
as such, the cost of maintaining fail-safety is paid outright and, most importantly, in the calling
thread. This behavior makes implementing algorithms involving relaxed consistency guarantees difficult,
if not outright impossible.
The following set of functions introduce a mechanism that allows one to delay the persistent publication
of a set of prepared actions to an arbitrary moment in time of the execution of a program.
The publication is fail-safe atomic in the scope of the entire collection of actions. If a program exits
without publishing the actions, or the actions are canceled, any resources reserved by those actions are
released and placed back in the pool.
A single action is represented by a single struct pobj_action. Functions that create actions take that
structure by pointer, whereas functions that publish actions take array of actions and the size of the
array. The actions can be created, and published, from different threads. When creating actions, the
act argument must be non-NULL and point to a struct pobj_action, the structure will be populated by the
function and must not be modified or deallocated until after publishing.
The pmemobj_reserve() functions performs a transient reservation of an object. Behaves similarly to
pmemobj_alloc(3), but performs no modification to the persistent state. The object returned by this
function can be freely modified without worrying about fail-safe atomicity until the object has been
published. Any modifications of the object must be manually persisted, just like in the case of the
atomic API.
pmemobj_xreserve() is equivalent to pmemobj_reserve(), but with an additional flags argument that is a
bitmask of the following values:
• POBJ_XALLOC_ZERO - zero the allocated object (and persist it)
• POBJ_CLASS_ID(class_id) - allocate an object from the allocation class class_id. The class id cannot
be 0.
• POBJ_ARENA_ID(arena_id) - allocate an object from the arena specified by arena_id. The arena must
exist, otherwise, the behavior is undefined. If arena_id is equal 0, then arena assigned to the
current thread will be used.
pmemobj_defer_free() function creates a deferred free action, meaning that the provided object will be
freed when the action is published. Calling this function with a NULL OID is invalid and causes
undefined behavior.
The pmemobj_set_value function prepares an action that, once published, will modify the memory location
pointed to by ptr to value.
The pmemobj_publish function publishes the provided set of actions. The publication is fail-safe atomic.
Once done, the persistent state will reflect the changes contained in the actions.
The pmemobj_tx_publish function moves the provided actions to the scope of the transaction in which it is
called. Only object reservations are supported in transactional publish. Once done, the reserved
objects will follow normal transactional semantics. Can only be called during TX_STAGE_WORK.
The pmemobj_tx_xpublish() function behaves exactly the same as pmemobj_tx_publish() when flags equals
zero. flags is a bitmask of the following values:
• POBJ_XPUBLISH_NO_ABORT - if the function does not end successfully, do not abort the transaction.
The pmemobj_cancel function releases any resources held by the provided set of actions and invalidates
all actions.
The POBJ_RESERVE_NEW macro is a typed variant of pmemobj_reserve. The size of the reservation is
determined from the provided type t.
The POBJ_RESERVE_ALLOC macro is a typed variant of pmemobj_reserve. The size of the reservation is user-
provided.
The POBJ_XRESERVE_NEW and the POBJ_XRESERVE_ALLOC macros are equivalent to POBJ_RESERVE_NEW and the
POBJ_RESERVE_ALLOC, but with an additional flags argument defined for pmemobj_xreserve().
EXAMPLES
The following code shows atomic append of two objects into a singly linked list.
struct list_node {
int value;
PMEMoid next;
};
/* statically allocate the array of actions */
struct pobj_action actv[4];
/* reserve, populate and persist the first object */
PMEMoid tail = pmemobj_reserve(pop, &actv[0], sizeof(struct list_node), 0);
if (TOID_IS_NULL(tail))
return -1;
D_RW(tail)->value = 1;
D_RW(tail)->next = OID_NULL;
pmemobj_persist(pop, D_RW(tail), sizeof(struct list_node));
/* reserve, populate and persist the second object */
PMEMoid head = pmemobj_reserve(pop, &actv[1], sizeof(struct list_node), 0);
if (TOID_IS_NULL(head))
return -1;
D_RW(head)->value = 2;
D_RW(head)->next = tail;
pmemobj_persist(pop, D_RW(head), sizeof(struct list_node));
/* create actions to set the PMEMoid to the new values */
pmemobj_set_value(pop, &actv[2], &D_RO(root)->head.pool_uuid_lo, head.pool_uuid_lo);
pmemobj_set_value(pop, &actv[3], &D_RO(root)->head.off, head.off);
/* atomically publish the above actions */
pmemobj_publish(pop, actv, 4);
RETURN VALUE
On success, pmemobj_reserve() functions return a handle to the newly reserved object. Otherwise an
OID_NULL is returned.
On success, pmemobj_tx_publish() returns 0. Otherwise, the transaction is aborted, the stage is changed
to TX_STAGE_ONABORT and errno is set appropriately.
On success, pmemobj_tx_xpublish() returns 0. Otherwise, the error number is returned, errno is set and
when flags do not contain POBJ_XPUBLISH_NO_ABORT, the transaction is aborted.
On success, pmemobj_publish() returns 0. Otherwise, returns -1 and errno is set appropriately.
SEE ALSO
pmemobj_alloc(3), pmemobj_tx_alloc(3), libpmemobj(7) and <https://pmem.io>