1PMEMOBJ_ACTION(3) PMDK Programmer's Manual PMEMOBJ_ACTION(3)
2
6 pmemobj_reserve(), pmemobj_xreserve(), pmemobj_defer_free(), pmemo‐
7 bj_set_value(), pmemobj_publish(), pmemobj_tx_publish(), pmemobj_can‐
8 cel(), POBJ_RESERVE_NEW(), POBJ_RESERVE_ALLOC(), POBJ_XRE‐
9 SERVE_NEW(),POBJ_XRESERVE_ALLOC() - Delayed atomicity actions (EXPERI‐
10 MENTAL)
11
13 #include <libpmemobj.h>
14 PMEMoid pmemobj_reserve(PMEMobjpool *pop, struct pobj_action *act,
16 size_t size, uint64_t type_num); (EXPERIMENTAL)
17 PMEMoid pmemobj_xreserve(PMEMobjpool *pop, struct pobj_action *act,
18 size_t size, uint64_t type_num, uint64_t flags); (EXPERIMENTAL)
19 void pmemobj_defer_free(PMEMobjpool *pop, PMEMoid oid, struct pobj_action *act);
20 void pmemobj_set_value(PMEMobjpool *pop, struct pobj_action *act,
21 uint64_t *ptr, uint64_t value); (EXPERIMENTAL)
22 int pmemobj_publish(PMEMobjpool *pop, struct pobj_action *actv,
23 size_t actvcnt); (EXPERIMENTAL)
24 int pmemobj_tx_publish(struct pobj_action *actv, size_t actvcnt); (EXPERIMENTAL)
25 pmemobj_cancel(PMEMobjpool *pop, struct pobj_action *actv,
26 size_t actvcnt); (EXPERIMENTAL)
27 POBJ_RESERVE_NEW(pop, t, act) (EXPERIMENTAL)
29 POBJ_RESERVE_ALLOC(pop, t, size, act) (EXPERIMENTAL)
30 POBJ_XRESERVE_NEW(pop, t, act, flags) (EXPERIMENTAL)
31 POBJ_XRESERVE_ALLOC(pop, t, size, act, flags) (EXPERIMENTAL)
32
34 All of the functions described so far have an immediate effect on the
35 persistent state of the pool, and as such, the cost of maintaining
36 fail-safety is paid outright and, most importantly, in the calling
37 thread. This behavior makes implementing algorithms involving relaxed
38 consistency guarantees difficult, if not outright impossible.
39 The following set of functions introduce a mechanism that allows one to
41 delay the persistent publication of a set of prepared actions to an ar‐
42 bitrary moment in time of the execution of a program.
43 The publication is fail-safe atomic in the scope of the entire collec‐
45 tion of actions. If a program exits without publishing the actions, or
46 the actions are canceled, any resources reserved by those actions are
47 released and placed back in the pool.
48 A single action is represented by a single struct pobj_action. Func‐
50 tions that create actions take that structure by pointer, whereas func‐
51 tions that publish actions take array of actions and the size of the
52 array. The actions can be created, and published, from different
53 threads. When creating actions, the act argument must be non-NULL and
54 point to a struct pobj_action, the structure will be populated by the
55 function and must not be modified or deallocated until after publish‐
56 ing.
57 The pmemobj_reserve() functions performs a transient reservation of an
59 object. Behaves similarly to pmemobj_alloc(3), but performs no modifi‐
60 cation to the persistent state. The object returned by this function
61 can be freely modified without worrying about fail-safe atomicity until
62 the object has been published. Any modifications of the object must be
63 manually persisted, just like in the case of the atomic API.
64 pmemobj_xreserve() is equivalent to pmemobj_reserve(), but with an ad‐
66 ditional flags argument that is a bitmask of the following values:
67 · POBJ_XALLOC_ZERO - zero the object (and persist it)
69 · POBJ_CLASS_ID(class_id) - allocate the object from allocation class
71 class_id. The class id cannot be 0.
72 pmemobj_defer_free() function creates a deferred free action, meaning
74 that the provided object will be freed when the action is published.
75 Calling this function with a NULL OID is invalid and causes undefined
76 behavior.
77 The pmemobj_set_value function prepares an action that, once published,
79 will modify the memory location pointed to by ptr to value.
80 The pmemobj_publish function publishes the provided set of actions.
82 The publication is fail-safe atomic. Once done, the persistent state
83 will reflect the changes contained in the actions.
84 The pmemobj_tx_publish function moves the provided actions to the scope
86 of the transaction in which it is called. Only object reservations are
87 supported in transactional publish. Once done, the reserved objects
88 will follow normal transactional semantics. Can only be called during
89 TX_STAGE_WORK.
90 The pmemobj_cancel function releases any resources held by the provided
92 set of actions and invalidates all actions.
93 The POBJ_RESERVE_NEW macro is a typed variant of pmemobj_reserve. The
95 size of the reservation is determined from the provided type t.
96 The POBJ_RESERVE_ALLOC macro is a typed variant of pmemobj_reserve.
98 The size of the reservation is user-provided.
99 The POBJ_XRESERVE_NEW and the POBJ_XRESERVE_ALLOC macros are equivalent
101 to POBJ_RESERVE_NEW and the POBJ_RESERVE_ALLOC, but with an additional
102 flags argument defined for pmemobj_xreserve().
103
105 The following code shows atomic append of two objects into a singly
106 linked list.
107 struct list_node {
109 int value;
110 PMEMoid next;
111 };
112 /* statically allocate the array of actions */
113 struct pobj_action actv[4];
114 /* reserve, populate and persist the first object */
116 PMEMoid tail = pmemobj_reserve(pop, &actv[0], sizeof(struct list_node), 0);
117 if (TOID_IS_NULL(tail))
118 return -1;
119 D_RW(tail)->value = 1;
120 D_RW(tail)->next = OID_NULL;
121 pmemobj_persist(pop, D_RW(tail), sizeof(struct list_node));
122 /* reserve, populate and persist the second object */
124 PMEMoid head = pmemobj_reserve(pop, &actv[1], sizeof(struct list_node), 0);
125 if (TOID_IS_NULL(head))
126 return -1;
127 D_RW(head)->value = 2;
128 D_RW(head)->next = tail;
129 pmemobj_persist(pop, D_RW(head), sizeof(struct list_node));
130 /* create actions to set the PMEMoid to the new values */
132 pmemobj_set_value(pop, &actv[2], &D_RO(root)->head.pool_uuid_lo, head.pool_uuid_lo);
133 pmemobj_set_value(pop, &actv[3], &D_RO(root)->head.off, head.off);
134 /* atomically publish the above actions */
136 pmemobj_publish(pop, actv, 4);
137
139 On success, pmemobj_reserve() functions return a handle to the newly
140 reserved object, otherwise an OID_NULL is returned.
141 On success, pmemobj_tx_publish() returns 0, otherwise, stage changes to
143 TX_STAGE_ONABORT and errno is set appropriately
144 On success, pmemobj_publish() returns 0, otherwise, returns -1 and er‐
146 rno is set appropriately.
147
149 pmemobj_alloc(3), pmemobj_tx_alloc(3), libpmemobj(7) and
150 <http://pmem.io>
151PMDK - pmemobj API version 2.3 2018-10-01 PMEMOBJ_ACTION(3)