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 void 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)
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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 allocated object (and persist it)
69 · POBJ_CLASS_ID(class_id) - allocate an object from the allocation
71 class class_id. The class id cannot be 0.
72 · POBJ_ARENA_ID(arena_id) - allocate an object from the arena specified
74 by arena_id. The arena must exist, otherwise, the behavior is unde‐
75 fined. If arena_id is equal 0, then arena assigned to the current
76 thread will be used.
77 pmemobj_defer_free() function creates a deferred free action, meaning
79 that the provided object will be freed when the action is published.
80 Calling this function with a NULL OID is invalid and causes undefined
81 behavior.
82 The pmemobj_set_value function prepares an action that, once published,
84 will modify the memory location pointed to by ptr to value.
85 The pmemobj_publish function publishes the provided set of actions.
87 The publication is fail-safe atomic. Once done, the persistent state
88 will reflect the changes contained in the actions.
89 The pmemobj_tx_publish function moves the provided actions to the scope
91 of the transaction in which it is called. Only object reservations are
92 supported in transactional publish. Once done, the reserved objects
93 will follow normal transactional semantics. Can only be called during
94 TX_STAGE_WORK.
95 The pmemobj_cancel function releases any resources held by the provided
97 set of actions and invalidates all actions.
98 The POBJ_RESERVE_NEW macro is a typed variant of pmemobj_reserve. The
100 size of the reservation is determined from the provided type t.
101 The POBJ_RESERVE_ALLOC macro is a typed variant of pmemobj_reserve.
103 The size of the reservation is user-provided.
104 The POBJ_XRESERVE_NEW and the POBJ_XRESERVE_ALLOC macros are equivalent
106 to POBJ_RESERVE_NEW and the POBJ_RESERVE_ALLOC, but with an additional
107 flags argument defined for pmemobj_xreserve().
108
110 The following code shows atomic append of two objects into a singly
111 linked list.
112 struct list_node {
114 int value;
115 PMEMoid next;
116 };
117 /* statically allocate the array of actions */
118 struct pobj_action actv[4];
119 /* reserve, populate and persist the first object */
121 PMEMoid tail = pmemobj_reserve(pop, &actv[0], sizeof(struct list_node), 0);
122 if (TOID_IS_NULL(tail))
123 return -1;
124 D_RW(tail)->value = 1;
125 D_RW(tail)->next = OID_NULL;
126 pmemobj_persist(pop, D_RW(tail), sizeof(struct list_node));
127 /* reserve, populate and persist the second object */
129 PMEMoid head = pmemobj_reserve(pop, &actv[1], sizeof(struct list_node), 0);
130 if (TOID_IS_NULL(head))
131 return -1;
132 D_RW(head)->value = 2;
133 D_RW(head)->next = tail;
134 pmemobj_persist(pop, D_RW(head), sizeof(struct list_node));
135 /* create actions to set the PMEMoid to the new values */
137 pmemobj_set_value(pop, &actv[2], &D_RO(root)->head.pool_uuid_lo, head.pool_uuid_lo);
138 pmemobj_set_value(pop, &actv[3], &D_RO(root)->head.off, head.off);
139 /* atomically publish the above actions */
141 pmemobj_publish(pop, actv, 4);
142
144 On success, pmemobj_reserve() functions return a handle to the newly
145 reserved object, otherwise an OID_NULL is returned.
146 On success, pmemobj_tx_publish() returns 0, otherwise, stage changes to
148 TX_STAGE_ONABORT and errno is set appropriately
149 On success, pmemobj_publish() returns 0, otherwise, returns -1 and er‐
151 rno is set appropriately.
152
154 pmemobj_alloc(3), pmemobj_tx_alloc(3), libpmemobj(7) and
155 <http://pmem.io>
156PMDK - pmemobj API version 2.3 2019-03-01 PMEMOBJ_ACTION(3)