pmemobj_alloc - Man Page

non-transactional atomic allocations

Synopsis

#include <libpmemobj.h>

typedef int (*pmemobj_constr)(**PMEMobjpool *pop, void *ptr, void *arg);
int pmemobj_alloc(PMEMobjpool *pop, PMEMoid *oidp, size_t size,
    uint64_t type_num, pmemobj_constr constructor, void *arg);
int pmemobj_xalloc(PMEMobjpool *pop, PMEMoid *oidp, size_t size,
    uint64_t type_num, uint64_t flags, pmemobj_constr constructor,
    void *arg); (EXPERIMENTAL)
int pmemobj_zalloc(PMEMobjpool *pop, PMEMoid *oidp, size_t size,
    uint64_t type_num);
void pmemobj_free(PMEMoid *oidp);
int pmemobj_realloc(PMEMobjpool *pop, PMEMoid *oidp, size_t size,
    uint64_t type_num);
int pmemobj_zrealloc(PMEMobjpool *pop, PMEMoid *oidp, size_t size,
    uint64_t type_num);
int pmemobj_strdup(PMEMobjpool *pop, PMEMoid *oidp, const char *s,
    uint64_t type_num);
int pmemobj_wcsdup(PMEMobjpool *pop, PMEMoid *oidp, const wchar_t *s,
    uint64_t type_num);
size_t pmemobj_alloc_usable_size(PMEMoid oid);
int pmemobj_defrag(PMEMobjpool *pop, PMEMoid **oidv, size_t oidcnt,
    struct pobj_defrag_result *result);

POBJ_NEW(PMEMobjpool *pop, TOID *oidp, TYPE, pmemobj_constr constructor,
    void *arg)
POBJ_ALLOC(PMEMobjpool *pop, TOID *oidp, TYPE, size_t size,
    pmemobj_constr constructor, void *arg)
POBJ_ZNEW(PMEMobjpool *pop, TOID *oidp, TYPE)
POBJ_ZALLOC(PMEMobjpool *pop, TOID *oidp, TYPE, size_t size)
POBJ_REALLOC(PMEMobjpool *pop, TOID *oidp, TYPE, size_t size)
POBJ_ZREALLOC(PMEMobjpool *pop, TOID *oidp, TYPE, size_t size)
POBJ_FREE(TOID *oidp)

Description

Functions described in this document provide the mechanism to allocate, resize and free objects from the persistent memory pool in a thread-safe and fail-safe manner. All the routines are atomic with respect to other threads and any power-fail interruptions. If any of these operations is torn by program failure or system crash, on recovery they are guaranteed to be entirely completed or discarded, leaving the persistent memory heap and internal object containers in a consistent state.

All these functions should be used outside transactions. If executed within an open transaction they are considered durable immediately after completion. Changes made with these functions will not be rolled back if the transaction is aborted or interrupted. They have no information about other changes made by transactional API, so if the same data is modified in a single transaction using transactional and then non-transactional API, transaction abort will likely corrupt the data.

The allocations are always aligned to a cache-line boundary.

The pmemobj_constr type represents a constructor for atomic allocation from the persistent memory heap associated with memory pool pop. ptr is a pointer to the allocated memory area and arg is a user-defined argument passed to the constructor.

The pmemobj_alloc() function allocates a new object from the persistent memory heap associated with memory pool pop. The PMEMoid of the allocated object is stored in oidp. If oidp is NULL, then the newly allocated object may be accessed only by iterating objects in the object container associated with the type number type_num, as described in POBJ_FOREACH(3). If oidp points to a memory location from the pmemobj heap, oidp is modified atomically. Before returning, pmemobj_alloc() calls the constructor function, passing the pool handle pop, the pointer to the newly allocated object in ptr, and the arg argument. It is guaranteed that the allocated object is either properly initialized, or if the allocation is interrupted before the constructor completes, the memory space reserved for the object is reclaimed. size can be any non-zero value; however, due to internal padding and object metadata, the actual size of the allocation will differ from the requested size by at least 64 bytes. For this reason, making allocations of a size less than 64 bytes is extremely inefficient and discouraged. The allocated object is added to the internal container associated with type_num.

pmemobj_xalloc() is equivalent to pmemobj_alloc(), but with an additional flags argument that is a bitmask of the following values:

The pmemobj_zalloc() function allocates a new zeroed object from the persistent memory heap associated with memory pool pop. The PMEMoid of the allocated object is stored in oidp. If oidp is NULL, then the newly allocated object may be accessed only by iterating objects in the object container associated with the type number type_num, as described in POBJ_FOREACH(3). If oidp points to a memory location from the pmemobj heap, oidp is modified atomically. size can be any non-zero value; however, due to internal padding and object metadata, the actual size of the allocation will differ from the requested one by at least 64 bytes. For this reason, making allocations of a size less than 64 bytes is extremely inefficient and discouraged. The allocated object is added to the internal container associated with type_num.

The pmemobj_free() function frees the memory space represented by oidp, which must have been allocated by a previous call to pmemobj_alloc(), pmemobj_xalloc(), pmemobj_zalloc(), pmemobj_realloc(), or pmemobj_zrealloc(). pmemobj_free() provides the same semantics as free(3), but instead of operating on the process heap supplied by the system, it operates on the persistent memory heap. If oidp is OID_NULL, no operation is performed. If oidp is NULL or if it points to the root object’s OID, the behavior of pmemobj_free() is undefined. oidp is set to OID_NULL after the memory is freed. If oidp points to a memory location from the pmemobj heap, oidp is modified atomically.

The pmemobj_realloc() function changes the size of the object represented by oidp to size bytes. pmemobj_realloc() provides similar semantics to realloc(3), but operates on the persistent memory heap associated with memory pool pop. The resized object is also added or moved to the internal container associated with type number type_num. The contents will be unchanged in the range from the start of the region up to the minimum of the old and new sizes. If the new size is larger than the old size, the added memory will not be initialized. If oidp is OID_NULL, then the call is equivalent to pmemobj_alloc(pop, size, type_num). If size is equal to zero, and oidp is not OID_NULL, then the call is equivalent to pmemobj_free(oid). Unless oidp is OID_NULL, it must have been allocated by an earlier call to pmemobj_alloc(), pmemobj_xalloc(), pmemobj_zalloc(), pmemobj_realloc(), or pmemobj_zrealloc(). Note that the object handle value may change as a result of reallocation. If the object was moved, the memory space represented by oid is reclaimed. If oidp points to a memory location from the pmemobj heap, oidp is modified atomically. If oidp is NULL or if it points to the root object’s OID, the behavior of pmemobj_realloc() is undefined.

pmemobj_zrealloc() is equivalent to pmemobj_realloc(), except that if the new size is larger than the old size, the added memory will be zeroed.

The pmemobj_strdup() function stores a handle to a new object in oidp which is a duplicate of the string s. pmemobj_strdup() provides the same semantics as strdup(3), but operates on the persistent memory heap associated with memory pool pop. If oidp is NULL, then the newly allocated object may be accessed only by iterating objects in the object container associated with type number type_num, as described in POBJ_FOREACH(3). If oidp points to a memory location from the pmemobj heap, oidp is modified atomically. The allocated string object is also added to the internal container associated with type number type_num. Memory for the new string is obtained with pmemobj_alloc(), on the given memory pool, and can be freed with pmemobj_free() on the same memory pool.

pmemobj_wcsdup() is equivalent to pmemobj_strdup(), but operates on a wide character string (wchar_t) rather than a standard character string.

The pmemobj_alloc_usable_size() function provides the same semantics as malloc_usable_size(3), but instead of the process heap supplied by the system, it operates on the persistent memory heap.

The POBJ_NEW() macro is a wrapper around the pmemobj_alloc() function. Instead of taking a pointer to PMEMoid, it takes a pointer to the typed OID of type name TYPE, and passes the size and type number from the typed OID to pmemobj_alloc().

The POBJ_ALLOC() macro is equivalent to POBJ_NEW, except that instead of using the size of the typed OID, passes size to pmemobj_alloc().

The POBJ_ZNEW() macro is a wrapper around the pmemobj_zalloc() function. Instead of taking a pointer to PMEMoid, it takes a pointer to the typed OID of type name TYPE, and passes the size and type number from the typed OID to pmemobj_zalloc().

The POBJ_ZALLOC() macro is equivalent to POBJ_ZNEW, except that instead of using the size of the typed OID, passes size to pmemobj_zalloc().

The POBJ_REALLOC() macro is a wrapper around the pmemobj_realloc() function. Instead of taking a pointer to PMEMoid, it takes a pointer to the typed OID of type name TYPE, and passes the type number from the typed OID to pmemobj_realloc().

The POBJ_ZREALLOC() macro is a wrapper around the pmemobj_zrealloc() function. Instead of taking a pointer to PMEMoid, it takes a pointer to the typed OID of type name TYPE, and passes the type number from the typed OID to pmemobj_zrealloc().

The POBJ_FREE() macro is a wrapper around the pmemobj_free() function which takes a pointer to the typed OID instead of to PMEMoid.

The pmemobj_defrag() function performs defragmentation on the objects provided through the array of pointers to PMEMoids oidv with size oidcnt. If an object from the provided array is selected to be moved to a new location in the heap, it is reallocated and all provided pointers to that object are atomically updated. To maintain data structure consistency, applications should always provide all pointers for an object to pmemobj_defrag method. This ensures that, even in the presence of failures, all pointers to the object will either point to the old or a new location. All objects and pointers to objects should belong to the pool pop or, in case of pointers, can also reside in volatile memory. Defragmentation across pools is not supported. Objects in the array that are OID_NULL are skipped over and no operation is performed on them. All other objects must have been allocated by an earlier call to pmemobj_alloc(), pmemobj_xalloc(), pmemobj_zalloc(), pmemobj_realloc(), pmemobj_zrealloc(), pmemobj_strdup() or pmemobj_wcsdup(). The result variable is an instance of struct pobj_defrag_result and, if not NULL, can be used to read total, the number of objects found that were processed, and relocated, the number of objects that were relocated during defragmentation. These variables are always initialized and can be non-zero, even if the return value of pmemobj_defrag() indicated a failure. This is because the failure might have occurred after some objects were already processed.

Return Value

On success, pmemobj_alloc() and pmemobj_xalloc return 0. If oidp is not NULL, the PMEMoid of the newly allocated object is stored in oidp. If the allocation fails, -1 is returned and errno is set appropriately. If the constructor returns a non-zero value, the allocation is canceled, -1 is returned, and errno is set to ECANCELED. If size equals 0, or the flags for pmemobj_xalloc are invalid, -1 is returned, errno is set to EINVAL, and oidp is left untouched.

On success, pmemobj_zalloc() returns 0. If oidp is not NULL, the PMEMoid of the newly allocated object is stored in oidp. If the allocation fails, it returns -1 and sets errno appropriately. If size equals 0, it returns -1, sets errno to EINVAL, and leaves oidp untouched.

The pmemobj_free() function returns no value.

On success, pmemobj_realloc() and pmemobj_zrealloc() return 0 and update oidp if necessary. On error, they return -1 and set errno appropriately.

On success, pmemobj_strdup() and pmemobj_wcsdup() return 0. If oidp is not NULL, the PMEMoid of the duplicated string object is stored in oidp. If s is NULL, they return -1, set errno to EINVAL, and leave oidp untouched. On other errors, they return -1 and set errno appropriately.

The pmemobj_alloc_usable_size() function returns the number of usable bytes in the object represented by oid. If oid is OID_NULL, it returns 0.

On success, pmemobj_defrag() returns 0. If defragmentation was unsuccessful or only partially successful (i.e. if it was aborted halfway through due to lack of resources), -1 is returned.

See Also

free(3), POBJ_FOREACH(3), realloc(3), strdup(3), wcsdup(3), libpmemobj(7) and <https://pmem.io>

Referenced By

libpmemobj(7), pmemobj_action(3), pmemobj_mutex_zero(3), pmemobj_tx_begin(3).

The man pages pmemobj_alloc_usable_size(3), pmemobj_defrag(3), pmemobj_free(3), pmemobj_realloc(3), pmemobj_strdup(3), pmemobj_wcsdup(3), pmemobj_xalloc(3), pmemobj_zalloc(3), pmemobj_zrealloc(3), pobj_alloc(3), pobj_free(3), pobj_new(3), pobj_realloc(3), pobj_zalloc(3), pobj_znew(3) and pobj_zrealloc(3) are aliases of pmemobj_alloc(3).

2020-07-03 PMDK - pmemobj API version 2.3 PMDK Programmer's Manual