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NAME

pmemobj_persist(), pmemobj_xpersist(), pmemobj_flush(), pmemobj_xflush(), pmemobj_drain(), pmemobj_memcpy(), pmemobj_memmove(), pmemobj_memset(), pmemobj_memcpy_persist(), pmemobj_memset_persist() - low-level memory manipulation functions

SYNOPSIS

    #include <libpmemobj.h>
    void pmemobj_persist(PMEMobjpool *pop, const void *addr,
        size_t len);
    void pmemobj_flush(PMEMobjpool *pop, const void *addr,
        size_t len);
    void pmemobj_drain(PMEMobjpool *pop);
    int pmemobj_xpersist(PMEMobjpool *pop, const void *addr,
        size_t len, unsigned flags);
    int pmemobj_xflush(PMEMobjpool *pop, const void *addr,
        size_t len, unsigned flags);
    void *pmemobj_memcpy(PMEMobjpool *pop, void *dest,
        const void *src, size_t len, unsigned flags);
    void *pmemobj_memmove(PMEMobjpool *pop, void *dest,
        const void *src, size_t len, unsigned flags);
    void *pmemobj_memset(PMEMobjpool *pop, void *dest,
        int c, size_t len, unsigned flags);
    void *pmemobj_memcpy_persist(PMEMobjpool *pop, void *dest,
        const void *src, size_t len);
    void *pmemobj_memset_persist(PMEMobjpool *pop, void *dest,
        int c, size_t len);

DESCRIPTION

The libpmemobj-specific low-level memory manipulation functions described here leverage the knowledge of the additional configuration options available for libpmemobj(7) pools, such as replication. They also take advantage of the type of storage behind the pool and use appropriate flush/drain functions. It is advised to use these functions in conjunction with libpmemobj(7) objects rather than using low-level memory manipulation functions from libpmem.

pmemobj_persist() forces any changes in the range [addr, addr+len) to be stored durably in persistent memory. Internally this may call either pmem_msync(3) or pmem_persist(3). There are no alignment restrictions on the range described by addr and len, but pmemobj_persist() may expand the range as necessary to meet platform alignment requirements.

    WARNING: Like msync(2), there is nothing atomic or transactional about this call. Any unwritten stores in the given range will be written, but some stores may have already been written by virtue of normal cache eviction/replacement policies. Correctly written code must not depend on stores waiting until pmemobj_persist() is called to become persistent - they can become persistent at any time before pmemobj_persist() is called.

The pmemobj_flush() and pmemobj_drain() functions provide partial versions of the pmemobj_persist() function described above. These functions allow advanced programs to create their own variations of pmemobj_persist(). For example, a program that needs to flush several discontiguous ranges can call pmemobj_flush() for each range and then follow up by calling pmemobj_drain() once. For more information on partial flushing operations, see pmem_flush(3).

pmemobj_xpersist() is a version of pmemobj_persist() function with additional flags argument. It supports only the PMEMOBJ_F_RELAXED flag. This flag indicates that memory transfer operation does not require 8-byte atomicity guarantees.

pmemobj_xflush() is a version of pmemobj_flush() function with additional flags argument. It supports only the PMEMOBJ_F_RELAXED flag.

The pmemobj_memmove(), pmemobj_memcpy() and pmemobj_memset() functions provide the same memory copying as their namesakes memmove(3), memcpy(3), and memset(3), and ensure that the result has been flushed to persistence before returning (unless PMEMOBJ_MEM_NOFLUSH flag was used). Valid flags for those functions:

•   PMEMOBJ_F_RELAXED - This flag indicates that memory transfer operation does not require 8-byte atomicity guarantees.

•   PMEMOBJ_F_MEM_NOFLUSH - Don’t flush anything. This implies PMEMOBJ_F_MEM_NODRAIN. Using this flag only makes sense when it’s followed by any function that flushes data.

The remaining flags say how the operation should be done, and are merely hints.

•   PMEMOBJ_F_MEM_NONTEMPORAL - Use non-temporal instructions. This flag is mutually exclusive with PMEMOBJ_F_MEM_TEMPORAL. On x86_64 this flag is mutually exclusive with PMEMOBJ_F_MEM_NOFLUSH.

•   PMEMOBJ_F_MEM_TEMPORAL - Use temporal instructions. This flag is mutually exclusive with PMEMOBJ_F_MEM_NONTEMPORAL.

•   PMEMOBJ_F_MEM_WC - Use write combining mode. This flag is mutually exclusive with PMEMOBJ_F_MEM_WB. On x86_64 this is an alias for PMEMOBJ_F_MEM_NONTEMPORAL. On x86_64 this flag is mutually exclusive with PMEMOBJ_F_MEM_NOFLUSH.

•   PMEMOBJ_F_MEM_WB - Use write back mode. This flag is mutually exclusive with PMEMOBJ_F_MEM_WC. On x86_64 this is an alias for PMEMOBJ_F_MEM_TEMPORAL.

pmemobj_memcpy_persist() is an alias for pmemobj_memcpy() with flags equal to 0.

pmemobj_memset_persist() is an alias for pmemobj_memset() with flags equal to 0.

RETURN VALUE

pmemobj_memmove(), pmemobj_memcpy(), pmemobj_memset(), pmemobj_memcpy_persist() and pmemobj_memset_persist() return destination buffer.

pmemobj_persist(), pmemobj_flush() and pmemobj_drain() do not return any value.

pmemobj_xpersist() and pmemobj_xflush() returns non-zero value and sets errno to EINVAL only if not supported flags has been provided.

EXAMPLES

The following code is functionally equivalent to pmemobj_memcpy_persist():

    void *
    pmemobj_memcpy_persist(PMEMobjpool *pop, void *dest,
        const void *src, size_t len)
    {
        void *retval = memcpy(dest, src, len);
        pmemobj_persist(pop, dest, len);
        return retval;
    }

pmemobj_persist() can be thought of as this:

    void
    pmemobj_persist(PMEMobjpool *pop, const void *addr, size_t len)
    {
        /* flush the processor caches */
        pmemobj_flush(pop, addr, len);
        /* wait for any pmem stores to drain from HW buffers */
        pmemobj_drain(pop);
    }

SEE ALSO

memcpy(3), memset(3), pmem_msync(3), pmem_persist(3), libpmem(7) libpmemobj(7) and <https://pmem.io>