PMEMOBJ_MEMCPY_PERSIST(3)

NAME

pmemobj_memcpy_persist(), pmemobj_memset_persist(), pmemobj_persist(), pmemobj_flush(), pmemobj_drain() - low-level memory manipulation functions

SYNOPSIS

    #include <libpmemobj.h>

    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);
    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);

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.

The pmemobj_memcpy_persist() and pmemobj_memset_persist() functions provide the same memory copying as their namesakes memcpy(3), and memset(3), and ensure that the result has been flushed to persistence before returning.

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).

RETURN VALUE

The pmemobj_memcpy_persist() and pmemobj_memset_persist() functions return the same values as their namesakes memcpy(3), and memset(3).

pmemobj_persist(), pmemobj_flush() and pmemobj_drain() return no value.

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 <http://pmem.io>