NAME

       memcached_cas - Atomic Compare and Swap

SYNOPSIS

       #include <libmemcached/memcached.h>
              Compile and link with -lmemcached

       memcached_return_t  memcached_cas(memcached_st  *ptr,  const char *key, size_t key_length,
       const char *value, size_t value_length, time_t expiration, uint32_t flags, uint64_t cas)

       memcached_return_t memcached_cas_by_key(memcached_st *ptr, const char  *group_key,  size_t
       group_key_length,   const   char  *key,  size_t  key_length,  const  char  *value,  size_t
       value_length, time_t expiration, uint32_t flags, uint64_t cas)

              Parameters

                     • ptr -- pointer to an initialized memcached_st struct

                     • group_key -- key namespace

                     • group_key_length -- length of the group_key without any trailing zero

                     • key -- the key to check

                     • key_length -- the length of the key without any trailing zero

                     • value -- the value to set

                     • value_length -- the length of the value without any trailing zero

                     • expiration -- expiration time  as  unix  timestamp  or  relative  time  in
                       seconds

                     • flags -- 16 bit flags

                     • cas -- the cas value to compare

              Returns
                     memcached_return_t indicating success

DESCRIPTION

       memcached_cas()  overwrites  data in the server as long as the cas value is still the same
       in the server. You can get the cas value of a result by calling memcached_result_cas()  on
       a memcached_result_st structure.

       memcached_cas_by_key()  method  behaves  in  a  similar  way  as the non key methods.  The
       difference is that it uses the group_key parameter to map objects to particular servers.

       memcached_cas() is tested with the MEMCACHED_BEHAVIOR_USE_UDP behavior  enabled.  However,
       when  using  these  operations  with this behavior on, there are limits to the size of the
       payload being sent to the server.  The reason for  these  limits  is  that  the  Memcached
       Server does not allow multi-datagram requests and the current server implementation sets a
       datagram size to 1400 bytes. Due to protocol  overhead,  the  actual  limit  of  the  user
       supplied  data  is less than 1400 bytes and depends on the protocol in use as, well as the
       operation    being    executed.    When    running    with    the     binary     protocol,
       MEMCACHED_BEHAVIOR_BINARY_PROTOCOL,  the  size of the key,value, flags and expiry combined
       may not exceed 1368  bytes.  When  running  with  the  ASCII  protocol,  the  exact  limit
       fluctuates depending on which function is being executed and whether the function is a cas
       operation or not. For non-cas  ASCII  set  operations,  there  are  at  least  1335  bytes
       available  to  split  among the key, key_prefix, and value; for cas ASCII operations there
       are at least 1318 bytes available to split among the key, key_prefix  and  value.  If  the
       total    size    of   the   command,   including   overhead,   exceeds   1400   bytes,   a
       MEMCACHED_WRITE_FAILURE will be returned.

RETURN VALUE

       All methods return a value of type memcached_return_t.   On  success  the  value  will  be
       MEMCACHED_SUCCESS.   Use  memcached_strerror()  to  translate  this  value  to a printable
       string.

SEE ALSO

       memcached(1) libmemcached(3)  memcached_strerror(3)  memcached_set(3)  memcached_append(3)
       memcached_add(3) memcached_prepend(3) memcached_replace(3)