module Netmcore_mempool:Memory poolssig
..end
A memory pool is a block of shared memory that is set aside for storing shared data structures. The pool needs to be created before the worker processes are forked off that are going to use the pool. The worker processes do not map the pool to some random address, but rather the processes inherit the pool from the common master process which ensures that all processes will see the pool at the same address.
In order to allow inheritance, the function Netmcore.start
for starting workers needs to get an additional argument
~inherit_resources
. The resource ID of the pool must be put
into this list - otherwise the worker does not get access to
the pool.
It is not possible to enlarge the pool later (because of the
inheritance method for making the pool accessible). It is advised
to make the pool large enough for all possible data cases, and
to let the user configure this size.
exception Out_of_pool_memory
val create_mempool : ?alloc_really:bool -> int -> Netmcore.res_id
Note that the process calling this function cannot use the pool,
but only worker processes that are forked later. It is possible
to call create_mempool
before running Netmcore.startup
.
Option alloc_really
: On some operating systems (namely Linux)
shared memory is not fully included into the memory bookkeeping
as long as nothing is written into it (so-called
overcommitment). This means that the memory is not reserved, and
when something is written for the first time, it might happen
that the system cannot grant the request. The consequence is a
bus error. By setting alloc_really
to true, all allocated
memory pages are immediately written to, and thus the problem is
avoided (or better, if memory is really tight, you get the bus
error now immediately, at least).
val alloc_mem : Netmcore.res_id -> int -> Netsys_mem.memory
memory
object. The size is rounded up to the next
multiple of pages.
Blocks are actually allocated in units of pages.
Raises Out_of_pool_memory
if there is not enough contiguous
space in the pool.
val size_mem : Netmcore.res_id -> Netsys_mem.memory -> int
Not_found
val size_mem_at_addr : Netmcore.res_id -> nativeint -> int
Not_found
val free_mem : Netmcore.res_id -> Netsys_mem.memory -> unit
val stats : Netmcore.res_id -> int * int * int
(total, free, contiguous)
wheretotal
is the total size of the poolfree
is the number of free bytescontiguous
is the size of the largest contiguous free blockval debug_info : Netmcore.res_id -> string
val shm_name : Netmcore.res_id -> string
module Debug:sig
..end