Module fmmap 

Custom implementation of mmap(2)

Constraints

FrozenMMap treats the mapped file as raw storage for values of T. Because of that, T must be a POD type which is safe to persist and later reinterpret from bytes.

Required properties for T,

• Must use #[repr(C)]
• Should be 8-bytes aligned
• Must not implement Drop
• size_of::<T>() should be multiple of 8

NOTE: T must not contain heap owning or process-local pointers like Vec, String, Box, references and function pointers, or other fields whose bit-pattern is not stable across reopen.

These constrains are enforced as FrozenMMap does not serialize or deserialize values. It directly reads and writes T inside a memory mapped file. That means T must have a stable layout and must remain valid when the file is reopened in a later process.

Example

use frozen_core::fmmap::{FrozenMMap, FMCfg};

const MODULE_ID: u8 = 0;

let dir = tempfile::tempdir().unwrap();
let path = dir.path().join("tmp_frozen_mmap");

let cfg = FMCfg {
    initial_count: 0x0A,
    flush_duration: std::time::Duration::from_micros(0x96),
};

let mmap = FrozenMMap::<u64, MODULE_ID>::new(&path, cfg.clone()).unwrap();
assert_eq!(mmap.total_slots(), 0x0A);

let epoch = unsafe { mmap.write(0, |v| *v = 0xDEADC0DE) }.unwrap();
mmap.wait_for_durability(epoch).unwrap();

let val = unsafe { mmap.read(0, |v| *v) }.unwrap();
assert_eq!(val, 0xDEADC0DE);

drop(mmap);

let reopened = FrozenMMap::<u64, MODULE_ID>::new_grown(&path, cfg, 0x05).unwrap();
assert_eq!(reopened.total_slots(), 0x0A + 0x05);

let val = unsafe { reopened.read(0, |v| *v) }.unwrap();
assert_eq!(val, 0xDEADC0DE);

Structs

FMCfg

Config for FrozenMMap

FMTransaction

A context for grouping multi write ops into a single atomic operation

FrozenMMap

Custom implementation of mmap(2)

Type Aliases

TEpoch

type for epoch used by write ops