Comments (4)
each thread's output will be unique to that thread, but each thread does NOT get its own slice.
If you can guarantee this within your application, you should be able to start from a single MmapRaw
and hand out a raw pointer which is then dereferenced by each thread using unsafe code. I don't think that a pre-existing abstraction will capture the specific use case.
But essentially, if you start from a single MmapRaw
or MmapMut
, the synchronization task is exactly the same as if you start from a single &mut [u8]
which is accessed by the threads in the manner you describe. (Basically, your application would not care whether it writes to memory buffer backed by anonymous memory handed out by the heap allocator or backed by a file and obtained directly using mmap
.)
from memmap2-rs.
As a further illustration of the above even though it might not be helpful for your use case: As the byte slice provided by MmapMut
is just that, it can be used with e.g. Rayon's ParallelSliceMut
and slice::IterMut
to operate on in parallel.
from memmap2-rs.
@adamreichold thank you for your quick reply!!! I'm still new to Rust (fun to learn it though!), so I might need a bit more guidance. Could you show a simple example (maybe even later add it to the docs?) that demonstrates how I can do this? Ideally this method should be usable from the rayon::iter::ParallelBridge
-- par_map_reduce()
. For a while I was considering to open the same file once from each thread with a localstore, but then it becomes a nightmare to manage them when used from a threadpool - each file has to be properly closed, which is not simple when the pool is managed by rayon. Thanks!!!
P.S. A user has offered a somewhat different example -- but i cannot evaluate if that approach has merit or not (see code)
from memmap2-rs.
The technique shown in https://stackoverflow.com/questions/33818141/how-do-i-pass-disjoint-slices-from-a-vector-to-different-threads is basically what I am suggesting. As written above, your could should start off with &mut [u8]
and not care how that reference was produced.
Also as written above, you will probably need to pass *mut u8
and have each thread produce non-overlapping exclusive references via
fn some_thread(ptr: *mut u8, pos: usize) {
// SAFETY: Only one thread will access the data at pos s.t. `val` will not alias any other references.
let val = unsafe { &mut *ptr.add(pos) };
...
}
if you cannot use an existing chunking mechanism like par_chunks
or par_iter
.
(I don't think AtomicU8
enters the picture if your threads never touch overlapping parts of the initial slice just as it does not enter if you do [u8]::split_at
and pass the resulting subslices to two different threads.)
from memmap2-rs.
Related Issues (20)
- Migrate to `safer_owning_ref` HOT 1
- why does memmap2::Mmap::map need to be unsafe? HOT 4
- Implement AsRawFd, IntoRawFd, AsRawHandle, IntoRawHandle and Into<Stdio> for MMap HOT 2
- Composite memory maps currently impossible HOT 7
- mmap'd anon pages fail in io_uring IOSQE_BUFFER_SELECT usage HOT 2
- advise_writes_unsafely_to_part_of_map test fails on powerpc64le-unknown-linux-gnu HOT 2
- error[E0433]: failed to resolve: could not find `Advice` in `memmap2` HOT 1
- PermissionDenied, message: "Access is denied." at remove file after read on Github Action WIndows HOT 2
- Doesn't compile for freebsd HOT 3
- v0.9.2 build failed for android target. HOT 3
- Support for `MS_INVALIDATE`? HOT 8
- Mac osx support HOT 1
- Support `mremap(2)` HOT 1
- Mapping beyond 4GB offset if broken on 32 bit glibc (Linux) HOT 3
- Support multiple advice HOT 2
- Contributing a migration from rustix to libc HOT 9
- MSRV and edition HOT 5
- Merging changes with memmapix HOT 24
- memmap2 `advise` is unsound HOT 8
- Interest is supporting mbind HOT 10
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from memmap2-rs.