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Fix alignment of atomics in shared memory communication channel #612

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merged 2 commits into from
Aug 9, 2024
Merged

Fix alignment of atomics in shared memory communication channel #612

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350f15f
Fix alignment of atomics in shared memory communication channel
phil-opp Aug 7, 2024
b20cef6
Fix: Use correct pointer for `align_offset` call
phil-opp Aug 8, 2024
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37 changes: 29 additions & 8 deletions libraries/shared-memory-server/src/channel.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,8 @@ use raw_sync_2::events::{Event, EventImpl, EventInit, EventState};
use serde::{Deserialize, Serialize};
use shared_memory_extended::Shmem;
use std::{
mem, slice,
mem::{self, align_of},
slice,
sync::atomic::{AtomicBool, AtomicU64},
time::Duration,
};
Expand All @@ -27,7 +28,7 @@ impl ShmemChannel {
unsafe { Event::new(memory.as_ptr().wrapping_add(server_event_len), true) }
.map_err(|err| eyre!("failed to open raw client event: {err}"))?;
let (disconnect_offset, len_offset, data_offset) =
offsets(server_event_len, client_event_len);
offsets(memory.as_ptr(), server_event_len, client_event_len);

server_event
.set(EventState::Clear)
Expand Down Expand Up @@ -68,7 +69,7 @@ impl ShmemChannel {
unsafe { Event::from_existing(memory.as_ptr().wrapping_add(server_event_len)) }
.map_err(|err| eyre!("failed to open raw client event: {err}"))?;
let (disconnect_offset, len_offset, data_offset) =
offsets(server_event_len, client_event_len);
offsets(memory.as_ptr(), server_event_len, client_event_len);

Ok(Self {
memory,
Expand Down Expand Up @@ -188,11 +189,31 @@ impl ShmemChannel {
}
}

fn offsets(server_event_len: usize, client_event_len: usize) -> (usize, usize, usize) {
let disconnect_offset = server_event_len + client_event_len;
let len_offset = disconnect_offset + mem::size_of::<AtomicBool>();
let data_offset = len_offset + mem::size_of::<AtomicU64>();
(disconnect_offset, len_offset, data_offset)
fn offsets(
base_ptr: *mut u8,
server_event_len: usize,
client_event_len: usize,
) -> (usize, usize, usize) {
let (disconnect, len, data) = offset_ptrs(
base_ptr
.wrapping_add(server_event_len)
.wrapping_add(client_event_len),
);
let base = base_ptr as usize;
(
disconnect as usize - base,
len as usize - base,
data as usize - base,
)
}

fn offset_ptrs(next_free: *mut u8) -> (*mut AtomicBool, *mut AtomicU64, *mut u8) {
let disconnect_ptr = next_free.wrapping_add(next_free.align_offset(align_of::<AtomicBool>()));
let len_ptr_unaligned = disconnect_ptr.wrapping_add(mem::size_of::<AtomicBool>());
let len_ptr =
len_ptr_unaligned.wrapping_add(len_ptr_unaligned.align_offset(align_of::<AtomicU64>()));
let data_ptr = len_ptr.wrapping_add(mem::size_of::<AtomicU64>());
(disconnect_ptr.cast(), len_ptr.cast(), data_ptr)
}

unsafe impl Send for ShmemChannel {}
Expand Down
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