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use eyre::{eyre, Context};
use raw_sync_2::events::{Event, EventImpl, EventInit, EventState};
use serde::{Deserialize, Serialize};
use shared_memory_extended::Shmem;
use std::{
mem, slice,
sync::atomic::{AtomicBool, AtomicU64},
time::Duration,
};
pub struct ShmemChannel {
memory: Shmem,
server_event: Box<dyn EventImpl>,
client_event: Box<dyn EventImpl>,
disconnect_offset: usize,
len_offset: usize,
data_offset: usize,
server: bool,
}
#[allow(clippy::missing_safety_doc)]
impl ShmemChannel {
pub unsafe fn new_server(memory: Shmem) -> eyre::Result<Self> {
let (server_event, server_event_len) = unsafe { Event::new(memory.as_ptr(), true) }
.map_err(|err| eyre!("failed to open raw server event: {err}"))?;
let (client_event, client_event_len) =
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);
server_event
.set(EventState::Clear)
.map_err(|err| eyre!("failed to init server_event: {err}"))?;
client_event
.set(EventState::Clear)
.map_err(|err| eyre!("failed to init client_event: {err}"))?;
unsafe {
memory
.as_ptr()
.wrapping_add(disconnect_offset)
.cast::<AtomicBool>()
.write(AtomicBool::new(false));
}
unsafe {
memory
.as_ptr()
.wrapping_add(len_offset)
.cast::<AtomicU64>()
.write(AtomicU64::new(0));
}
Ok(Self {
memory,
server_event,
client_event,
disconnect_offset,
len_offset,
data_offset,
server: true,
})
}
pub unsafe fn new_client(memory: Shmem) -> eyre::Result<Self> {
let (server_event, server_event_len) = unsafe { Event::from_existing(memory.as_ptr()) }
.map_err(|err| eyre!("failed to open raw server event: {err}"))?;
let (client_event, client_event_len) =
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);
Ok(Self {
memory,
server_event,
client_event,
disconnect_offset,
len_offset,
data_offset,
server: false,
})
}
pub fn send<T>(&mut self, value: &T) -> eyre::Result<()>
where
T: Serialize + std::fmt::Debug,
{
let msg = bincode::serialize(value).wrap_err("failed to serialize value")?;
self.send_raw(&msg)
}
fn send_raw(&mut self, msg: &[u8]) -> Result<(), eyre::ErrReport> {
assert!(msg.len() <= self.memory.len() - self.data_offset);
// write data first
unsafe {
self.data_mut()
.copy_from_nonoverlapping(msg.as_ptr(), msg.len());
}
// write len second for synchronization
self.data_len()
.store(msg.len() as u64, std::sync::atomic::Ordering::Release);
// signal event
let event = if self.server {
&self.client_event
} else {
&self.server_event
};
event
.set(EventState::Signaled)
.map_err(|err| eyre!("failed to send message over ShmemChannel: {err}"))?;
let disconnected = self.disconnect().load(std::sync::atomic::Ordering::Acquire);
if disconnected {
eyre::bail!("server closed the connection");
}
Ok(())
}
pub fn receive<T>(&mut self, timeout: Option<Duration>) -> eyre::Result<Option<T>>
where
T: for<'a> Deserialize<'a> + std::fmt::Debug,
{
// wait for event
let event = if self.server {
&self.server_event
} else {
&self.client_event
};
let timeout = timeout
.map(raw_sync_2::Timeout::Val)
.unwrap_or(raw_sync_2::Timeout::Infinite);
event
.wait(timeout)
.map_err(|err| eyre!("failed to receive from ShmemChannel: {err}"))?;
// check for disconnect first
if self.disconnect().load(std::sync::atomic::Ordering::Acquire) {
if self.server {
tracing::trace!("shm client disconnected");
} else {
tracing::error!("shm server disconnected");
}
return Ok(None);
}
// then read len for synchronization
let msg_len = self.data_len().load(std::sync::atomic::Ordering::Acquire) as usize;
assert_ne!(msg_len, 0);
assert!(msg_len < self.memory.len() - self.data_offset);
// finally read the data
let value_raw = unsafe { slice::from_raw_parts(self.data(), msg_len) };
bincode::deserialize(value_raw)
.wrap_err("failed to deserialize value")
.map(|v| Some(v))
}
fn disconnect(&self) -> &AtomicBool {
unsafe {
&*self
.memory
.as_ptr()
.wrapping_add(self.disconnect_offset)
.cast::<AtomicBool>()
}
}
fn data_len(&self) -> &AtomicU64 {
unsafe {
&*self
.memory
.as_ptr()
.wrapping_add(self.len_offset)
.cast::<AtomicU64>()
}
}
fn data(&self) -> *const u8 {
self.memory.as_ptr().wrapping_add(self.data_offset)
}
fn data_mut(&mut self) -> *mut u8 {
self.memory.as_ptr().wrapping_add(self.data_offset)
}
}
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)
}
unsafe impl Send for ShmemChannel {}
impl Drop for ShmemChannel {
fn drop(&mut self) {
if self.server {
// server must only exit after client is disconnected
let disconnected = self.disconnect().load(std::sync::atomic::Ordering::Acquire);
if disconnected {
tracing::debug!("closing ShmemServer after client disconnect");
} else {
tracing::error!("ShmemServer closed before client disconnect");
self.disconnect()
.store(true, std::sync::atomic::Ordering::Release);
}
} else {
tracing::debug!("disconnecting client");
self.disconnect()
.store(true, std::sync::atomic::Ordering::Release);
// wake up server
if let Err(err) = self.server_event.set(EventState::Signaled) {
tracing::warn!("failed to signal ShmemChannel disconnect: {err}");
}
}
}
}
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