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use std::ptr::NonNull;
use std::sync::atomic::Ordering;
use bytemuck::AnyBitPattern;
use crate::{
error::QueError, page_size::PageSize, shmem::Shmem, MAGIC,
};
use super::{burst_amount, Channel};
#[repr(C, align(128))]
pub struct Producer<T, const N: usize> {
spsc: NonNull<Channel<T, N>>,
tail: usize,
/// Number of elements written since last sync
written: usize,
last_consumer_heartbeat: usize,
}
unsafe impl<T, const N: usize> Send for Producer<T, N> {}
impl<T: AnyBitPattern, const N: usize> Producer<T, N> {
/// Joins or creates a channel backed by shared memory as a
/// producer.
pub unsafe fn join_or_create_shmem(
shmem_id: &str,
#[cfg(target_os = "linux")] page_size: PageSize,
) -> Result<Producer<T, N>, QueError> {
#[cfg(not(target_os = "linux"))]
let page_size = PageSize::Standard;
// Calculate buffer size.
// If using huge pages, we must uplign to page size.
let buffer_size: i64 = page_size
.mem_size(core::mem::size_of::<Channel<T, N>>())
.try_into()
.map_err(|_| QueError::InvalidSize)?;
// Open or create shmem
let shmem = Shmem::open_or_create(
shmem_id,
buffer_size,
#[cfg(target_os = "linux")]
page_size,
)?;
// Zerocopy deserialize the SPSC
let spsc: &Channel<T, N> =
unsafe { &*shmem.get_mut_ptr().cast() };
// Check magic
let magic = spsc.magic.load(Ordering::Acquire);
let capacity = spsc.capacity.load(Ordering::Acquire);
if magic == MAGIC {
// Check capacity
if capacity != N {
return Err(QueError::IncorrectCapacity(capacity));
}
// Successful join if magic and capacity is correct
Ok(Producer {
spsc: NonNull::new(shmem.get_mut_ptr().cast()).unwrap(),
tail: spsc.tail.load(Ordering::Acquire),
written: 0,
last_consumer_heartbeat: spsc
.consumer_heartbeat
.load(Ordering::Acquire),
})
} else if magic == 0 {
// Initialize
let Channel {
tail,
// consumer will set this
head: _,
capacity,
producer_heartbeat,
consumer_heartbeat: _,
magic,
buffer: _unused,
padding: _,
} = spsc;
tail.store(0, Ordering::Release);
producer_heartbeat.store(0, Ordering::Release);
capacity.store(N, Ordering::Release);
magic.store(MAGIC, Ordering::Release);
Ok(Producer {
spsc: NonNull::new(shmem.get_mut_ptr().cast()).unwrap(),
tail: 0,
written: 0,
last_consumer_heartbeat: spsc
.consumer_heartbeat
.load(Ordering::Acquire),
})
} else {
// Magic is not MAGIC and not zero
Err(QueError::CorruptionDetected)
}
}
/// Initializes a channel backed by `buffer` and joins as a
/// producer.
///
/// SAFETY:
/// This must point to a buffer of proper size and alignment.
pub unsafe fn initialize_in(
buffer: *mut u8,
) -> Result<Producer<T, N>, QueError> {
assert!(
N > 0 && N.is_power_of_two(),
"Capacity must be a power of two"
);
assert!(buffer as usize % 128 == 0, "unaligned");
// Zerocopy deserialize the SPSC
let spsc: &Channel<T, N> = &*buffer.cast();
// Check magic
let magic = spsc.magic.load(Ordering::Acquire);
let capacity = spsc.capacity.load(Ordering::Acquire);
if magic == MAGIC {
// Check capacity
if capacity != N {
return Err(QueError::IncorrectCapacity(capacity));
}
spsc.producer_heartbeat
.fetch_add(1, Ordering::Release);
// Successful join if magic and capacity is correct
Ok(Producer {
spsc: NonNull::new(buffer.cast()).unwrap(),
tail: spsc.tail.load(Ordering::Acquire),
written: 0,
last_consumer_heartbeat: spsc
.consumer_heartbeat
.load(Ordering::Acquire),
})
} else if magic == 0 {
// Initialize
let Channel {
tail,
// consumer will set this
head: _,
capacity,
producer_heartbeat,
consumer_heartbeat: _,
magic,
buffer: _unused,
padding: _,
} = spsc;
tail.store(0, Ordering::Release);
producer_heartbeat.store(0, Ordering::Release);
capacity.store(N, Ordering::Release);
magic.store(MAGIC, Ordering::Release);
Ok(Producer {
spsc: NonNull::new(buffer.cast()).unwrap(),
tail: 0,
written: 0,
last_consumer_heartbeat: spsc
.consumer_heartbeat
.load(Ordering::Acquire),
})
} else {
// Magic is not MAGIC and not zero
Err(QueError::CorruptionDetected)
}
}
/// Joins an existing channel backed by `buffer` as a producer.
///
/// SAFETY:
/// This must point to a buffer of proper size and alignment.
pub unsafe fn join(
buffer: *mut u8,
) -> Result<Producer<T, N>, QueError> {
assert!(
N > 0 && N.is_power_of_two(),
"Capacity must be a power of two"
);
assert!(buffer as usize % 128 == 0, "unaligned");
// Zerocopy deserialize the SPSC
let spsc: &Channel<T, N> = &*buffer.cast();
let magic = spsc.magic.load(Ordering::Acquire);
let capacity = spsc.capacity.load(Ordering::Acquire);
if magic == MAGIC {
if capacity != N {
return Err(QueError::IncorrectCapacity(capacity));
}
// Successful join if magic and capacity is correct
Ok(Producer {
spsc: NonNull::new(buffer.cast()).unwrap(),
tail: spsc.tail.load(Ordering::Acquire),
written: 0,
last_consumer_heartbeat: spsc
.consumer_heartbeat
.load(Ordering::Acquire),
})
} else if magic == 0 {
// Technically could be corrupted but uninitialized
// is most likely explanation
Err(QueError::Uninitialized)
} else {
// Magic is not MAGIC and not zero
Err(QueError::CorruptionDetected)
}
}
/// Attempts to write a new element to the channel. If full, returns
/// [QueError::Full].
#[inline(always)]
pub fn push(&mut self, value: &T) -> Result<(), QueError> {
// Check if full
let is_full = self.tail
== unsafe {
(*self.spsc.as_ptr())
.head
.load(Ordering::Relaxed)
} + N;
if is_full {
return Err(QueError::Full);
}
// Write value if not full
let index = self.tail & (N - 1);
unsafe {
*(*self.spsc.as_ptr())
.buffer
.as_mut_ptr()
.add(index) = *value;
};
// Increment tail and written counter
self.tail += 1;
self.written += 1;
// Update tail if we've written past burst amount and haven't
// updated shared atomic.
if self.written == burst_amount::<N>() {
self.sync();
}
Ok(())
}
/// Increments the producer heartbeat.
///
/// Can be read by the consumer to see that the producer is still
/// online if done periodically. Can also be used to ack individual
/// messages or alert that we've joined.
pub fn beat(&self) {
unsafe {
(*self.spsc.as_ptr())
.producer_heartbeat
.fetch_add(1, Ordering::Release);
}
}
/// Synchronizes the local tail with the atomic tail in the channel,
/// publishing newly written values.
#[inline(always)]
pub fn sync(&mut self) {
self.written = 0;
unsafe {
(*self.spsc.as_ptr())
.tail
.store(self.tail, Ordering::Release)
}
}
/// Checks if a consumer has incremented its heartbeat since last
/// called. Can be used by the producer to see if the consumer is
/// still online if done periodically. Can also be used to ack
/// individual messages or alert that we've joined.
pub fn consumer_heartbeat(&mut self) -> bool {
let heartbeat = unsafe {
(*self.spsc.as_ptr())
.consumer_heartbeat
.load(Ordering::Acquire)
};
if heartbeat != self.last_consumer_heartbeat {
self.last_consumer_heartbeat = heartbeat;
true
} else {
false
}
}
/// Returns pointer to inner padding.
///
/// User is responsible for safe usage.
///
/// Can be used to store metadata (e.g. hash seed).
///
/// Byte array is 128 byte aligned.
pub fn get_padding_ptr(&self) -> NonNull<[u8; 112]> {
unsafe {
NonNull::new_unchecked(
self.spsc.cast::<u8>().as_ptr().add(512),
)
.cast()
}
}
}