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bbbuffer.rs
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bbbuffer.rs
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use crate::{
framed::{FrameConsumer, FrameProducer},
Error, Result,
};
use core::{
cell::UnsafeCell,
cmp::min,
marker::PhantomData,
mem::{forget, transmute, MaybeUninit},
ops::{Deref, DerefMut},
ptr::NonNull,
result::Result as CoreResult,
slice::from_raw_parts_mut,
sync::atomic::{
AtomicBool, AtomicUsize,
Ordering::{AcqRel, Acquire, Release},
},
};
#[derive(Debug)]
/// A backing structure for a BBQueue. Can be used to create either
/// a BBQueue or a split Producer/Consumer pair
pub struct BBBuffer<const N: usize> {
buf: UnsafeCell<MaybeUninit<[u8; N]>>,
/// Where the next byte will be written
write: AtomicUsize,
/// Where the next byte will be read from
read: AtomicUsize,
/// Used in the inverted case to mark the end of the
/// readable streak. Otherwise will == sizeof::<self.buf>().
/// Writer is responsible for placing this at the correct
/// place when entering an inverted condition, and Reader
/// is responsible for moving it back to sizeof::<self.buf>()
/// when exiting the inverted condition
last: AtomicUsize,
/// Used by the Writer to remember what bytes are currently
/// allowed to be written to, but are not yet ready to be
/// read from
reserve: AtomicUsize,
/// Is there an active read grant?
read_in_progress: AtomicBool,
/// Is there an active write grant?
write_in_progress: AtomicBool,
/// Have we already split?
already_split: AtomicBool,
}
unsafe impl<const A: usize> Sync for BBBuffer<A> {}
impl<'a, const N: usize> BBBuffer<N> {
/// Attempt to split the `BBBuffer` into `Consumer` and `Producer` halves to gain access to the
/// buffer. If buffer has already been split, an error will be returned.
///
/// NOTE: When splitting, the underlying buffer will be explicitly initialized
/// to zero. This may take a measurable amount of time, depending on the size
/// of the buffer. This is necessary to prevent undefined behavior. If the buffer
/// is placed at `static` scope within the `.bss` region, the explicit initialization
/// will be elided (as it is already performed as part of memory initialization)
///
/// NOTE: If the `thumbv6` feature is selected, this function takes a short critical section
/// while splitting.
///
/// ```rust
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (prod, cons) = buffer.try_split().unwrap();
///
/// // Not possible to split twice
/// assert!(buffer.try_split().is_err());
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn try_split(&'a self) -> Result<(Producer<'a, N>, Consumer<'a, N>)> {
if atomic::swap(&self.already_split, true, AcqRel) {
return Err(Error::AlreadySplit);
}
unsafe {
// Explicitly zero the data to avoid undefined behavior.
// This is required, because we hand out references to the buffers,
// which mean that creating them as references is technically UB for now
let mu_ptr = self.buf.get();
(*mu_ptr).as_mut_ptr().write_bytes(0u8, 1);
let nn1 = NonNull::new_unchecked(self as *const _ as *mut _);
let nn2 = NonNull::new_unchecked(self as *const _ as *mut _);
Ok((
Producer {
bbq: nn1,
pd: PhantomData,
},
Consumer {
bbq: nn2,
pd: PhantomData,
},
))
}
}
/// Attempt to split the `BBBuffer` into `FrameConsumer` and `FrameProducer` halves
/// to gain access to the buffer. If buffer has already been split, an error
/// will be returned.
///
/// NOTE: When splitting, the underlying buffer will be explicitly initialized
/// to zero. This may take a measurable amount of time, depending on the size
/// of the buffer. This is necessary to prevent undefined behavior. If the buffer
/// is placed at `static` scope within the `.bss` region, the explicit initialization
/// will be elided (as it is already performed as part of memory initialization)
///
/// NOTE: If the `thumbv6` feature is selected, this function takes a short critical
/// section while splitting.
pub fn try_split_framed(&'a self) -> Result<(FrameProducer<'a, N>, FrameConsumer<'a, N>)> {
let (producer, consumer) = self.try_split()?;
Ok((FrameProducer { producer }, FrameConsumer { consumer }))
}
/// Attempt to release the Producer and Consumer
///
/// This re-initializes the buffer so it may be split in a different mode at a later
/// time. There must be no read or write grants active, or an error will be returned.
///
/// The `Producer` and `Consumer` must be from THIS `BBBuffer`, or an error will
/// be returned.
///
/// ```rust
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (prod, cons) = buffer.try_split().unwrap();
///
/// // Not possible to split twice
/// assert!(buffer.try_split().is_err());
///
/// // Release the producer and consumer
/// assert!(buffer.try_release(prod, cons).is_ok());
///
/// // Split the buffer in framed mode
/// let (fprod, fcons) = buffer.try_split_framed().unwrap();
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn try_release(
&'a self,
prod: Producer<'a, N>,
cons: Consumer<'a, N>,
) -> CoreResult<(), (Producer<'a, N>, Consumer<'a, N>)> {
// Note: Re-entrancy is not possible because we require ownership
// of the producer and consumer, which are not cloneable. We also
// can assume the buffer has been split, because
// Are these our producers and consumers?
let our_prod = prod.bbq.as_ptr() as *const Self == self;
let our_cons = cons.bbq.as_ptr() as *const Self == self;
if !(our_prod && our_cons) {
// Can't release, not our producer and consumer
return Err((prod, cons));
}
let wr_in_progress = self.write_in_progress.load(Acquire);
let rd_in_progress = self.read_in_progress.load(Acquire);
if wr_in_progress || rd_in_progress {
// Can't release, active grant(s) in progress
return Err((prod, cons));
}
// Drop the producer and consumer halves
drop(prod);
drop(cons);
// Re-initialize the buffer (not totally needed, but nice to do)
self.write.store(0, Release);
self.read.store(0, Release);
self.reserve.store(0, Release);
self.last.store(0, Release);
// Mark the buffer as ready to be split
self.already_split.store(false, Release);
Ok(())
}
/// Attempt to release the Producer and Consumer in Framed mode
///
/// This re-initializes the buffer so it may be split in a different mode at a later
/// time. There must be no read or write grants active, or an error will be returned.
///
/// The `FrameProducer` and `FrameConsumer` must be from THIS `BBBuffer`, or an error
/// will be returned.
pub fn try_release_framed(
&'a self,
prod: FrameProducer<'a, N>,
cons: FrameConsumer<'a, N>,
) -> CoreResult<(), (FrameProducer<'a, N>, FrameConsumer<'a, N>)> {
self.try_release(prod.producer, cons.consumer)
.map_err(|(producer, consumer)| {
// Restore the wrapper types
(FrameProducer { producer }, FrameConsumer { consumer })
})
}
}
impl<const A: usize> BBBuffer<A> {
/// Create a new constant inner portion of a `BBBuffer`.
///
/// NOTE: This is only necessary to use when creating a `BBBuffer` at static
/// scope, and is generally never used directly. This process is necessary to
/// work around current limitations in `const fn`, and will be replaced in
/// the future.
///
/// ```rust,no_run
/// use bbqueue::BBBuffer;
///
/// static BUF: BBBuffer<6> = BBBuffer::new();
///
/// fn main() {
/// let (prod, cons) = BUF.try_split().unwrap();
/// }
/// ```
pub const fn new() -> Self {
Self {
// This will not be initialized until we split the buffer
buf: UnsafeCell::new(MaybeUninit::uninit()),
/// Owned by the writer
write: AtomicUsize::new(0),
/// Owned by the reader
read: AtomicUsize::new(0),
/// Cooperatively owned
///
/// NOTE: This should generally be initialized as size_of::<self.buf>(), however
/// this would prevent the structure from being entirely zero-initialized,
/// and can cause the .data section to be much larger than necessary. By
/// forcing the `last` pointer to be zero initially, we place the structure
/// in an "inverted" condition, which will be resolved on the first commited
/// bytes that are written to the structure.
///
/// When read == last == write, no bytes will be allowed to be read (good), but
/// write grants can be given out (also good).
last: AtomicUsize::new(0),
/// Owned by the Writer, "private"
reserve: AtomicUsize::new(0),
/// Owned by the Reader, "private"
read_in_progress: AtomicBool::new(false),
/// Owned by the Writer, "private"
write_in_progress: AtomicBool::new(false),
/// We haven't split at the start
already_split: AtomicBool::new(false),
}
}
}
/// `Producer` is the primary interface for pushing data into a `BBBuffer`.
/// There are various methods for obtaining a grant to write to the buffer, with
/// different potential tradeoffs. As all grants are required to be a contiguous
/// range of data, different strategies are sometimes useful when making the decision
/// between maximizing usage of the buffer, and ensuring a given grant is successful.
///
/// As a short summary of currently possible grants:
///
/// * `grant_exact(N)`
/// * User will receive a grant `sz == N` (or receive an error)
/// * This may cause a wraparound if a grant of size N is not available
/// at the end of the ring.
/// * If this grant caused a wraparound, the bytes that were "skipped" at the
/// end of the ring will not be available until the reader reaches them,
/// regardless of whether the grant commited any data or not.
/// * Maximum possible waste due to skipping: `N - 1` bytes
/// * `grant_max_remaining(N)`
/// * User will receive a grant `0 < sz <= N` (or receive an error)
/// * This will only cause a wrap to the beginning of the ring if exactly
/// zero bytes are available at the end of the ring.
/// * Maximum possible waste due to skipping: 0 bytes
///
/// See [this github issue](https://github.com/jamesmunns/bbqueue/issues/38) for a
/// discussion of grant methods that could be added in the future.
pub struct Producer<'a, const N: usize> {
bbq: NonNull<BBBuffer<N>>,
pd: PhantomData<&'a ()>,
}
unsafe impl<'a, const N: usize> Send for Producer<'a, N> {}
impl<'a, const N: usize> Producer<'a, N> {
/// Request a writable, contiguous section of memory of exactly
/// `sz` bytes. If the buffer size requested is not available,
/// an error will be returned.
///
/// This method may cause the buffer to wrap around early if the
/// requested space is not available at the end of the buffer, but
/// is available at the beginning
///
/// ```rust
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (mut prod, cons) = buffer.try_split().unwrap();
///
/// // Successfully obtain and commit a grant of four bytes
/// let mut grant = prod.grant_exact(4).unwrap();
/// assert_eq!(grant.buf().len(), 4);
/// grant.commit(4);
///
/// // Try to obtain a grant of three bytes
/// assert!(prod.grant_exact(3).is_err());
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn grant_exact(&mut self, sz: usize) -> Result<GrantW<'a, N>> {
let inner = unsafe { &self.bbq.as_ref() };
if atomic::swap(&inner.write_in_progress, true, AcqRel) {
return Err(Error::GrantInProgress);
}
// Writer component. Must never write to `read`,
// be careful writing to `load`
let write = inner.write.load(Acquire);
let read = inner.read.load(Acquire);
let max = N;
let already_inverted = write < read;
let start = if already_inverted {
if (write + sz) < read {
// Inverted, room is still available
write
} else {
// Inverted, no room is available
inner.write_in_progress.store(false, Release);
return Err(Error::InsufficientSize);
}
} else {
if write + sz <= max {
// Non inverted condition
write
} else {
// Not inverted, but need to go inverted
// NOTE: We check sz < read, NOT <=, because
// write must never == read in an inverted condition, since
// we will then not be able to tell if we are inverted or not
if sz < read {
// Invertible situation
0
} else {
// Not invertible, no space
inner.write_in_progress.store(false, Release);
return Err(Error::InsufficientSize);
}
}
};
// Safe write, only viewed by this task
inner.reserve.store(start + sz, Release);
// This is sound, as UnsafeCell, MaybeUninit, and GenericArray
// are all `#[repr(Transparent)]
let start_of_buf_ptr = inner.buf.get().cast::<u8>();
let grant_slice =
unsafe { from_raw_parts_mut(start_of_buf_ptr.offset(start as isize), sz) };
Ok(GrantW {
buf: grant_slice,
bbq: self.bbq,
to_commit: 0,
})
}
/// Request a writable, contiguous section of memory of up to
/// `sz` bytes. If a buffer of size `sz` is not available without
/// wrapping, but some space (0 < available < sz) is available without
/// wrapping, then a grant will be given for the remaining size at the
/// end of the buffer. If no space is available for writing, an error
/// will be returned.
///
/// ```
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (mut prod, mut cons) = buffer.try_split().unwrap();
///
/// // Successfully obtain and commit a grant of four bytes
/// let mut grant = prod.grant_max_remaining(4).unwrap();
/// assert_eq!(grant.buf().len(), 4);
/// grant.commit(4);
///
/// // Release the four initial commited bytes
/// let mut grant = cons.read().unwrap();
/// assert_eq!(grant.buf().len(), 4);
/// grant.release(4);
///
/// // Try to obtain a grant of three bytes, get two bytes
/// let mut grant = prod.grant_max_remaining(3).unwrap();
/// assert_eq!(grant.buf().len(), 2);
/// grant.commit(2);
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn grant_max_remaining(&mut self, mut sz: usize) -> Result<GrantW<'a, N>> {
let inner = unsafe { &self.bbq.as_ref() };
if atomic::swap(&inner.write_in_progress, true, AcqRel) {
return Err(Error::GrantInProgress);
}
// Writer component. Must never write to `read`,
// be careful writing to `load`
let write = inner.write.load(Acquire);
let read = inner.read.load(Acquire);
let max = N;
let already_inverted = write < read;
let start = if already_inverted {
// In inverted case, read is always > write
let remain = read - write - 1;
if remain != 0 {
sz = min(remain, sz);
write
} else {
// Inverted, no room is available
inner.write_in_progress.store(false, Release);
return Err(Error::InsufficientSize);
}
} else {
if write != max {
// Some (or all) room remaining in un-inverted case
sz = min(max - write, sz);
write
} else {
// Not inverted, but need to go inverted
// NOTE: We check read > 1, NOT read >= 1, because
// write must never == read in an inverted condition, since
// we will then not be able to tell if we are inverted or not
if read > 1 {
sz = min(read - 1, sz);
0
} else {
// Not invertible, no space
inner.write_in_progress.store(false, Release);
return Err(Error::InsufficientSize);
}
}
};
// Safe write, only viewed by this task
inner.reserve.store(start + sz, Release);
// This is sound, as UnsafeCell, MaybeUninit, and GenericArray
// are all `#[repr(Transparent)]
let start_of_buf_ptr = inner.buf.get().cast::<u8>();
let grant_slice =
unsafe { from_raw_parts_mut(start_of_buf_ptr.offset(start as isize), sz) };
Ok(GrantW {
buf: grant_slice,
bbq: self.bbq,
to_commit: 0,
})
}
}
/// `Consumer` is the primary interface for reading data from a `BBBuffer`.
pub struct Consumer<'a, const N: usize> {
bbq: NonNull<BBBuffer<N>>,
pd: PhantomData<&'a ()>,
}
unsafe impl<'a, const N: usize> Send for Consumer<'a, N> {}
impl<'a, const N: usize> Consumer<'a, N> {
/// Obtains a contiguous slice of committed bytes. This slice may not
/// contain ALL available bytes, if the writer has wrapped around. The
/// remaining bytes will be available after all readable bytes are
/// released
///
/// ```rust
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (mut prod, mut cons) = buffer.try_split().unwrap();
///
/// // Successfully obtain and commit a grant of four bytes
/// let mut grant = prod.grant_max_remaining(4).unwrap();
/// assert_eq!(grant.buf().len(), 4);
/// grant.commit(4);
///
/// // Obtain a read grant
/// let mut grant = cons.read().unwrap();
/// assert_eq!(grant.buf().len(), 4);
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn read(&mut self) -> Result<GrantR<'a, N>> {
let inner = unsafe { &self.bbq.as_ref() };
if atomic::swap(&inner.read_in_progress, true, AcqRel) {
return Err(Error::GrantInProgress);
}
let write = inner.write.load(Acquire);
let last = inner.last.load(Acquire);
let mut read = inner.read.load(Acquire);
// Resolve the inverted case or end of read
if (read == last) && (write < read) {
read = 0;
// This has some room for error, the other thread reads this
// Impact to Grant:
// Grant checks if read < write to see if inverted. If not inverted, but
// no space left, Grant will initiate an inversion, but will not trigger it
// Impact to Commit:
// Commit does not check read, but if Grant has started an inversion,
// grant could move Last to the prior write position
// MOVING READ BACKWARDS!
inner.read.store(0, Release);
}
let sz = if write < read {
// Inverted, only believe last
last
} else {
// Not inverted, only believe write
write
} - read;
if sz == 0 {
inner.read_in_progress.store(false, Release);
return Err(Error::InsufficientSize);
}
// This is sound, as UnsafeCell, MaybeUninit, and GenericArray
// are all `#[repr(Transparent)]
let start_of_buf_ptr = inner.buf.get().cast::<u8>();
let grant_slice = unsafe { from_raw_parts_mut(start_of_buf_ptr.offset(read as isize), sz) };
Ok(GrantR {
buf: grant_slice,
bbq: self.bbq,
to_release: 0,
})
}
/// Obtains two disjoint slices, which are each contiguous of committed bytes.
/// Combined these contain all previously commited data.
pub fn split_read(&mut self) -> Result<SplitGrantR<'a, N>> {
let inner = unsafe { &self.bbq.as_ref() };
if atomic::swap(&inner.read_in_progress, true, AcqRel) {
return Err(Error::GrantInProgress);
}
let write = inner.write.load(Acquire);
let last = inner.last.load(Acquire);
let mut read = inner.read.load(Acquire);
// Resolve the inverted case or end of read
if (read == last) && (write < read) {
read = 0;
// This has some room for error, the other thread reads this
// Impact to Grant:
// Grant checks if read < write to see if inverted. If not inverted, but
// no space left, Grant will initiate an inversion, but will not trigger it
// Impact to Commit:
// Commit does not check read, but if Grant has started an inversion,
// grant could move Last to the prior write position
// MOVING READ BACKWARDS!
inner.read.store(0, Release);
}
let (sz1, sz2) = if write < read {
// Inverted, only believe last
(last - read, write)
} else {
// Not inverted, only believe write
(write - read, 0)
};
if sz1 == 0 {
inner.read_in_progress.store(false, Release);
return Err(Error::InsufficientSize);
}
// This is sound, as UnsafeCell, MaybeUninit, and GenericArray
// are all `#[repr(Transparent)]
let start_of_buf_ptr = inner.buf.get().cast::<u8>();
let grant_slice1 =
unsafe { from_raw_parts_mut(start_of_buf_ptr.offset(read as isize), sz1) };
let grant_slice2 = unsafe { from_raw_parts_mut(start_of_buf_ptr, sz2) };
Ok(SplitGrantR {
buf1: grant_slice1,
buf2: grant_slice2,
bbq: self.bbq,
to_release: 0,
})
}
}
impl<const N: usize> BBBuffer<N> {
/// Returns the size of the backing storage.
///
/// This is the maximum number of bytes that can be stored in this queue.
///
/// ```rust
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// assert_eq!(buffer.capacity(), 6);
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub const fn capacity(&self) -> usize {
N
}
}
/// A structure representing a contiguous region of memory that
/// may be written to, and potentially "committed" to the queue.
///
/// NOTE: If the grant is dropped without explicitly commiting
/// the contents, or by setting a the number of bytes to
/// automatically be committed with `to_commit()`, then no bytes
/// will be comitted for writing.
///
/// If the `thumbv6` feature is selected, dropping the grant
/// without committing it takes a short critical section,
#[derive(Debug, PartialEq)]
pub struct GrantW<'a, const N: usize> {
pub(crate) buf: &'a mut [u8],
bbq: NonNull<BBBuffer<N>>,
pub(crate) to_commit: usize,
}
unsafe impl<'a, const N: usize> Send for GrantW<'a, N> {}
/// A structure representing a contiguous region of memory that
/// may be read from, and potentially "released" (or cleared)
/// from the queue
///
/// NOTE: If the grant is dropped without explicitly releasing
/// the contents, or by setting the number of bytes to automatically
/// be released with `to_release()`, then no bytes will be released
/// as read.
///
///
/// If the `thumbv6` feature is selected, dropping the grant
/// without releasing it takes a short critical section,
#[derive(Debug, PartialEq)]
pub struct GrantR<'a, const N: usize> {
pub(crate) buf: &'a mut [u8],
bbq: NonNull<BBBuffer<N>>,
pub(crate) to_release: usize,
}
/// A structure representing up to two contiguous regions of memory that
/// may be read from, and potentially "released" (or cleared)
/// from the queue
#[derive(Debug, PartialEq)]
pub struct SplitGrantR<'a, const N: usize> {
pub(crate) buf1: &'a mut [u8],
pub(crate) buf2: &'a mut [u8],
bbq: NonNull<BBBuffer<N>>,
pub(crate) to_release: usize,
}
unsafe impl<'a, const N: usize> Send for GrantR<'a, N> {}
unsafe impl<'a, const N: usize> Send for SplitGrantR<'a, N> {}
impl<'a, const N: usize> GrantW<'a, N> {
/// Finalizes a writable grant given by `grant()` or `grant_max()`.
/// This makes the data available to be read via `read()`. This consumes
/// the grant.
///
/// If `used` is larger than the given grant, the maximum amount will
/// be commited
///
/// NOTE: If the `thumbv6` feature is selected, this function takes a short critical
/// section while committing.
pub fn commit(mut self, used: usize) {
self.commit_inner(used);
forget(self);
}
/// Obtain access to the inner buffer for writing
///
/// ```rust
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (mut prod, mut cons) = buffer.try_split().unwrap();
///
/// // Successfully obtain and commit a grant of four bytes
/// let mut grant = prod.grant_max_remaining(4).unwrap();
/// grant.buf().copy_from_slice(&[1, 2, 3, 4]);
/// grant.commit(4);
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn buf(&mut self) -> &mut [u8] {
self.buf
}
/// Sometimes, it's not possible for the lifetimes to check out. For example,
/// if you need to hand this buffer to a function that expects to receive a
/// `&'static mut [u8]`, it is not possible for the inner reference to outlive the
/// grant itself.
///
/// You MUST guarantee that in no cases, the reference that is returned here outlives
/// the grant itself. Once the grant has been released, referencing the data contained
/// WILL cause undefined behavior.
///
/// Additionally, you must ensure that a separate reference to this data is not created
/// to this data, e.g. using `DerefMut` or the `buf()` method of this grant.
pub unsafe fn as_static_mut_buf(&mut self) -> &'static mut [u8] {
transmute::<&mut [u8], &'static mut [u8]>(self.buf)
}
#[inline(always)]
pub(crate) fn commit_inner(&mut self, used: usize) {
let inner = unsafe { &self.bbq.as_ref() };
// If there is no grant in progress, return early. This
// generally means we are dropping the grant within a
// wrapper structure
if !inner.write_in_progress.load(Acquire) {
return;
}
// Writer component. Must never write to READ,
// be careful writing to LAST
// Saturate the grant commit
let len = self.buf.len();
let used = min(len, used);
let write = inner.write.load(Acquire);
atomic::fetch_sub(&inner.reserve, len - used, AcqRel);
let max = N;
let last = inner.last.load(Acquire);
let new_write = inner.reserve.load(Acquire);
if (new_write < write) && (write != max) {
// We have already wrapped, but we are skipping some bytes at the end of the ring.
// Mark `last` where the write pointer used to be to hold the line here
inner.last.store(write, Release);
} else if new_write > last {
// We're about to pass the last pointer, which was previously the artificial
// end of the ring. Now that we've passed it, we can "unlock" the section
// that was previously skipped.
//
// Since new_write is strictly larger than last, it is safe to move this as
// the other thread will still be halted by the (about to be updated) write
// value
inner.last.store(max, Release);
}
// else: If new_write == last, either:
// * last == max, so no need to write, OR
// * If we write in the end chunk again, we'll update last to max next time
// * If we write to the start chunk in a wrap, we'll update last when we
// move write backwards
// Write must be updated AFTER last, otherwise read could think it was
// time to invert early!
inner.write.store(new_write, Release);
// Allow subsequent grants
inner.write_in_progress.store(false, Release);
}
/// Configures the amount of bytes to be commited on drop.
pub fn to_commit(&mut self, amt: usize) {
self.to_commit = self.buf.len().min(amt);
}
}
impl<'a, const N: usize> GrantR<'a, N> {
/// Release a sequence of bytes from the buffer, allowing the space
/// to be used by later writes. This consumes the grant.
///
/// If `used` is larger than the given grant, the full grant will
/// be released.
///
/// NOTE: If the `thumbv6` feature is selected, this function takes a short critical
/// section while releasing.
pub fn release(mut self, used: usize) {
// Saturate the grant release
let used = min(self.buf.len(), used);
self.release_inner(used);
forget(self);
}
pub(crate) fn shrink(&mut self, len: usize) {
let mut new_buf: &mut [u8] = &mut [];
core::mem::swap(&mut self.buf, &mut new_buf);
let (new, _) = new_buf.split_at_mut(len);
self.buf = new;
}
/// Obtain access to the inner buffer for reading
///
/// ```
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (mut prod, mut cons) = buffer.try_split().unwrap();
///
/// // Successfully obtain and commit a grant of four bytes
/// let mut grant = prod.grant_max_remaining(4).unwrap();
/// grant.buf().copy_from_slice(&[1, 2, 3, 4]);
/// grant.commit(4);
///
/// // Obtain a read grant, and copy to a buffer
/// let mut grant = cons.read().unwrap();
/// let mut buf = [0u8; 4];
/// buf.copy_from_slice(grant.buf());
/// assert_eq!(&buf, &[1, 2, 3, 4]);
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]
/// # bbqtest();
/// # }
/// ```
pub fn buf(&self) -> &[u8] {
self.buf
}
/// Obtain mutable access to the read grant
///
/// This is useful if you are performing in-place operations
/// on an incoming packet, such as decryption
pub fn buf_mut(&mut self) -> &mut [u8] {
self.buf
}
/// Sometimes, it's not possible for the lifetimes to check out. For example,
/// if you need to hand this buffer to a function that expects to receive a
/// `&'static [u8]`, it is not possible for the inner reference to outlive the
/// grant itself.
///
/// You MUST guarantee that in no cases, the reference that is returned here outlives
/// the grant itself. Once the grant has been released, referencing the data contained
/// WILL cause undefined behavior.
///
/// Additionally, you must ensure that a separate reference to this data is not created
/// to this data, e.g. using `Deref` or the `buf()` method of this grant.
pub unsafe fn as_static_buf(&self) -> &'static [u8] {
transmute::<&[u8], &'static [u8]>(self.buf)
}
#[inline(always)]
pub(crate) fn release_inner(&mut self, used: usize) {
let inner = unsafe { &self.bbq.as_ref() };
// If there is no grant in progress, return early. This
// generally means we are dropping the grant within a
// wrapper structure
if !inner.read_in_progress.load(Acquire) {
return;
}
// This should always be checked by the public interfaces
debug_assert!(used <= self.buf.len());
// This should be fine, purely incrementing
let _ = atomic::fetch_add(&inner.read, used, Release);
inner.read_in_progress.store(false, Release);
}
/// Configures the amount of bytes to be released on drop.
pub fn to_release(&mut self, amt: usize) {
self.to_release = self.buf.len().min(amt);
}
}
impl<'a, const N: usize> SplitGrantR<'a, N> {
/// Release a sequence of bytes from the buffer, allowing the space
/// to be used by later writes. This consumes the grant.
///
/// If `used` is larger than the given grant, the full grant will
/// be released.
///
/// NOTE: If the `thumbv6` feature is selected, this function takes a short critical
/// section while releasing.
pub fn release(mut self, used: usize) {
// Saturate the grant release
let used = min(self.combined_len(), used);
self.release_inner(used);
forget(self);
}
/// Obtain access to both inner buffers for reading
///
/// ```
/// # // bbqueue test shim!
/// # fn bbqtest() {
/// use bbqueue::BBBuffer;
///
/// // Create and split a new buffer of 6 elements
/// let buffer: BBBuffer<6> = BBBuffer::new();
/// let (mut prod, mut cons) = buffer.try_split().unwrap();
///
/// // Successfully obtain and commit a grant of four bytes
/// let mut grant = prod.grant_max_remaining(4).unwrap();
/// grant.buf().copy_from_slice(&[1, 2, 3, 4]);
/// grant.commit(4);
///
/// // Obtain a read grant, and copy to a buffer
/// let mut grant = cons.read().unwrap();
/// let mut buf = [0u8; 4];
/// buf.copy_from_slice(grant.buf());
/// assert_eq!(&buf, &[1, 2, 3, 4]);
/// # // bbqueue test shim!
/// # }
/// #
/// # fn main() {
/// # #[cfg(not(feature = "thumbv6"))]