CSY/reowolf Changeset - 0e1a76667937 · Centrum Wiskunde & Informatica (CWI)

Changeset - 0e1a76667937

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MH - 3 years ago 2022-01-05 12:11:03
contact@maxhenger.nl

Started work on speculationless runtime

11 files changed with 1184 insertions and 246 deletions:

Cargo.toml

src/protocol/eval/executor.rs

src/protocol/eval/mod.rs

src/runtime2/communication.rs

src/runtime2/component.rs

216

src/runtime2/mod.rs

src/runtime2/runtime.rs

100

240

src/runtime2/scheduler.rs

src/runtime2/store/component.rs

559

src/runtime2/store/mod.rs

src/runtime2/store/unfair_se_lock.rs

194

0 comments (0 inline, 0 general)

Cargo.toml

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@@ @@ -33,9 +33,8 @@ libc = { version = "^0.2", optional = true } @@
 os_socketaddr = { version = "0.1.0", optional = true }
 [dev-dependencies]
 # test-generator = "0.3.0"
 crossbeam-utils = "0.7.2"
 lazy_static = "1.4.0"
 rand = "0.8.4"
 rand_pcg = "0.3.1"
 [lib]
 crate-type = [

src/protocol/eval/executor.rs

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@@ @@ -196,7 +196,7 @@ impl Frame { @@
+    }
+}
 type EvalResult = Result<EvalContinuation, EvalError>;
+pub type EvalResult = Result<EvalContinuation, EvalError>;
 #[derive(Debug)]
 pub enum EvalContinuation {

src/protocol/eval/mod.rs

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@@ @@ -27,5 +27,5 @@ pub(crate) mod error; @@
 pub use error::EvalError;
 pub use value::{PortId, Value, ValueGroup};
 pub use executor::{EvalContinuation, Prompt};
+pub use executor::{EvalContinuation, EvalResult, Prompt};

src/runtime2/communication.rs

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 use super::runtime::*;
 #[derive(Copy, Clone)]
 pub struct PortId(pub u32);
 impl PortId {
     pub fn new_invalid() -> Self {
         return Self(u32::MAX);
+    }
+}
 pub struct Peer {
     pub id: CompId,
     pub(crate) handle: CompHandle,
+}
 pub enum PortKind {
     Putter,
     Getter,
+}
 pub enum PortState {
     Open,
     Closed,
+}
 pub struct Port {
     pub self_id: PortId,
     pub peer_id: PortId,
     pub kind: PortKind,
     pub state: PortState,
     pub local_peer_index: u32,
+}
 /// Public inbox: accessible by all threads. Essentially a MPSC channel
 pub struct InboxPublic {
+}
@@ \ No newline at end of file @@

src/runtime2/component.rs

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 use crate::protocol::*;
 use crate::protocol::eval::{
     PortId as EvalPortId, Prompt,
     ValueGroup, Value,
     EvalContinuation, EvalResult, EvalError
 };
 use super::runtime::*;
 use super::scheduler::SchedulerCtx;
 use super::communication::*;
 pub enum CompScheduling {
     Immediate,
     Requeue,
     Sleep,
     Exit,
+}
 pub struct CompCtx {
     pub id: CompId,
     pub ports: Vec<Port>,
     pub peers: Vec<Peer>,
     pub messages: Vec<ValueGroup>, // same size as "ports"
+}
 impl CompCtx {
     fn take_message(&mut self, port_id: PortId) -> Option<ValueGroup> {
         let old_value = &mut self.messages[port_id.0 as usize];
         if old_value.values.is_empty() {
             return None;
+        }
         // Replace value in array with an empty one
         let mut message = ValueGroup::new_stack(Vec::new());
         std::mem::swap(old_value, &mut message);
         return Some(message);
+    }
     fn find_peer(&self, port_id: PortId) -> &Peer {
         let port_info = &self.ports[port_id.0 as usize];
         let peer_info = &self.peers[port_info.local_peer_index as usize];
         return peer_info;
+    }
+}
 pub enum ExecStmt {
     CreatedChannel((Value, Value)),
     PerformedPut,
     PerformedGet(ValueGroup),
     None,
+}
 impl ExecStmt {
     fn take(&mut self) -> ExecStmt {
         let mut value = ExecStmt::None;
         std::mem::swap(self, &mut value);
         return value;
+    }
     fn is_none(&self) -> bool {
         match self {
             ExecStmt::None => return true,
             _ => return false,
+        }
+    }
+}
 pub struct ExecCtx {
     stmt: ExecStmt,
+}
 impl RunContext for ExecCtx {
     fn performed_put(&mut self, _port: EvalPortId) -> bool {
         match self.stmt.take() {
             ExecStmt::None => return false,
             ExecStmt::PerformedPut => return true,
             _ => unreachable!(),
+        }
+    }
     fn performed_get(&mut self, _port: EvalPortId) -> Option<ValueGroup> {
         match self.stmt.take() {
             ExecStmt::None => return None,
             ExecStmt::PerformedGet(value) => return Some(value),
             _ => unreachable!(),
+        }
+    }
     fn fires(&mut self, _port: EvalPortId) -> Option<Value> {
         todo!("remove fires")
+    }
     fn performed_fork(&mut self) -> Option<bool> {
         todo!("remove fork")
+    }
     fn created_channel(&mut self) -> Option<(Value, Value)> {
         match self.stmt.take() {
             ExecStmt::None => return None,
             ExecStmt::CreatedChannel(ports) => return Some(ports),
             _ => unreachable!(),
+        }
+    }
+}
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub(crate) enum Mode {
     NonSync,
     Sync,
     BlockedGet,
     BlockedPut,
+}
 pub(crate) struct CompPDL {
     pub mode: Mode,
     pub mode_port: PortId, // when blocked on a port
     pub mode_value: ValueGroup, // when blocked on a put
     pub prompt: Prompt,
     pub exec_ctx: ExecCtx,
+}
 impl CompPDL {
     pub(crate) fn new(initial_state: Prompt) -> Self {
         return Self{
             mode: Mode::NonSync,
             mode_port: PortId::new_invalid(),
             mode_value: ValueGroup::default(),
             prompt: initial_state,
             exec_ctx: ExecCtx{
                 stmt: ExecStmt::None,
+            }
+        }
+    }
     pub(crate) fn run(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) -> Result<CompScheduling, EvalError> {
         use EvalContinuation as EC;
         let run_result = self.execute_prompt(&sched_ctx)?;
         match run_result {
             EC::Stepping => unreachable!(), // execute_prompt runs until this is no longer returned
             EC::BranchInconsistent | EC::NewFork | EC::BlockFires(_) => todo!("remove these"),
             // Results that can be returned in sync mode
             EC::SyncBlockEnd => {
                 debug_assert_eq!(self.mode, Mode::Sync);
                 self.handle_sync_end(sched_ctx, comp_ctx);
             },
             EC::BlockGet(port_id) => {
                 debug_assert_eq!(self.mode, Mode::Sync);
                 let port_id = transform_port_id(port_id);
                 if let Some(message) = comp_ctx.take_message(port_id) {
                     // We can immediately receive and continue
                     debug_assert!(self.exec_ctx.stmt.is_none());
                     self.exec_ctx.stmt = ExecStmt::PerformedGet(message);
                     return Ok(CompScheduling::Immediate);
                 } else {
                     // We need to wait
                     self.mode = Mode::BlockedGet;
                     self.mode_port = port_id;
                     return Ok(CompScheduling::Sleep);
+                }
             },
             EC::Put(port_id, value) => {
                 debug_assert_eq!(self.mode, Mode::Sync);
                 let port_id = transform_port_id(port_id);
                 let peer = comp_ctx.find_peer(port_id);
             },
             // Results that can be returned outside of sync mode
             EC::ComponentTerminated => {
                 debug_assert_eq!(self.mode, Mode::NonSync);
             },
             EC::SyncBlockStart => {
                 debug_assert_eq!(self.mode, Mode::NonSync);
                 self.handle_sync_start(sched_ctx, comp_ctx);
             },
             EC::NewComponent(definition_id, monomorph_idx, arguments) => {
                 debug_assert_eq!(self.mode, Mode::NonSync);
             },
             EC::NewChannel => {
                 debug_assert_eq!(self.mode, Mode::NonSync);
+            }
+        }
         return Ok(CompScheduling::Sleep);
+    }
     fn execute_prompt(&mut self, sched_ctx: &SchedulerCtx) -> EvalResult {
         let mut step_result = EvalContinuation::Stepping;
         while let EvalContinuation::Stepping = step_result {
             step_result = self.prompt.step(
                 &sched_ctx.runtime.protocol.types, &sched_ctx.runtime.protocol.heap,
                 &sched_ctx.runtime.protocol.modules, &mut self.exec_ctx,
             )?;
+        }
         return Ok(step_result)
+    }
     fn handle_sync_start(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) {
+    }
     fn handle_sync_end(&mut self, sched_ctx: &SchedulerCtx, comp_ctx: &mut CompCtx) {
+    }
+}
 #[inline]
 fn transform_port_id(port_id: EvalPortId) -> PortId {
     return PortId(port_id.id);
+}
@@ \ No newline at end of file @@

src/runtime2/mod.rs

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+mod store;
 mod runtime;
 mod component;
 mod communication;
 mod scheduler;
@@ \ No newline at end of file @@

src/runtime2/runtime.rs

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 use std::mem::{size_of, align_of, transmute};
 use std::alloc::{alloc, dealloc, Layout};
 use std::sync::Arc;
 use std::sync::atomic::{AtomicU32, AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex, Condvar};
 use std::sync::atomic::{AtomicU32, AtomicBool, Ordering};
 use std::collections::VecDeque;
 use crate::protocol::*;
 use super::component::{CompCtx, CompPDL};
 use super::store::ComponentStore;
 // -----------------------------------------------------------------------------
 // Component
 // -----------------------------------------------------------------------------
@@ @@ -12,37 +14,77 @@ use crate::protocol::*; @@
 /// Key to a component. Type system somewhat ensures that there can only be one
 /// of these. Only with a key one may retrieve privately-accessible memory for
 /// a component. Practically just a generational index, like `CompId` is.
 #[derive(Copy, Clone)]
 pub(crate) struct CompKey(CompId);
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub(crate) struct CompKey(u32);
 impl CompKey {
     pub(crate) fn downgrade(&self) -> CompId {
         return CompId(self.0);
+    }
+}
 /// Generational ID of a component
 #[derive(Copy, Clone)]
 pub(crate) struct CompId {
     pub index: u32,
     pub generation: u32,
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
 pub struct CompId(u32);
 impl CompId {
     pub(crate) fn new_invalid() -> CompId {
         return CompId(u32::MAX);
+    }
 impl PartialEq for CompId {
     fn eq(&self, other: &Self) -> bool {
         return self.index.eq(&other.index);
     /// Upgrade component ID to component key. Unsafe because the caller needs
     /// to make sure that only one component key can exist at a time (to ensure
     /// a component can only be scheduled/executed by one thread).
     pub(crate) unsafe fn upgrade(&self) -> CompKey {
         return CompKey(self.0);
+    }
+}
 impl Eq for CompId {}
 /// In-runtime storage of a component
 pub(crate) struct RtComp {
 pub(crate) struct RuntimeComp {
     pub public: CompPublic,
     pub private: CompPrivate,
+}
 /// Should contain everything that is accessible in a thread-safe manner
 pub(crate) struct CompPublic {
     pub sleeping: AtomicBool,
     pub num_handles: AtomicU32, // modified upon creating/dropping `CompHandle` instances
+}
 /// Handle to public part of a component.
 pub(crate) struct CompHandle {
     target: *const CompPublic,
+}
 impl std::ops::Deref for CompHandle {
     type Target = CompPublic;
     fn deref(&self) -> &Self::Target {
         return unsafe{ &*self.target };
+    }
+}
 /// May contain non thread-safe fields. Accessed only by the scheduler which
 /// will temporarily "own" the component.
 pub(crate) struct CompPrivate {
     pub code: CompPDL,
     pub ctx: CompCtx,
+}
 // -----------------------------------------------------------------------------
 // Runtime
 // -----------------------------------------------------------------------------
 type RuntimeHandle = Arc<Runtime>;
+pub type RuntimeHandle = Arc<Runtime>;
 /// Memory that is maintained by "the runtime". In practice it is maintained by
 /// multiple schedulers, and this serves as the common interface to that memory.
 pub struct Runtime {
     pub protocol: ProtocolDescription,
     components: ComponentStore<RuntimeComp>,
     work_queue: Mutex<VecDeque<CompKey>>,
     work_condvar: Condvar,
     active_elements: AtomicU32, // active components and APIs (i.e. component creators)
+}
@@ @@ -50,253 +92,71 @@ impl Runtime { @@
     pub fn new(num_threads: u32, protocol_description: ProtocolDescription) -> Runtime {
         assert!(num_threads > 0, "need a thread to perform work");
         return Runtime{
             protocol: protocol_description,
             components: ComponentStore::new(128),
             work_queue: Mutex::new(VecDeque::with_capacity(128)),
             work_condvar: Condvar::new(),
             active_elements: AtomicU32::new(0),
         };
+    }
+}
 // -----------------------------------------------------------------------------
 // Runtime containers
 // -----------------------------------------------------------------------------
 /// Component storage. Note that it shouldn't be polymorphic, but making it so
 /// allows us to test it more easily. The container is essentially a
 /// thread-safe freelist. The list always contains *all* free entries in the
 /// storage array.
 ///
 /// The freelist itself is implemented using a thread-safe ringbuffer. But there
 /// are some very important properties we exploit in this specific
 /// implementation of a ringbuffer. Note that writing to the ringbuffer (i.e.
 /// adding to the freelist) corresponds to destroying a component, and reading
 /// from the ringbuffer corresponds to creating a component. The aforementioned
 /// properties are: one can never write more to the ringbuffer than has been
 /// read from it (i.e. destroying more components than are created), we may
 /// safely assume that when the `CompStore` is dropped that no thread can access
 /// it (because they've all been shut down). This simplifies deallocation code.
 ///
 /// Internally each individual instance of `T` will be (de)allocated. So we will
 /// not store an array of `T`, but an array of `*T`. This keeps the storage of
 /// `T` pointer-stable (as is required for the schedulers actually running the
 /// components, because they'll fetch a component and then continue running it
 /// while this component storage might get reallocated).
 ///
 /// Note that there is still some unsafety here that is kept in check by the
 /// owner of this `CompStore`: the `CompId` and `CompKey` system ensures that
 /// only one mutable reference will ever be obtained, and potentially multiple
 /// immutable references. But in practice the `&mut T` will be used to access
 /// so-called "public" fields immutably, and "private" fields mutable. While the
 /// `&T` will only be used to access the "public" fields immutably.
 struct CompStore<T: Sized> {
     freelist: *mut u32,
     data: *mut *mut T,
     count: usize,
     mask: usize,
     byte_size: usize, // used for dealloc
     write_head: AtomicUsize,
     limit_head: AtomicUsize,
     read_head: AtomicUsize,
+}
 const fn compute_realloc_flag() -> usize {
     match size_of::<usize>() {
 => return 1 << 31, // 32-bit system
 => return 1 << 63, // 64-bit system
         _ => panic!("unexpected byte size for 'usize'")
+    }
+}
 impl<T: Sized> CompStore<T> {
     const REALLOC_FLAG: usize = compute_realloc_flag();
     fn new(initial_count: usize) -> Self {
         // Allocate data
         debug_assert!(size_of::<T>() > 0); // No ZST during testing (and definitely not in production)
         let (freelist, data, byte_size) = Self::alloc_buffer(initial_count);
         unsafe {
             // Init the freelist to all of the indices in the array of data
             let mut target = freelist;
             for idx in 0..initial_count as u32 {
                 *target = idx;
                 target += 1;
+            }
             // And init the data such that they're all NULL pointers
             std::ptr::write_bytes(data, 0, initial_count);
+        }
         return CompStore{
             freelist, data,
             count: initial_count,
             mask: initial_count - 1,
             byte_size,
             write_head: AtomicUsize::new(initial_count),
             limit_head: AtomicUsize::new(initial_count),
             read_head: AtomicUsize::new(0),
         };
+    }
     fn get_index_from_freelist(&self) -> u32 {
         let compare_mask = (self.count * 2) - 1;
         let mut read_index = self.read_head.load(Ordering::Acquire); // read index first
         'try_loop: loop {
             let limit_index = self.limit_head.load(Ordering::Acquire); // limit index second
     // Scheduling and retrieving work
             // By definition we always have `read_index <= limit_index` (if we would
             // have an infinite buffer, in reality we will wrap).
             if (read_index & compare_mask) == (limit_index & compare_mask) {
                 // We need to create a bigger buffer. Note that no reader can
                 // *ever* set the read index to beyond the limit index, and it
                 // is currently equal. So we're certain that there is no other
                 // reader currently updating the read_head.
                 //
                 // To test if we are supposed to resize the backing buffer we
                 // try set the REALLOC_FLAG on the limit index. Note that the
                 // stored indices are always in the range [0, 2*count). So if
                 // we add REALLOC_FLAG to the limit index, then the masked
                 // condition above still holds! Other potential readers will end
                 // up here and are allowed to wait until we resized the backing
                 // container.
                 //
                 // Furthermore, setting the limit index to this high value also
                 // notifies the writer that any of it writes should be tried
                 // again, as they're writing to a buffer that is going to get
                 // trashed.
                 todo!("finish reallocation code");
                 match self.limit_head.compare_exchange(limit_index, limit_index | Self::REALLOC_FLAG, Ordering::SeqCst, Ordering::Acquire) {
                     Ok(_) => {
                         // Limit index has changed, so we're now the ones that
                         // are supposed to resize the
+                    }
+                }
             } else {
                 // It seems we have space to read
                 let preemptive_read = unsafe { *self.freelist.add(read_index & self.mask) };
                 if let Err(new_read_index) = self.read_head.compare_exchange(read_index, (read_index + 1) & compare_mask, Ordering::SeqCst, Ordering::Acquire) {
                     // Failed to do the CAS, try again. We need to start at the
                     // start again because we might have had other readers that
                     // were successful, so at the very least, the preemptive
                     // read we did is no longer correct.
                     read_index = new_read_index;
                     continue 'try_loop;
     pub(crate) fn take_work(&self) -> Option<CompKey> {
         let mut lock = self.work_queue.lock().unwrap();
         while lock.is_empty() && self.active_elements.load(Ordering::Acquire) != 0 {
             lock = self.work_condvar.wait(lock).unwrap();
+        }
                 // We now "own" the value at the read index
                 return preemptive_read;
+            }
+        }
         return lock.pop_front();
+    }
     fn put_back_index_into_freelist(&self, index: u32) {
         let mut compare_mask = (self.count * 2) - 1;
         let mut write_index = self.write_head.load(Ordering::Acquire);
         while let Err(new_write_index) = self.write_head.compare_exchange(write_index, (write_index + 1) & compare_mask, Ordering::SeqCst, Ordering::Acquire) {
             // Failed to do the CAS, try again
             write_index = new_write_index;
     pub(crate) fn enqueue_work(&self, key: CompKey) {
         let mut lock = self.work_queue.lock().unwrap();
         lock.push_back(key);
         self.work_condvar.notify_one();
+    }
         'try_write_loop: loop {
             // We are now the only ones that can write at `write_index`. Try to
             // do so
             unsafe { *self.freelist.add(write_index & self.mask) = index; }
     // Creating/destroying components
             // But we still need to move the limit head. Only succesful writers
             // may move it so we expect it to move from the `write_index` to
             // `write_index + 1`, but we might have to spin to achieve it.
             // Furthermore, the `limit_head` is used by the index-retrieval
             // function to indicate that a read is in progress.
             'commit_to_write_loop: loop {
                 match self.limit_head.compare_exchange(write_index, (write_index + 1) & compare_mask, Ordering::SeqCst, Ordering::Acquire) {
                     Ok(_) => break,
                     Err(new_value) => {
                         // Two options: the limit is not yet what we expect it
                         // to be. If so, just try again with the old values.
                         // But if it is very large (relatively) then this is the
                         // signal from the reader that the entire storage is
                         // being resized
                         if new_value & Self::REALLOC_FLAG != 0 {
                             // Someone is resizing, wait until that is no longer
                             // true.
                             while self.limit_head.load(Ordering::Acquire) & Self::REALLOC_FLAG != 0 {
                                 // still resizing
+                            }
                             // Not resizing anymore, try everything again, our
                             // old write has now become invalid. But our index
                             // hasn't! So we need to finish our write and our
                             // increment of the limit head
                             continue 'try_write_loop;
                         } else {
                             // Just try again
                             continue 'commit_to_write_loop;
+                        }
+                    }
     pub(crate) fn create_pdl_component(&self, comp: CompPDL, initially_sleeping: bool) -> CompKey {
         let comp = RuntimeComp{
             public: CompPublic{
                 sleeping: AtomicBool::new(initially_sleeping),
                 num_handles: AtomicU32::new(1), // the component itself acts like a handle
             },
             private: CompPrivate{
                 code: comp,
                 ctx: CompCtx{
                     id: CompId(0),
                     ports: Vec::new(),
                     peers: Vec::new(),
                     messages: Vec::new(),
+                }
+            }
         };
             // We updated the limit head, so we're done :)
             return;
+        }
+    }
         let index = self.components.create(comp);
     /// Retrieves a `&T` from the store. This should be retrieved using `create`
     /// and not yet given back by calling `destroy`.
     fn get(&self, index: u32) -> &T {
         // TODO: just do a reserve_index followed by a consume_index or something
         self.components.get_mut(index).private.ctx.id = CompId(index);
         return CompKey(index);
+    }
     /// Same as `get`, but now returning a mutable `&mut T`. Make sure that you
     /// know what you're doing :)
     fn get_mut(&self, index: u32) -> &mut T {
     pub(crate) fn get_component(&self, key: CompKey) -> &mut RuntimeComp {
         let component = self.components.get_mut(key.0);
         return component;
+    }
     fn alloc_buffer(num: usize) -> (*mut u32, *mut *mut T, usize) {
         // Probably overkill considering the amount of memory that is needed to
         // exceed this number. But still: ensure `num` adheres to the
         // requirements needed for correct functioning of the store.
         assert!(
             num >= 8 && num <= u32::MAX as usize / 4 && num.is_power_of_two(),
             "invalid allocation count for CompStore buffer"
         );
         // Compute byte size of freelist (so we assume alignment of `u32`)
         let mut byte_size = num * size_of::<u32>();
         // Align to `*mut T`, then reserve space for all of the pointers
         byte_size = Self::align_to(byte_size, align_of::<*mut T>());
         let byte_offset_data = byte_size;
         byte_size += num * size_of::<T>;
         unsafe {
             // Allocate, then retrieve pointers to allocated regions
             let layout = Self::layout_for(byte_size);
             let memory = alloc(layout);
             let base_free: *mut u32 = transmute(memory);
             let base_data: *mut *mut T = transmute(memory.add(byte_offset_data));
             return (base_free, base_data, byte_size);
+        }
+    }
     fn dealloc_buffer(freelist: *mut u32, _data: *mut *mut T, byte_size: usize) {
         // Note: we only did one allocation, freelist is at the front
         let layout = Self::layout_for(byte_size);
         unsafe {
             let base: *mut u8 = transmute(freelist);
             dealloc(base, layout);
+        }
     pub(crate) fn get_component_public(&self, id: CompId) -> &CompPublic {
         let component = self.components.get(id.0);
         return &component.public;
+    }
     fn layout_for(byte_size: usize) -> Layout {
         debug_assert!(byte_size % size_of::<u32>() == 0);
         return unsafe{ Layout::from_size_align_unchecked(byte_size, align_of::<u32>()) };
     pub(crate) fn destroy_component(&self, key: CompKey) {
         self.components.destroy(key.0);
+    }
     fn align_to(offset: usize, alignment: usize) -> usize {
         debug_assert!(alignment.is_power_of_two());
         let mask = alignment - 1;
         return (offset + mask) & !mask;
+    }
     // Interacting with components
+}

src/runtime2/scheduler.rs

➞

Show inline comments

@@ new file 100644 @@
 use std::sync::atomic::Ordering;
 use super::component::*;
 use super::runtime::*;
 /// Data associated with a scheduler thread
 pub(crate) struct Scheduler {
     runtime: RuntimeHandle,
     scheduler_id: u32,
+}
 pub(crate) struct SchedulerCtx<'a> {
     pub runtime: &'a Runtime,
+}
 impl Scheduler {
     // public interface to thread
     pub fn new(runtime: RuntimeHandle, scheduler_id: u32) -> Self {
         return Scheduler{ runtime, scheduler_id }
+    }
     pub fn run(&mut self) {
         let scheduler_ctx = SchedulerCtx{ runtime: &*self.runtime };
         'run_loop: loop {
             // Wait until we have something to do (or need to quit)
             let comp_key = self.runtime.take_work();
             if comp_key.is_none() {
                 break 'run_loop;
+            }
             let comp_key = comp_key.unwrap();
             let comp_id = comp_key.downgrade();
             let component = self.runtime.get_component(comp_key);
             // Run the component until it no longer indicates that it needs to
             // be re-executed immediately.
             let mut new_scheduling = CompScheduling::Immediate;
             while let CompScheduling::Immediate = new_scheduling {
                 new_scheduling = component.private.code.run(&scheduler_ctx, &mut component.private.ctx).expect("TODO: Handle error");
+            }
             // Handle the new scheduling
             match new_scheduling {
                 CompScheduling::Immediate => unreachable!(),
                 CompScheduling::Requeue => { self.runtime.enqueue_work(comp_key); },
                 CompScheduling::Sleep => { self.mark_component_as_sleeping(comp_key, component); },
                 CompScheduling::Exit => { self.mark_component_as_exiting(comp_key, component); }
+            }
+        }
+    }
     // local utilities
     fn mark_component_as_sleeping(&self, key: CompKey, component: &mut RuntimeComp) {
         debug_assert_eq!(key.downgrade(), component.private.ctx.id); // make sure component matches key
         debug_assert_eq!(component.public.sleeping.load(Ordering::Acquire), false); // we're executing it, so it cannot be sleeping
         component.public.sleeping.store(true, Ordering::Release);
         todo!("check for messages");
+    }
     fn mark_component_as_exiting(&self, key: CompKey, component: &mut RuntimeComp) {
         todo!("do something")
+    }
+}
@@ \ No newline at end of file @@

src/runtime2/store/component.rs

➞

Show inline comments

@@ new file 100644 @@
 /*
  * Component Store
+ *
  * Concurrent datastructure for creating/destroying/retrieving components using
  * their ID. It is essentially a variation on a concurrent freelist. We store an
  * array of (potentially null) pointers to data. Indices into this array that
  * are unused (but may be left allocated) are in a freelist. So creating a new
  * bit of data involves taking an index from this freelist. Destruction involves
  * putting the index back.
+ *
  * This datastructure takes care of the threadsafe implementation of the
  * freelist and calling the data's destructor when needed. Note that it is not
  * completely safe (in Rust's sense of the word) because it is possible to
  * get more than one mutable reference to a piece of data. Likewise it is
  * possible to put back bogus indices into the freelist, which will destroy the
  * integrity of the datastructure.
+ *
  * Some underlying assumptions that led to this design (note that I haven't
  * actually checked these conditions or performed any real profiling, yet):
  *  - Resizing the freelist should be very rare. The datastructure should grow
  *    to some kind of maximum size and stay at that size.
  *  - Creation should (preferably) be faster than deletion of data. Reason being
  *    that creation implies we're creating a component that has code to be
  *    executed. Better to quickly be able to execute code than being able to
  *    quickly tear down finished components.
  *  - Retrieval is much more likely than creation/destruction.
+ *
  * Some obvious flaws with this implementation:
  *  - Because of the freelist implementation we will generally allocate all of
  *    the data pointers that are available (i.e. if we have a buffer of size
  *    64, but we generally use 33 elements, than we'll have 64 elements
  *    allocated), which might be wasteful at larger array sizes (which are
  *    always powers of two).
  *  - A lot of concurrent operations are not necessary: we may move some of the
  *    access to the global concurrent datastructure by an initial access to some
  *    kind of thread-local datastructure.
  */
 use std::mem::transmute;
 use std::alloc::{alloc, dealloc, Layout};
 use std::ptr;
 use std::sync::atomic::{AtomicUsize, Ordering};
 use super::unfair_se_lock::{UnfairSeLock, UnfairSeLockSharedGuard};
 pub struct ComponentStore<T: Sized> {
     inner: UnfairSeLock<Inner<T>>,
     read_head: AtomicUsize,
     write_head: AtomicUsize,
     limit_head: AtomicUsize,
+}
 unsafe impl<T: Sized> Send for ComponentStore<T>{}
 unsafe impl<T: Sized> Sync for ComponentStore<T>{}
 struct Inner<T: Sized> {
     freelist: Vec<u32>,
     data: Vec<*mut T>,
     size: usize,
     compare_mask: usize,
     index_mask: usize,
+}
 type InnerRead<'a, T> = UnfairSeLockSharedGuard<'a, Inner<T>>;
 impl<T: Sized> ComponentStore<T> {
     pub fn new(initial_size: usize) -> Self {
         Self::assert_valid_size(initial_size);
         // Fill initial freelist and preallocate data array
         let mut initial_freelist = Vec::with_capacity(initial_size);
         for idx in 0..initial_size {
             initial_freelist.push(idx as u32)
+        }
         let mut initial_data = Vec::new();
         initial_data.resize(initial_size, ptr::null_mut());
         // Return initial store
         return Self{
             inner: UnfairSeLock::new(Inner{
                 freelist: initial_freelist,
                 data: initial_data,
                 size: initial_size,
                 compare_mask: 2*initial_size - 1,
                 index_mask: initial_size - 1,
             }),
             read_head: AtomicUsize::new(0),
             write_head: AtomicUsize::new(initial_size),
             limit_head: AtomicUsize::new(initial_size),
         };
+    }
     /// Creates a new element initialized to the provided `value`. This returns
     /// the index at which the element can be retrieved.
     pub fn create(&self, value: T) -> u32 {
         let lock = self.inner.lock_shared();
         let (lock, index) = self.pop_freelist_index(lock);
         self.initialize_at_index(lock, index, value);
         return index;
+    }
     /// Destroys an element at the provided `index`. The caller must make sure
     /// that it does not use any previously received references to the data at
     /// this index, and that no more calls to `get` are performed using this
     /// index. This is allowed again if the index has been reacquired using
     /// `create`.
     pub fn destroy(&self, index: u32) {
         let lock = self.inner.lock_shared();
         self.destruct_at_index(&lock, index);
         self.push_freelist_index(&lock, index);
+    }
     /// Retrieves an element by reference
     pub fn get(&self, index: u32) -> &T {
         let lock = self.inner.lock_shared();
         let value = lock.data[index as usize];
         unsafe {
             debug_assert!(!value.is_null());
             return &*value;
+        }
+    }
     /// Retrieves an element by mutable reference. The caller should ensure that
     /// use of that mutability is thread-safe
     pub fn get_mut(&self, index: u32) -> &mut T {
         let lock = self.inner.lock_shared();
         let value = lock.data[index as usize];
         unsafe {
             debug_assert!(!value.is_null());
             return &mut *value;
+        }
+    }
     #[inline]
     fn pop_freelist_index<'a>(&'a self, mut read_lock: InnerRead<'a, T>) -> (InnerRead<'a, T>, u32) {
         'attempt_read: loop {
             // Load indices and check for reallocation condition
             let current_size = read_lock.size;
             let mut read_index = self.read_head.load(Ordering::Relaxed);
             let limit_index = self.limit_head.load(Ordering::Acquire);
             if read_index == limit_index {
                 read_lock = self.reallocate(current_size, read_lock);
                 continue 'attempt_read;
+            }
             loop {
                 let preemptive_read = read_lock.freelist[read_index & read_lock.index_mask];
                 if let Err(actual_read_index) = self.read_head.compare_exchange(
                     read_index, (read_index + 1) & read_lock.compare_mask,
                     Ordering::AcqRel, Ordering::Acquire
                 ) {
                     // We need to try again
                     read_index = actual_read_index;
                     continue 'attempt_read;
+                }
                 // If here then we performed the read
                 return (read_lock, preemptive_read);
+            }
+        }
+    }
     #[inline]
     fn initialize_at_index(&self, read_lock: InnerRead<T>, index: u32, value: T) {
         let mut target_ptr = read_lock.data[index as usize];
         unsafe {
             if target_ptr.is_null() {
                 let layout = Layout::for_value(&value);
                 target_ptr = std::alloc::alloc(layout).cast();
                 let rewrite: *mut *mut T = transmute(read_lock.data.as_ptr());
                 *rewrite.add(index as usize) = target_ptr;
+            }
             std::ptr::write(target_ptr, value);
+        }
+    }
     #[inline]
     fn push_freelist_index(&self, read_lock: &InnerRead<T>, index_to_put_back: u32) {
         // Acquire an index in the freelist to which we can write
         let mut cur_write_index = self.write_head.load(Ordering::Relaxed);
         let mut new_write_index = (cur_write_index + 1) & read_lock.compare_mask;
         while let Err(actual_write_index) = self.write_head.compare_exchange(
             cur_write_index, new_write_index,
             Ordering::AcqRel, Ordering::Acquire
         ) {
             cur_write_index = actual_write_index;
             new_write_index = (cur_write_index + 1) & read_lock.compare_mask;
+        }
         // We own the data at the index, write to it and notify reader through
         // limit_head that it can be read from. Note that we cheat around the
         // rust mutability system here :)
         unsafe {
             let target: *mut u32 = transmute(read_lock.freelist.as_ptr());
             *(target.add(cur_write_index & read_lock.index_mask)) = index_to_put_back;
+        }
         // Essentially spinlocking, relaxed failure ordering because the logic
         // is that a write first moves the `write_head`, then the `limit_head`.
         while let Err(_) = self.limit_head.compare_exchange(
             cur_write_index, new_write_index,
             Ordering::AcqRel, Ordering::Relaxed
         ) {};
+    }
     #[inline]
     fn destruct_at_index(&self, read_lock: &InnerRead<T>, index: u32) {
         let target_ptr = read_lock.data[index as usize];
         unsafe{ ptr::drop_in_place(target_ptr); }
+    }
     fn reallocate(&self, old_size: usize, inner: InnerRead<T>) -> InnerRead<T> {
         drop(inner);
+        {
             // After dropping read lock, acquire write lock
             let mut lock = self.inner.lock_exclusive();
             if old_size == lock.size {
                 // We are the thread that is supposed to reallocate
                 let new_size = old_size * 2;
                 Self::assert_valid_size(new_size);
                 // Note that the atomic indices are in the range [0, new_size)
                 // already, so we need to be careful
                 let new_index_mask = new_size - 1;
                 let new_compare_mask = (2 * new_size) - 1;
                 lock.data.resize(new_size, ptr::null_mut());
                 lock.freelist.resize(new_size, 0);
                 for idx in 0..old_size {
                     lock.freelist[old_size + idx] = lock.freelist[idx];
+                }
                 // We need to fill the freelist with the indices of all of the
                 // new elements that we have just created.
                 debug_assert_eq!(self.limit_head.load(Ordering::SeqCst), self.write_head.load(Ordering::SeqCst));
                 let old_read_index = self.read_head.load(Ordering::SeqCst);
                 let old_write_index = self.write_head.load(Ordering::SeqCst);
                 if old_read_index > old_write_index {
                     // Read index wraps, so keep it as-is and fill
                     let new_read_index = old_read_index + old_size;
                     for index in 0..old_size {
                         let target_idx = (new_read_index + index) & new_index_mask;
                         lock.freelist[target_idx] = (old_size + index) as u32;
+                    }
                     self.read_head.store(new_read_index, Ordering::SeqCst);
                     debug_assert!(new_read_index < 2*new_size);
                     debug_assert!(old_write_index.wrapping_sub(new_read_index) & new_compare_mask <= new_size);
                 } else {
                     // No wrapping, so increment write index
                     let new_write_index = old_write_index + old_size;
                     for index in 0..old_size {
                         let target_idx = (old_write_index + index) & new_index_mask;
                         lock.freelist[target_idx] = (old_size + index) as u32;
+                    }
                     // Update write/limit heads
                     self.write_head.store(new_write_index, Ordering::SeqCst);
                     self.limit_head.store(new_write_index, Ordering::SeqCst);
                     debug_assert!(new_write_index < 2*new_size);
                     debug_assert!(new_write_index.wrapping_sub(old_read_index) & new_compare_mask <= new_size);
+                }
                 // Update sizes and masks
                 lock.size = new_size;
                 lock.compare_mask = new_compare_mask;
                 lock.index_mask = new_index_mask;
             } // else: someone else allocated, so we don't have to
+        }
         // We've dropped the write lock, acquire the read lock again
         return self.inner.lock_shared();
+    }
     #[inline]
     fn assert_valid_size(size: usize) {
         // Condition the size needs to adhere to. Some are a bit excessive, but
         // we don't hit this check very often
         assert!(
             size.is_power_of_two() &&
                 size >= 4 &&
                 size <= usize::MAX / 2 &&
                 size <= u32::MAX as usize
         );
+    }
+}
 impl<T: Sized> Drop for ComponentStore<T> {
     fn drop(&mut self) {
         let value_layout = Layout::from_size_align(
             std::mem::size_of::<T>(), std::mem::align_of::<T>()
         ).unwrap();
         // Note that if the indices exist in the freelist then the destructor
         // has already been called. So handle them first
         let mut lock = self.inner.lock_exclusive();
         let read_index = self.read_head.load(Ordering::Acquire);
         let write_index = self.write_head.load(Ordering::Acquire);
         debug_assert_eq!(write_index, self.limit_head.load(Ordering::Acquire));
         let mut index = read_index;
         while index != write_index {
             let dealloc_index = lock.freelist[index & lock.index_mask] as usize;
             let target_ptr = lock.data[dealloc_index];
             unsafe {
                 dealloc(target_ptr.cast(), value_layout);
                 lock.data[dealloc_index] = ptr::null_mut();
+            }
             index += 1;
             index &= lock.compare_mask;
+        }
         // With all of those set to null, we'll just iterate through all
         // pointers and destruct+deallocate the ones not set to null yet
         for target_ptr in lock.data.iter().copied() {
             if !target_ptr.is_null() {
                 unsafe {
                     ptr::drop_in_place(target_ptr);
                     dealloc(target_ptr.cast(), value_layout);
+                }
+            }
+        }
+    }
+}
 #[cfg(test)]
 mod tests {
     use super::*;
     use rand::prelude::*;
     use rand_pcg::Pcg32;
     use std::sync::Arc;
     use std::sync::atomic::{AtomicU64, Ordering};
     pub struct Resource {
         dtor: Arc<AtomicU64>,
         val: u64,
+    }
     impl Resource {
         fn new(ctor: Arc<AtomicU64>, dtor: Arc<AtomicU64>, val: u64) -> Self {
             ctor.fetch_add(1, Ordering::SeqCst);
             return Self{ dtor, val };
+        }
+    }
     impl Drop for Resource {
         fn drop(&mut self) {
             self.dtor.fetch_add(1, Ordering::SeqCst);
+        }
+    }
     fn seeds() -> Vec<[u8;16]> {
         return vec![
             [241, 47, 70, 87, 240, 246, 20, 173, 219, 143, 74, 23, 158, 58, 205, 172],
             [178, 112, 230, 205, 230, 178, 2, 90, 162, 218, 49, 196, 224, 222, 208, 43],
             [245, 42, 35, 167, 153, 205, 221, 144, 200, 253, 144, 117, 176, 231, 17, 70],
             [143, 39, 177, 216, 124, 96, 225, 39, 30, 82, 239, 193, 133, 58, 255, 193],
             [25, 105, 10, 52, 161, 212, 190, 112, 178, 193, 68, 249, 167, 153, 172, 144],
+        ]
+    }
     #[test]
     fn test_ctor_dtor_simple_unthreaded() {
         const NUM_ROUNDS: usize = 5;
         const NUM_ELEMENTS: usize = 1024;
         let store = ComponentStore::new(32);
         let ctor_counter = Arc::new(AtomicU64::new(0));
         let dtor_counter = Arc::new(AtomicU64::new(0));
         let mut indices = Vec::with_capacity(NUM_ELEMENTS);
         for _round_index in 0..NUM_ROUNDS {
             // Creation round
             for value in 0..NUM_ELEMENTS {
                 let new_resource = Resource::new(ctor_counter.clone(), dtor_counter.clone(), value as u64);
                 let new_index = store.create(new_resource);
                 indices.push(new_index);
+            }
             // Checking round
             for el_index in indices.iter().copied() {
                 let element = store.get(el_index);
                 assert_eq!(element.val, el_index as u64);
+            }
             // Destruction round
             for el_index in indices.iter().copied() {
                 store.destroy(el_index);
+            }
             indices.clear();
+        }
         let num_ctor_calls = ctor_counter.load(Ordering::Acquire);
         let num_dtor_calls = dtor_counter.load(Ordering::Acquire);
         assert_eq!(num_ctor_calls, num_dtor_calls);
         assert_eq!(num_ctor_calls, (NUM_ROUNDS * NUM_ELEMENTS) as u64);
+    }
     #[test]
     fn test_ctor_dtor_simple_threaded() {
         const MAX_SIZE: usize = 1024;
         const NUM_THREADS: usize = 4;
         const NUM_PER_THREAD: usize = MAX_SIZE / NUM_THREADS;
         const NUM_ROUNDS: usize = 4;
         assert!(MAX_SIZE % NUM_THREADS == 0);
         let store = Arc::new(ComponentStore::new(16));
         let ctor_counter = Arc::new(AtomicU64::new(0));
         let dtor_counter = Arc::new(AtomicU64::new(0));
         let mut threads = Vec::with_capacity(NUM_THREADS);
         for thread_index in 0..NUM_THREADS {
             // Setup local clones to move into the thread
             let store = store.clone();
             let first_index = thread_index * NUM_PER_THREAD;
             let last_index = (thread_index + 1) * NUM_PER_THREAD;
             let ctor_counter = ctor_counter.clone();
             let dtor_counter = dtor_counter.clone();
             let handle = std::thread::spawn(move || {
                 let mut indices = Vec::with_capacity(last_index - first_index);
                 for _round_index in 0..NUM_ROUNDS {
                     // Creation round
                     for value in first_index..last_index {
                         let el_index = store.create(Resource::new(ctor_counter.clone(), dtor_counter.clone(), value as u64));
                         indices.push(el_index);
+                    }
                     // Checking round
                     for (value_offset, el_index) in indices.iter().copied().enumerate() {
                         let element = store.get(el_index);
                         assert_eq!(element.val, (first_index + value_offset) as u64);
+                    }
                     // Destruction round
                     for el_index in indices.iter().copied() {
                         store.destroy(el_index);
+                    }
                     indices.clear();
+                }
             });
             threads.push(handle);
+        }
         for thread in threads {
             thread.join().expect("clean exit");
+        }
         let num_ctor_calls = ctor_counter.load(Ordering::Acquire);
         let num_dtor_calls = dtor_counter.load(Ordering::Acquire);
         assert_eq!(num_ctor_calls, num_dtor_calls);
         assert_eq!(num_ctor_calls, (NUM_ROUNDS * MAX_SIZE) as u64);
+    }
     #[test]
     fn test_ctor_dtor_random_threaded() {
         const NUM_ROUNDS: usize = 4;
         const NUM_THREADS: usize = 4;
         const NUM_OPERATIONS: usize = 1024;
         const NUM_OPS_PER_THREAD: usize = NUM_OPERATIONS / NUM_THREADS;
         const NUM_OPS_PER_ROUND: usize = NUM_OPS_PER_THREAD / NUM_ROUNDS;
         const NUM_STORED_PER_THREAD: usize = 32;
         assert!(NUM_OPERATIONS % NUM_THREADS == 0);
         assert!(NUM_OPS_PER_THREAD / 2 > NUM_STORED_PER_THREAD);
         let seeds = seeds();
         for seed_index in 0..seeds.len() {
             // Setup store, counters and threads
             let store = Arc::new(ComponentStore::new(16));
             let ctor_counter = Arc::new(AtomicU64::new(0));
             let dtor_counter = Arc::new(AtomicU64::new(0));
             let mut threads = Vec::with_capacity(NUM_THREADS);
             for thread_index in 0..NUM_THREADS {
                 // Setup local clones to move into the thread
                 let store = store.clone();
                 let ctor_counter = ctor_counter.clone();
                 let dtor_counter = dtor_counter.clone();
                 // Setup local rng
                 let mut seed = seeds[seed_index];
                 for seed_val_idx in 0..16 {
                     seed[seed_val_idx] ^= thread_index as u8; // blegh
+                }
                 let mut rng = Pcg32::from_seed(seed);
                 let handle = std::thread::spawn(move || {
                     let mut stored = Vec::with_capacity(NUM_STORED_PER_THREAD);
                     for _round_index in 0..NUM_ROUNDS {
                         // Modify store elements in the store randomly, for some
                         // silly definition of random
                         for _op_index in 0..NUM_OPS_PER_ROUND {
                             // Perform a single operation, depending on current
                             // size of the number of values owned by this thread
                             let new_value = rng.next_u64();
                             let should_create = rng.next_u32() % 2 == 0;
                             let is_empty = stored.is_empty();
                             let is_full = stored.len() == NUM_STORED_PER_THREAD;
                             if is_empty || (!is_full && should_create) {
                                 // Must create
                                 let el_index = store.create(Resource::new(
                                     ctor_counter.clone(), dtor_counter.clone(), new_value
                                 ));
                                 stored.push((el_index, new_value));
                             } else {
                                 // Must destroy
                                 let stored_index = new_value as usize % stored.len();
                                 let (el_index, el_value) = stored.remove(stored_index);
                                 store.destroy(el_index);
+                            }
+                        }
                         // Checking if the values we own still make sense
                         for (el_index, value) in stored.iter().copied() {
                             let gotten = store.get(el_index);
                             assert_eq!(value, gotten.val, "failed at thread {} value {}", thread_index, el_index);
+                        }
+                    }
                     return stored.len(); // return number of remaining elements
                 });
                 threads.push(handle);
+            }
             // Done with the current round
             let mut total_left_allocated = 0;
             for thread in threads {
                 let num_still_stored = thread.join().unwrap();
                 total_left_allocated += num_still_stored as u64;
+            }
             // Before store is dropped
             let num_ctor_calls = ctor_counter.load(Ordering::Acquire);
             let num_dtor_calls = dtor_counter.load(Ordering::Acquire);
             assert_eq!(num_ctor_calls - total_left_allocated, num_dtor_calls);
             // After store is dropped
             drop(store);
             let num_dtor_calls = dtor_counter.load(Ordering::Acquire);
             assert_eq!(num_ctor_calls, num_dtor_calls);
+        }
+    }
+}
@@ \ No newline at end of file @@

src/runtime2/store/mod.rs

➞

Show inline comments

@@ new file 100644 @@
 pub mod component;
 pub mod unfair_se_lock;
 pub(crate) use component::ComponentStore;

src/runtime2/store/unfair_se_lock.rs

➞

Show inline comments

@@ new file 100644 @@
 use std::cell::UnsafeCell;
 use std::sync::atomic::{AtomicU32, Ordering};
 /// An unfair shared/exclusive lock. One may quickly describe this to be an
 /// unfair RwLock where a thread that wishes to write will get to write as fast
 /// as possible (i.e. waiting for readers to finish), but others writers in line
 /// may have to wait for another round of readers acquiring the lock.
 ///
 /// However, this is NOT a read/write lock. It is a shared/exclusive lock. It is
 /// used in concurrent datastructures (implemented with atomics), so particular
 /// kinds of writing may still occur by the threads holding a shared lock. In
 /// that case the programmer must make sure that these writes are coordinated
 /// in a thread-safe manner.
 ///
 /// It was designed with resizable (ring)buffers in mind: most often you have
 /// the standard atomic pointers/indices moving around in the ringbuffer. But
 /// when the buffer needs to be resized you need to be sure that no-one is
 /// reading/writing the wrong/old/deallocated buffer pointer. Hence the
 /// shared/exclusive terminology.
 ///
 /// For this reason the `UnfairSeLock` was written assuming that exclusive locks
 /// are only held sometime: shared locks are obtained most of the time.
 // Note: preliminary benchmark batches shows this is ~2x faster than a RwLock
 // when under some contention.
 pub struct UnfairSeLock<T> {
     // Uses 31 bits to track number of shared locks, and the high bit is set if
     // an exclusive lock is supposed to be held. 31 bits is more than sufficient
     // because in this project shared locks will be held by individual threads.
     shared: AtomicU32,
     cell: UnsafeCell<T>,
+}
 // Exclusive bit is set in the atomic value when a thread wishes to hold an
 // exclusive lock.
 const EXCLUSIVE_BIT: u32 = 1 << 31;
 impl<T> UnfairSeLock<T> {
     pub fn new(value: T) -> Self {
         return Self{
             shared: AtomicU32::new(0),
             cell: UnsafeCell::new(value),
+        }
+    }
     /// Get shared access to the underlying data.
     #[must_use]
     pub fn lock_shared(&self) -> UnfairSeLockSharedGuard<T> {
         let mut shared = self.shared.load(Ordering::Relaxed);
         loop {
             if shared & EXCLUSIVE_BIT != 0 {
                 shared = self.wait_until_not_exclusive(shared);
+            }
             // Spinlock until we've incremented. If we fail we need to check the
             // exclusive bit again.
             let new_shared = shared + 1;
             match self.shared.compare_exchange(shared, new_shared, Ordering::AcqRel, Ordering::Acquire) {
                 Ok(_) => return UnfairSeLockSharedGuard::new(self, new_shared),
                 Err(actual_value) => { shared = actual_value; },
+            }
+        }
+    }
     /// Get exclusive access to the underlying data.
     #[must_use]
     pub fn lock_exclusive(&self) -> UnfairSeLockExclusiveGuard<T> {
         let mut shared = self.shared.load(Ordering::Relaxed);
         loop {
             if shared & EXCLUSIVE_BIT != 0 {
                 shared = self.wait_until_not_exclusive(shared);
+            }
             // We want to set the write bit
             let new_shared = shared | EXCLUSIVE_BIT;
             match self.shared.compare_exchange(shared, new_shared, Ordering::AcqRel, Ordering::Acquire) {
                 Ok(_) => {
                     // We've acquired the write lock, but we still might have
                     // to wait until the reader count is at 0.
                     shared = new_shared;
                     if shared != EXCLUSIVE_BIT {
                         shared = self.wait_until_not_shared(shared);
+                    }
                     return UnfairSeLockExclusiveGuard::new(self);
                 },
                 Err(actual_value) => { shared = actual_value; }
+            }
+        }
+    }
     fn wait_until_not_exclusive(&self, mut shared: u32) -> u32 {
         // Assume this is only called when the EXCLUSIVE_BIT is set
         debug_assert_eq!(shared & EXCLUSIVE_BIT, EXCLUSIVE_BIT);
         loop {
             // So spin until no longer held
             shared = self.shared.load(Ordering::Acquire);
             if shared & EXCLUSIVE_BIT == 0 {
                 return shared;
+            }
+        }
+    }
     #[inline]
     fn wait_until_not_shared(&self, mut shared: u32) -> u32 {
         // This is only called when someone has signaled the exclusive bit, but
         // there are still threads holding the shared lock.
         loop {
             debug_assert_eq!(shared & EXCLUSIVE_BIT, EXCLUSIVE_BIT);
             if shared == EXCLUSIVE_BIT {
                 // shared count is 0
                 return shared;
+            }
             shared = self.shared.load(Ordering::Acquire);
+        }
+    }
+}
 /// A guard signifying that the owner has shared access to the underlying
 /// `UnfairSeLock`.
 pub struct UnfairSeLockSharedGuard<'a, T> {
     lock: &'a UnfairSeLock<T>,
     initial_value: u32,
+}
 impl<'a, T> UnfairSeLockSharedGuard<'a, T> {
     fn new(lock: &'a UnfairSeLock<T>, initial_value: u32) -> Self {
         return Self{ lock, initial_value };
+    }
     /// Force retrieval of the underlying type `T` in the mutable sense. Note
     /// that the caller is now responsible for ensuring that concurrent mutable
     /// access takes place in a correct fashion.
     #[inline]
     pub unsafe fn get_mut(&self) -> &mut T {
         return unsafe{ &mut *self.lock.cell.get() };
+    }
+}
 impl<'a, T> Drop for UnfairSeLockSharedGuard<'a, T> {
     fn drop(&mut self) {
         // Spinlock until we've decremented the number of shared locks.
         let mut value = self.initial_value;
         while let Err(actual_value) = self.lock.shared.compare_exchange_weak(
             value, value - 1, Ordering::AcqRel, Ordering::Acquire
         ) {
             value = actual_value;
+        }
+    }
+}
 impl<'a, T> std::ops::Deref for UnfairSeLockSharedGuard<'a, T> {
     type Target = T;
     fn deref(&self) -> &Self::Target {
         return unsafe{ &*self.lock.cell.get() };
+    }
+}
 /// A guard signifying that the owner has exclusive access to the underlying
 /// `UnfairSeLock`.
 pub struct UnfairSeLockExclusiveGuard<'a, T> {
     lock: &'a UnfairSeLock<T>,
+}
 impl<'a, T> UnfairSeLockExclusiveGuard<'a, T> {
     fn new(lock: &'a UnfairSeLock<T>) -> Self {
         return Self{ lock };
+    }
+}
 impl<'a, T> Drop for UnfairSeLockExclusiveGuard<'a, T> {
     fn drop(&mut self) {
         // We have the exclusive bit set, and this type was constructed when
         // the number of shared locks was at 0, we can safely store a `0` into
         // the atomic
         debug_assert_eq!(self.lock.shared.load(Ordering::Relaxed), EXCLUSIVE_BIT); // relaxed because we acquired it before
         self.lock.shared.store(0, Ordering::Release);
+    }
+}
 impl<'a, T> std::ops::Deref for UnfairSeLockExclusiveGuard<'a, T> {
     type Target = T;
     fn deref(&self) -> &Self::Target {
         return unsafe{ &*self.lock.cell.get() };
+    }
+}
 impl<'a, T> std::ops::DerefMut for UnfairSeLockExclusiveGuard<'a, T> {
     fn deref_mut(&mut self) -> &mut Self::Target {
         return unsafe{ &mut *self.lock.cell.get() };
+    }
+}
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