slight refactoring

src/concurrency/init_once.rs

@@ -0,0 +1,209 @@
+use std::collections::VecDeque;
+use std::num::NonZeroU32;
+
+use rustc_index::vec::Idx;
+
+use super::sync::EvalContextExtPriv;
+use super::thread::MachineCallback;
+use super::vector_clock::VClock;
+use crate::*;
+
+declare_id!(InitOnceId);
+
+/// A thread waiting on an InitOnce object.
+struct InitOnceWaiter<'mir, 'tcx> {
+    /// The thread that is waiting.
+    thread: ThreadId,
+    /// The callback that should be executed, after the thread has been woken up.
+    callback: Box<dyn MachineCallback<'mir, 'tcx> + 'tcx>,
+}
+
+impl<'mir, 'tcx> std::fmt::Debug for InitOnceWaiter<'mir, 'tcx> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("InitOnce")
+            .field("thread", &self.thread)
+            .field("callback", &"dyn MachineCallback")
+            .finish()
+    }
+}
+
+#[derive(Default, Debug, Copy, Clone, PartialEq, Eq)]
+/// The current status of a one time initialization.
+pub enum InitOnceStatus {
+    #[default]
+    Uninitialized,
+    Begun,
+    Complete,
+}
+
+/// The one time initialization state.
+#[derive(Default, Debug)]
+pub(super) struct InitOnce<'mir, 'tcx> {
+    status: InitOnceStatus,
+    waiters: VecDeque<InitOnceWaiter<'mir, 'tcx>>,
+    data_race: VClock,
+}
+
+impl<'mir, 'tcx> VisitTags for InitOnce<'mir, 'tcx> {
+    fn visit_tags(&self, visit: &mut dyn FnMut(SbTag)) {
+        for waiter in self.waiters.iter() {
+            waiter.callback.visit_tags(visit);
+        }
+    }
+}
+
+impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
+pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
+    fn init_once_get_or_create_id(
+        &mut self,
+        lock_op: &OpTy<'tcx, Provenance>,
+        offset: u64,
+    ) -> InterpResult<'tcx, InitOnceId> {
+        let this = self.eval_context_mut();
+        this.init_once_get_or_create(|ecx, next_id| ecx.get_or_create_id(next_id, lock_op, offset))
+    }
+
+    #[inline]
+    /// Create state for a new one time initialization.
+    fn init_once_create(&mut self) -> InitOnceId {
+        let this = self.eval_context_mut();
+        this.machine.threads.sync.init_onces.push(Default::default())
+    }
+
+    #[inline]
+    /// Provides the closure with the next InitOnceId. Creates that InitOnce if the closure returns None,
+    /// otherwise returns the value from the closure
+    fn init_once_get_or_create<F>(&mut self, existing: F) -> InterpResult<'tcx, InitOnceId>
+    where
+        F: FnOnce(
+            &mut MiriInterpCx<'mir, 'tcx>,
+            InitOnceId,
+        ) -> InterpResult<'tcx, Option<InitOnceId>>,
+    {
+        let this = self.eval_context_mut();
+        let next_index = this.machine.threads.sync.init_onces.next_index();
+        if let Some(old) = existing(this, next_index)? {
+            Ok(old)
+        } else {
+            let new_index = this.machine.threads.sync.init_onces.push(Default::default());
+            assert_eq!(next_index, new_index);
+            Ok(new_index)
+        }
+    }
+
+    #[inline]
+    fn init_once_status(&mut self, id: InitOnceId) -> InitOnceStatus {
+        let this = self.eval_context_ref();
+        this.machine.threads.sync.init_onces[id].status
+    }
+
+    /// Put the thread into the queue waiting for the initialization.
+    #[inline]
+    fn init_once_enqueue_and_block(
+        &mut self,
+        id: InitOnceId,
+        thread: ThreadId,
+        callback: Box<dyn MachineCallback<'mir, 'tcx> + 'tcx>,
+    ) {
+        let this = self.eval_context_mut();
+        let init_once = &mut this.machine.threads.sync.init_onces[id];
+        assert_ne!(init_once.status, InitOnceStatus::Complete, "queueing on complete init once");
+        init_once.waiters.push_back(InitOnceWaiter { thread, callback });
+        this.block_thread(thread);
+    }
+
+    /// Begin initializing this InitOnce. Must only be called after checking that it is currently
+    /// uninitialized.
+    #[inline]
+    fn init_once_begin(&mut self, id: InitOnceId) {
+        let this = self.eval_context_mut();
+        let init_once = &mut this.machine.threads.sync.init_onces[id];
+        assert_eq!(
+            init_once.status,
+            InitOnceStatus::Uninitialized,
+            "begining already begun or complete init once"
+        );
+        init_once.status = InitOnceStatus::Begun;
+    }
+
+    #[inline]
+    fn init_once_complete(&mut self, id: InitOnceId) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+        let current_thread = this.get_active_thread();
+        let init_once = &mut this.machine.threads.sync.init_onces[id];
+
+        assert_eq!(
+            init_once.status,
+            InitOnceStatus::Begun,
+            "completing already complete or uninit init once"
+        );
+
+        init_once.status = InitOnceStatus::Complete;
+
+        // Each complete happens-before the end of the wait
+        if let Some(data_race) = &this.machine.data_race {
+            data_race.validate_lock_release(&mut init_once.data_race, current_thread);
+        }
+
+        // Wake up everyone.
+        // need to take the queue to avoid having `this` be borrowed multiple times
+        for waiter in std::mem::take(&mut init_once.waiters) {
+            this.unblock_thread(waiter.thread);
+
+            this.set_active_thread(waiter.thread);
+            waiter.callback.call(this)?;
+            this.set_active_thread(current_thread);
+
+            if let Some(data_race) = &this.machine.data_race {
+                data_race.validate_lock_acquire(
+                    &this.machine.threads.sync.init_onces[id].data_race,
+                    waiter.thread,
+                );
+            }
+        }
+
+        Ok(())
+    }
+
+    #[inline]
+    fn init_once_fail(&mut self, id: InitOnceId) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+        let current_thread = this.get_active_thread();
+        let init_once = &mut this.machine.threads.sync.init_onces[id];
+        assert_eq!(
+            init_once.status,
+            InitOnceStatus::Begun,
+            "failing already completed or uninit init once"
+        );
+
+        // Each complete happens-before the end of the wait
+        // FIXME: should this really induce synchronization? If we think of it as a lock, then yes,
+        // but the docs don't talk about such details.
+        if let Some(data_race) = &this.machine.data_race {
+            data_race.validate_lock_release(&mut init_once.data_race, current_thread);
+        }
+
+        // Wake up one waiting thread, so they can go ahead and try to init this.
+        if let Some(waiter) = init_once.waiters.pop_front() {
+            // try initializing again on a different thread
+            init_once.status = InitOnceStatus::Begun;
+
+            this.unblock_thread(waiter.thread);
+
+            this.set_active_thread(waiter.thread);
+            waiter.callback.call(this)?;
+            this.set_active_thread(current_thread);
+
+            if let Some(data_race) = &this.machine.data_race {
+                data_race.validate_lock_acquire(
+                    &this.machine.threads.sync.init_onces[id].data_race,
+                    waiter.thread,
+                );
+            }
+        } else {
+            init_once.status = InitOnceStatus::Uninitialized;
+        }
+
+        Ok(())
+    }
+}

src/concurrency/mod.rs

@@ -1,6 +1,8 @@
 pub mod data_race;
 mod range_object_map;
+#[macro_use]
 pub mod sync;
+pub mod init_once;
 pub mod thread;
 mod vector_clock;
 pub mod weak_memory;