crates/sel4-one-ref-cell: Introduce

Signed-off-by: Nick Spinale <[email protected]>

Cargo.toml

@@ -95,6 +95,7 @@ members = [
     "crates/sel4-microkit/message",
     "crates/sel4-microkit/message/types",
     "crates/sel4-newlib",
+    "crates/sel4-one-ref-cell",
     "crates/sel4-panicking",
     "crates/sel4-panicking/env",
     "crates/sel4-platform-info",

crates/private/meta/Cargo.toml

@@ -28,6 +28,7 @@ sel4-logging = { path = "../../sel4-logging" }
 sel4-microkit = { path = "../../sel4-microkit", features = ["full"], optional = true }
 sel4-microkit-message = { path = "../../sel4-microkit/message", optional = true }
 sel4-microkit-message-types = { path = "../../sel4-microkit/message/types", optional = true }
+sel4-one-ref-cell = { path = "../../sel4-one-ref-cell" }
 sel4-root-task = { path = "../../sel4-root-task", features = ["full"], optional = true }
 sel4-shared-ring-buffer = { path = "../../sel4-shared-ring-buffer" }
 sel4-shared-ring-buffer-block-io = { path = "../../sel4-shared-ring-buffer/block-io" }

crates/private/meta/src/lib.rs

@@ -76,6 +76,7 @@ definitely! {
     sel4
     sel4_async_block_io
     sel4_async_block_io_cpiofs
+    sel4_async_block_io_fat
     sel4_async_network
     sel4_async_request_statuses
     sel4_async_single_threaded_executor
@@ -86,6 +87,7 @@ definitely! {
     sel4_immediate_sync_once_cell
     sel4_immutable_cell
     sel4_logging
+    sel4_one_ref_cell
     sel4_shared_ring_buffer
     sel4_shared_ring_buffer_block_io
     sel4_shared_ring_buffer_block_io_types

crates/sel4-one-ref-cell/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "sel4-one-ref-cell"
+version = "0.1.0"
+authors = ["Nick Spinale <[email protected]>"]
+edition = "2021"
+license = "BSD-2-Clause"

crates/sel4-one-ref-cell/src/lib.rs

@@ -0,0 +1,45 @@
+#![no_std]
+#![feature(sync_unsafe_cell)]
+
+use core::cell::SyncUnsafeCell;
+use core::sync::atomic::{AtomicBool, Ordering};
+
+pub struct OneRefCell<T> {
+    taken: AtomicBool,
+    value: SyncUnsafeCell<T>,
+}
+
+impl<T: Default> Default for OneRefCell<T> {
+    fn default() -> Self {
+        Self::new(Default::default())
+    }
+}
+
+impl<T> From<T> for OneRefCell<T> {
+    fn from(t: T) -> Self {
+        Self::new(t)
+    }
+}
+
+impl<T> OneRefCell<T> {
+    pub const fn new(value: T) -> Self {
+        Self {
+            taken: AtomicBool::new(false),
+            value: SyncUnsafeCell::new(value),
+        }
+    }
+
+    pub fn take(&self) -> Result<&mut T, Error> {
+        if self.taken.swap(true, Ordering::SeqCst) {
+            Err(Error::AlreadyTaken)
+        } else {
+            let ptr = self.value.get();
+            Ok(unsafe { ptr.as_mut() }.unwrap())
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub enum Error {
+    AlreadyTaken,
+}

hacking/cargo-manifest-sources/crates/private/meta/crate.nix

@@ -25,6 +25,7 @@ mk {
     sel4-immediate-sync-once-cell
     sel4-immutable-cell
     sel4-logging
+    sel4-one-ref-cell
     sel4-shared-ring-buffer
     sel4-shared-ring-buffer-block-io
     sel4-shared-ring-buffer-block-io-types

hacking/cargo-manifest-sources/crates/sel4-one-ref-cell/crate.nix

@@ -0,0 +1,5 @@
+{ mk }:
+
+mk {
+  package.name = "sel4-one-ref-cell";
+}