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Slightly more ergonomic task mutation

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This commit is contained in:
Dustin J. Mitchell
2022-01-30 23:42:52 +00:00
parent 452ae2074f
commit 364ca57736
4 changed files with 61 additions and 98 deletions
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73
lib/src/task.rs
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@@ -11,10 +11,16 @@ use taskchampion::{Task, TaskMut};
/// A task carries no reference to the replica that created it, and can
/// be used until it is freed or converted to a TaskMut.
pub enum TCTask {
/// A regular, immutable task
Immutable(Task),
Mutable(TaskMut<'static>),
/// A transitional state for a TCTask as it goes from mutable to immutable.
/// A mutable task, together with the replica to which it holds an exclusive
/// reference.
Mutable(TaskMut<'static>, *mut TCReplica),
/// A transitional state for a TCTask as it goes from mutable to immutable and back. A task
/// can only be in this state outside of [`to_mut`] and [`to_immut`] if a panic occurs during
/// one of those methods.
Invalid,
}
@@ -52,24 +58,38 @@ impl TCTask {
/// Make an immutable TCTask into a mutable TCTask. Does nothing if the task
/// is already mutable.
fn to_mut(&mut self, tcreplica: &'static mut TCReplica) {
///
/// # Safety
///
/// The tcreplica pointer must not be NULL, and the replica it points to must not
/// be freed before TCTask.to_immut completes.
unsafe fn to_mut(&mut self, tcreplica: *mut TCReplica) {
*self = match std::mem::replace(self, TCTask::Invalid) {
TCTask::Immutable(task) => {
let rep_ref = tcreplica.borrow_mut();
TCTask::Mutable(task.into_mut(rep_ref))
// SAFETY:
// - tcreplica is not null (promised by caller)
// - tcreplica outlives the pointer in this variant (promised by caller)
let tcreplica_ref: &mut TCReplica = TCReplica::from_arg_ref(tcreplica);
let rep_ref = tcreplica_ref.borrow_mut();
TCTask::Mutable(task.into_mut(rep_ref), tcreplica)
}
TCTask::Mutable(task) => TCTask::Mutable(task),
TCTask::Mutable(task, tcreplica) => TCTask::Mutable(task, tcreplica),
TCTask::Invalid => unreachable!(),
}
}
/// Make an mutable TCTask into a immutable TCTask. Does nothing if the task
/// is already immutable.
fn to_immut(&mut self, tcreplica: &mut TCReplica) {
fn to_immut(&mut self) {
*self = match std::mem::replace(self, TCTask::Invalid) {
TCTask::Immutable(task) => TCTask::Immutable(task),
TCTask::Mutable(task) => {
tcreplica.release_borrow();
TCTask::Mutable(task, tcreplica) => {
// SAFETY:
// - tcreplica is not null (promised by caller of to_mut, which created this
// variant)
// - tcreplica is still alive (promised by caller of to_mut)
let tcreplica_ref: &mut TCReplica = unsafe { TCReplica::from_arg_ref(tcreplica) };
tcreplica_ref.release_borrow();
TCTask::Immutable(task.into_immut())
}
TCTask::Invalid => unreachable!(),
@@ -94,7 +114,7 @@ where
let tctask: &'a TCTask = unsafe { TCTask::from_arg_ref(task) };
let task: &'a Task = match tctask {
TCTask::Immutable(t) => t,
TCTask::Mutable(t) => t.deref(),
TCTask::Mutable(t, _) => t.deref(),
TCTask::Invalid => unreachable!(),
};
f(task)
@@ -112,7 +132,7 @@ where
let tctask: &'a mut TCTask = unsafe { TCTask::from_arg_ref_mut(task) };
let task: &'a mut TaskMut = match tctask {
TCTask::Immutable(_) => panic!("Task is immutable"),
TCTask::Mutable(ref mut t) => t,
TCTask::Mutable(ref mut t, _) => t,
TCTask::Invalid => unreachable!(),
};
// TODO: add TCTask error handling, like replica
@@ -121,10 +141,11 @@ where
/// Convert an immutable task into a mutable task.
///
/// The task is modified in-place, and becomes mutable.
/// The task must not be NULL. It is modified in-place, and becomes mutable.
///
/// The replica _cannot be used at all_ until this task is made immutable again. This implies that
/// it is not allowed for more than one task associated with a replica to be mutable at any time.
/// The replica must not be NULL. After this function returns, the replica _cannot be used at all_
/// until this task is made immutable again. This implies that it is not allowed for more than one
/// task associated with a replica to be mutable at any time.
///
/// Typical mutation of tasks is bracketed with `tc_task_to_mut` and `tc_task_to_immut`:
///
@@ -135,22 +156,30 @@ where
/// if (!success) { ... }
/// ```
#[no_mangle]
pub extern "C" fn tc_task_to_mut<'a>(task: *mut TCTask, rep: *mut TCReplica) {
pub extern "C" fn tc_task_to_mut<'a>(task: *mut TCTask, tcreplica: *mut TCReplica) {
// SAFETY:
// - task is not null (promised by caller)
// - task outlives 'a (promised by caller)
let tctask: &'a mut TCTask = unsafe { TCTask::from_arg_ref_mut(task) };
let tcreplica: &'static mut TCReplica = unsafe { TCReplica::from_arg_ref(rep) };
tctask.to_mut(tcreplica);
// SAFETY:
// - tcreplica is not NULL (promised by caller)
// - tcreplica lives until later call to to_immut via tc_task_to_immut (promised by caller,
// who cannot call tc_replica_free during this time)
unsafe { tctask.to_mut(tcreplica) };
}
/// Convert a mutable task into an immutable task.
///
/// The task is modified in-place, and becomes immutable.
/// The task must not be NULL. It is modified in-place, and becomes immutable.
///
/// The replica may be used freely after this call.
/// The replica passed to `tc_task_to_mut` may be used freely after this call.
#[no_mangle]
pub extern "C" fn tc_task_to_immut<'a>(task: *mut TCTask, rep: *mut TCReplica) {
pub extern "C" fn tc_task_to_immut<'a>(task: *mut TCTask) {
// SAFETY:
// - task is not null (promised by caller)
// - task outlives 'a (promised by caller)
let tctask: &'a mut TCTask = unsafe { TCTask::from_arg_ref_mut(task) };
let tcreplica: &'static mut TCReplica = unsafe { TCReplica::from_arg_ref(rep) };
tctask.to_immut(tcreplica);
tctask.to_immut();
}
/// Get a task's UUID.