internal/pkg: abort all pending cures

This cancels all current pending cures without closing the cache.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg.go

@@ -542,6 +542,20 @@ const (
 	CHostAbstract
 )
 
+// toplevel holds [context.WithCancel] over caller-supplied context, where all
+// [Artifact] context are derived from.
+type toplevel struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+}
+
+// newToplevel returns the address of a new toplevel via ctx.
+func newToplevel(ctx context.Context) *toplevel {
+	var t toplevel
+	t.ctx, t.cancel = context.WithCancel(ctx)
+	return &t
+}
+
 // pendingCure provides synchronisation and cancellation for pending cures.
 type pendingCure struct {
 	// Closed on cure completion.
@@ -557,11 +571,10 @@ type Cache struct {
 	// implementation and receives an equal amount of elements after.
 	cures chan struct{}
 
-	// [context.WithCancel] over caller-supplied context, used by [Artifact] and
-	// all dependency curing goroutines.
-	ctx context.Context
-	// Cancels ctx.
-	cancel context.CancelFunc
+	// Parent context which toplevel was derived from.
+	parent context.Context
+	// For deriving curing context, must not be accessed directly.
+	toplevel atomic.Pointer[toplevel]
 	// For waiting on dependency curing goroutines.
 	wg sync.WaitGroup
 	// Reports new cures and passed to [Artifact].
@@ -596,8 +609,10 @@ type Cache struct {
 
 	// Unlocks the on-filesystem cache. Must only be called from Close.
 	unlock func()
-	// Synchronises calls to Close.
-	closeOnce sync.Once
+	// Whether [Cache] is considered closed.
+	closed bool
+	// Synchronises calls to Abort and Close.
+	closeMu sync.Mutex
 
 	// Whether EnterExec has not yet returned.
 	inExec atomic.Bool
@@ -1053,7 +1068,7 @@ func (c *Cache) loadOrStoreIdent(id unique.Handle[ID]) (
 
 	d := make(chan struct{})
 	pending = &pendingCure{done: d}
-	ctx, pending.cancel = context.WithCancel(c.ctx)
+	ctx, pending.cancel = context.WithCancel(c.toplevel.Load().ctx)
 	c.identPending[id] = pending
 	c.identMu.Unlock()
 	done = d
@@ -1295,7 +1310,7 @@ func (c *Cache) Cure(a Artifact) (
 	checksum unique.Handle[Checksum],
 	err error,
 ) {
-	if err = c.ctx.Err(); err != nil {
+	if err = c.toplevel.Load().ctx.Err(); err != nil {
 		return
 	}
 
@@ -1382,15 +1397,16 @@ func (c *Cache) enterCure(a Artifact, curesExempt bool) error {
 		return nil
 	}
 
+	ctx := c.toplevel.Load().ctx
 	select {
 	case c.cures <- struct{}{}:
 		return nil
 
-	case <-c.ctx.Done():
+	case <-ctx.Done():
 		if a.IsExclusive() {
 			c.exclMu.Unlock()
 		}
-		return c.ctx.Err()
+		return ctx.Err()
 	}
 }
 
@@ -1855,14 +1871,33 @@ func (c *Cache) OpenStatus(a Artifact) (r io.ReadSeekCloser, err error) {
 	return
 }
 
+// Abort cancels all pending cures but does not close the store. Abort does not
+// wait for cures to complete.
+func (c *Cache) Abort() {
+	c.closeMu.Lock()
+	defer c.closeMu.Unlock()
+
+	if c.closed {
+		return
+	}
+
+	c.toplevel.Swap(newToplevel(c.parent)).cancel()
+}
+
 // Close cancels all pending cures and waits for them to clean up.
 func (c *Cache) Close() {
-	c.closeOnce.Do(func() {
-		c.cancel()
-		c.wg.Wait()
-		close(c.cures)
-		c.unlock()
-	})
+	c.closeMu.Lock()
+	defer c.closeMu.Unlock()
+
+	if c.closed {
+		return
+	}
+
+	c.closed = true
+	c.toplevel.Load().cancel()
+	c.wg.Wait()
+	close(c.cures)
+	c.unlock()
 }
 
 // Open returns the address of a newly opened instance of [Cache].
@@ -1916,6 +1951,8 @@ func open(
 	}
 
 	c := Cache{
+		parent: ctx,
+
 		cures: make(chan struct{}, cures),
 		flags: flags,
 		jobs:  jobs,
@@ -1932,7 +1969,7 @@ func open(
 		brPool: sync.Pool{New: func() any { return new(bufio.Reader) }},
 		bwPool: sync.Pool{New: func() any { return new(bufio.Writer) }},
 	}
-	c.ctx, c.cancel = context.WithCancel(ctx)
+	c.toplevel.Store(newToplevel(ctx))
 
 	if lock || !testing.Testing() {
 		if unlock, err := lockedfile.MutexAt(