the applying flag is atomic; its test waits instead of polling

The race detector found my own new flag: Apply writes it on a worker
and Close reads it from the main loop. The test was polling a plain
field too, where the real window hears about the apply on the main
loop, which orders the writes.

1 files changed, 8 insertions, 5 deletions

diff --git a/gui/internal/model/plan.go b/gui/internal/model/plan.go
index 31a783b..31c12dd 100644
--- a/gui/internal/model/plan.go
+++ b/gui/internal/model/plan.go
@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"sort"
+	"sync/atomic"
 	"time"
 
 	"git.labunix.xyz/krino/internal/engine"
@@ -53,14 +54,16 @@ type PlanTab struct {
 	dp   *engine.DirPlan
 	lock *lock.Lock
 
-	// applying is set while Apply is in flight. Close must refuse then:
+	// applying is set while Apply is in flight, and read from the main loop
+	// while the apply runs on a worker, so it is atomic. Close must refuse
+	// while it is set:
 	// releasing the lock and closing the log under a running apply moves
 	// files the log never records, so undo cannot see them, and unlocks a
 	// directory krino is still working in. The window can reach Close from
 	// several places while an apply runs - saving rules or settings, adding
 	// a directory, closing the window - so the refusal lives here rather
 	// than in whichever of them remembers.
-	applying bool
+	applying atomic.Bool
 
 	// testBeforeApply, when set, is called just before the engine's Apply
 	// begins, so a test can act while the apply is in flight.
@@ -113,7 +116,7 @@ func (t *PlanTab) Run() string { return t.sess.Run() }
 // Close releases the directory's lock and ends the run, which Apply also
 // does once the plan is history. Closing twice is not an error.
 func (t *PlanTab) Close() error {
-	if t.applying {
+	if t.applying.Load() {
 		return ErrApplying
 	}
 	if t.lock == nil {
@@ -341,12 +344,12 @@ func (t *PlanTab) Apply(ctx context.Context) (*engine.ApplyResult, error) {
 			approved[r.Rel] = true
 		}
 	}
-	t.applying = true
+	t.applying.Store(true)
 	if t.testBeforeApply != nil {
 		t.testBeforeApply()
 	}
 	res, err := t.sess.Apply(ctx, t.dp, approved)
-	t.applying = false
+	t.applying.Store(false)
 	t.Applied = true
 	// An applied plan is history: the run is over and the directory free
 	// again, without closing the window (GUI design §3).