internal/pkg: per-cache SCHED_IDLE

This is cleaner than setting it globally, and is impossible to race.

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

cmd/mbf/main.go

@@ -88,10 +88,12 @@ func main() {
 		} else if base, err = check.NewAbs(flagBase); err != nil {
 			return
 		}
-		cache, err = pkg.Open(ctx, msg, 0, flagCures, base)
+
+		var flags int
 		if flagIdle {
-			pkg.SetSchedIdle = true
+			flags &= pkg.CSchedIdle
 		}
+		cache, err = pkg.Open(ctx, msg, flags, flagCures, base)
 
 		return
 	}).Flag(

internal/pkg/exec.go

@@ -40,9 +40,6 @@ type ExecPath struct {
 	W bool
 }
 
-// SetSchedIdle is whether to set [ext.SCHED_IDLE] scheduling priority.
-var SetSchedIdle bool
-
 // GetArtifactFunc is the function signature of [FContext.GetArtifact].
 type GetArtifactFunc func(Artifact) (*check.Absolute, unique.Handle[Checksum])
 
@@ -427,7 +424,6 @@ func (a *execArtifact) makeContainer(
 	z.ParentPerm = 0700
 	z.HostNet = hostNet
 	z.Hostname = "cure"
-	z.SetScheduler = SetSchedIdle
 	z.SchedPolicy = ext.SCHED_IDLE
 	if z.HostNet {
 		z.Hostname = "cure-net"
@@ -609,6 +605,7 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 	); err != nil {
 		return
 	}
+	z.SetScheduler = f.cache.flags&CSchedIdle != 0
 
 	var status io.Writer
 	if status, err = f.GetStatusWriter(); err != nil {

internal/pkg/pkg.go

@@ -503,6 +503,10 @@ const (
 	// This behaviour significantly reduces performance and is not recommended
 	// outside of testing a custom [Artifact] implementation.
 	CValidateKnown = 1 << iota
+
+	// CSchedIdle arranges for the [ext.SCHED_IDLE] scheduling priority to be
+	// set for [KindExec] and [KindExecNet] containers.
+	CSchedIdle
 )
 
 // Cache is a support layer that implementations of [Artifact] can use to store