internal/pkg: loadavg target in container environment

This exposes preferred loadavg target to the container initial process.

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

internal/pkg/exec.go

@@ -30,10 +30,16 @@ import (
 // AbsWork is the container pathname [TContext.GetWorkDir] is mounted on.
 var AbsWork = fhs.AbsRoot.Append("work/")
 
-// EnvJobs is the name of the environment variable holding a decimal
-// representation of the preferred job count. Its value must not affect cure
-// outcome.
-const EnvJobs = "CURE_JOBS"
+const (
+	// EnvJobs is the name of the environment variable holding a decimal
+	// representation of the preferred job count. Its value must not affect cure
+	// outcome.
+	EnvJobs = "CURE_JOBS"
+	// EnvLoad is the name of the environment variable holding a decimal
+	// representation of the preferred loadavg target. Its value must not affect
+	// cure outcome.
+	EnvLoad = "CURE_LOAD"
+)
 
 // ExecPath is a slice of [Artifact] and the [check.Absolute] pathname to make
 // it available at under in the container.
@@ -471,7 +477,7 @@ const SeccompPresets = std.PresetStrict &
 func (a *execArtifact) makeContainer(
 	ctx context.Context,
 	msg message.Msg,
-	flags, jobs int,
+	flags, jobs, load int,
 	hostNet bool,
 	temp, work *check.Absolute,
 	getArtifact GetArtifactFunc,
@@ -508,7 +514,10 @@ func (a *execArtifact) makeContainer(
 	z.Quiet = flags&CSuppressInit != 0
 	z.Uid, z.Gid = (1<<10)-1, (1<<10)-1
 	z.Dir, z.Path, z.Args = a.dir, a.path, a.args
-	z.Env = slices.Concat(a.env, []string{EnvJobs + "=" + strconv.Itoa(jobs)})
+	z.Env = slices.Concat(a.env, []string{
+		EnvJobs + "=" + strconv.Itoa(jobs),
+		EnvLoad + "=" + strconv.Itoa(load),
+	})
 	z.Grow(len(a.paths) + 4)
 
 	if a.arch != runtime.GOARCH {
@@ -651,6 +660,7 @@ func (c *Cache) EnterExec(
 		ctx, c.msg,
 		c.attr.Flags,
 		c.attr.Jobs,
+		c.attr.Load,
 		hostNet,
 		temp, work,
 		func(a Artifact) (*check.Absolute, unique.Handle[Checksum]) {
@@ -693,7 +703,7 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 	msg := f.GetMessage()
 	var z *container.Container
 	if z, err = a.makeContainer(
-		ctx, msg, f.cache.attr.Flags, f.GetJobs(), hostNet,
+		ctx, msg, f.cache.attr.Flags, f.GetJobs(), f.GetLoad(), hostNet,
 		f.GetTempDir(), f.GetWorkDir(),
 		f.GetArtifact,
 		f.cache.Ident,

internal/pkg/internal/testtool/main.go

@@ -38,7 +38,15 @@ func main() {
 	}
 
 	environ := slices.DeleteFunc(slices.Clone(os.Environ()), func(s string) bool {
-		return s == "CURE_JOBS="+strconv.Itoa(runtime.NumCPU())
+		for _, t := range []string{
+			"CURE_JOBS=" + strconv.Itoa(runtime.NumCPU()),
+			"CURE_LOAD=" + strconv.Itoa(runtime.NumCPU()+2),
+		} {
+			if s == t {
+				return true
+			}
+		}
+		return false
 	})
 
 	var hostNet, layers, promote bool

internal/pkg/pkg.go

@@ -281,6 +281,10 @@ func (c *common) GetMessage() message.Msg { return c.cache.msg }
 // value must not affect cure outcome.
 func (c *common) GetJobs() int { return c.cache.attr.Jobs }
 
+// GetLoad returns the preferred load average target, when applicable. Its
+// value must not affect cure outcome.
+func (c *common) GetLoad() int { return c.cache.attr.Load }
+
 // GetWorkDir returns a pathname to a directory which [Artifact] is expected to
 // write its output to. This is not the final resting place of the [Artifact]
 // and this pathname should not be directly referred to in the final contents.
@@ -2684,6 +2688,8 @@ type CacheAttr struct {
 	Flags int
 	// Preferred job count, when applicable.
 	Jobs int
+	// Preferred loadavg target, when applicable.
+	Load int
 
 	// Omit the [lockedfile] lock.
 	skipLock bool
@@ -2716,15 +2722,19 @@ func Open(
 		panic("attempting to open cache with incomplete variant setup")
 	}
 
-	if attr == nil {
-		attr = new(CacheAttr)
+	var a CacheAttr
+	if attr != nil {
+		a = *attr
 	}
 
-	if attr.Cures < 1 {
-		attr.Cures = runtime.NumCPU()
+	if a.Cures < 1 {
+		a.Cures = runtime.NumCPU()
 	}
-	if attr.Jobs < 1 {
-		attr.Jobs = runtime.NumCPU()
+	if a.Jobs < 1 {
+		a.Jobs = runtime.NumCPU()
+	}
+	if a.Load < 1 {
+		a.Load = runtime.NumCPU() + 2
 	}
 
 	for _, name := range []string{
@@ -2746,8 +2756,8 @@ func Open(
 	c := Cache{
 		parent: ctx,
 
-		cures: make(chan struct{}, attr.Cures),
-		attr:  *attr,
+		cures: make(chan struct{}, a.Cures),
+		attr:  a,
 
 		msg:  msg,
 		base: base,
@@ -2764,7 +2774,7 @@ func Open(
 	}
 	c.toplevel.Store(newToplevel(ctx))
 
-	if !attr.skipLock || !testing.Testing() {
+	if !a.skipLock || !testing.Testing() {
 		if unlock, err := lockedfile.MutexAt(
 			base.Append(fileLock).String(),
 		).Lock(); err != nil {
@@ -2825,7 +2835,7 @@ func Open(
 		}
 	} else if s := string(p); s == "" {
 		if extension != "" {
-			if attr.Flags&CPromoteVariant == 0 {
+			if a.Flags&CPromoteVariant == 0 {
 				c.unlock()
 				return nil, ErrWouldPromote
 			}