internal/pkg: exclusive artifacts

This alleviates scheduler overhead when curing many artifacts.

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

internal/pkg/exec.go

@@ -105,6 +105,9 @@ type execArtifact struct {
 	// equivalent to execTimeoutDefault. This value is never encoded in Params
 	// because it cannot affect outcome.
 	timeout time.Duration
+
+	// Caller-supplied exclusivity value, returned as is by IsExclusive.
+	exclusive bool
 }
 
 var _ fmt.Stringer = new(execArtifact)
@@ -123,7 +126,7 @@ var _ KnownChecksum = new(execNetArtifact)
 func (a *execNetArtifact) Checksum() Checksum { return a.checksum }
 
 // Kind returns the hardcoded [Kind] constant.
-func (a *execNetArtifact) Kind() Kind { return KindExecNet }
+func (*execNetArtifact) Kind() Kind { return KindExecNet }
 
 // Params is [Checksum] concatenated with [KindExec] params.
 func (a *execNetArtifact) Params(ctx *IContext) {
@@ -157,13 +160,14 @@ func (a *execNetArtifact) Cure(f *FContext) error {
 // negative timeout value is equivalent tp [ExecTimeoutDefault], a timeout value
 // greater than [ExecTimeoutMax] is equivalent to [ExecTimeoutMax].
 //
-// The user-facing name is not accessible from the container and does not
+// The user-facing name and exclusivity value are not accessible from the
-// affect curing outcome. Because of this, it is omitted from parameter data
+// container and does not affect curing outcome. Because of this, it is omitted
-// for computing identifier.
+// from parameter data for computing identifier.
 func NewExec(
 	name string,
 	checksum *Checksum,
 	timeout time.Duration,
+	exclusive bool,
 
 	dir *check.Absolute,
 	env []string,
@@ -181,7 +185,7 @@ func NewExec(
 	if timeout > ExecTimeoutMax {
 		timeout = ExecTimeoutMax
 	}
-	a := execArtifact{name, paths, dir, env, pathname, args, timeout}
+	a := execArtifact{name, paths, dir, env, pathname, args, timeout, exclusive}
 	if checksum == nil {
 		return &a
 	}
@@ -189,7 +193,7 @@ func NewExec(
 }
 
 // Kind returns the hardcoded [Kind] constant.
-func (a *execArtifact) Kind() Kind { return KindExec }
+func (*execArtifact) Kind() Kind { return KindExec }
 
 // Params writes paths, executable pathname and args.
 func (a *execArtifact) Params(ctx *IContext) {
@@ -237,6 +241,9 @@ func (a *execArtifact) Dependencies() []Artifact {
 	return slices.Concat(artifacts...)
 }
 
+// IsExclusive returns the caller-supplied exclusivity value.
+func (a *execArtifact) IsExclusive() bool { return a.exclusive }
+
 // String returns the caller-supplied reporting name.
 func (a *execArtifact) String() string { return a.name }
 

internal/pkg/exec_test.go

@@ -39,7 +39,7 @@ func TestExec(t *testing.T) {
 
 			cureMany(t, c, []cureStep{
 				{"container", pkg.NewExec(
-					"exec-offline", nil, 0,
+					"exec-offline", nil, 0, false,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1"},
 					check.MustAbs("/opt/bin/testtool"),
@@ -62,7 +62,7 @@ func TestExec(t *testing.T) {
 				), ignorePathname, wantChecksumOffline, nil},
 
 				{"error passthrough", pkg.NewExec(
-					"", nil, 0,
+					"", nil, 0, true,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1"},
 					check.MustAbs("/opt/bin/testtool"),
@@ -85,7 +85,7 @@ func TestExec(t *testing.T) {
 				}},
 
 				{"invalid paths", pkg.NewExec(
-					"", nil, 0,
+					"", nil, 0, false,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1"},
 					check.MustAbs("/opt/bin/testtool"),
@@ -98,7 +98,7 @@ func TestExec(t *testing.T) {
 			// check init failure passthrough
 			var exitError *exec.ExitError
 			if _, _, err := c.Cure(pkg.NewExec(
-				"", nil, 0,
+				"", nil, 0, false,
 				pkg.AbsWork,
 				nil,
 				check.MustAbs("/opt/bin/testtool"),
@@ -120,7 +120,7 @@ func TestExec(t *testing.T) {
 			)
 			cureMany(t, c, []cureStep{
 				{"container", pkg.NewExec(
-					"exec-net", &wantChecksum, 0,
+					"exec-net", &wantChecksum, 0, false,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1"},
 					check.MustAbs("/opt/bin/testtool"),
@@ -152,7 +152,7 @@ func TestExec(t *testing.T) {
 
 			cureMany(t, c, []cureStep{
 				{"container", pkg.NewExec(
-					"exec-overlay-root", nil, 0,
+					"exec-overlay-root", nil, 0, false,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
 					check.MustAbs("/opt/bin/testtool"),
@@ -178,7 +178,7 @@ func TestExec(t *testing.T) {
 
 			cureMany(t, c, []cureStep{
 				{"container", pkg.NewExec(
-					"exec-overlay-work", nil, 0,
+					"exec-overlay-work", nil, 0, false,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
 					check.MustAbs("/work/bin/testtool"),
@@ -209,7 +209,7 @@ func TestExec(t *testing.T) {
 
 			cureMany(t, c, []cureStep{
 				{"container", pkg.NewExec(
-					"exec-multiple-layers", nil, 0,
+					"exec-multiple-layers", nil, 0, false,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
 					check.MustAbs("/opt/bin/testtool"),
@@ -262,7 +262,7 @@ func TestExec(t *testing.T) {
 
 			cureMany(t, c, []cureStep{
 				{"container", pkg.NewExec(
-					"exec-layer-promotion", nil, 0,
+					"exec-layer-promotion", nil, 0, true,
 					pkg.AbsWork,
 					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
 					check.MustAbs("/opt/bin/testtool"),

internal/pkg/file.go

@@ -37,13 +37,16 @@ func NewFile(name string, data []byte) FileArtifact {
 }
 
 // Kind returns the hardcoded [Kind] constant.
-func (a *fileArtifact) Kind() Kind { return KindFile }
+func (*fileArtifact) Kind() Kind { return KindFile }
 
 // Params writes the result of Cure.
 func (a *fileArtifact) Params(ctx *IContext) { ctx.GetHash().Write(*a) }
 
 // Dependencies returns a nil slice.
-func (a *fileArtifact) Dependencies() []Artifact { return nil }
+func (*fileArtifact) Dependencies() []Artifact { return nil }
+
+// IsExclusive returns false: Cure returns a prepopulated buffer.
+func (*fileArtifact) IsExclusive() bool { return false }
 
 // Checksum computes and returns the checksum of caller-supplied data.
 func (a *fileArtifact) Checksum() Checksum {

internal/pkg/net.go

@@ -40,7 +40,7 @@ func NewHTTPGet(
 }
 
 // Kind returns the hardcoded [Kind] constant.
-func (a *httpArtifact) Kind() Kind { return KindHTTPGet }
+func (*httpArtifact) Kind() Kind { return KindHTTPGet }
 
 // Params writes the backing url string. Client is not represented as it does
 // not affect [Cache.Cure] outcome.
@@ -49,7 +49,10 @@ func (a *httpArtifact) Params(ctx *IContext) {
 }
 
 // Dependencies returns a nil slice.
-func (a *httpArtifact) Dependencies() []Artifact { return nil }
+func (*httpArtifact) Dependencies() []Artifact { return nil }
+
+// IsExclusive returns false: Cure returns as soon as a response is received.
+func (*httpArtifact) IsExclusive() bool { return false }
 
 // Checksum returns the caller-supplied checksum.
 func (a *httpArtifact) Checksum() Checksum { return a.checksum.Value() }

internal/pkg/pkg.go

@@ -253,6 +253,24 @@ type Artifact interface {
 	//
 	// Result must remain identical across multiple invocations.
 	Dependencies() []Artifact
+
+	// IsExclusive returns whether the [Artifact] is exclusive. Exclusive
+	// artifacts might not run in parallel with each other, and are still
+	// subject to the cures limit.
+	//
+	// Some implementations may saturate the CPU for a nontrivial amount of
+	// time. Curing multiple such implementations simultaneously causes
+	// significant CPU scheduler overhead. An exclusive artifact will generally
+	// not be cured alongside another exclusive artifact, thus alleviating this
+	// overhead.
+	//
+	// Note that [Cache] reserves the right to still cure exclusive
+	// artifacts concurrently as this is not a synchronisation primitive but
+	// an optimisation one. Implementations are forbidden from accessing global
+	// state regardless of exclusivity.
+	//
+	// Result must remain identical across multiple invocations.
+	IsExclusive() bool
 }
 
 // FloodArtifact refers to an [Artifact] requiring its entire dependency graph
@@ -472,6 +490,8 @@ type Cache struct {
 	// Synchronises access to ident and corresponding filesystem entries.
 	identMu sync.RWMutex
 
+	// Synchronises entry into exclusive artifacts for the cure method.
+	exclMu sync.Mutex
 	// Buffered I/O free list, must not be accessed directly.
 	bufioPool sync.Pool
 
@@ -1215,7 +1235,10 @@ func (e *DependencyCureError) Error() string {
 }
 
 // enterCure must be called before entering an [Artifact] implementation.
-func (c *Cache) enterCure(curesExempt bool) error {
+func (c *Cache) enterCure(a Artifact, curesExempt bool) error {
+	if a.IsExclusive() {
+		c.exclMu.Lock()
+	}
 	if curesExempt {
 		return nil
 	}
@@ -1225,15 +1248,23 @@ func (c *Cache) enterCure(curesExempt bool) error {
 		return nil
 
 	case <-c.ctx.Done():
+		if a.IsExclusive() {
+			c.exclMu.Unlock()
+		}
 		return c.ctx.Err()
 	}
 }
 
 // exitCure must be called after exiting an [Artifact] implementation.
-func (c *Cache) exitCure(curesExempt bool) {
+func (c *Cache) exitCure(a Artifact, curesExempt bool) {
-	if !curesExempt {
+	if a.IsExclusive() {
-		<-c.cures
+		c.exclMu.Unlock()
 	}
+	if curesExempt {
+		return
+	}
+
+	<-c.cures
 }
 
 // getWriter is like [bufio.NewWriter] but for bufioPool.
@@ -1456,7 +1487,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 		}()
 
 		var r io.ReadCloser
-		if err = c.enterCure(curesExempt); err != nil {
+		if err = c.enterCure(a, curesExempt); err != nil {
 			return
 		}
 		r, err = f.Cure(&RContext{c})
@@ -1505,7 +1536,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 				err = closeErr
 			}
 		}
-		c.exitCure(curesExempt)
+		c.exitCure(a, curesExempt)
 		if err != nil {
 			return
 		}
@@ -1539,11 +1570,11 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 	switch ca := a.(type) {
 	case TrivialArtifact:
 		defer t.destroy(&err)
-		if err = c.enterCure(curesExempt); err != nil {
+		if err = c.enterCure(a, curesExempt); err != nil {
 			return
 		}
 		err = ca.Cure(&t)
-		c.exitCure(curesExempt)
+		c.exitCure(a, curesExempt)
 		if err != nil {
 			return
 		}
@@ -1573,11 +1604,11 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 		}
 
 		defer f.destroy(&err)
-		if err = c.enterCure(curesExempt); err != nil {
+		if err = c.enterCure(a, curesExempt); err != nil {
 			return
 		}
 		err = ca.Cure(&f)
-		c.exitCure(curesExempt)
+		c.exitCure(a, curesExempt)
 		if err != nil {
 			return
 		}

internal/pkg/pkg_test.go

@@ -96,12 +96,14 @@ func (a *stubArtifact) Kind() pkg.Kind               { return a.kind }
 func (a *stubArtifact) Params(ctx *pkg.IContext)     { ctx.GetHash().Write(a.params) }
 func (a *stubArtifact) Dependencies() []pkg.Artifact { return a.deps }
 func (a *stubArtifact) Cure(t *pkg.TContext) error   { return a.cure(t) }
+func (*stubArtifact) IsExclusive() bool              { return false }
 
 // A stubArtifactF implements [FloodArtifact] with hardcoded behaviour.
 type stubArtifactF struct {
 	kind   pkg.Kind
 	params []byte
 	deps   []pkg.Artifact
+	excl   bool
 
 	cure func(f *pkg.FContext) error
 }
@@ -110,6 +112,7 @@ func (a *stubArtifactF) Kind() pkg.Kind               { return a.kind }
 func (a *stubArtifactF) Params(ctx *pkg.IContext)     { ctx.GetHash().Write(a.params) }
 func (a *stubArtifactF) Dependencies() []pkg.Artifact { return a.deps }
 func (a *stubArtifactF) Cure(f *pkg.FContext) error   { return a.cure(f) }
+func (a *stubArtifactF) IsExclusive() bool            { return a.excl }
 
 // A stubFile implements [FileArtifact] with hardcoded behaviour.
 type stubFile struct {

internal/pkg/tar.go

@@ -80,6 +80,9 @@ func (a *tarArtifact) Dependencies() []Artifact {
 	return []Artifact{a.f}
 }
 
+// IsExclusive returns false: decompressor and tar reader are fully sequential.
+func (a *tarArtifact) IsExclusive() bool { return false }
+
 // A DisallowedTypeflagError describes a disallowed typeflag encountered while
 // unpacking a tarball.
 type DisallowedTypeflagError byte

internal/rosa/acl.go

@@ -7,7 +7,7 @@ func (t Toolchain) newAttr() pkg.Artifact {
 		version  = "2.5.2"
 		checksum = "YWEphrz6vg1sUMmHHVr1CRo53pFXRhq_pjN-AlG8UgwZK1y6m7zuDhxqJhD0SV0l"
 	)
-	return t.New("attr-"+version, []pkg.Artifact{
+	return t.New("attr-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(Perl),
 	}, nil, nil, `
@@ -75,7 +75,7 @@ func (t Toolchain) newACL() pkg.Artifact {
 		version  = "2.3.2"
 		checksum = "-fY5nwH4K8ZHBCRXrzLdguPkqjKI6WIiGu4dBtrZ1o0t6AIU73w8wwJz_UyjIS0P"
 	)
-	return t.New("acl-"+version, []pkg.Artifact{
+	return t.New("acl-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 
 		t.Load(Attr),

internal/rosa/busybox.go

@@ -25,6 +25,9 @@ func (a busyboxBin) Kind() pkg.Kind { return kindBusyboxBin }
 // Params is a noop.
 func (a busyboxBin) Params(*pkg.IContext) {}
 
+// IsExclusive returns false: Cure performs a trivial filesystem write.
+func (busyboxBin) IsExclusive() bool { return false }
+
 // Dependencies returns the underlying busybox [pkg.File].
 func (a busyboxBin) Dependencies() []pkg.Artifact {
 	return []pkg.Artifact{a.bin}
@@ -80,7 +83,8 @@ func newBusyboxBin() pkg.Artifact {
 		checksum = "L7OBIsPu9enNHn7FqpBT1kOg_mCLNmetSeNMA3i4Y60Z5jTgnlX3qX3zcQtLx5AB"
 	)
 	return pkg.NewExec(
-		"busybox-bin-"+version, nil, pkg.ExecTimeoutMax, fhs.AbsRoot, []string{
+		"busybox-bin-"+version, nil, pkg.ExecTimeoutMax, false,
+		fhs.AbsRoot, []string{
 			"PATH=/system/bin",
 		},
 		AbsSystem.Append("bin", "busybox"),
@@ -111,7 +115,7 @@ func (t Toolchain) newBusybox() pkg.Artifact {
 		env = append(env, "EXTRA_LDFLAGS=-static")
 	}
 
-	return t.New("busybox-"+version, stage3Concat(t, []pkg.Artifact{},
+	return t.New("busybox-"+version, false, stage3Concat(t, []pkg.Artifact{},
 		t.Load(Make),
 		t.Load(KernelHeaders),
 	), nil, slices.Concat([]string{

internal/rosa/cmake.go

@@ -13,7 +13,7 @@ func (t Toolchain) newCMake() pkg.Artifact {
 		version  = "4.2.1"
 		checksum = "Y3OdbMsob6Xk2y1DCME6z4Fryb5_TkFD7knRT8dTNIRtSqbiCJyyDN9AxggN_I75"
 	)
-	return t.New("cmake-"+version, []pkg.Artifact{
+	return t.New("cmake-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(KernelHeaders),
 	}, nil, nil, `
@@ -59,6 +59,9 @@ type CMakeAttr struct {
 
 	// Override the default installation prefix [AbsSystem].
 	Prefix *check.Absolute
+
+	// Return an exclusive artifact.
+	Exclusive bool
 }
 
 // NewViaCMake returns a [pkg.Artifact] for compiling and installing via CMake.
@@ -94,7 +97,7 @@ chmod -R +w "${ROSA_SOURCE}"
 	}
 
 	sourcePath := AbsUsrSrc.Append(name)
-	return t.New(name+"-"+variant+"-"+version, stage3Concat(t, attr.Extra,
+	return t.New(name+"-"+variant+"-"+version, attr.Exclusive, stage3Concat(t, attr.Extra,
 		t.Load(CMake),
 		t.Load(Ninja),
 	), nil, slices.Concat([]string{

internal/rosa/etc.go

@@ -89,6 +89,9 @@ func (cureEtc) Kind() pkg.Kind { return kindEtc }
 // Params is a noop.
 func (cureEtc) Params(*pkg.IContext) {}
 
+// IsExclusive returns false: Cure performs a few trivial filesystem writes.
+func (cureEtc) IsExclusive() bool { return false }
+
 // Dependencies returns a slice containing the backing iana-etc release.
 func (a cureEtc) Dependencies() []pkg.Artifact {
 	if a.iana != nil {

internal/rosa/git.go

@@ -9,7 +9,7 @@ func (t Toolchain) newGit() pkg.Artifact {
 		version  = "2.52.0"
 		checksum = "uH3J1HAN_c6PfGNJd2OBwW4zo36n71wmkdvityYnrh8Ak0D1IifiAvEWz9Vi9DmS"
 	)
-	return t.New("git-"+version, stage3Concat(t, []pkg.Artifact{},
+	return t.New("git-"+version, false, stage3Concat(t, []pkg.Artifact{},
 		t.Load(Make),
 		t.Load(Perl),
 		t.Load(M4),

internal/rosa/gnu.go

@@ -7,7 +7,7 @@ func (t Toolchain) newMake() pkg.Artifact {
 		version  = "4.4.1"
 		checksum = "YS_B07ZcAy9PbaK5_vKGj64SrxO2VMpnMKfc9I0Q9IC1rn0RwOH7802pJoj2Mq4a"
 	)
-	return t.New("make-"+version, nil, nil, nil, `
+	return t.New("make-"+version, false, nil, nil, nil, `
 cd "$(mktemp -d)"
 /usr/src/make/configure \
 	--prefix=/system \
@@ -29,7 +29,7 @@ func (t Toolchain) newM4() pkg.Artifact {
 		version  = "1.4.20"
 		checksum = "RT0_L3m4Co86bVBY3lCFAEs040yI1WdeNmRylFpah8IZovTm6O4wI7qiHJN3qsW9"
 	)
-	return t.New("m4-"+version, []pkg.Artifact{
+	return t.New("m4-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd /usr/src/m4
@@ -55,7 +55,7 @@ func (t Toolchain) newAutoconf() pkg.Artifact {
 		version  = "2.72"
 		checksum = "-c5blYkC-xLDer3TWEqJTyh1RLbOd1c5dnRLKsDnIrg_wWNOLBpaqMY8FvmUFJ33"
 	)
-	return t.New("autoconf-"+version, []pkg.Artifact{
+	return t.New("autoconf-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(M4),
 		t.Load(Perl),
@@ -83,7 +83,7 @@ func (t Toolchain) newGettext() pkg.Artifact {
 		version  = "0.26"
 		checksum = "IMu7yDZX7xL5UO1ZxXc-iBMbY9LLEUlOroyuSlHMZwg9MKtxG7HIm8F2LheDua0y"
 	)
-	return t.New("gettext-"+version, []pkg.Artifact{
+	return t.New("gettext-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd /usr/src/gettext
@@ -119,7 +119,7 @@ func (t Toolchain) newDiffutils() pkg.Artifact {
 		version  = "3.12"
 		checksum = "9J5VAq5oA7eqwzS1Yvw-l3G5o-TccUrNQR3PvyB_lgdryOFAfxtvQfKfhdpquE44"
 	)
-	return t.New("diffutils-"+version, []pkg.Artifact{
+	return t.New("diffutils-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd /usr/src/diffutils
@@ -148,7 +148,7 @@ func (t Toolchain) newPatch() pkg.Artifact {
 		version  = "2.8"
 		checksum = "MA0BQc662i8QYBD-DdGgyyfTwaeALZ1K0yusV9rAmNiIsQdX-69YC4t9JEGXZkeR"
 	)
-	return t.New("patch-"+version, []pkg.Artifact{
+	return t.New("patch-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd /usr/src/patch
@@ -177,7 +177,7 @@ func (t Toolchain) newBash() pkg.Artifact {
 		version  = "5.3"
 		checksum = "4LQ_GRoB_ko-Ih8QPf_xRKA02xAm_TOxQgcJLmFDT6udUPxTAWrsj-ZNeuTusyDq"
 	)
-	return t.New("bash-"+version, []pkg.Artifact{
+	return t.New("bash-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd "$(mktemp -d)"
@@ -201,7 +201,7 @@ func (t Toolchain) newCoreutils() pkg.Artifact {
 		version  = "9.9"
 		checksum = "B1_TaXj1j5aiVIcazLWu8Ix03wDV54uo2_iBry4qHG6Y-9bjDpUPlkNLmU_3Nvw6"
 	)
-	return t.New("coreutils-"+version, []pkg.Artifact{
+	return t.New("coreutils-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(Perl),
 
@@ -232,7 +232,7 @@ func (t Toolchain) newGperf() pkg.Artifact {
 		version  = "3.3"
 		checksum = "RtIy9pPb_Bb8-31J2Nw-rRGso2JlS-lDlVhuNYhqR7Nt4xM_nObznxAlBMnarJv7"
 	)
-	return t.New("gperf-"+version, []pkg.Artifact{
+	return t.New("gperf-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd "$(mktemp -d)"

internal/rosa/go.go

@@ -10,7 +10,7 @@ import (
 // newGoBootstrap returns the Go bootstrap toolchain.
 func (t Toolchain) newGoBootstrap() pkg.Artifact {
 	const checksum = "8o9JL_ToiQKadCTb04nvBDkp8O1xiWOolAxVEqaTGodieNe4lOFEjlOxN3bwwe23"
-	return t.New("go1.4-bootstrap", []pkg.Artifact{
+	return t.New("go1.4-bootstrap", false, []pkg.Artifact{
 		t.Load(Bash),
 	}, nil, []string{
 		"CGO_ENABLED=0",
@@ -50,7 +50,7 @@ func (t Toolchain) newGo(
 	script string,
 	extra ...pkg.Artifact,
 ) pkg.Artifact {
-	return t.New("go"+version, slices.Concat([]pkg.Artifact{
+	return t.New("go"+version, false, slices.Concat([]pkg.Artifact{
 		t.Load(Bash),
 	}, extra), nil, slices.Concat([]string{
 		"CC=cc",

internal/rosa/kernel.go

@@ -8,6 +8,7 @@ import (
 
 // newKernel is a helper for interacting with Kbuild.
 func (t Toolchain) newKernel(
+	exclusive bool,
 	patches [][2]string,
 	script string,
 	extra ...pkg.Artifact,
@@ -16,7 +17,7 @@ func (t Toolchain) newKernel(
 		version  = "6.18.5"
 		checksum = "-V1e1WWl7HuePkmm84sSKF7nLuHfUs494uNMzMqXEyxcNE_PUE0FICL0oGWn44mM"
 	)
-	return t.New("kernel-"+version, slices.Concat([]pkg.Artifact{
+	return t.New("kernel-"+version, exclusive, slices.Concat([]pkg.Artifact{
 		t.Load(Make),
 	}, extra), nil, nil, `
 export LLVM=1
@@ -34,7 +35,7 @@ cd /usr/src/linux
 }
 
 func (t Toolchain) newKernelHeaders() pkg.Artifact {
-	return t.newKernel(nil, `
+	return t.newKernel(false, nil, `
 make "-j$(nproc)" \
 	INSTALL_HDR_PATH=/work/system \
 	headers_install

internal/rosa/libexpat.go

@@ -11,7 +11,7 @@ func (t Toolchain) newLibexpat() pkg.Artifact {
 		version  = "2.7.3"
 		checksum = "GmkoD23nRi9cMT0cgG1XRMrZWD82UcOMzkkvP1gkwSFWCBgeSXMuoLpa8-v8kxW-"
 	)
-	return t.New("libexpat-"+version, []pkg.Artifact{
+	return t.New("libexpat-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(Bash),
 	}, nil, nil, `

internal/rosa/libffi.go

@@ -7,7 +7,7 @@ func (t Toolchain) newLibffi() pkg.Artifact {
 		version  = "3.4.5"
 		checksum = "apIJzypF4rDudeRoI_n3K7N-zCeBLTbQlHRn9NSAZqdLAWA80mR0gXPTpHsL7oMl"
 	)
-	return t.New("libffi-"+version, []pkg.Artifact{
+	return t.New("libffi-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(KernelHeaders),
 	}, nil, nil, `

internal/rosa/libgd.go

@@ -7,7 +7,7 @@ func (t Toolchain) newLibgd() pkg.Artifact {
 		version  = "2.3.3"
 		checksum = "8T-sh1_FJT9K9aajgxzh8ot6vWIF-xxjcKAHvTak9MgGUcsFfzP8cAvvv44u2r36"
 	)
-	return t.New("libgd-"+version, []pkg.Artifact{
+	return t.New("libgd-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 
 		t.Load(Zlib),

internal/rosa/libseccomp.go

@@ -9,7 +9,7 @@ func (t Toolchain) newLibseccomp() pkg.Artifact {
 		version  = "2.6.0"
 		checksum = "mMu-iR71guPjFbb31u-YexBaanKE_nYPjPux-vuBiPfS_0kbwJdfCGlkofaUm-EY"
 	)
-	return t.New("libseccomp-"+version, []pkg.Artifact{
+	return t.New("libseccomp-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(Bash),
 		t.Load(Gperf),

internal/rosa/libxml2.go

@@ -11,7 +11,7 @@ func (t Toolchain) newLibxml2() pkg.Artifact {
 		version  = "2.15.1"
 		checksum = "pYzAR3cNrEHezhEMirgiq7jbboLzwMj5GD7SQp0jhSIMdgoU4G9oU9Gxun3zzUIU"
 	)
-	return t.New("libxml2-"+version, []pkg.Artifact{
+	return t.New("libxml2-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd /usr/src/

internal/rosa/llvm.go

@@ -197,6 +197,8 @@ cp -r /system/include /usr/include && rm -rf /system/include
 			"ROSA_LLVM_RUNTIMES=" + strings.Join(runtimes, ";"),
 		}, attr.env),
 		ScriptEarly: scriptEarly, Script: script + attr.script,
+
+		Exclusive: true,
 	})
 }
 

internal/rosa/meson.go

@@ -7,7 +7,7 @@ func (t Toolchain) newMeson() pkg.Artifact {
 		version  = "1.10.1"
 		checksum = "w895BXF_icncnXatT_OLCFe2PYEtg4KrKooMgUYdN-nQVvbFX3PvYWHGEpogsHtd"
 	)
-	return t.New("meson-"+version, []pkg.Artifact{
+	return t.New("meson-"+version, false, []pkg.Artifact{
 		t.Load(Python),
 		t.Load(Setuptools),
 	}, nil, nil, `

internal/rosa/musl.go

@@ -42,7 +42,7 @@ rmdir -v /work/lib
 		script = ""
 	}
 
-	return t.New("musl-"+version, stage3Concat(t, attr.Extra,
+	return t.New("musl-"+version, false, stage3Concat(t, attr.Extra,
 		t.Load(Make),
 	), nil, slices.Concat([]string{
 		"ROSA_MUSL_TARGET=" + target,

internal/rosa/ninja.go

@@ -7,7 +7,7 @@ func (t Toolchain) newNinja() pkg.Artifact {
 		version  = "1.13.2"
 		checksum = "ygKWMa0YV2lWKiFro5hnL-vcKbc_-RACZuPu0Io8qDvgQlZ0dxv7hPNSFkt4214v"
 	)
-	return t.New("ninja-"+version, []pkg.Artifact{
+	return t.New("ninja-"+version, false, []pkg.Artifact{
 		t.Load(CMake),
 		t.Load(Python),
 	}, nil, nil, `

internal/rosa/perl.go

@@ -7,7 +7,7 @@ func (t Toolchain) newPerl() pkg.Artifact {
 		version  = "5.42.0"
 		checksum = "2KR7Jbpk-ZVn1a30LQRwbgUvg2AXlPQZfzrqCr31qD5-yEsTwVQ_W76eZH-EdxM9"
 	)
-	return t.New("perl-"+version, []pkg.Artifact{
+	return t.New("perl-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 chmod -R +w /usr/src/perl && cd /usr/src/perl

internal/rosa/pkg-config.go

@@ -7,7 +7,7 @@ func (t Toolchain) newPkgConfig() pkg.Artifact {
 		version  = "0.29.2"
 		checksum = "gi7yAvkwo20Inys1tHbeYZ3Wjdm5VPkrnO0Q6_QZPCAwa1zrA8F4a63cdZDd-717"
 	)
-	return t.New("pkg-config-"+version, []pkg.Artifact{
+	return t.New("pkg-config-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd "$(mktemp -d)"

internal/rosa/python.go

@@ -32,7 +32,7 @@ func (t Toolchain) newPython() pkg.Artifact {
 		// breaks on llvm
 		"test_dbm_gnu",
 	}
-	return t.New("python-"+version, []pkg.Artifact{
+	return t.New("python-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(Zlib),
 		t.Load(Libffi),
@@ -69,7 +69,7 @@ func (t Toolchain) newSetuptools() pkg.Artifact {
 		version  = "80.10.1"
 		checksum = "p3rlwEmy1krcUH1KabprQz1TCYjJ8ZUjOQknQsWh3q-XEqLGEd3P4VrCc7ouHGXU"
 	)
-	return t.New("setuptools-"+version, []pkg.Artifact{
+	return t.New("setuptools-"+version, false, []pkg.Artifact{
 		t.Load(Python),
 	}, nil, nil, `
 pip3 install \

internal/rosa/rosa.go

@@ -176,6 +176,7 @@ var absCureScript = fhs.AbsUsrBin.Append(".cure-script")
 // New returns a [pkg.Artifact] compiled on this toolchain.
 func (t Toolchain) New(
 	name string,
+	exclusive bool,
 	extra []pkg.Artifact,
 	checksum *pkg.Checksum,
 	env []string,
@@ -206,7 +207,7 @@ func (t Toolchain) New(
 		args[0] = "bash"
 		support = slices.Concat([]pkg.Artifact{
 			cureEtc{},
-			toolchainBusybox.New("stage3-"+version, nil, nil, nil, `
+			toolchainBusybox.New("stage3-"+version, false, nil, nil, nil, `
 tar -C /work -xf /usr/src/stage3.tar.xz
 rm -rf /work/dev/ /work/proc/
 ln -vs ../usr/bin /work/bin
@@ -258,7 +259,7 @@ ln -vs ../usr/bin /work/bin
 	}
 
 	return pkg.NewExec(
-		name, checksum, pkg.ExecTimeoutMax,
+		name, checksum, pkg.ExecTimeoutMax, exclusive,
 		fhs.AbsRoot, env,
 		path, args,
 
@@ -307,7 +308,7 @@ cat /usr/src/` + name + `-patches/* | \
 `
 		aname += "-patched"
 	}
-	return t.New(aname, stage3Concat(t, []pkg.Artifact{},
+	return t.New(aname, false, stage3Concat(t, []pkg.Artifact{},
 		t.Load(Patch),
 	), nil, nil, script, paths...)
 }

internal/rosa/rsync.go

@@ -7,7 +7,7 @@ func (t Toolchain) newRsync() pkg.Artifact {
 		version  = "3.4.1"
 		checksum = "VBlTsBWd9z3r2-ex7GkWeWxkUc5OrlgDzikAC0pK7ufTjAJ0MbmC_N04oSVTGPiv"
 	)
-	return t.New("rsync-"+version, []pkg.Artifact{
+	return t.New("rsync-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd "$(mktemp -d)"

internal/rosa/wayland.go

@@ -7,7 +7,7 @@ func (t Toolchain) newWayland() pkg.Artifact {
 		version  = "1.24.0"
 		checksum = "JxgLiFRRGw2D3uhVw8ZeDbs3V7K_d4z_ypDog2LBqiA_5y2vVbUAk5NT6D5ozm0m"
 	)
-	return t.New("wayland-"+version, []pkg.Artifact{
+	return t.New("wayland-"+version, false, []pkg.Artifact{
 		t.Load(Python),
 		t.Load(Meson),
 		t.Load(PkgConfig),
@@ -50,7 +50,7 @@ func (t Toolchain) newWaylandProtocols() pkg.Artifact {
 		version  = "1.47"
 		checksum = "B_NodZ7AQfCstcx7kgbaVjpkYOzbAQq0a4NOk-SA8bQixAE20FY3p1-6gsbPgHn9"
 	)
-	return t.New("wayland-protocols-"+version, []pkg.Artifact{
+	return t.New("wayland-protocols-"+version, false, []pkg.Artifact{
 		t.Load(Python),
 		t.Load(Meson),
 		t.Load(PkgConfig),

internal/rosa/zlib.go

@@ -7,7 +7,7 @@ func (t Toolchain) newZlib() pkg.Artifact {
 		version  = "1.3.1"
 		checksum = "E-eIpNzE8oJ5DsqH4UuA_0GDKuQF5csqI8ooDx2w7Vx-woJ2mb-YtSbEyIMN44mH"
 	)
-	return t.New("zlib-"+version, []pkg.Artifact{
+	return t.New("zlib-"+version, false, []pkg.Artifact{
 		t.Load(Make),
 	}, nil, nil, `
 cd "$(mktemp -d)"