Feat v0.7.12 batch exec (#66)

Co-authored-by: Jeffrey Smith <jasafpro@gmail.com>
Co-committed-by: Jeffrey Smith <jasafpro@gmail.com>

server/sandbox/batch_module.go

@@ -0,0 +1,140 @@
+// Package sandbox — batch_module.go
+//
+// Permission: batch.exec
+//
+// Starlark API:
+//   results, errors = batch.exec([fn_a, fn_b, fn_c], timeout=10)
+//
+// Runs a list of zero-arg callables concurrently, each in its own
+// starlark.Thread with an independent step budget. Results and errors
+// are returned in input order. Max 8 callables per call.
+//
+// Each branch gets a fresh Sandbox (thread + step counter) and a
+// child context with the per-branch timeout. The callable's closed-over
+// bindings (frozen library structs, module builtins) are used as-is —
+// the Go resources underneath (*sql.DB, http.Client) are concurrent-safe.
+//
+// lib.require() is not available inside branches (Option A).
+// print() output from branches is discarded.
+// Nested batch.exec() is prohibited via an atomic flag.
+package sandbox
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"go.starlark.net/starlark"
+	"go.starlark.net/starlarkstruct"
+)
+
+const (
+	batchMaxCallables   = 8
+	batchDefaultTimeout = 10
+	batchMaxTimeout     = 30
+)
+
+// BuildBatchModule creates the "batch" module.
+// The runner/packageID/manifest/rc/lc parameters are stored for future
+// expansion (Option B: per-branch lib.require) but are not used in v1.
+func BuildBatchModule(
+	ctx context.Context,
+	runner *Runner,
+	packageID string,
+	manifest map[string]any,
+	rc *RunContext,
+	lc *libContext,
+) *starlarkstruct.Module {
+	var running atomic.Bool
+
+	return MakeModule("batch", starlark.StringDict{
+		"exec": starlark.NewBuiltin("batch.exec", batchExec(ctx, &running)),
+	})
+}
+
+// batchExec returns the batch.exec builtin implementation.
+func batchExec(
+	ctx context.Context,
+	running *atomic.Bool,
+) func(*starlark.Thread, *starlark.Builtin, starlark.Tuple, []starlark.Tuple) (starlark.Value, error) {
+	return func(
+		thread *starlark.Thread, b *starlark.Builtin,
+		args starlark.Tuple, kwargs []starlark.Tuple,
+	) (starlark.Value, error) {
+		// Nesting guard: parent thread is blocked in wg.Wait(), so only
+		// a branch goroutine could re-enter. The captured builtin reference
+		// makes this reachable even though branches don't get fresh modules.
+		if !running.CompareAndSwap(false, true) {
+			return nil, fmt.Errorf("batch.exec: nested calls are not allowed")
+		}
+		defer running.Store(false)
+
+		var callableList *starlark.List
+		var timeout int = batchDefaultTimeout
+
+		if err := starlark.UnpackArgs(b.Name(), args, kwargs,
+			"callables", &callableList,
+			"timeout?", &timeout,
+		); err != nil {
+			return nil, err
+		}
+
+		n := callableList.Len()
+		if n == 0 {
+			return nil, fmt.Errorf("batch.exec: callables list is empty")
+		}
+		if n > batchMaxCallables {
+			return nil, fmt.Errorf("batch.exec: max %d callables, got %d", batchMaxCallables, n)
+		}
+		if timeout < 1 || timeout > batchMaxTimeout {
+			timeout = batchDefaultTimeout
+		}
+
+		// Validate all elements are callable before spawning goroutines.
+		callables := make([]starlark.Callable, n)
+		for i := 0; i < n; i++ {
+			c, ok := callableList.Index(i).(starlark.Callable)
+			if !ok {
+				return nil, fmt.Errorf("batch.exec: element %d is %s, not callable",
+					i, callableList.Index(i).Type())
+			}
+			callables[i] = c
+		}
+
+		// Execute concurrently.
+		results := make([]starlark.Value, n)
+		errors := make([]starlark.Value, n)
+		var wg sync.WaitGroup
+
+		for i, callable := range callables {
+			wg.Add(1)
+			go func(idx int, fn starlark.Callable) {
+				defer wg.Done()
+
+				branchCtx, cancel := context.WithTimeout(ctx,
+					time.Duration(timeout)*time.Second)
+				defer cancel()
+
+				sb := New(DefaultConfig())
+				val, _, callErr := sb.Call(branchCtx, fn, nil, nil)
+
+				if callErr != nil {
+					results[idx] = starlark.None
+					errors[idx] = starlark.String(callErr.Error())
+				} else {
+					results[idx] = val
+					errors[idx] = starlark.None
+				}
+			}(i, callable)
+		}
+
+		wg.Wait()
+
+		return starlark.Tuple{
+			starlark.NewList(results),
+			starlark.NewList(errors),
+		}, nil
+	}
+}

server/sandbox/batch_module_test.go

@@ -0,0 +1,324 @@
+package sandbox
+
+import (
+	"context"
+	"strings"
+	"testing"
+	"time"
+
+	"go.starlark.net/starlark"
+)
+
+// execWithBatch runs a Starlark script with the batch module available.
+func execWithBatch(t *testing.T, script string) (*Result, error) {
+	t.Helper()
+	ctx := context.Background()
+	batchMod := BuildBatchModule(ctx, nil, "test-pkg", nil, nil, nil)
+	sb := New(DefaultConfig())
+	return sb.Exec(ctx, "test.star", script, map[string]starlark.Value{
+		"batch": batchMod,
+	})
+}
+
+// ─── Parallel Ordering ──────────────────────
+
+func TestBatchExec_ParallelOrdering(t *testing.T) {
+	result, err := execWithBatch(t, `
+results, errors = batch.exec([
+    lambda: 10,
+    lambda: 20,
+    lambda: 30,
+])
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	// Verify results are in input order.
+	globals := result.Globals
+	results := globals["results"].(*starlark.List)
+	errors := globals["errors"].(*starlark.List)
+
+	if results.Len() != 3 {
+		t.Fatalf("expected 3 results, got %d", results.Len())
+	}
+
+	for i, want := range []int{10, 20, 30} {
+		v, _ := starlark.AsInt32(results.Index(i))
+		got := int(v)
+		if got != want {
+			t.Errorf("results[%d] = %d, want %d", i, got, want)
+		}
+		if errors.Index(i) != starlark.None {
+			t.Errorf("errors[%d] = %v, want None", i, errors.Index(i))
+		}
+	}
+}
+
+// ─── Partial Failure ────────────────────────
+
+func TestBatchExec_PartialFailure(t *testing.T) {
+	result, err := execWithBatch(t, `
+def ok_a():
+    return "a"
+
+def bad():
+    return 1 // 0
+
+def ok_c():
+    return "c"
+
+results, errors = batch.exec([ok_a, bad, ok_c])
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	results := result.Globals["results"].(*starlark.List)
+	errors := result.Globals["errors"].(*starlark.List)
+
+	// results[0] = "a", results[2] = "c"
+	if s, _ := starlark.AsString(results.Index(0)); s != "a" {
+		t.Errorf("results[0] = %v, want 'a'", results.Index(0))
+	}
+	if s, _ := starlark.AsString(results.Index(2)); s != "c" {
+		t.Errorf("results[2] = %v, want 'c'", results.Index(2))
+	}
+
+	// results[1] = None (failed)
+	if results.Index(1) != starlark.None {
+		t.Errorf("results[1] = %v, want None", results.Index(1))
+	}
+
+	// errors[0] and errors[2] = None (succeeded)
+	if errors.Index(0) != starlark.None {
+		t.Errorf("errors[0] = %v, want None", errors.Index(0))
+	}
+	if errors.Index(2) != starlark.None {
+		t.Errorf("errors[2] = %v, want None", errors.Index(2))
+	}
+
+	// errors[1] should be a string containing the error
+	errStr, ok := starlark.AsString(errors.Index(1))
+	if !ok || errStr == "" {
+		t.Errorf("errors[1] = %v, want non-empty error string", errors.Index(1))
+	}
+}
+
+// ─── Timeout Per-Branch ─────────────────────
+
+func TestBatchExec_TimeoutPerBranch(t *testing.T) {
+	// Use a tight timeout. The slow lambda burns steps in an infinite loop,
+	// which will hit either the step limit or the context timeout.
+	result, err := execWithBatch(t, `
+def fast():
+    return "done"
+
+def slow():
+    x = 0
+    for i in range(999999999):
+        x = x + 1
+    return x
+
+results, errors = batch.exec([fast, slow], timeout=1)
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	results := result.Globals["results"].(*starlark.List)
+	errors := result.Globals["errors"].(*starlark.List)
+
+	// Fast branch should succeed.
+	if s, _ := starlark.AsString(results.Index(0)); s != "done" {
+		t.Errorf("results[0] = %v, want 'done'", results.Index(0))
+	}
+	if errors.Index(0) != starlark.None {
+		t.Errorf("errors[0] = %v, want None", errors.Index(0))
+	}
+
+	// Slow branch should fail (step limit or timeout).
+	if results.Index(1) != starlark.None {
+		t.Errorf("results[1] = %v, want None", results.Index(1))
+	}
+	errStr, _ := starlark.AsString(errors.Index(1))
+	if errStr == "" {
+		t.Errorf("errors[1] should contain error string")
+	}
+}
+
+// ─── Parent Cancellation ────────────────────
+
+func TestBatchExec_ParentCancellation(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // cancel immediately
+
+	batchMod := BuildBatchModule(ctx, nil, "test-pkg", nil, nil, nil)
+	sb := New(DefaultConfig())
+	result, err := sb.Exec(ctx, "test.star", `
+results, errors = batch.exec([lambda: 1, lambda: 2])
+`, map[string]starlark.Value{"batch": batchMod})
+
+	// Either the Exec itself fails (context cancelled before script runs)
+	// or the batch.exec branches all fail.
+	if err != nil {
+		// Script-level cancellation — acceptable.
+		return
+	}
+
+	errors := result.Globals["errors"].(*starlark.List)
+	allErrored := true
+	for i := 0; i < errors.Len(); i++ {
+		if errors.Index(i) == starlark.None {
+			allErrored = false
+		}
+	}
+	if !allErrored {
+		t.Errorf("expected all branches to error on cancelled context, errors=%v", errors)
+	}
+}
+
+// ─── Cap Enforcement ────────────────────────
+
+func TestBatchExec_CapEnforcement(t *testing.T) {
+	_, err := execWithBatch(t, `
+fns = [lambda: i for i in range(9)]
+batch.exec(fns)
+`)
+	if err == nil {
+		t.Fatal("expected error for 9 callables, got nil")
+	}
+	if !strings.Contains(err.Error(), "max 8") {
+		t.Errorf("error = %q, want to contain 'max 8'", err.Error())
+	}
+}
+
+// ─── Empty List ─────────────────────────────
+
+func TestBatchExec_EmptyList(t *testing.T) {
+	_, err := execWithBatch(t, `batch.exec([])`)
+	if err == nil {
+		t.Fatal("expected error for empty list, got nil")
+	}
+	if !strings.Contains(err.Error(), "empty") {
+		t.Errorf("error = %q, want to contain 'empty'", err.Error())
+	}
+}
+
+// ─── Non-Callable Element ───────────────────
+
+func TestBatchExec_NonCallableElement(t *testing.T) {
+	_, err := execWithBatch(t, `batch.exec([1, 2])`)
+	if err == nil {
+		t.Fatal("expected error for non-callable, got nil")
+	}
+	if !strings.Contains(err.Error(), "not callable") {
+		t.Errorf("error = %q, want to contain 'not callable'", err.Error())
+	}
+}
+
+// ─── Permission Gating ──────────────────────
+
+func TestBatchExec_PermissionGating(t *testing.T) {
+	sb := New(DefaultConfig())
+	_, err := sb.Exec(context.Background(), "test.star",
+		`batch.exec([lambda: 1])`,
+		map[string]starlark.Value{}, // no batch module
+	)
+	if err == nil {
+		t.Fatal("expected error when batch module not available")
+	}
+	if !strings.Contains(err.Error(), "batch") {
+		t.Errorf("error = %q, want to mention 'batch'", err.Error())
+	}
+}
+
+// ─── Frozen Struct Sharing ──────────────────
+
+func TestBatchExec_FrozenStructSharing(t *testing.T) {
+	// Two branches read the same frozen tuple. Should not race.
+	result, err := execWithBatch(t, `
+data = (1, 2, 3)  # tuples are frozen/immutable
+
+results, errors = batch.exec([
+    lambda: data[0] + data[1],
+    lambda: data[1] + data[2],
+])
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	results := result.Globals["results"].(*starlark.List)
+
+	got0, _ := starlark.AsInt32(results.Index(0))
+	got1, _ := starlark.AsInt32(results.Index(1))
+	if got0 != 3 {
+		t.Errorf("results[0] = %d, want 3", got0)
+	}
+	if got1 != 5 {
+		t.Errorf("results[1] = %d, want 5", got1)
+	}
+}
+
+// ─── Nested batch.exec ──────────────────────
+
+func TestBatchExec_NestedBatchExec(t *testing.T) {
+	result, err := execWithBatch(t, `
+results, errors = batch.exec([
+    lambda: batch.exec([lambda: 1]),
+])
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	// The inner batch.exec should fail with nesting error.
+	errors := result.Globals["errors"].(*starlark.List)
+	errStr, _ := starlark.AsString(errors.Index(0))
+	if !strings.Contains(errStr, "nested") {
+		t.Errorf("errors[0] = %q, want to contain 'nested'", errStr)
+	}
+}
+
+// ─── Default Timeout ────────────────────────
+
+func TestBatchExec_DefaultTimeout(t *testing.T) {
+	// Call without explicit timeout — should succeed.
+	result, err := execWithBatch(t, `
+results, errors = batch.exec([lambda: 42])
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	results := result.Globals["results"].(*starlark.List)
+	got, _ := starlark.AsInt32(results.Index(0))
+	if got != 42 {
+		t.Errorf("results[0] = %d, want 42", got)
+	}
+}
+
+// ─── Timeout Clamping ───────────────────────
+
+func TestBatchExec_TimeoutClamp(t *testing.T) {
+	// timeout=0 should be clamped to default, not crash.
+	start := time.Now()
+	result, err := execWithBatch(t, `
+results, errors = batch.exec([lambda: "ok"], timeout=0)
+`)
+	elapsed := time.Since(start)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+
+	results := result.Globals["results"].(*starlark.List)
+	if s, _ := starlark.AsString(results.Index(0)); s != "ok" {
+		t.Errorf("results[0] = %v, want 'ok'", results.Index(0))
+	}
+
+	// Should complete quickly (clamped to default 10s, but lambda is instant).
+	if elapsed > 2*time.Second {
+		t.Errorf("took %v, expected fast completion", elapsed)
+	}
+}

server/sandbox/runner.go

@@ -338,6 +338,7 @@ func (r *Runner) buildModulesWithLibCtx(ctx context.Context, packageID string, m
 
 	// Track db permission level: 0=none, 1=read, 2=write
 	dbLevel := 0
+	hasBatchExec := false
 
 	for _, perm := range granted {
 		switch perm {
@@ -374,6 +375,9 @@ func (r *Runner) buildModulesWithLibCtx(ctx context.Context, packageID string, m
 			if r.bus != nil {
 				modules["realtime"] = BuildRealtimeModule(ctx, r.bus, packageID)
 			}
+
+		case models.ExtPermBatchExec:
+			hasBatchExec = true
 		}
 	}
 
@@ -404,5 +408,12 @@ func (r *Runner) buildModulesWithLibCtx(ctx context.Context, packageID string, m
 		modules["lib"] = BuildLibModule(ctx, r, packageID, rc, lc)
 	}
 
+	// Concurrent execution primitive — wired after all other modules
+	// so the runner reference can construct per-branch module sets if
+	// needed in future (Option B).
+	if hasBatchExec {
+		modules["batch"] = BuildBatchModule(ctx, r, packageID, manifest, rc, lc)
+	}
+
 	return modules, nil
 }