authorize: build evaluators cache in parallel (#4731)

authorize: build evaluators cache in parallel (#4722)

* authorize: build evaluators cache in parallel

* session: add unit tests for gRPC wrapper methods (#4713)

* core/config: add support for maps in environments (#4717)

* reconciler: allow custom comparison function (#4726)

* add loopvar alias

---------

Co-authored-by: Denis Mishin <dmishin@pomerium.com>
Co-authored-by: Kenneth Jenkins <51246568+kenjenkins@users.noreply.github.com>
Co-authored-by: Caleb Doxsey <cdoxsey@pomerium.com>

internal/errgrouputil/builder.go

@@ -0,0 +1,54 @@
+// Package errgrouputil contains methods for working with errgroup code.
+package errgrouputil
+
+import (
+	"context"
+	"runtime"
+
+	"golang.org/x/sync/errgroup"
+
+	"github.com/pomerium/pomerium/pkg/slices"
+)
+
+// BuilderFunc is a function that builds a value of type T
+type BuilderFunc[T any] func(ctx context.Context) (*T, error)
+
+// Build builds a slice of values of type T using the provided builders concurrently
+// and returns the results and any errors.
+func Build[T any](
+	ctx context.Context,
+	builders ...BuilderFunc[T],
+) ([]*T, []error) {
+	eg, ctx := errgroup.WithContext(ctx)
+	eg.SetLimit(runtime.NumCPU()/2 + 1)
+
+	results := make([]*T, len(builders))
+	errors := make([]error, len(builders))
+
+	fn := func(i int) func() error {
+		return func() error {
+			result, err := builders[i](ctx)
+			if err != nil {
+				errors[i] = err
+				return nil
+			}
+			results[i] = result
+			return nil
+		}
+	}
+
+	for i := range builders {
+		eg.Go(fn(i))
+	}
+
+	err := eg.Wait()
+	if err != nil {
+		return nil, []error{err} // not happening
+	}
+
+	return slices.Filter(results, func(t *T) bool {
+			return t != nil
+		}), slices.Filter(errors, func(err error) bool {
+			return err != nil
+		})
+}