"sync"
)

// PipeWriter is similar to io.PipeWriter with wait group
type PipeWriter struct {
	*io.PipeWriter
	once sync.Once
	done func()
}

// CloseWithError close with supplied error the writer end.
func (w *PipeWriter) CloseWithError(err error) error {
	err = w.PipeWriter.CloseWithError(err)
	w.once.Do(func() {
		w.done()
	})
	return err
}

// PipeReader is similar to io.PipeReader with wait group

	gp := getg()
	var mp *m
	if gp != nil {
		mp = gp.m
	}
	if mp != nil && mp.libcallsp == 0 {
		mp.libcallg.set(gp)
		mp.libcallpc = getcallerpc()
		// sp must be the last, because once async cpu profiler finds
		// all three values to be non-zero, it will use them
		mp.libcallsp = getcallersp()
	} else {
		mp = nil // See comment in sys_darwin.go:libcCall
	}

	var libcall libcall

	"os/exec"
	"runtime"
	"slices"
	"sync"
)

type gitHandler struct {
	once       sync.Once
	gitPath    string
	gitPathErr error
}

func (h *gitHandler) Available() bool {
	if runtime.GOOS == "plan9" {
		// The Git command is usually not the real Git on Plan 9.
		// See https://golang.org/issues/29640.
		return false
	}
	h.once.Do(func() {
		h.gitPath, h.gitPathErr = exec.LookPath("git")
	})

package toolchain

import (
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"sync"

	"cmd/go/internal/gover"
)

// pathExts is a cached PATHEXT list.
var pathExts struct {
	once sync.Once
	list []string
}

func initPathExts() {
	var exts []string
	x := os.Getenv(`PATHEXT`)
	if x != "" {
		for _, e := range strings.Split(strings.ToLower(x), `;`) {
			if e == "" {
				continue
			}

)

// Regexp is a wrapper around [regexp.Regexp], where the underlying regexp will be
// compiled the first time it is needed.
type Regexp struct {
	str  string
	once sync.Once
	rx   *regexp.Regexp
}

func (r *Regexp) re() *regexp.Regexp {
	r.once.Do(r.build)
	return r.rx
}

func (r *Regexp) build() {
	r.rx = regexp.MustCompile(r.str)
	r.str = ""
}

func (r *Regexp) FindSubmatch(s []byte) [][]byte {

 *     <li>{@link #locking()} would create a lazy wrapper which performs locking when calling the supplier: the supplier will only be called once. Reading is done without locking once initialized.</li>
 * </ul>
 *
 * @param <T> the type of the lazy value
 */
public interface Lazy<T> extends Supplier<T> {
    /**
     * Executes an operation on the lazily computed value
     *

	".pdf":  "application/pdf",
	".png":  "image/png",
	".svg":  "image/svg+xml",
	".wasm": "application/wasm",
	".webp": "image/webp",
	".xml":  "text/xml; charset=utf-8",
}

var once sync.Once // guards initMime

var testInitMime, osInitMime func()

func initMime() {
	if fn := testInitMime; fn != nil {
		fn()
	} else {
		setMimeTypes(builtinTypesLower, builtinTypesLower)
		osInitMime()
	}

	configurationName string

	initObjectSelector sync.Once
	objectSelector     labels.Selector
	objectSelectorErr  error

	initNamespaceSelector sync.Once
	namespaceSelector     labels.Selector
	namespaceSelectorErr  error

	initClient sync.Once
	client     *rest.RESTClient
	clientErr  error

	compileMatcher  sync.Once
	compiledMatcher matchconditions.Matcher
}

package once

import (
	"context"
	"sync"
	"sync/atomic"
)

// Inspired from Golang sync.Once but it is only marked
// initialized when the provided function returns nil.

// Init represents the structure.
type Init struct {
	done uint32
	m    sync.Mutex
}

// Do is similar to sync.Once.Do - makes one successful

	"go.uber.org/atomic"
)

// SetForTest sets a variable for the duration of a test, then resets it once the test is complete.
func SetForTest[T any](t Failer, vv *T, v T) {
	old := *vv
	*vv = v
	t.Cleanup(func() {
		*vv = old
	})
}

// SetEnvForTest sets an environment variable for the duration of a test, then resets it once the test is complete.
func SetEnvForTest(t Failer, k, v string) {
	old, oldset := os.LookupEnv(k)