util/expvarx: remove unused package (#19519)

Added in 2024 and appears to be unused.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

2 files changed, 0 insertions, 230 deletions

diff --git a/util/expvarx/expvarx.go b/util/expvarx/expvarx.go
deleted file mode 100644
index 6dc2379b9..000000000
--- a/util/expvarx/expvarx.go
+++ /dev/null
@@ -1,89 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-// Package expvarx provides some extensions to the [expvar] package.
-package expvarx
-
-import (
-	"encoding/json"
-	"expvar"
-	"time"
-
-	"tailscale.com/syncs"
-	"tailscale.com/types/lazy"
-)
-
-// SafeFunc is a wrapper around [expvar.Func] that guards against unbounded call
-// time and ensures that only a single call is in progress at any given time.
-type SafeFunc struct {
-	f      expvar.Func
-	limit  time.Duration
-	onSlow func(time.Duration, any)
-
-	mu       syncs.Mutex
-	inflight *lazy.SyncValue[any]
-}
-
-// NewSafeFunc returns a new SafeFunc that wraps f.
-// If f takes longer than limit to execute then Value calls return nil.
-// If onSlow is non-nil, it is called when f takes longer than limit to execute.
-// onSlow is called with the duration of the slow call and the final computed
-// value.
-func NewSafeFunc(f expvar.Func, limit time.Duration, onSlow func(time.Duration, any)) *SafeFunc {
-	return &SafeFunc{f: f, limit: limit, onSlow: onSlow}
-}
-
-// Value acts similarly to [expvar.Func.Value], but if the underlying function
-// takes longer than the configured limit, all callers will receive nil until
-// the underlying operation completes. On completion of the underlying
-// operation, the onSlow callback is called if set.
-func (s *SafeFunc) Value() any {
-	s.mu.Lock()
-
-	if s.inflight == nil {
-		s.inflight = new(lazy.SyncValue[any])
-	}
-	var inflight = s.inflight
-	s.mu.Unlock()
-
-	// inflight ensures that only a single work routine is spawned at any given
-	// time, but if the routine takes too long inflight is populated with a nil
-	// result. The long running computed value is lost forever.
-	return inflight.Get(func() any {
-		start := time.Now()
-		result := make(chan any, 1)
-
-		// work is spawned in routine so that the caller can timeout.
-		go func() {
-			// Allow new work to be started after this work completes
-			defer func() {
-				s.mu.Lock()
-				s.inflight = nil
-				s.mu.Unlock()
-
-			}()
-
-			v := s.f.Value()
-			result <- v
-		}()
-
-		select {
-		case v := <-result:
-			return v
-		case <-time.After(s.limit):
-			if s.onSlow != nil {
-				go func() {
-					s.onSlow(time.Since(start), <-result)
-				}()
-			}
-			return nil
-		}
-	})
-}
-
-// String implements stringer in the same pattern as [expvar.Func], calling
-// Value and serializing the result as JSON, ignoring errors.
-func (s *SafeFunc) String() string {
-	v, _ := json.Marshal(s.Value())
-	return string(v)
-}
diff --git a/util/expvarx/expvarx_test.go b/util/expvarx/expvarx_test.go
deleted file mode 100644
index f8d2139d3..000000000
--- a/util/expvarx/expvarx_test.go
+++ /dev/null
@@ -1,141 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-package expvarx
-
-import (
-	"expvar"
-	"fmt"
-	"sync"
-	"sync/atomic"
-	"testing"
-	"testing/synctest"
-	"time"
-)
-
-func ExampleNewSafeFunc() {
-	// An artificial blocker to emulate a slow operation.
-	blocker := make(chan struct{})
-
-	// limit is the amount of time a call can take before Value returns nil. No
-	// new calls to the unsafe func will be started until the slow call
-	// completes, at which point onSlow will be called.
-	limit := time.Millisecond
-
-	// onSlow is called with the final call duration and the final value in the
-	// event a slow call.
-	onSlow := func(d time.Duration, v any) {
-		_ = d // d contains the time the call took
-		_ = v // v contains the final value computed by the slow call
-		fmt.Println("slow call!")
-	}
-
-	// An unsafe expvar.Func that blocks on the blocker channel.
-	unsafeFunc := expvar.Func(func() any {
-		for range blocker {
-		}
-		return "hello world"
-	})
-
-	// f implements the same interface as expvar.Func, but returns nil values
-	// when the unsafe func is too slow.
-	f := NewSafeFunc(unsafeFunc, limit, onSlow)
-
-	fmt.Println(f.Value())
-	fmt.Println(f.Value())
-	close(blocker)
-	time.Sleep(time.Millisecond)
-	fmt.Println(f.Value())
-	// Output: <nil>
-	// <nil>
-	// slow call!
-	// hello world
-}
-
-func TestSafeFuncHappyPath(t *testing.T) {
-	synctest.Test(t, func(t *testing.T) {
-		var count int
-		f := NewSafeFunc(expvar.Func(func() any {
-			count++
-			return count
-		}), time.Second, nil)
-
-		if got, want := f.Value(), 1; got != want {
-			t.Errorf("got %v, want %v", got, want)
-		}
-		time.Sleep(5 * time.Second) // (fake time in synctest)
-		if got, want := f.Value(), 2; got != want {
-			t.Errorf("got %v, want %v", got, want)
-		}
-	})
-}
-
-func TestSafeFuncSlow(t *testing.T) {
-	var count int
-	blocker := make(chan struct{})
-	var wg sync.WaitGroup
-	wg.Add(1)
-	f := NewSafeFunc(expvar.Func(func() any {
-		defer wg.Done()
-		count++
-		<-blocker
-		return count
-	}), time.Millisecond, nil)
-
-	if got := f.Value(); got != nil {
-		t.Errorf("got %v; want nil", got)
-	}
-	if got := f.Value(); got != nil {
-		t.Errorf("got %v; want nil", got)
-	}
-
-	close(blocker)
-	wg.Wait()
-
-	if count != 1 {
-		t.Errorf("got count=%d; want 1", count)
-	}
-}
-
-func TestSafeFuncSlowOnSlow(t *testing.T) {
-	var count int
-	blocker := make(chan struct{})
-	var wg sync.WaitGroup
-	wg.Add(2)
-	var slowDuration atomic.Pointer[time.Duration]
-	var slowCallCount atomic.Int32
-	var slowValue atomic.Value
-	f := NewSafeFunc(expvar.Func(func() any {
-		defer wg.Done()
-		count++
-		<-blocker
-		return count
-	}), time.Millisecond, func(d time.Duration, v any) {
-		defer wg.Done()
-		slowDuration.Store(&d)
-		slowCallCount.Add(1)
-		slowValue.Store(v)
-	})
-
-	for range 10 {
-		if got := f.Value(); got != nil {
-			t.Fatalf("got value=%v; want nil", got)
-		}
-	}
-
-	close(blocker)
-	wg.Wait()
-
-	if count != 1 {
-		t.Errorf("got count=%d; want 1", count)
-	}
-	if got, want := *slowDuration.Load(), 1*time.Millisecond; got < want {
-		t.Errorf("got slowDuration=%v; want at least %d", got, want)
-	}
-	if got, want := slowCallCount.Load(), int32(1); got != want {
-		t.Errorf("got slowCallCount=%d; want %d", got, want)
-	}
-	if got, want := slowValue.Load().(int), 1; got != want {
-		t.Errorf("got slowValue=%d, want %d", got, want)
-	}
-}