Replace benbjohnson/clock with custom MockClock (#1349)

This drops the dependency on benbjohnson/clock as it's no longer
maintained.
It replaces it with a hand-rolled mock clock implementation.

The core of the functionality of MockClock is provided by the following:

- waiter: a function waiting to be executed
- runAt: schedules a function to be executed when time progresses
- Add: moves time forward, running all functions in range

The rest of the necessary functionality is built on top of these.

This is a pretty simple implementation.
We schedule work, but nothing happens until Add is called.
There are no goroutines running additional work in the background.

Resolves #1331

benchmarks/go.mod

@@ -16,7 +16,6 @@ require (
 )
 
 require (
-	github.com/benbjohnson/clock v1.3.0 // indirect
 	github.com/go-logfmt/logfmt v0.5.1 // indirect
 	github.com/go-stack/stack v1.8.1 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect

benchmarks/go.sum

@@ -5,8 +5,6 @@ github.com/aphistic/golf v0.0.0-20180712155816-02c07f170c5a/go.mod h1:3NqKYiepwy
 github.com/aphistic/sweet v0.2.0/go.mod h1:fWDlIh/isSE9n6EPsRmC0det+whmX6dJid3stzu0Xys=
 github.com/aws/aws-sdk-go v1.20.6/go.mod h1:KmX6BPdI08NWTb3/sm4ZGu5ShLoqVDhKgpiN924inxo=
 github.com/aybabtme/rgbterm v0.0.0-20170906152045-cc83f3b3ce59/go.mod h1:q/89r3U2H7sSsE2t6Kca0lfwTK8JdoNGS/yzM/4iH5I=
-github.com/benbjohnson/clock v1.3.0 h1:ip6w0uFQkncKQ979AypyG0ER7mqUSBdKLOgAle/AT8A=
-github.com/benbjohnson/clock v1.3.0/go.mod h1:J11/hYXuz8f4ySSvYwY0FKfm+ezbsZBKZxNJlLklBHA=
 github.com/coreos/go-systemd/v22 v22.3.3-0.20220203105225-a9a7ef127534/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=

exp/go.sum

@@ -1,4 +1,3 @@
-github.com/benbjohnson/clock v1.3.0 h1:ip6w0uFQkncKQ979AypyG0ER7mqUSBdKLOgAle/AT8A=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=

go.mod

@@ -3,7 +3,6 @@ module go.uber.org/zap
 go 1.19
 
 require (
-	github.com/benbjohnson/clock v1.3.0
 	github.com/stretchr/testify v1.8.1
 	go.uber.org/goleak v1.2.0
 	go.uber.org/multierr v1.10.0

go.sum

@@ -1,5 +1,3 @@
-github.com/benbjohnson/clock v1.3.0 h1:ip6w0uFQkncKQ979AypyG0ER7mqUSBdKLOgAle/AT8A=
-github.com/benbjohnson/clock v1.3.0/go.mod h1:J11/hYXuz8f4ySSvYwY0FKfm+ezbsZBKZxNJlLklBHA=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=

internal/ztest/clock.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2021 Uber Technologies, Inc.
+// Copyright (c) 2023 Uber Technologies, Inc.
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
@@ -21,30 +21,133 @@
 package ztest
 
 import (
+	"sort"
+	"sync"
 	"time"
-
-	"github.com/benbjohnson/clock"
 )
 
-// MockClock provides control over the time.
-type MockClock struct{ m *clock.Mock }
+// MockClock is a fake source of time.
+// It implements standard time operations,
+// but allows the user to control the passage of time.
+//
+// Use the [Add] method to progress time.
+type MockClock struct {
+	mu  sync.RWMutex
+	now time.Time
+
+	// The MockClock works by maintaining a list of waiters.
+	// Each waiter knows the time at which it should be resolved.
+	// When the clock advances, all waiters that are in range are resolved
+	// in chronological order.
+	waiters []waiter
+}
 
-// NewMockClock builds a new mock clock that provides control of time.
+// NewMockClock builds a new mock clock
+// using the current actual time as the initial time.
 func NewMockClock() *MockClock {
-	return &MockClock{clock.NewMock()}
+	return &MockClock{
+		now: time.Now(),
+	}
 }
 
 // Now reports the current time.
 func (c *MockClock) Now() time.Time {
-	return c.m.Now()
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.now
 }
 
 // NewTicker returns a time.Ticker that ticks at the specified frequency.
+//
+// As with [time.NewTicker],
+// the ticker will drop ticks if the receiver is slow,
+// and the channel is never closed.
+//
+// Calling Stop on the returned ticker is a no-op.
+// The ticker only runs when the clock is advanced.
 func (c *MockClock) NewTicker(d time.Duration) *time.Ticker {
-	return &time.Ticker{C: c.m.Ticker(d).C}
+	ch := make(chan time.Time, 1)
+
+	var tick func(time.Time)
+	tick = func(now time.Time) {
+		next := now.Add(d)
+		c.runAt(next, func() {
+			defer tick(next)
+
+			select {
+			case ch <- next:
+				// ok
+			default:
+				// The receiver is slow.
+				// Drop the tick and continue.
+			}
+		})
+	}
+	tick(c.Now())
+
+	return &time.Ticker{C: ch}
+}
+
+// runAt schedules the given function to be run at the given time.
+// The function runs without a lock held, so it may schedule more work.
+func (c *MockClock) runAt(t time.Time, fn func()) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.waiters = append(c.waiters, waiter{until: t, fn: fn})
+}
+
+type waiter struct {
+	until time.Time
+	fn    func()
 }
 
 // Add progresses time by the given duration.
+// Other operations waiting for the time to advance
+// will be resolved if they are within range.
+//
+// Side effects of operations waiting for the time to advance
+// will take effect on a best-effort basis.
+// Avoid racing with operations that have side effects.
+//
+// Panics if the duration is negative.
 func (c *MockClock) Add(d time.Duration) {
-	c.m.Add(d)
+	if d < 0 {
+		panic("cannot add negative duration")
+	}
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	sort.Slice(c.waiters, func(i, j int) bool {
+		return c.waiters[i].until.Before(c.waiters[j].until)
+	})
+
+	newTime := c.now.Add(d)
+	// newTime won't be recorded until the end of this method.
+	// This ensures that any waiters that are resolved
+	// are resolved at the time they were expecting.
+
+	for len(c.waiters) > 0 {
+		w := c.waiters[0]
+		if w.until.After(newTime) {
+			break
+		}
+		c.waiters[0] = waiter{} // avoid memory leak
+		c.waiters = c.waiters[1:]
+
+		// The waiter is within range.
+		// Travel to the time of the waiter and resolve it.
+		c.now = w.until
+
+		// The waiter may schedule more work
+		// so we must release the lock.
+		c.mu.Unlock()
+		w.fn()
+		// Sleeping here is necessary to let the side effects of waiters
+		// take effect before we continue.
+		time.Sleep(1 * time.Millisecond)
+		c.mu.Lock()
+	}
+
+	c.now = newTime
 }

internal/ztest/clock_test.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2021 Uber Technologies, Inc.
+// Copyright (c) 2023 Uber Technologies, Inc.
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
@@ -55,3 +55,26 @@ func TestMockClock_NewTicker(t *testing.T) {
 	assert.Equal(t, int32(2), n.Load())
 	close(quit)
 }
+
+func TestMockClock_NewTicker_slowConsumer(t *testing.T) {
+	clock := NewMockClock()
+
+	ticker := clock.NewTicker(time.Microsecond)
+	defer ticker.Stop()
+
+	// Two ticks, only one consumed.
+	clock.Add(2 * time.Microsecond)
+	<-ticker.C
+
+	select {
+	case <-ticker.C:
+		t.Fatal("unexpected tick")
+	default:
+		// ok
+	}
+}
+
+func TestMockClock_Add_negative(t *testing.T) {
+	clock := NewMockClock()
+	assert.Panics(t, func() { clock.Add(-1) })
+}

zapgrpc/internal/test/go.sum

@@ -2,8 +2,6 @@ cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMT
 cloud.google.com/go v0.34.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/antihax/optional v1.0.0/go.mod h1:uupD/76wgC+ih3iEmQUL+0Ugr19nfwCT1kdvxnR2qWY=
-github.com/benbjohnson/clock v1.3.0 h1:ip6w0uFQkncKQ979AypyG0ER7mqUSBdKLOgAle/AT8A=
-github.com/benbjohnson/clock v1.3.0/go.mod h1:J11/hYXuz8f4ySSvYwY0FKfm+ezbsZBKZxNJlLklBHA=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=