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testsync.go
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testsync.go
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// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package http2
import (
"context"
"sync"
"time"
)
// testSyncHooks coordinates goroutines in tests.
//
// For example, a call to ClientConn.RoundTrip involves several goroutines, including:
// - the goroutine running RoundTrip;
// - the clientStream.doRequest goroutine, which writes the request; and
// - the clientStream.readLoop goroutine, which reads the response.
//
// Using testSyncHooks, a test can start a RoundTrip and identify when all these goroutines
// are blocked waiting for some condition such as reading the Request.Body or waiting for
// flow control to become available.
//
// The testSyncHooks also manage timers and synthetic time in tests.
// This permits us to, for example, start a request and cause it to time out waiting for
// response headers without resorting to time.Sleep calls.
type testSyncHooks struct {
// active/inactive act as a mutex and condition variable.
//
// - neither chan contains a value: testSyncHooks is locked.
// - active contains a value: unlocked, and at least one goroutine is not blocked
// - inactive contains a value: unlocked, and all goroutines are blocked
active chan struct{}
inactive chan struct{}
// goroutine counts
total int // total goroutines
condwait map[*sync.Cond]int // blocked in sync.Cond.Wait
blocked []*testBlockedGoroutine // otherwise blocked
// fake time
now time.Time
timers []*fakeTimer
// Transport testing: Report various events.
newclientconn func(*ClientConn)
newstream func(*clientStream)
}
// testBlockedGoroutine is a blocked goroutine.
type testBlockedGoroutine struct {
f func() bool // blocked until f returns true
ch chan struct{} // closed when unblocked
}
func newTestSyncHooks() *testSyncHooks {
h := &testSyncHooks{
active: make(chan struct{}, 1),
inactive: make(chan struct{}, 1),
condwait: map[*sync.Cond]int{},
}
h.inactive <- struct{}{}
h.now = time.Date(2000, 1, 1, 0, 0, 0, 0, time.UTC)
return h
}
// lock acquires the testSyncHooks mutex.
func (h *testSyncHooks) lock() {
select {
case <-h.active:
case <-h.inactive:
}
}
// waitInactive waits for all goroutines to become inactive.
func (h *testSyncHooks) waitInactive() {
for {
<-h.inactive
if !h.unlock() {
break
}
}
}
// unlock releases the testSyncHooks mutex.
// It reports whether any goroutines are active.
func (h *testSyncHooks) unlock() (active bool) {
// Look for a blocked goroutine which can be unblocked.
blocked := h.blocked[:0]
unblocked := false
for _, b := range h.blocked {
if !unblocked && b.f() {
unblocked = true
close(b.ch)
} else {
blocked = append(blocked, b)
}
}
h.blocked = blocked
// Count goroutines blocked on condition variables.
condwait := 0
for _, count := range h.condwait {
condwait += count
}
if h.total > condwait+len(blocked) {
h.active <- struct{}{}
return true
} else {
h.inactive <- struct{}{}
return false
}
}
// goRun starts a new goroutine.
func (h *testSyncHooks) goRun(f func()) {
h.lock()
h.total++
h.unlock()
go func() {
defer func() {
h.lock()
h.total--
h.unlock()
}()
f()
}()
}
// blockUntil indicates that a goroutine is blocked waiting for some condition to become true.
// It waits until f returns true before proceeding.
//
// Example usage:
//
// h.blockUntil(func() bool {
// // Is the context done yet?
// select {
// case <-ctx.Done():
// default:
// return false
// }
// return true
// })
// // Wait for the context to become done.
// <-ctx.Done()
//
// The function f passed to blockUntil must be non-blocking and idempotent.
func (h *testSyncHooks) blockUntil(f func() bool) {
if f() {
return
}
ch := make(chan struct{})
h.lock()
h.blocked = append(h.blocked, &testBlockedGoroutine{
f: f,
ch: ch,
})
h.unlock()
<-ch
}
// broadcast is sync.Cond.Broadcast.
func (h *testSyncHooks) condBroadcast(cond *sync.Cond) {
h.lock()
delete(h.condwait, cond)
h.unlock()
cond.Broadcast()
}
// broadcast is sync.Cond.Wait.
func (h *testSyncHooks) condWait(cond *sync.Cond) {
h.lock()
h.condwait[cond]++
h.unlock()
}
// newTimer creates a new fake timer.
func (h *testSyncHooks) newTimer(d time.Duration) timer {
h.lock()
defer h.unlock()
t := &fakeTimer{
hooks: h,
when: h.now.Add(d),
c: make(chan time.Time),
}
h.timers = append(h.timers, t)
return t
}
// afterFunc creates a new fake AfterFunc timer.
func (h *testSyncHooks) afterFunc(d time.Duration, f func()) timer {
h.lock()
defer h.unlock()
t := &fakeTimer{
hooks: h,
when: h.now.Add(d),
f: f,
}
h.timers = append(h.timers, t)
return t
}
func (h *testSyncHooks) contextWithTimeout(ctx context.Context, d time.Duration) (context.Context, context.CancelFunc) {
ctx, cancel := context.WithCancel(ctx)
t := h.afterFunc(d, cancel)
return ctx, func() {
t.Stop()
cancel()
}
}
func (h *testSyncHooks) timeUntilEvent() time.Duration {
h.lock()
defer h.unlock()
var next time.Time
for _, t := range h.timers {
if next.IsZero() || t.when.Before(next) {
next = t.when
}
}
if d := next.Sub(h.now); d > 0 {
return d
}
return 0
}
// advance advances time and causes synthetic timers to fire.
func (h *testSyncHooks) advance(d time.Duration) {
h.lock()
defer h.unlock()
h.now = h.now.Add(d)
timers := h.timers[:0]
for _, t := range h.timers {
t := t // remove after go.mod depends on go1.22
t.mu.Lock()
switch {
case t.when.After(h.now):
timers = append(timers, t)
case t.when.IsZero():
// stopped timer
default:
t.when = time.Time{}
if t.c != nil {
close(t.c)
}
if t.f != nil {
h.total++
go func() {
defer func() {
h.lock()
h.total--
h.unlock()
}()
t.f()
}()
}
}
t.mu.Unlock()
}
h.timers = timers
}
// A timer wraps a time.Timer, or a synthetic equivalent in tests.
// Unlike time.Timer, timer is single-use: The timer channel is closed when the timer expires.
type timer interface {
C() <-chan time.Time
Stop() bool
Reset(d time.Duration) bool
}
// timeTimer implements timer using real time.
type timeTimer struct {
t *time.Timer
c chan time.Time
}
// newTimeTimer creates a new timer using real time.
func newTimeTimer(d time.Duration) timer {
ch := make(chan time.Time)
t := time.AfterFunc(d, func() {
close(ch)
})
return &timeTimer{t, ch}
}
// newTimeAfterFunc creates an AfterFunc timer using real time.
func newTimeAfterFunc(d time.Duration, f func()) timer {
return &timeTimer{
t: time.AfterFunc(d, f),
}
}
func (t timeTimer) C() <-chan time.Time { return t.c }
func (t timeTimer) Stop() bool { return t.t.Stop() }
func (t timeTimer) Reset(d time.Duration) bool { return t.t.Reset(d) }
// fakeTimer implements timer using fake time.
type fakeTimer struct {
hooks *testSyncHooks
mu sync.Mutex
when time.Time // when the timer will fire
c chan time.Time // closed when the timer fires; mutually exclusive with f
f func() // called when the timer fires; mutually exclusive with c
}
func (t *fakeTimer) C() <-chan time.Time { return t.c }
func (t *fakeTimer) Stop() bool {
t.mu.Lock()
defer t.mu.Unlock()
stopped := t.when.IsZero()
t.when = time.Time{}
return stopped
}
func (t *fakeTimer) Reset(d time.Duration) bool {
if t.c != nil || t.f == nil {
panic("fakeTimer only supports Reset on AfterFunc timers")
}
t.mu.Lock()
defer t.mu.Unlock()
t.hooks.lock()
defer t.hooks.unlock()
active := !t.when.IsZero()
t.when = t.hooks.now.Add(d)
if !active {
t.hooks.timers = append(t.hooks.timers, t)
}
return active
}