Move //pkg/gate.Gate to //pkg/sync.

- Use atomic add rather than CAS in every Gate method, which is slightly
  faster in most cases.

- Implement Close wakeup using gopark/goready to avoid channel allocation.

New benchmarks:
name                         old time/op  new time/op  delta
GateEnterLeave-12            16.7ns ± 1%  10.3ns ± 1%  -38.44%  (p=0.000 n=9+8)
GateClose-12                 50.2ns ± 8%  42.4ns ± 6%  -15.44%  (p=0.000 n=10+10)
GateEnterLeaveAsyncClose-12   972ns ± 2%   640ns ± 7%  -34.15%  (p=0.000 n=9+10)

PiperOrigin-RevId: 359336344

1 files changed, 0 insertions, 192 deletions

diff --git a/pkg/gate/gate_test.go b/pkg/gate/gate_test.go
deleted file mode 100644
index 316015e06..000000000
--- a/pkg/gate/gate_test.go
+++ /dev/null
@@ -1,192 +0,0 @@
-// Copyright 2018 The gVisor Authors.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package gate_test
-
-import (
-	"runtime"
-	"testing"
-	"time"
-
-	"gvisor.dev/gvisor/pkg/gate"
-	"gvisor.dev/gvisor/pkg/sync"
-)
-
-func TestBasicEnter(t *testing.T) {
-	var g gate.Gate
-
-	if !g.Enter() {
-		t.Fatalf("Failed to enter when it should be allowed")
-	}
-
-	g.Leave()
-
-	g.Close()
-
-	if g.Enter() {
-		t.Fatalf("Allowed to enter when it should fail")
-	}
-}
-
-func enterFunc(t *testing.T, g *gate.Gate, enter, leave, reenter chan struct{}, done1, done2, done3 *sync.WaitGroup) {
-	// Wait until instructed to enter.
-	<-enter
-	if !g.Enter() {
-		t.Errorf("Failed to enter when it should be allowed")
-	}
-
-	done1.Done()
-
-	// Wait until instructed to leave.
-	<-leave
-	g.Leave()
-
-	done2.Done()
-
-	// Wait until instructed to reenter.
-	<-reenter
-	if g.Enter() {
-		t.Errorf("Allowed to enter when it should fail")
-	}
-	done3.Done()
-}
-
-func TestConcurrentEnter(t *testing.T) {
-	var g gate.Gate
-	var done1, done2, done3 sync.WaitGroup
-
-	// Create 1000 worker goroutines.
-	enter := make(chan struct{})
-	leave := make(chan struct{})
-	reenter := make(chan struct{})
-	done1.Add(1000)
-	done2.Add(1000)
-	done3.Add(1000)
-	for i := 0; i < 1000; i++ {
-		go enterFunc(t, &g, enter, leave, reenter, &done1, &done2, &done3)
-	}
-
-	// Tell them all to enter, then leave.
-	close(enter)
-	done1.Wait()
-
-	close(leave)
-	done2.Wait()
-
-	// Close the gate, then have the workers try to enter again.
-	g.Close()
-	close(reenter)
-	done3.Wait()
-}
-
-func closeFunc(g *gate.Gate, done chan struct{}) {
-	g.Close()
-	close(done)
-}
-
-func TestCloseWaits(t *testing.T) {
-	var g gate.Gate
-
-	// Enter 10 times.
-	for i := 0; i < 10; i++ {
-		if !g.Enter() {
-			t.Fatalf("Failed to enter when it should be allowed")
-		}
-	}
-
-	// Launch closer. Check that it doesn't complete.
-	done := make(chan struct{})
-	go closeFunc(&g, done)
-
-	for i := 0; i < 10; i++ {
-		select {
-		case <-done:
-			t.Fatalf("Close function completed too soon")
-		case <-time.After(100 * time.Millisecond):
-		}
-
-		g.Leave()
-	}
-
-	// Now the closer must complete.
-	<-done
-}
-
-func TestMultipleSerialCloses(t *testing.T) {
-	var g gate.Gate
-
-	// Enter 10 times.
-	for i := 0; i < 10; i++ {
-		if !g.Enter() {
-			t.Fatalf("Failed to enter when it should be allowed")
-		}
-	}
-
-	// Launch closer. Check that it doesn't complete.
-	done := make(chan struct{})
-	go closeFunc(&g, done)
-
-	for i := 0; i < 10; i++ {
-		select {
-		case <-done:
-			t.Fatalf("Close function completed too soon")
-		case <-time.After(100 * time.Millisecond):
-		}
-
-		g.Leave()
-	}
-
-	// Now the closer must complete.
-	<-done
-
-	// Close again should not block.
-	done = make(chan struct{})
-	go closeFunc(&g, done)
-
-	select {
-	case <-done:
-	case <-time.After(2 * time.Second):
-		t.Fatalf("Second Close is blocking")
-	}
-}
-
-func worker(g *gate.Gate, done *sync.WaitGroup) {
-	for {
-		if !g.Enter() {
-			break
-		}
-		// Golang before v1.14 doesn't preempt busyloops.
-		runtime.Gosched()
-		g.Leave()
-	}
-	done.Done()
-}
-
-func TestConcurrentAll(t *testing.T) {
-	var g gate.Gate
-	var done sync.WaitGroup
-
-	// Launch 1000 goroutines to concurrently enter/leave.
-	done.Add(1000)
-	for i := 0; i < 1000; i++ {
-		go worker(&g, &done)
-	}
-
-	// Wait for the goroutines to do some work, then close the gate.
-	time.Sleep(2 * time.Second)
-	g.Close()
-
-	// Wait for all of them to complete.
-	done.Wait()
-}