From 8c0112889f2792e8bc24bfcf1b1830f3c3657d35 Mon Sep 17 00:00:00 2001
From: dkhorkin <dmitryhorkin@gmail.com>
Date: Tue, 13 Apr 2021 14:06:23 +0300
Subject: [PATCH] [rwmutex] Added new tests

---
 rwmutex/rwmutex_test.go | 163 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)

diff --git a/rwmutex/rwmutex_test.go b/rwmutex/rwmutex_test.go
index 6917345..df9761a 100644
--- a/rwmutex/rwmutex_test.go
+++ b/rwmutex/rwmutex_test.go
@@ -2,9 +2,12 @@ package rwmutex
 
 import (
 	"fmt"
+	"math/rand"
 	"runtime"
+	"sync"
 	"sync/atomic"
 	"testing"
+	"time"
 )
 
 func parallelReader(m *RWMutex, clocked, cunlock, cdone chan bool) {
@@ -114,3 +117,163 @@ func TestRWMutex(t *testing.T) {
 	HammerRWMutex(10, 10, n)
 	HammerRWMutex(10, 5, n)
 }
+
+type CriticalSection struct {
+	mu                         sync.Mutex
+	readersCount, writersCount int
+}
+
+func (cs *CriticalSection) AddToVariable(value *int, count int) {
+	cs.mu.Lock()
+	*value += count
+	cs.mu.Unlock()
+}
+
+func (cs *CriticalSection) Reader(t *testing.T, duration time.Duration) {
+	cs.AddToVariable(&cs.readersCount, 1)
+	cs.Check(t)
+	time.Sleep(duration) // do some work
+	cs.AddToVariable(&cs.readersCount, -1)
+}
+
+func (cs *CriticalSection) Writer(t *testing.T, duration time.Duration) {
+	cs.AddToVariable(&cs.writersCount, 1)
+	cs.Check(t)
+	time.Sleep(duration) // do some work
+	cs.AddToVariable(&cs.writersCount, -1)
+}
+
+func (cs *CriticalSection) Check(t *testing.T) {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
+	if cs.writersCount > 1 {
+		t.Errorf("To much writers: %d", cs.writersCount)
+	}
+	if cs.writersCount == 1 && cs.readersCount > 0 {
+		t.Errorf("We have %d readers and %d writers", cs.readersCount, cs.writersCount)
+	}
+}
+
+func TestAFewReaders(t *testing.T) {
+	var wg sync.WaitGroup
+	readersCount := 100
+	rwm := New()
+	cs := new(CriticalSection)
+	ch := make(chan struct{})
+	wg.Add(readersCount)
+	for i := 0; i < readersCount; i++ {
+		go func() {
+			rwm.RLock()
+			cs.Reader(t, 20*time.Millisecond)
+			rwm.RUnlock()
+			defer wg.Done()
+		}()
+	}
+	go func() {
+		wg.Wait()
+		ch <- struct{}{}
+	}()
+	select {
+	case <-ch: //ok
+	case <-time.After(25 * time.Millisecond):
+		t.Error("too slow, your readers are blocked")
+	}
+}
+
+func TestAFewWriters(t *testing.T) {
+	var wg sync.WaitGroup
+	writersCount := 10
+	rwm := New()
+	cs := new(CriticalSection)
+	wg.Add(writersCount)
+	for i := 0; i < writersCount; i++ {
+		go func() {
+			rwm.Lock()
+			cs.Writer(t, 10*time.Millisecond)
+			rwm.Unlock()
+			defer wg.Done()
+		}()
+	}
+	wg.Wait()
+}
+
+func TestWriterAfterReaders(t *testing.T) {
+	var wg sync.WaitGroup
+	rwm := New()
+	cs := new(CriticalSection)
+	readersCount := 10
+	wg.Add(readersCount + 1)
+	for i := 0; i < readersCount; i++ {
+		go func() {
+			rwm.RLock()
+			cs.Reader(t, 100*time.Millisecond)
+			rwm.RUnlock()
+			defer wg.Done()
+		}()
+	}
+
+	time.Sleep(10 * time.Millisecond)
+
+	go func() {
+		rwm.Lock()
+		cs.Writer(t, 10*time.Millisecond)
+		rwm.Unlock()
+		defer wg.Done()
+	}()
+	wg.Wait()
+}
+
+func TestReadersAfterWriters(t *testing.T) {
+	var wg sync.WaitGroup
+	rwm := New()
+	cs := new(CriticalSection)
+	RWCount := 10
+	wg.Add(2 * RWCount)
+	for i := 0; i < RWCount; i++ {
+		go func() {
+			rwm.Lock()
+			cs.Writer(t, 100*time.Millisecond)
+			rwm.Unlock()
+			defer wg.Done()
+		}()
+	}
+
+	time.Sleep(20 * time.Millisecond)
+
+	for i := 0; i < RWCount; i++ {
+		go func() {
+			rwm.RLock()
+			cs.Reader(t, 10*time.Millisecond)
+			rwm.RUnlock()
+			defer wg.Done()
+		}()
+	}
+	wg.Wait()
+}
+
+func TestRWStress(t *testing.T) {
+	var wg sync.WaitGroup
+	rwm := New()
+	cs := new(CriticalSection)
+	RWCount := 20
+	for j := 0; j < 100; j++ {
+		wg.Add(2 * RWCount)
+		for i := 0; i < RWCount; i++ {
+			go func() {
+				time.Sleep(time.Duration(rand.Intn(5)) * time.Millisecond) // some delay
+				rwm.Lock()
+				cs.Writer(t, time.Millisecond)
+				rwm.Unlock()
+				defer wg.Done()
+			}()
+			go func() {
+				time.Sleep(time.Duration(rand.Intn(5)) * time.Millisecond) // some delay
+				rwm.RLock()
+				cs.Reader(t, time.Millisecond)
+				rwm.RUnlock()
+				defer wg.Done()
+			}()
+		}
+		wg.Wait()
+	}
+}