syncs: add Map (#6260)

Map is a concurrent safe map that is a trivial wrapper
over a Go map and a sync.RWMutex.

It is optimized for use-cases where the entries change often,
which is the opposite use-case of what sync.Map is optimized for.

The API is patterned off of sync.Map, but made generic.

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

syncs/syncs_test.go

@@ -6,7 +6,10 @@ package syncs
 
 import (
 	"context"
+	"sync"
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 func TestWaitGroupChan(t *testing.T) {
@@ -73,3 +76,66 @@ func TestSemaphore(t *testing.T) {
 	s.Release()
 	s.Release()
 }
+
+func TestMap(t *testing.T) {
+	var m Map[string, int]
+	if v, ok := m.Load("noexist"); v != 0 || ok {
+		t.Errorf(`Load("noexist") = (%v, %v), want (0, false)`, v, ok)
+	}
+	m.Store("one", 1)
+	if v, ok := m.LoadOrStore("one", -1); v != 1 || !ok {
+		t.Errorf(`LoadOrStore("one", 1) = (%v, %v), want (1, true)`, v, ok)
+	}
+	if v, ok := m.Load("one"); v != 1 || !ok {
+		t.Errorf(`Load("one") = (%v, %v), want (1, true)`, v, ok)
+	}
+	if v, ok := m.LoadOrStore("two", 2); v != 2 || ok {
+		t.Errorf(`LoadOrStore("two", 2) = (%v, %v), want (2, false)`, v, ok)
+	}
+	got := map[string]int{}
+	want := map[string]int{"one": 1, "two": 2}
+	m.Range(func(k string, v int) bool {
+		got[k] = v
+		return true
+	})
+	if d := cmp.Diff(got, want); d != "" {
+		t.Errorf("Range mismatch (-got +want):\n%s", d)
+	}
+	if v, ok := m.LoadAndDelete("two"); v != 2 || !ok {
+		t.Errorf(`LoadAndDelete("two) = (%v, %v), want (2, true)`, v, ok)
+	}
+	if v, ok := m.LoadAndDelete("two"); v != 0 || ok {
+		t.Errorf(`LoadAndDelete("two) = (%v, %v), want (0, false)`, v, ok)
+	}
+	m.Delete("one")
+	m.Delete("noexist")
+	got = map[string]int{}
+	want = map[string]int{}
+	m.Range(func(k string, v int) bool {
+		got[k] = v
+		return true
+	})
+	if d := cmp.Diff(got, want); d != "" {
+		t.Errorf("Range mismatch (-got +want):\n%s", d)
+	}
+
+	t.Run("LoadOrStore", func(t *testing.T) {
+		var m Map[string, string]
+		var wg sync.WaitGroup
+		wg.Add(2)
+		var ok1, ok2 bool
+		go func() {
+			defer wg.Done()
+			_, ok1 = m.LoadOrStore("", "")
+		}()
+		go func() {
+			defer wg.Done()
+			_, ok2 = m.LoadOrStore("", "")
+		}()
+		wg.Wait()
+
+		if ok1 == ok2 {
+			t.Errorf("exactly one LoadOrStore should load")
+		}
+	})
+}