client-go: add unit test for Request thread safety

staging/src/k8s.io/client-go/rest/request_test.go

@@ -31,6 +31,7 @@ import (
 	"reflect"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"syscall"
 	"testing"
 	"time"
@@ -3987,3 +3988,50 @@ func TestRetryableConditions(t *testing.T) {
 		}
 	}
 }
+
+func TestRequestConcurrencyWithRetry(t *testing.T) {
+	var attempts int32
+	client := clientForFunc(func(req *http.Request) (*http.Response, error) {
+		defer func() {
+			atomic.AddInt32(&attempts, 1)
+		}()
+
+		// always send a retry-after response
+		return &http.Response{
+			StatusCode: http.StatusInternalServerError,
+			Header:     http.Header{"Retry-After": []string{"1"}},
+		}, nil
+	})
+
+	req := &Request{
+		verb: "POST",
+		c: &RESTClient{
+			content: defaultContentConfig(),
+			Client:  client,
+		},
+		backoff:    &noSleepBackOff{},
+		maxRetries: 9, // 10 attempts in total, including the first
+		retryFn:    defaultRequestRetryFn,
+	}
+
+	concurrency := 20
+	wg := sync.WaitGroup{}
+	wg.Add(concurrency)
+	startCh := make(chan struct{})
+	for i := 0; i < concurrency; i++ {
+		go func() {
+			defer wg.Done()
+			<-startCh
+			req.Do(context.Background())
+		}()
+	}
+
+	close(startCh)
+	wg.Wait()
+
+	// we expect (concurrency*req.maxRetries+1) attempts to be recorded
+	expected := concurrency * (req.maxRetries + 1)
+	if atomic.LoadInt32(&attempts) != int32(expected) {
+		t.Errorf("Expected attempts: %d, but got: %d", expected, attempts)
+	}
+}