chore: add comments

Author: jayantxie

connstate/conn_test.go

@@ -95,9 +95,17 @@ func (r *mockRawConn) Control(f func(fd uintptr)) error {
 func TestListenConnState_Err(t *testing.T) {
 	testMutex.Lock()
 	defer testMutex.Unlock()
-	var expectDetach bool
-	pollInitOnce.Do(func() {})
+	// replace poll
+	pollInitOnce.Do(createPoller)
 	oldPoll := poll
+	defer func() {
+		poll = oldPoll
+	}()
+	// test detach
+	var expectDetach bool
+	defer func() {
+		assert.True(t, expectDetach)
+	}()
 	cases := []struct {
 		name            string
 		connControlFunc func(f func(fd uintptr)) error
@@ -151,12 +159,6 @@ func TestListenConnState_Err(t *testing.T) {
 			assert.Equal(t, c.expectErr, err)
 		})
 	}
-	assert.True(t, expectDetach)
-	if oldPoll != nil {
-		poll = oldPoll
-	} else {
-		createPoller()
-	}
 }
 
 func BenchmarkListenConnState(b *testing.B) {

connstate/poll_linux.go

@@ -32,6 +32,8 @@ type epoller struct {
 func (p *epoller) wait() error {
 	events := make([]syscall.EpollEvent, 1024)
 	for {
+		// epoll wait is a blocking syscall, so we need to call entersyscallblock to handoff P,
+		// and let the P run other goroutines.
 		n, err := isyscall.EpollWait(p.epfd, events, -1)
 		if err != nil && err != syscall.EINTR {
 			return err