bneradt commented on a change in pull request #8443:
URL: https://github.com/apache/trafficserver/pull/8443#discussion_r738533219
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File path: include/tscore/PendingAction.h
##########
@@ -89,22 +91,32 @@ PendingAction::empty() const
inline PendingAction &
PendingAction::operator=(Action *action)
{
- // Apparently HttpSM depends on not canceling the previous action if anew
+ // Apparently @c HttpSM depends on not canceling the previous action if a new
// one completes immediately. Canceling the contained action in that case
- // cause the HttpSm to permanently stall.
+ // cause the @c HttpSM to permanently stall.
if (ACTION_RESULT_DONE != action) {
- if (action != pending_action && pending_action != nullptr) {
- pending_action->cancel();
+ Action *expected; // Need for exchange, and to load @a pending_action only
once.
+ // Avoid race conditions - for each assigned action, ensure exactly one
thread
+ // cancels it. Assigning @a expected in the @c while expression avoids
potential
+ // races if two calls to this method have the same @a action.
+ while ((expected = pending_action) != action) {
Review comment:
Ah, right.
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