On Tue, 5 Mar 2024 08:53:42 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
>> src/hotspot/share/prims/jvmtiEnvBase.cpp line 1507:
>>
>>> 1505: nWait = 0;
>>> 1506: for (ObjectWaiter* waiter = mon->first_waiter();
>>> 1507: waiter != nullptr && (nWait == 0 || waiter !=
>>> mon->first_waiter());
>>
>> Sorry I do not understand the logic of this line. `waiters` is just a
>> linked-list of `ObjectWaiter`s so all we need to do is traverse it and count
>> the number of elements.
>
> The loop is endless without this extra condition, so we are getting a test
> execution timeout.
> The `waiters` seems to be `circular doubly linked list` as we can see below:
>
> inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
> assert(node != nullptr, "should not add null node");
> assert(node->_prev == nullptr, "node already in list");
> assert(node->_next == nullptr, "node already in list");
> // put node at end of queue (circular doubly linked list)
> if (_WaitSet == nullptr) {
> _WaitSet = node;
> node->_prev = node;
> node->_next = node;
> } else {
> ObjectWaiter* head = _WaitSet;
> ObjectWaiter* tail = head->_prev;
> assert(tail->_next == head, "invariant check");
> tail->_next = node;
> head->_prev = node;
> node->_next = head;
> node->_prev = tail;
> }
> }
>
> I'll make sure nothing is missed and check the old code again.
Okay. Now I see why the old code did not have endless loops.
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PR Review Comment: https://git.openjdk.org/jdk/pull/17680#discussion_r1512409266
