On Mon, 22 Dec 2025 22:00:40 GMT, David Holmes <[email protected]> wrote:
>> I've not look deep into this issue yet but it seems the approach below can
>> be used to avoid suspends in JNI critical sections:
>>
>> HandshakeOperation* HandshakeState::get_op_for_self(bool allow_suspend, bool
>> check_async_exception) {
>> assert(_handshakee == Thread::current(), "Must be called by self");
>> assert(_lock.owned_by_self(), "Lock must be held");
>> assert(allow_suspend || !check_async_exception, "invalid case");
>> #if INCLUDE_JVMTI
>> if (allow_suspend && _handshakee->is_disable_suspend()) {
>> <== !!!
>> // filter out suspend operations while JavaThread is in disable_suspend
>> mode
>> allow_suspend = false;
>> }
>> #endif
>> if (!allow_suspend) {
>> return _queue.peek(no_suspend_no_async_exception_filter);
>> } else if (check_async_exception && !_async_exceptions_blocked) {
>> return _queue.peek();
>> } else {
>> return _queue.peek(no_async_exception_filter);
>> }
>> }
>>
>>
>> The `_handshakee->in_critical_atomic()` can be checked directly in the
>> `HandshakeState::get_op_for_self()` or the
>> `_handshakee->is_disable_suspend()` can be set instead.
>>
>> Update: It looks like my suggestion above is not useful as the target thread
>> can be suspended when it is in native and then try to enter a JNI critical
>> section.
>
> @sspitsyn The use of `is_disable_suspend` is what was originally proposed but
> it does not work as it does not do what might be expected. Further none of
> these suggestions deep in the handshake code deal with the problem that the
> thread requesting the suspend has to block as long as any target is "in
> critical". I cannot see a relatively simple solution to this, but rather we
> would need a new (and complex) protocol for trying to deal with this. One
> possible approach may be to use a Dekker-style dual check and also permit
> JNI-critical to be blocked if a suspend request is pending.
@dholmes-ora Probably, you missed this update at the end of my comment:
> Update: It looks like my suggestion above is not useful as the target thread
> can be suspended when it is in native and then try to enter a JNI critical
> section.
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PR Comment: https://git.openjdk.org/jdk/pull/28884#issuecomment-3684354390
