RFR: 8257831: Suspend with handshakes [v10]

[Richard Reingruber]

On Mon, 19 Apr 2021 05:48:44 GMT, David Holmes <dholmes at openjdk.org> wrote:

> It is still not at all clear to me what suspended has to do with the execution
> of this method. The new code just ignores thread suspension.

The caller enters a safe state. It can be suspended iff safe, so the old code
checked for suspension. With the new code suspension is part of handshake
processing, so it is sufficient to check for pending handshakes.

> It seems to me that the old code could also have ignored suspension if the
> checks in handle_special_runtime_exit_condition had be reordered.

In that case JavaThread::java_suspend_self_with_safepoint_check() would have to
be changed to check for `Thread::is_obj_deopt_suspend()` and handle it.

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PR: https://git.openjdk.java.net/jdk/pull/3191