RFR(XXS): 8225004: Remove invalid assertion in jfr_conditional_flush()

[Markus Gronlund]

Greetings,

Please review this small change to remove an invalid assertion.

Bug: https://bugs.openjdk.java.net/browse/JDK-8225004

Change:

diff -r c1ad2862d0dd -r 0c17f2ea252e src/hotspot/share/jfr/support/jfrFlush.cpp
--- a/src/hotspot/share/jfr/support/jfrFlush.cpp        Wed May 29 09:53:28 2019 -0700
+++ b/src/hotspot/share/jfr/support/jfrFlush.cpp        Wed May 29 19:04:34 2019 +0200
@@ -62,7 +62,6 @@
 }

 void jfr_conditional_flush(JfrEventId id, size_t size, Thread* t) {
-  assert(jfr_is_event_enabled(id), "invariant");
   if (t->jfr_thread_local()->has_native_buffer()) {
     JfrStorage::Buffer* const buffer = t->jfr_thread_local()->native_buffer();
     if (LessThanSize<JfrStorage::Buffer>::evaluate(buffer, size)) {


Description:

JfrConditionalFlush(Thread* t) {
    if (jfr_is_event_enabled(Event::eventId)) { <<--------------- evaluates to true
      jfr_conditional_flush(Event::eventId, sizeof(Event), t);
    }
  }

void jfr_conditional_flush(JfrEventId id, size_t size, Thread* t) {
  assert(jfr_is_event_enabled(id), "invariant"); <<-------------------- could evaluate to false
  if (t->jfr_thread_local()->has_native_buffer()) {
    JfrStorage::Buffer* const buffer = t->jfr_thread_local()->native_buffer();
    if (LessThanSize<JfrStorage::Buffer>::evaluate(buffer, size)) {
      JfrFlush f(buffer, 0, 0, t);
    }
  }
}

Event settings are updated asynchronously, where event disablement happens after the recording has stopped.

A thread could have evaluated the initial check to true to enter jfr_conditional_flush(). Depending on visibility, context switching and preemption, another thread could have disabled the event before the thread runs jfr_conditional_flush().

There is no validity to be asserted at this location, so the assertion needs to be removed.

Thanks
Markus