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8222034: Thread-SMR functions should be updated to remove work around

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Reviewed-by: mdoerr, eosterlund
This commit is contained in:
Daniel D. Daugherty 2019-04-11 14:14:30 -04:00
parent 11c8caf157
commit a8e94de188
1 changed files with 7 additions and 20 deletions
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27
src/hotspot/share/runtime/threadSMR.cpp
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@ -1,5 +1,5 @@
/* /*
* Copyright (c) 2017, 2018, Oracle and/or its affiliates. All rights reserved. * Copyright (c) 2017, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
* *
* This code is free software; you can redistribute it and/or modify it * This code is free software; you can redistribute it and/or modify it
@ -590,12 +590,9 @@ ThreadsList *ThreadsList::add_thread(ThreadsList *list, JavaThread *java_thread)
} }
void ThreadsList::dec_nested_handle_cnt() { void ThreadsList::dec_nested_handle_cnt() {
// The decrement needs to be MO_ACQ_REL. At the moment, the Atomic::dec // The decrement only needs to be MO_ACQ_REL since the reference
// backend on PPC does not yet conform to these requirements. Therefore // counter is volatile (and the hazard ptr is already NULL).
// the decrement is simulated with an Atomic::sub(1, &addr). Atomic::dec(&_nested_handle_cnt);
// Without this MO_ACQ_REL Atomic::dec simulation, the nested SMR mechanism
// is not generally safe to use.
Atomic::sub(1, &_nested_handle_cnt);
} }
int ThreadsList::find_index_of_JavaThread(JavaThread *target) { int ThreadsList::find_index_of_JavaThread(JavaThread *target) {
@ -626,19 +623,9 @@ JavaThread* ThreadsList::find_JavaThread_from_java_tid(jlong java_tid) const {
} }
void ThreadsList::inc_nested_handle_cnt() { void ThreadsList::inc_nested_handle_cnt() {
// The increment needs to be MO_SEQ_CST. At the moment, the Atomic::inc // The increment needs to be MO_SEQ_CST so that the reference counter
// backend on PPC does not yet conform to these requirements. Therefore // update is seen before the subsequent hazard ptr update.
// the increment is simulated with a load phi; cas phi + 1; loop. Atomic::inc(&_nested_handle_cnt);
// Without this MO_SEQ_CST Atomic::inc simulation, the nested SMR mechanism
// is not generally safe to use.
intx sample = OrderAccess::load_acquire(&_nested_handle_cnt);
for (;;) {
if (Atomic::cmpxchg(sample + 1, &_nested_handle_cnt, sample) == sample) {
return;
} else {
sample = OrderAccess::load_acquire(&_nested_handle_cnt);
}
}
} }
bool ThreadsList::includes(const JavaThread * const p) const { bool ThreadsList::includes(const JavaThread * const p) const {