1 /* 2 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "utilities/globalCounter.hpp" 27 #include "runtime/orderAccess.inline.hpp" 28 #include "runtime/thread.hpp" 29 #include "runtime/threadSMR.inline.hpp" 30 #include "runtime/vmThread.hpp" 31 #include "utilities/spinYield.hpp" 32 33 GlobalCounter::PaddedCounter GlobalCounter::_global_counter; 34 35 class GlobalCounter::CounterThreadCheck : public ThreadClosure { 36 private: 37 uintx _gbl_cnt; 38 public: 39 CounterThreadCheck(uintx gbl_cnt) : _gbl_cnt(gbl_cnt) {} 40 void do_thread(Thread* thread) { 41 SpinYield yield; 42 // Loops on this thread until it has exited the critical read section. 43 while(true) { 44 uintx cnt = OrderAccess::load_acquire(thread->get_rcu_counter()); 45 // This checks if the thread's counter is active. And if so is the counter 46 // for a pre-existing reader (belongs to this grace period). A pre-existing 47 // reader will have a lower counter than the global counter version for this 48 // generation. If the counter is larger than the global counter version this 49 // is a new reader and we can continue. 50 if (((cnt & COUNTER_ACTIVE) != 0) && (cnt - _gbl_cnt) > (max_uintx / 2)) { 51 yield.wait(); 52 } else { 53 break; 54 } 55 } 56 } 57 }; 58 59 void GlobalCounter::write_synchronize() { 60 assert((*Thread::current()->get_rcu_counter() & COUNTER_ACTIVE) == 0x0, "must be outside a critcal section"); 61 // Atomic::add must provide fence since we have storeload dependency. 62 volatile uintx gbl_cnt = Atomic::add((uintx)COUNTER_INCREMENT, &_global_counter._counter, 63 memory_order_conservative); 64 // Do all RCU threads. 65 CounterThreadCheck ctc(gbl_cnt); 66 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) { 67 ctc.do_thread(thread); 68 } 69 ctc.do_thread(VMThread::vm_thread()); 70 }