1 /* 2 * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved. 3 * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 * 24 */ 25 #ifndef SHARE_GC_SHARED_OWSTTASKTERMINATOR_HPP 26 #define SHARE_GC_SHARED_OWSTTASKTERMINATOR_HPP 27 28 #include "memory/allocation.hpp" 29 #include "runtime/mutex.hpp" 30 #include "runtime/thread.hpp" 31 32 // Define this to enable additional tracing probes. 33 #undef TRACESPINNING 34 35 class TaskQueueSetSuper; 36 class TerminatorTerminator; 37 38 /* 39 * Provides a task termination protocol. OWST stands for Optimized Work Stealing Threads 40 * 41 * This is an enhanced implementation of Google's work stealing task termination 42 * protocol, which is described in the paper: 43 * "Wessam Hassanein. 2016. Understanding and improving JVM GC work 44 * stealing at the data center scale. In Proceedings of the 2016 ACM 45 * SIGPLAN International Symposium on Memory Management (ISMM 2016). ACM, 46 * New York, NY, USA, 46-54. DOI: https://doi.org/10.1145/2926697.2926706" 47 * 48 * Instead of a dedicated spin-master, our implementation will let spin-master relinquish 49 * the role before it goes to sleep/wait, allowing newly arrived threads to compete for the role. 50 * The intention of above enhancement is to reduce spin-master's latency on detecting new tasks 51 * for stealing and termination condition. 52 */ 53 class OWSTTaskTerminator : public CHeapObj<mtGC> { 54 uint _n_threads; 55 TaskQueueSetSuper* _queue_set; 56 57 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0); 58 volatile uint _offered_termination; 59 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile uint)); 60 61 #ifdef ASSERT 62 bool peek_in_queue_set(); 63 #endif 64 void yield(); 65 66 Monitor* _blocker; 67 Thread* _spin_master; 68 69 #ifdef TRACESPINNING 70 static uint _total_yields; 71 static uint _total_spins; 72 static uint _total_peeks; 73 #endif 74 75 // If we should exit current termination protocol 76 bool exit_termination(size_t tasks, TerminatorTerminator* terminator); 77 78 size_t tasks_in_queue_set() const; 79 80 // Perform spin-master task. 81 // Return true if termination condition is detected, otherwise return false 82 bool do_spin_master_work(TerminatorTerminator* terminator); 83 84 NONCOPYABLE(OWSTTaskTerminator); 85 86 public: 87 OWSTTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set); 88 ~OWSTTaskTerminator(); 89 90 // The current thread has no work, and is ready to terminate if everyone 91 // else is. If returns "true", all threads are terminated. If returns 92 // "false", available work has been observed in one of the task queues, 93 // so the global task is not complete. 94 bool offer_termination() { 95 return offer_termination(NULL); 96 } 97 98 // As above, but it also terminates if the should_exit_termination() 99 // method of the terminator parameter returns true. If terminator is 100 // NULL, then it is ignored. 101 bool offer_termination(TerminatorTerminator* terminator); 102 103 // Reset the terminator, so that it may be reused again. 104 // The caller is responsible for ensuring that this is done 105 // in an MT-safe manner, once the previous round of use of 106 // the terminator is finished. 107 void reset_for_reuse(); 108 // Same as above but the number of parallel threads is set to the 109 // given number. 110 void reset_for_reuse(uint n_threads); 111 112 #ifdef TRACESPINNING 113 static uint total_yields() { return _total_yields; } 114 static uint total_spins() { return _total_spins; } 115 static uint total_peeks() { return _total_peeks; } 116 static void print_termination_counts(); 117 #endif 118 }; 119 120 121 #endif // SHARE_GC_SHARED_OWSTTASKTERMINATOR_HPP