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_TASKTERMINATOR_HPP 26 #define SHARE_GC_SHARED_TASKTERMINATOR_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. 40 * 41 * This is an enhanced implementation of Google's OWST work stealing task termination 42 * protocol (OWST stands for Optimized Work Stealing Threads). 43 * 44 * It is described in the paper: 45 * "Wessam Hassanein. 2016. Understanding and improving JVM GC work 46 * stealing at the data center scale. In Proceedings of the 2016 ACM 47 * SIGPLAN International Symposium on Memory Management (ISMM 2016). ACM, 48 * New York, NY, USA, 46-54. DOI: https://doi.org/10.1145/2926697.2926706" 49 * 50 * Instead of a dedicated spin-master, our implementation will let spin-master relinquish 51 * the role before it goes to sleep/wait, allowing newly arrived threads to compete for the role. 52 * The intention of above enhancement is to reduce spin-master's latency on detecting new tasks 53 * for stealing and termination condition. 54 */ 55 class TaskTerminator : public CHeapObj<mtGC> { 56 uint _n_threads; 57 TaskQueueSetSuper* _queue_set; 58 59 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0); 60 volatile uint _offered_termination; 61 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile uint)); 62 63 #ifdef ASSERT 64 bool peek_in_queue_set(); 65 #endif 66 void yield(); 67 68 Monitor* _blocker; 69 Thread* _spin_master; 70 71 #ifdef TRACESPINNING 72 static uint _total_yields; 73 static uint _total_spins; 74 static uint _total_peeks; 75 #endif 76 77 // If we should exit current termination protocol 78 bool exit_termination(size_t tasks, TerminatorTerminator* terminator); 79 80 size_t tasks_in_queue_set() const; 81 82 // Perform spin-master task. 83 // Return true if termination condition is detected, otherwise return false 84 bool do_spin_master_work(TerminatorTerminator* terminator); 85 86 NONCOPYABLE(TaskTerminator); 87 88 public: 89 TaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set); 90 ~TaskTerminator(); 91 92 // The current thread has no work, and is ready to terminate if everyone 93 // else is. If returns "true", all threads are terminated. If returns 94 // "false", available work has been observed in one of the task queues, 95 // so the global task is not complete. 96 bool offer_termination() { 97 return offer_termination(NULL); 98 } 99 100 // As above, but it also terminates if the should_exit_termination() 101 // method of the terminator parameter returns true. If terminator is 102 // NULL, then it is ignored. 103 bool offer_termination(TerminatorTerminator* terminator); 104 105 // Reset the terminator, so that it may be reused again. 106 // The caller is responsible for ensuring that this is done 107 // in an MT-safe manner, once the previous round of use of 108 // the terminator is finished. 109 void reset_for_reuse(); 110 // Same as above but the number of parallel threads is set to the 111 // given number. 112 void reset_for_reuse(uint n_threads); 113 114 #ifdef TRACESPINNING 115 static uint total_yields() { return _total_yields; } 116 static uint total_spins() { return _total_spins; } 117 static uint total_peeks() { return _total_peeks; } 118 static void print_termination_counts(); 119 #endif 120 }; 121 122 #endif // SHARE_GC_SHARED_TASKTERMINATOR_HPP