1 /* 2 * Copyright (c) 2018, 2020, 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 "memory/padded.hpp" 30 #include "runtime/mutex.hpp" 31 32 class TaskQueueSetSuper; 33 class TerminatorTerminator; 34 class Thread; 35 36 /* 37 * Provides a task termination protocol. 38 * 39 * This is an enhanced implementation of Google's OWST work stealing task termination 40 * protocol (OWST stands for Optimized Work Stealing Threads). 41 * 42 * It 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 TaskTerminator : public CHeapObj<mtGC> { 54 struct DelayContext { 55 uint _yield_count; 56 // Number of hard spin loops done since last yield 57 uint _hard_spin_count; 58 // Number of iterations in the hard spin loop. 59 uint _hard_spin_limit; 60 61 DelayContext(); 62 }; 63 64 uint _n_threads; 65 TaskQueueSetSuper* _queue_set; 66 67 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, 0); 68 volatile uint _offered_termination; 69 DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile uint)); 70 71 void assert_queue_set_empty() const NOT_DEBUG_RETURN; 72 73 Monitor _blocker; 74 Thread* _spin_master; 75 76 // Prepare for return from offer_termination. Gives up the spin master token 77 // and wakes up up to tasks threads waiting on _blocker (the default value 78 // means to wake up everyone). 79 void prepare_for_return(Thread* this_thread, size_t tasks = SIZE_MAX); 80 81 // If we should exit current termination protocol 82 bool exit_termination(size_t tasks, TerminatorTerminator* terminator); 83 84 size_t tasks_in_queue_set() const; 85 86 // Perform one iteration of spin-master work. 87 bool do_delay_step(DelayContext& delay_context); 88 89 NONCOPYABLE(TaskTerminator); 90 91 public: 92 TaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set); 93 ~TaskTerminator(); 94 95 // The current thread has no work, and is ready to terminate if everyone 96 // else is. If returns "true", all threads are terminated. If returns 97 // "false", available work has been observed in one of the task queues, 98 // so the global task is not complete. 99 bool offer_termination() { 100 return offer_termination(NULL); 101 } 102 103 // As above, but it also terminates if the should_exit_termination() 104 // method of the terminator parameter returns true. If terminator is 105 // NULL, then it is ignored. 106 bool offer_termination(TerminatorTerminator* terminator); 107 108 // Reset the terminator, so that it may be reused again. 109 // The caller is responsible for ensuring that this is done 110 // in an MT-safe manner, once the previous round of use of 111 // the terminator is finished. 112 void reset_for_reuse(); 113 // Same as above but the number of parallel threads is set to the 114 // given number. 115 void reset_for_reuse(uint n_threads); 116 }; 117 118 #endif // SHARE_GC_SHARED_TASKTERMINATOR_HPP