1 /* 2 * Copyright (c) 2001, 2015, 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 #ifndef SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP 26 #define SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP 27 28 #include "gc/cms/concurrentMarkSweepGeneration.hpp" 29 #include "gc/shared/concurrentGCThread.hpp" 30 #include "runtime/thread.hpp" 31 32 class ConcurrentMarkSweepGeneration; 33 class CMSCollector; 34 35 // The Concurrent Mark Sweep GC Thread 36 class ConcurrentMarkSweepThread: public ConcurrentGCThread { 37 friend class VMStructs; 38 friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship 39 friend class CMSCollector; 40 public: 41 virtual void run(); 42 43 private: 44 static ConcurrentMarkSweepThread* _cmst; 45 static CMSCollector* _collector; 46 static SurrogateLockerThread* _slt; 47 static SurrogateLockerThread::SLT_msg_type _sltBuffer; 48 static Monitor* _sltMonitor; 49 50 static bool _should_terminate; 51 52 enum CMS_flag_type { 53 CMS_nil = NoBits, 54 CMS_cms_wants_token = nth_bit(0), 55 CMS_cms_has_token = nth_bit(1), 56 CMS_vm_wants_token = nth_bit(2), 57 CMS_vm_has_token = nth_bit(3) 58 }; 59 60 static int _CMS_flag; 61 62 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; } 63 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; } 64 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; } 65 void sleepBeforeNextCycle(); 66 67 // CMS thread should yield for a young gen collection and direct allocations 68 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing 69 static volatile jint _pending_yields; 70 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing 71 72 // debugging 73 void verify_ok_to_terminate() const PRODUCT_RETURN; 74 75 public: 76 // Constructor 77 ConcurrentMarkSweepThread(CMSCollector* collector); 78 79 static void makeSurrogateLockerThread(TRAPS); 80 static SurrogateLockerThread* slt() { return _slt; } 81 82 static void threads_do(ThreadClosure* tc); 83 84 // Printing 85 static void print_all_on(outputStream* st); 86 static void print_all() { print_all_on(tty); } 87 88 // Returns the CMS Thread 89 static ConcurrentMarkSweepThread* cmst() { return _cmst; } 90 static CMSCollector* collector() { return _collector; } 91 92 // Create and start the CMS Thread, or stop it on shutdown 93 static ConcurrentMarkSweepThread* start(CMSCollector* collector); 94 static void stop(); 95 static bool should_terminate() { return _should_terminate; } 96 97 // Synchronization using CMS token 98 static void synchronize(bool is_cms_thread); 99 static void desynchronize(bool is_cms_thread); 100 static bool vm_thread_has_cms_token() { 101 return CMS_flag_is_set(CMS_vm_has_token); 102 } 103 static bool cms_thread_has_cms_token() { 104 return CMS_flag_is_set(CMS_cms_has_token); 105 } 106 static bool vm_thread_wants_cms_token() { 107 return CMS_flag_is_set(CMS_vm_wants_token); 108 } 109 static bool cms_thread_wants_cms_token() { 110 return CMS_flag_is_set(CMS_cms_wants_token); 111 } 112 113 // Wait on CMS lock until the next synchronous GC 114 // or given timeout, whichever is earlier. A timeout value 115 // of 0 indicates that there is no upper bound on the wait time. 116 // A concurrent full gc request terminates the wait. 117 void wait_on_cms_lock(long t_millis); 118 119 // Wait on CMS lock until the next synchronous GC 120 // or given timeout, whichever is earlier. A timeout value 121 // of 0 indicates that there is no upper bound on the wait time. 122 // A concurrent full gc request terminates the wait. 123 void wait_on_cms_lock_for_scavenge(long t_millis); 124 125 // The CMS thread will yield during the work portion of its cycle 126 // only when requested to. 127 // A synchronous request is used for young gen collections and 128 // for direct allocations. The requesting thread increments 129 // _pending_yields at the beginning of an operation, and decrements 130 // _pending_yields when that operation is completed. 131 // In turn, the CMS thread yields when _pending_yields is positive, 132 // and continues to yield until the value reverts to 0. 133 134 static void increment_pending_yields() { 135 Atomic::inc(&_pending_yields); 136 assert(_pending_yields >= 0, "can't be negative"); 137 } 138 static void decrement_pending_yields() { 139 Atomic::dec(&_pending_yields); 140 assert(_pending_yields >= 0, "can't be negative"); 141 } 142 static bool should_yield() { return _pending_yields > 0; } 143 }; 144 145 // For scoped increment/decrement of (synchronous) yield requests 146 class CMSSynchronousYieldRequest: public StackObj { 147 public: 148 CMSSynchronousYieldRequest() { 149 ConcurrentMarkSweepThread::increment_pending_yields(); 150 } 151 ~CMSSynchronousYieldRequest() { 152 ConcurrentMarkSweepThread::decrement_pending_yields(); 153 } 154 }; 155 156 // Used to emit a warning in case of unexpectedly excessive 157 // looping (in "apparently endless loops") in CMS code. 158 class CMSLoopCountWarn: public StackObj { 159 private: 160 const char* _src; 161 const char* _msg; 162 const intx _threshold; 163 intx _ticks; 164 165 public: 166 inline CMSLoopCountWarn(const char* src, const char* msg, 167 const intx threshold) : 168 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { } 169 170 inline void tick() { 171 _ticks++; 172 if (CMSLoopWarn && _ticks % _threshold == 0) { 173 warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg); 174 } 175 } 176 }; 177 178 #endif // SHARE_VM_GC_CMS_CONCURRENTMARKSWEEPTHREAD_HPP