1 /* 2 * Copyright (c) 1998, 2019, 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_RUNTIME_MUTEX_HPP 26 #define SHARE_RUNTIME_MUTEX_HPP 27 28 #include "memory/allocation.hpp" 29 #include "runtime/os.hpp" 30 31 // A Mutex/Monitor is a simple wrapper around a native lock plus condition 32 // variable that supports lock ownership tracking, lock ranking for deadlock 33 // detection and coordinates with the safepoint protocol. 34 35 // The default length of monitor name was originally chosen to be 64 to avoid 36 // false sharing. Now, PaddedMonitor is available for this purpose. 37 // TODO: Check if _name[MONITOR_NAME_LEN] should better get replaced by const char*. 38 static const int MONITOR_NAME_LEN = 64; 39 40 class Monitor : public CHeapObj<mtSynchronizer> { 41 42 public: 43 // A special lock: Is a lock where you are guaranteed not to block while you are 44 // holding it, i.e., no vm operation can happen, taking other (blocking) locks, etc. 45 // The rank 'access' is similar to 'special' and has the same restrictions on usage. 46 // It is reserved for locks that may be required in order to perform memory accesses 47 // that require special barriers, e.g. SATB GC barriers, that in turn uses locks. 48 // The rank 'tty' is also similar to 'special' and has the same restrictions. 49 // It is reserved for the tty_lock. 50 // Since memory accesses should be able to be performed pretty much anywhere 51 // in the code, that requires locks required for performing accesses being 52 // inherently a bit more special than even locks of the 'special' rank. 53 // NOTE: It is critical that the rank 'special' be the lowest (earliest) 54 // (except for "event" and "access") for the deadlock detection to work correctly. 55 // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate, 56 // which being external to the VM are not subject to deadlock detection. 57 // While at a safepoint no mutexes of rank safepoint are held by any thread. 58 // The rank named "leaf" is probably historical (and should 59 // be changed) -- mutexes of this rank aren't really leaf mutexes 60 // at all. 61 enum lock_types { 62 event, 63 access = event + 1, 64 tty = access + 2, 65 special = tty + 2, 66 suspend_resume = special + 1, 67 vmweak = suspend_resume + 2, 68 leaf = vmweak + 2, 69 safepoint = leaf + 10, 70 barrier = safepoint + 1, 71 nonleaf = barrier + 1, 72 max_nonleaf = nonleaf + 900, 73 native = max_nonleaf + 1 74 }; 75 76 protected: // Monitor-Mutex metadata 77 Thread * volatile _owner; // The owner of the lock 78 os::PlatformMonitor _lock; // Native monitor implementation 79 char _name[MONITOR_NAME_LEN]; // Name of mutex/monitor 80 81 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode) 82 #ifndef PRODUCT 83 bool _allow_vm_block; 84 DEBUG_ONLY(int _rank;) // rank (to avoid/detect potential deadlocks) 85 DEBUG_ONLY(Monitor * _next;) // Used by a Thread to link up owned locks 86 DEBUG_ONLY(Thread* _last_owner;) // the last thread to own the lock 87 DEBUG_ONLY(static bool contains(Monitor * locks, Monitor * lock);) 88 DEBUG_ONLY(static Monitor * get_least_ranked_lock(Monitor * locks);) 89 DEBUG_ONLY(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);) 90 #endif 91 92 void set_owner_implementation(Thread* owner) PRODUCT_RETURN; 93 void check_prelock_state (Thread* thread, bool safepoint_check) PRODUCT_RETURN; 94 void check_block_state (Thread* thread) PRODUCT_RETURN; 95 void assert_owner (Thread* expected) NOT_DEBUG_RETURN; 96 97 public: 98 enum { 99 _no_safepoint_check_flag = true, 100 _allow_vm_block_flag = true, 101 _as_suspend_equivalent_flag = true 102 }; 103 104 // Locks can be acquired with or without safepoint check. 105 // Monitor::lock and Monitor::lock_without_safepoint_check 106 // checks these flags when acquiring a lock to ensure 107 // consistent checking for each lock. 108 // A few existing locks will sometimes have a safepoint check and 109 // sometimes not, but these locks are set up in such a way to avoid deadlocks. 110 // Note: monitors that may be shared between JavaThreads and the VMThread 111 // should never encounter a safepoint check whilst they are held, else a 112 // deadlock with the VMThread can occur. 113 enum SafepointCheckRequired { 114 _safepoint_check_never, // Monitors with this value will cause errors 115 // when acquired with a safepoint check. 116 _safepoint_check_sometimes, // Certain locks are called sometimes with and 117 // sometimes without safepoint checks. These 118 // locks will not produce errors when locked. 119 _safepoint_check_always // Causes error if locked without a safepoint 120 // check. 121 }; 122 123 NOT_PRODUCT(SafepointCheckRequired _safepoint_check_required;) 124 125 protected: 126 static void ClearMonitor (Monitor * m, const char* name = NULL) ; 127 Monitor() ; 128 129 public: 130 Monitor(int rank, const char *name, bool allow_vm_block = false, 131 SafepointCheckRequired safepoint_check_required = _safepoint_check_always); 132 ~Monitor(); 133 134 // Wait until monitor is notified (or times out). 135 // Defaults are to make safepoint checks, wait time is forever (i.e., 136 // zero), and not a suspend-equivalent condition. Returns true if wait 137 // times out; otherwise returns false. 138 bool wait(bool no_safepoint_check = !_no_safepoint_check_flag, 139 long timeout = 0, 140 bool as_suspend_equivalent = !_as_suspend_equivalent_flag); 141 void notify(); 142 void notify_all(); 143 144 145 void lock(); // prints out warning if VM thread blocks 146 void lock(Thread *thread); // overloaded with current thread 147 void unlock(); 148 bool is_locked() const { return _owner != NULL; } 149 150 bool try_lock(); // Like lock(), but unblocking. It returns false instead 151 152 void release_for_safepoint(); 153 154 // Lock without safepoint check. Should ONLY be used by safepoint code and other code 155 // that is guaranteed not to block while running inside the VM. 156 void lock_without_safepoint_check(); 157 void lock_without_safepoint_check (Thread * Self) ; 158 159 // Current owner - not not MT-safe. Can only be used to guarantee that 160 // the current running thread owns the lock 161 Thread* owner() const { return _owner; } 162 bool owned_by_self() const; 163 164 // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by 165 // non-Java thread. (We should really have a RawMonitor abstraction) 166 void jvm_raw_lock(); 167 void jvm_raw_unlock(); 168 const char *name() const { return _name; } 169 170 void print_on_error(outputStream* st) const; 171 172 #ifndef PRODUCT 173 void print_on(outputStream* st) const; 174 void print() const { print_on(::tty); } 175 DEBUG_ONLY(int rank() const { return _rank; }) 176 bool allow_vm_block() { return _allow_vm_block; } 177 178 DEBUG_ONLY(Monitor *next() const { return _next; }) 179 DEBUG_ONLY(void set_next(Monitor *next) { _next = next; }) 180 #endif 181 182 void set_owner(Thread* owner) { 183 #ifndef PRODUCT 184 set_owner_implementation(owner); 185 DEBUG_ONLY(void verify_Monitor(Thread* thr);) 186 #else 187 _owner = owner; 188 #endif 189 } 190 191 }; 192 193 class PaddedMonitor : public Monitor { 194 enum { 195 CACHE_LINE_PADDING = (int)DEFAULT_CACHE_LINE_SIZE - (int)sizeof(Monitor), 196 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1 197 }; 198 char _padding[PADDING_LEN]; 199 public: 200 PaddedMonitor(int rank, const char *name, bool allow_vm_block = false, 201 SafepointCheckRequired safepoint_check_required = _safepoint_check_always) : 202 Monitor(rank, name, allow_vm_block, safepoint_check_required) {}; 203 }; 204 205 // Normally we'd expect Monitor to extend Mutex in the sense that a monitor 206 // constructed from pthreads primitives might extend a mutex by adding 207 // a condvar and some extra metadata. In fact this was the case until J2SE7. 208 // 209 // Currently, however, the base object is a monitor. Monitor contains all the 210 // logic for wait(), notify(), etc. Mutex extends monitor and restricts the 211 // visibility of wait(), notify(), and notify_all(). 212 // 213 // Another viable alternative would have been to have Monitor extend Mutex and 214 // implement all the normal mutex and wait()-notify() logic in Mutex base class. 215 // The wait()-notify() facility would be exposed via special protected member functions 216 // (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait() 217 // as a call to _Wait(). That is, the public wait() would be a wrapper for the protected 218 // _Wait(). 219 // 220 // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead. 221 // After all, monitors are sufficient for Java-level synchronization. At one point in time 222 // there may have been some benefit to having distinct mutexes and monitors, but that time 223 // has past. 224 // 225 226 class Mutex : public Monitor { // degenerate Monitor 227 public: 228 Mutex(int rank, const char *name, bool allow_vm_block = false, 229 SafepointCheckRequired safepoint_check_required = _safepoint_check_always); 230 // default destructor 231 private: 232 void notify () { ShouldNotReachHere(); } 233 void notify_all() { ShouldNotReachHere(); } 234 bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) { 235 ShouldNotReachHere() ; 236 return false ; 237 } 238 }; 239 240 class PaddedMutex : public Mutex { 241 enum { 242 CACHE_LINE_PADDING = (int)DEFAULT_CACHE_LINE_SIZE - (int)sizeof(Mutex), 243 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1 244 }; 245 char _padding[PADDING_LEN]; 246 public: 247 PaddedMutex(int rank, const char *name, bool allow_vm_block = false, 248 SafepointCheckRequired safepoint_check_required = _safepoint_check_always) : 249 Mutex(rank, name, allow_vm_block, safepoint_check_required) {}; 250 }; 251 252 #endif // SHARE_RUNTIME_MUTEX_HPP