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.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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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 mutex name was originally chosen to be 64 to avoid
36 // false sharing. Now, PaddedMutex and PaddedMonitor are available for this purpose.
37 // TODO: Check if _name[MUTEX_NAME_LEN] should better get replaced by const char*.
38 static const int MUTEX_NAME_LEN = 64;
39
40 class Mutex : 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 was only for use in Mutexes created by JVM_RawMonitorCreate,
56 // which being external to the VM are not subject to deadlock detection,
57 // however it has now been used by other locks that don't fit into the
58 // deadlock detection scheme.
59 // While at a safepoint no mutexes of rank safepoint are held by any thread.
60 // The rank named "leaf" is probably historical (and should
61 // be changed) -- mutexes of this rank aren't really leaf mutexes
62 // at all.
63 enum lock_types {
64 event,
65 access = event + 1,
66 tty = access + 2,
67 special = tty + 1,
68 suspend_resume = special + 1,
69 oopstorage = suspend_resume + 2,
70 leaf = oopstorage + 2,
71 safepoint = leaf + 10,
72 barrier = safepoint + 1,
73 nonleaf = barrier + 1,
74 max_nonleaf = nonleaf + 900,
75 native = max_nonleaf + 1
76 };
77
78 protected: // Monitor-Mutex metadata
79 Thread * volatile _owner; // The owner of the lock
80 os::PlatformMonitor _lock; // Native monitor implementation
81 char _name[MUTEX_NAME_LEN]; // Name of mutex/monitor
82
83 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
84 #ifndef PRODUCT
85 bool _allow_vm_block;
86 DEBUG_ONLY(int _rank;) // rank (to avoid/detect potential deadlocks)
87 DEBUG_ONLY(Mutex* _next;) // Used by a Thread to link up owned locks
88 DEBUG_ONLY(Thread* _last_owner;) // the last thread to own the lock
89 DEBUG_ONLY(static bool contains(Mutex* locks, Mutex* lock);)
90 DEBUG_ONLY(static Mutex* get_least_ranked_lock(Mutex* locks);)
91 DEBUG_ONLY(Mutex* get_least_ranked_lock_besides_this(Mutex* locks);)
92 #endif
93
94 void set_owner_implementation(Thread* owner) PRODUCT_RETURN;
95 void check_prelock_state (Thread* thread, bool safepoint_check) PRODUCT_RETURN;
96 void check_block_state (Thread* thread) PRODUCT_RETURN;
97 void check_safepoint_state (Thread* thread, bool safepoint_check) NOT_DEBUG_RETURN;
98 void assert_owner (Thread* expected) NOT_DEBUG_RETURN;
99
100 public:
101 enum {
102 _allow_vm_block_flag = true,
103 _as_suspend_equivalent_flag = true
104 };
105
106 // Locks can be acquired with or without a safepoint check. NonJavaThreads do not follow
107 // the safepoint protocol when acquiring locks.
108
109 // Each lock can be acquired by only JavaThreads, only NonJavaThreads, or shared between
110 // Java and NonJavaThreads. When the lock is initialized with _safepoint_check_always,
111 // that means that whenever the lock is acquired by a JavaThread, it will verify that
112 // it is done with a safepoint check. In corollary, when the lock is initialized with
113 // _safepoint_check_never, that means that whenever the lock is acquired by a JavaThread
114 // it will verify that it is done without a safepoint check.
115
116
117 // There are a couple of existing locks that will sometimes have a safepoint check and
118 // sometimes not when acquired by a JavaThread, but these locks are set up carefully
119 // to avoid deadlocks. TODO: Fix these locks and remove _safepoint_check_sometimes.
120
121 // TODO: Locks that are shared between JavaThreads and NonJavaThreads
122 // should never encounter a safepoint check while they are held, or else a
123 // deadlock can occur. We should check this by noting which
124 // locks are shared, and walk held locks during safepoint checking.
125
126 enum SafepointCheckFlag {
127 _safepoint_check_flag,
128 _no_safepoint_check_flag
129 };
130
131 enum SafepointCheckRequired {
132 _safepoint_check_never, // Mutexes with this value will cause errors
133 // when acquired by a JavaThread with a safepoint check.
134 _safepoint_check_sometimes, // A couple of special locks are acquired by JavaThreads sometimes
135 // with and sometimes without safepoint checks. These
136 // locks will not produce errors when locked.
137 _safepoint_check_always // Mutexes with this value will cause errors
138 // when acquired by a JavaThread without a safepoint check.
139 };
140
141 NOT_PRODUCT(SafepointCheckRequired _safepoint_check_required;)
142
143 public:
144 Mutex(int rank, const char *name, bool allow_vm_block = false,
145 SafepointCheckRequired safepoint_check_required = _safepoint_check_always);
146 ~Mutex();
147
148 void lock(); // prints out warning if VM thread blocks
149 void lock(Thread *thread); // overloaded with current thread
150 void unlock();
151 bool is_locked() const { return _owner != NULL; }
152
153 bool try_lock(); // Like lock(), but unblocking. It returns false instead
154
155 void release_for_safepoint();
156
157 // Lock without safepoint check. Should ONLY be used by safepoint code and other code
158 // that is guaranteed not to block while running inside the VM.
159 void lock_without_safepoint_check();
160 void lock_without_safepoint_check(Thread* self);
161
162 // Current owner - not not MT-safe. Can only be used to guarantee that
163 // the current running thread owns the lock
164 Thread* owner() const { return _owner; }
165 bool owned_by_self() const;
166
167 const char *name() const { return _name; }
168
169 void print_on_error(outputStream* st) const;
170
171 #ifndef PRODUCT
172 void print_on(outputStream* st) const;
173 void print() const { print_on(::tty); }
174 DEBUG_ONLY(int rank() const { return _rank; })
175 bool allow_vm_block() { return _allow_vm_block; }
176
177 DEBUG_ONLY(Mutex *next() const { return _next; })
178 DEBUG_ONLY(void set_next(Mutex *next) { _next = next; })
179 #endif
180
181 void set_owner(Thread* owner) {
182 #ifndef PRODUCT
183 set_owner_implementation(owner);
184 DEBUG_ONLY(void verify_mutex(Thread* thr);)
185 #else
186 _owner = owner;
187 #endif
188 }
189 };
190
191 class Monitor : public Mutex {
192 void assert_wait_lock_state (Thread* self) NOT_DEBUG_RETURN;
193 public:
194 Monitor(int rank, const char *name, bool allow_vm_block = false,
195 SafepointCheckRequired safepoint_check_required = _safepoint_check_always);
196 // default destructor
197
198 // Wait until monitor is notified (or times out).
199 // Defaults are to make safepoint checks, wait time is forever (i.e.,
200 // zero), and not a suspend-equivalent condition. Returns true if wait
201 // times out; otherwise returns false.
202 bool wait(long timeout = 0,
203 bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
204 bool wait_without_safepoint_check(long timeout = 0);
205 void notify();
206 void notify_all();
207 };
208
209
210 class PaddedMutex : public Mutex {
211 enum {
212 CACHE_LINE_PADDING = (int)DEFAULT_CACHE_LINE_SIZE - (int)sizeof(Mutex),
213 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
214 };
215 char _padding[PADDING_LEN];
216 public:
217 PaddedMutex(int rank, const char *name, bool allow_vm_block = false,
218 SafepointCheckRequired safepoint_check_required = _safepoint_check_always) :
219 Mutex(rank, name, allow_vm_block, safepoint_check_required) {};
220 };
221
222 class PaddedMonitor : public Monitor {
223 enum {
224 CACHE_LINE_PADDING = (int)DEFAULT_CACHE_LINE_SIZE - (int)sizeof(Monitor),
225 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
226 };
227 char _padding[PADDING_LEN];
228 public:
229 PaddedMonitor(int rank, const char *name, bool allow_vm_block = false,
230 SafepointCheckRequired safepoint_check_required = _safepoint_check_always) :
231 Monitor(rank, name, allow_vm_block, safepoint_check_required) {};
232 };
233
234 #endif // SHARE_RUNTIME_MUTEX_HPP