1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_RUNTIME_MUTEX_HPP
26 #define SHARE_RUNTIME_MUTEX_HPP
27
28 #include "memory/allocation.hpp"
29 #include "runtime/atomic.hpp"
30 #include "runtime/semaphore.hpp"
31
32 #if defined(LINUX) || defined(AIX) || defined(BSD)
33 # include "mutex_posix.hpp"
34 #else
35 # include OS_HEADER(mutex)
36 #endif
37
38
39 // A Mutex/Monitor is a simple wrapper around a native lock plus condition
40 // variable that supports lock ownership tracking, lock ranking for deadlock
41 // detection and coordinates with the safepoint protocol.
42
43 // Locking is non-recursive: if you try to lock a mutex you already own then you
44 // will get an assertion failure in a debug build (which should suffice to expose
45 // usage bugs). If you call try_lock on a mutex you already own it will return false.
46 // The underlying PlatformMutex may support recursive locking but this is not exposed
47 // and we account for that possibility in try_lock.
48
49 // A thread is not allowed to safepoint while holding a mutex whose rank
50 // is nosafepoint or lower.
51
52 class Mutex : public CHeapObj<mtSynchronizer> {
53
54 friend class VMStructs;
55 public:
56 // Special low level locks are given names and ranges avoid overlap.
57 enum class Rank {
58 event,
59 service = event + 6,
60 stackwatermark = service + 3,
61 tty = stackwatermark + 3,
62 oopstorage = tty + 3,
63 nosafepoint = oopstorage + 6,
64 safepoint = nosafepoint + 20
65 };
66
67 // want C++later "using enum" directives.
68 static const Rank event = Rank::event;
69 static const Rank service = Rank::service;
70 static const Rank stackwatermark = Rank::stackwatermark;
71 static const Rank tty = Rank::tty;
72 static const Rank oopstorage = Rank::oopstorage;
73 static const Rank nosafepoint = Rank::nosafepoint;
74 static const Rank safepoint = Rank::safepoint;
75
76 static void assert_no_overlap(Rank orig, Rank adjusted, int adjust);
77
78 friend Rank operator-(Rank base, int adjust) {
79 Rank result = static_cast<Rank>(static_cast<int>(base) - adjust);
80 DEBUG_ONLY(assert_no_overlap(base, result, adjust));
81 return result;
82 }
83
84 friend constexpr bool operator<(Rank lhs, Rank rhs) {
85 return static_cast<int>(lhs) < static_cast<int>(rhs);
86 }
87
88 friend constexpr bool operator>(Rank lhs, Rank rhs) { return rhs < lhs; }
89 friend constexpr bool operator<=(Rank lhs, Rank rhs) { return !(lhs > rhs); }
90 friend constexpr bool operator>=(Rank lhs, Rank rhs) { return !(lhs < rhs); }
91
92 private:
93 // The _owner field is only set by the current thread, either to itself after it has acquired
94 // the low-level _lock, or to null before it has released the _lock. Accesses by any thread other
95 // than the lock owner are inherently racy.
96 Thread* volatile _owner;
97 void raw_set_owner(Thread* new_owner) { Atomic::store(&_owner, new_owner); }
98
99 protected: // Monitor-Mutex metadata
100 PlatformMonitor _lock; // Native monitor implementation
101 const char* _name; // Name of mutex/monitor
102 int _id; // ID for named mutexes
103
104 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
105 #ifndef PRODUCT
106 bool _allow_vm_block;
107 #endif
108 static Mutex** _mutex_array;
109 static int _num_mutex;
110
111 #ifdef ASSERT
112 Rank _rank; // rank (to avoid/detect potential deadlocks)
113 Mutex* _next; // Used by a Thread to link up owned locks
114 Thread* _last_owner; // the last thread to own the lock
115 bool _skip_rank_check; // read only by owner when doing rank checks
116
117 static Mutex* get_least_ranked_lock(Mutex* locks);
118 Mutex* get_least_ranked_lock_besides_this(Mutex* locks);
119 bool skip_rank_check() {
120 assert(owned_by_self(), "only the owner should call this");
121 return _skip_rank_check;
122 }
123
124 public:
125 Rank rank() const { return _rank; }
126 const char* rank_name() const;
127 Mutex* next() const { return _next; }
128 #endif // ASSERT
129
130 protected:
131 void set_owner_implementation(Thread* owner) NOT_DEBUG({ raw_set_owner(owner);});
132 void check_block_state (Thread* thread) NOT_DEBUG_RETURN;
133 void check_safepoint_state (Thread* thread) NOT_DEBUG_RETURN;
134 void check_no_safepoint_state(Thread* thread) NOT_DEBUG_RETURN;
135 void check_rank (Thread* thread) NOT_DEBUG_RETURN;
136 void assert_owner (Thread* expected) NOT_DEBUG_RETURN;
137
138 public:
139 static const bool _allow_vm_block_flag = true;
140
141 // Locks can be acquired with or without a safepoint check. NonJavaThreads do not follow
142 // the safepoint protocol when acquiring locks.
143
144 // Each lock can be acquired by only JavaThreads, only NonJavaThreads, or shared between
145 // Java and NonJavaThreads. When the lock is initialized with rank > nosafepoint,
146 // that means that whenever the lock is acquired by a JavaThread, it will verify that
147 // it is done with a safepoint check. In corollary, when the lock is initialized with
148 // rank <= nosafepoint, that means that whenever the lock is acquired by a JavaThread
149 // it will verify that it is done without a safepoint check.
150
151 // TODO: Locks that are shared between JavaThreads and NonJavaThreads
152 // should never encounter a safepoint check while they are held, or else a
153 // deadlock can occur. We should check this by noting which
154 // locks are shared, and walk held locks during safepoint checking.
155
156 enum class SafepointCheckFlag {
157 _safepoint_check_flag,
158 _no_safepoint_check_flag
159 };
160 // Bring the enumerator names into class scope.
161 static const SafepointCheckFlag _safepoint_check_flag =
162 SafepointCheckFlag::_safepoint_check_flag;
163 static const SafepointCheckFlag _no_safepoint_check_flag =
164 SafepointCheckFlag::_no_safepoint_check_flag;
165
166 public:
167 Mutex(Rank rank, const char *name, bool allow_vm_block);
168
169 Mutex(Rank rank, const char *name) :
170 Mutex(rank, name, rank > nosafepoint ? false : true) {}
171
172 ~Mutex();
173
174 void lock(); // prints out warning if VM thread blocks
175 void lock(Thread *thread); // overloaded with current thread
176 void unlock();
177 bool is_locked() const { return owner() != nullptr; }
178
179 bool try_lock(); // Like lock(), but unblocking. It returns false instead
180 private:
181 void lock_contended(Thread *thread); // contended slow-path
182 bool try_lock_inner(bool do_rank_checks);
183 public:
184
185 void release_for_safepoint();
186
187 // Lock without safepoint check. Should ONLY be used by safepoint code and other code
188 // that is guaranteed not to block while running inside the VM.
189 void lock_without_safepoint_check();
190 void lock_without_safepoint_check(Thread* self);
191 // A thread should not call this if failure to acquire ownership will blocks its progress
192 bool try_lock_without_rank_check();
193
194 // Current owner - note not MT-safe. Can only be used to guarantee that
195 // the current running thread owns the lock
196 Thread* owner() const { return Atomic::load(&_owner); }
197 void set_owner(Thread* owner) { set_owner_implementation(owner); }
198 bool owned_by_self() const;
199
200 const char *name() const { return _name; }
201
202 int id() const { return _id; }
203 // void set_id(int id) { _id = id; }
204
205 static void add_mutex(Mutex* var);
206
207 void print_on_error(outputStream* st) const;
208 #ifndef PRODUCT
209 void print_on(outputStream* st) const;
210 void print() const;
211 #endif
212
213 // Print all mutexes/monitors that are currently owned by a thread; called
214 // by fatal error handler.
215 static void print_owned_locks_on_error(outputStream* st);
216 static void print_lock_ranks(outputStream* st);
217
218 static int num_mutex() { return _num_mutex; }
219 };
220
221 class Monitor : public Mutex {
222 public:
223 Monitor(Rank rank, const char *name, bool allow_vm_block) :
224 Mutex(rank, name, allow_vm_block) {}
225
226 Monitor(Rank rank, const char *name) :
227 Mutex(rank, name) {}
228 // default destructor
229
230 // Wait until monitor is notified (or times out).
231 // Defaults are to make safepoint checks, wait time is forever (i.e.,
232 // zero). Returns true if wait times out; otherwise returns false.
233 bool wait(uint64_t timeout = 0);
234 bool wait_without_safepoint_check(uint64_t timeout = 0);
235 void notify();
236 void notify_all();
237 };
238
239
240 class PaddedMutex : public Mutex {
241 enum {
242 CACHE_LINE_PADDING = (int)DEFAULT_PADDING_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(Rank rank, const char *name, bool allow_vm_block) : Mutex(rank, name, allow_vm_block) {};
248 PaddedMutex(Rank rank, const char *name) : Mutex(rank, name) {};
249 };
250
251 class PaddedMonitor : public Monitor {
252 enum {
253 CACHE_LINE_PADDING = (int)DEFAULT_PADDING_SIZE - (int)sizeof(Monitor),
254 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
255 };
256 char _padding[PADDING_LEN];
257 public:
258 PaddedMonitor(Rank rank, const char *name, bool allow_vm_block) : Monitor(rank, name, allow_vm_block) {};
259 PaddedMonitor(Rank rank, const char *name) : Monitor(rank, name) {};
260 };
261
262 // RecursiveMutex is a minimal implementation, and has no safety and rank checks that Mutex has.
263 // There are also no checks that the recursive lock is not held when going to Java or to JNI, like
264 // other JVM mutexes have. This should be used only for cases where the alternatives with all the
265 // nice safety features don't work.
266 // Waiting on the RecursiveMutex partipates in the safepoint protocol if the current thread is a Java thread,
267 // (ie. waiting sets JavaThread to blocked)
268 class RecursiveMutex : public CHeapObj<mtThread> {
269 Semaphore _sem;
270 Thread* _owner;
271 int _recursions;
272
273 NONCOPYABLE(RecursiveMutex);
274 public:
275 RecursiveMutex();
276 void lock(Thread* current);
277 void unlock(Thread* current);
278 // For use in asserts
279 bool holds_lock(Thread* current) { return _owner == current; }
280 };
281
282 #endif // SHARE_RUNTIME_MUTEX_HPP