1 /*
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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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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
103 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
104 #ifndef PRODUCT
105 bool _allow_vm_block;
106 #endif
107 static Mutex** _mutex_array;
108 static int _num_mutex;
109
110 #ifdef ASSERT
111 Rank _rank; // rank (to avoid/detect potential deadlocks)
112 Mutex* _next; // Used by a Thread to link up owned locks
113 Thread* _last_owner; // the last thread to own the lock
114 bool _skip_rank_check; // read only by owner when doing rank checks
115
116 static Mutex* get_least_ranked_lock(Mutex* locks);
117 Mutex* get_least_ranked_lock_besides_this(Mutex* locks);
118 bool skip_rank_check() {
119 assert(owned_by_self(), "only the owner should call this");
120 return _skip_rank_check;
121 }
122
123 public:
124 Rank rank() const { return _rank; }
125 const char* rank_name() const;
126 Mutex* next() const { return _next; }
127 #endif // ASSERT
128
129 protected:
130 void set_owner_implementation(Thread* owner) NOT_DEBUG({ raw_set_owner(owner);});
131 void check_block_state (Thread* thread) NOT_DEBUG_RETURN;
132 void check_safepoint_state (Thread* thread) NOT_DEBUG_RETURN;
133 void check_no_safepoint_state(Thread* thread) NOT_DEBUG_RETURN;
134 void check_rank (Thread* thread) NOT_DEBUG_RETURN;
135 void assert_owner (Thread* expected) NOT_DEBUG_RETURN;
136
137 public:
138 static const bool _allow_vm_block_flag = true;
139
140 // Locks can be acquired with or without a safepoint check. NonJavaThreads do not follow
141 // the safepoint protocol when acquiring locks.
142
143 // Each lock can be acquired by only JavaThreads, only NonJavaThreads, or shared between
144 // Java and NonJavaThreads. When the lock is initialized with rank > nosafepoint,
145 // that means that whenever the lock is acquired by a JavaThread, it will verify that
146 // it is done with a safepoint check. In corollary, when the lock is initialized with
147 // rank <= nosafepoint, that means that whenever the lock is acquired by a JavaThread
148 // it will verify that it is done without a safepoint check.
149
150 // TODO: Locks that are shared between JavaThreads and NonJavaThreads
151 // should never encounter a safepoint check while they are held, or else a
152 // deadlock can occur. We should check this by noting which
153 // locks are shared, and walk held locks during safepoint checking.
154
155 enum class SafepointCheckFlag {
156 _safepoint_check_flag,
157 _no_safepoint_check_flag
158 };
159 // Bring the enumerator names into class scope.
160 static const SafepointCheckFlag _safepoint_check_flag =
161 SafepointCheckFlag::_safepoint_check_flag;
162 static const SafepointCheckFlag _no_safepoint_check_flag =
163 SafepointCheckFlag::_no_safepoint_check_flag;
164
165 public:
166 Mutex(Rank rank, const char *name, bool allow_vm_block);
167
168 Mutex(Rank rank, const char *name) :
169 Mutex(rank, name, rank > nosafepoint ? false : true) {}
170
171 ~Mutex();
172
173 void lock(); // prints out warning if VM thread blocks
174 void lock(Thread *thread); // overloaded with current thread
175 void unlock();
176 bool is_locked() const { return owner() != nullptr; }
177
178 bool try_lock(); // Like lock(), but unblocking. It returns false instead
179 private:
180 void lock_contended(Thread *thread); // contended slow-path
181 bool try_lock_inner(bool do_rank_checks);
182 public:
183
184 void release_for_safepoint();
185
186 // Lock without safepoint check. Should ONLY be used by safepoint code and other code
187 // that is guaranteed not to block while running inside the VM.
188 void lock_without_safepoint_check();
189 void lock_without_safepoint_check(Thread* self);
190 // A thread should not call this if failure to acquire ownership will blocks its progress
191 bool try_lock_without_rank_check();
192
193 // Current owner - note not MT-safe. Can only be used to guarantee that
194 // the current running thread owns the lock
195 Thread* owner() const { return Atomic::load(&_owner); }
196 void set_owner(Thread* owner) { set_owner_implementation(owner); }
197 bool owned_by_self() const;
198
199 const char *name() const { return _name; }
200
201 static void add_mutex(Mutex* var);
202
203 void print_on_error(outputStream* st) const;
204 #ifndef PRODUCT
205 void print_on(outputStream* st) const;
206 void print() const;
207 #endif
208
209 // Print all mutexes/monitors that are currently owned by a thread; called
210 // by fatal error handler.
211 static void print_owned_locks_on_error(outputStream* st);
212 static void print_lock_ranks(outputStream* st);
213 };
214
215 class Monitor : public Mutex {
216 public:
217 Monitor(Rank rank, const char *name, bool allow_vm_block) :
218 Mutex(rank, name, allow_vm_block) {}
219
220 Monitor(Rank rank, const char *name) :
221 Mutex(rank, name) {}
222 // default destructor
223
224 // Wait until monitor is notified (or times out).
225 // Defaults are to make safepoint checks, wait time is forever (i.e.,
226 // zero). Returns true if wait times out; otherwise returns false.
227 bool wait(uint64_t timeout = 0);
228 bool wait_without_safepoint_check(uint64_t timeout = 0);
229 void notify();
230 void notify_all();
231 };
232
233
234 class PaddedMutex : public Mutex {
235 enum {
236 CACHE_LINE_PADDING = (int)DEFAULT_PADDING_SIZE - (int)sizeof(Mutex),
237 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
238 };
239 char _padding[PADDING_LEN];
240 public:
241 PaddedMutex(Rank rank, const char *name, bool allow_vm_block) : Mutex(rank, name, allow_vm_block) {};
242 PaddedMutex(Rank rank, const char *name) : Mutex(rank, name) {};
243 };
244
245 class PaddedMonitor : public Monitor {
246 enum {
247 CACHE_LINE_PADDING = (int)DEFAULT_PADDING_SIZE - (int)sizeof(Monitor),
248 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
249 };
250 char _padding[PADDING_LEN];
251 public:
252 PaddedMonitor(Rank rank, const char *name, bool allow_vm_block) : Monitor(rank, name, allow_vm_block) {};
253 PaddedMonitor(Rank rank, const char *name) : Monitor(rank, name) {};
254 };
255
256 // RecursiveMutex is a minimal implementation, and has no safety and rank checks that Mutex has.
257 // There are also no checks that the recursive lock is not held when going to Java or to JNI, like
258 // other JVM mutexes have. This should be used only for cases where the alternatives with all the
259 // nice safety features don't work.
260 // Waiting on the RecursiveMutex partipates in the safepoint protocol if the current thread is a Java thread,
261 // (ie. waiting sets JavaThread to blocked)
262 class RecursiveMutex : public CHeapObj<mtThread> {
263 Semaphore _sem;
264 Thread* _owner;
265 int _recursions;
266
267 NONCOPYABLE(RecursiveMutex);
268 public:
269 RecursiveMutex();
270 void lock(Thread* current);
271 void unlock(Thread* current);
272 // For use in asserts
273 bool holds_lock(Thread* current) { return _owner == current; }
274 };
275
276 #endif // SHARE_RUNTIME_MUTEX_HPP