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 public:
55 // Special low level locks are given names and ranges avoid overlap.
56 enum class Rank {
57 event,
58 service = event + 6,
59 stackwatermark = service + 3,
60 tty = stackwatermark + 3,
61 oopstorage = tty + 3,
62 nosafepoint = oopstorage + 6,
63 safepoint = nosafepoint + 20
64 };
65
66 // want C++later "using enum" directives.
67 static const Rank event = Rank::event;
68 static const Rank service = Rank::service;
69 static const Rank stackwatermark = Rank::stackwatermark;
70 static const Rank tty = Rank::tty;
71 static const Rank oopstorage = Rank::oopstorage;
72 static const Rank nosafepoint = Rank::nosafepoint;
73 static const Rank safepoint = Rank::safepoint;
74
75 static void assert_no_overlap(Rank orig, Rank adjusted, int adjust);
76
77 friend Rank operator-(Rank base, int adjust) {
78 Rank result = static_cast<Rank>(static_cast<int>(base) - adjust);
79 DEBUG_ONLY(assert_no_overlap(base, result, adjust));
80 return result;
81 }
82
83 friend constexpr bool operator<(Rank lhs, Rank rhs) {
84 return static_cast<int>(lhs) < static_cast<int>(rhs);
85 }
86
87 friend constexpr bool operator>(Rank lhs, Rank rhs) { return rhs < lhs; }
88 friend constexpr bool operator<=(Rank lhs, Rank rhs) { return !(lhs > rhs); }
89 friend constexpr bool operator>=(Rank lhs, Rank rhs) { return !(lhs < rhs); }
90
91 private:
92 // The _owner field is only set by the current thread, either to itself after it has acquired
93 // the low-level _lock, or to null before it has released the _lock. Accesses by any thread other
94 // than the lock owner are inherently racy.
95 Thread* volatile _owner;
96 void raw_set_owner(Thread* new_owner) { Atomic::store(&_owner, new_owner); }
97
98 protected: // Monitor-Mutex metadata
99 PlatformMonitor _lock; // Native monitor implementation
100 const char* _name; // Name of mutex/monitor
101
102 // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
103 #ifndef PRODUCT
104 bool _allow_vm_block;
105 #endif
106 #ifdef ASSERT
107 Rank _rank; // rank (to avoid/detect potential deadlocks)
108 Mutex* _next; // Used by a Thread to link up owned locks
109 Thread* _last_owner; // the last thread to own the lock
110 bool _skip_rank_check; // read only by owner when doing rank checks
111
112 static Mutex* get_least_ranked_lock(Mutex* locks);
113 Mutex* get_least_ranked_lock_besides_this(Mutex* locks);
114 bool skip_rank_check() {
115 assert(owned_by_self(), "only the owner should call this");
116 return _skip_rank_check;
117 }
118
119 public:
120 Rank rank() const { return _rank; }
121 const char* rank_name() const;
122 Mutex* next() const { return _next; }
123 #endif // ASSERT
124
125 protected:
126 void set_owner_implementation(Thread* owner) NOT_DEBUG({ raw_set_owner(owner);});
127 void check_block_state (Thread* thread) NOT_DEBUG_RETURN;
128 void check_safepoint_state (Thread* thread) NOT_DEBUG_RETURN;
129 void check_no_safepoint_state(Thread* thread) NOT_DEBUG_RETURN;
130 void check_rank (Thread* thread) NOT_DEBUG_RETURN;
131 void assert_owner (Thread* expected) NOT_DEBUG_RETURN;
132
133 public:
134 static const bool _allow_vm_block_flag = true;
135
136 // Locks can be acquired with or without a safepoint check. NonJavaThreads do not follow
137 // the safepoint protocol when acquiring locks.
138
139 // Each lock can be acquired by only JavaThreads, only NonJavaThreads, or shared between
140 // Java and NonJavaThreads. When the lock is initialized with rank > nosafepoint,
141 // that means that whenever the lock is acquired by a JavaThread, it will verify that
142 // it is done with a safepoint check. In corollary, when the lock is initialized with
143 // rank <= nosafepoint, that means that whenever the lock is acquired by a JavaThread
144 // it will verify that it is done without a safepoint check.
145
146 // TODO: Locks that are shared between JavaThreads and NonJavaThreads
147 // should never encounter a safepoint check while they are held, or else a
148 // deadlock can occur. We should check this by noting which
149 // locks are shared, and walk held locks during safepoint checking.
150
151 enum class SafepointCheckFlag {
152 _safepoint_check_flag,
153 _no_safepoint_check_flag
154 };
155 // Bring the enumerator names into class scope.
156 static const SafepointCheckFlag _safepoint_check_flag =
157 SafepointCheckFlag::_safepoint_check_flag;
158 static const SafepointCheckFlag _no_safepoint_check_flag =
159 SafepointCheckFlag::_no_safepoint_check_flag;
160
161 public:
162 Mutex(Rank rank, const char *name, bool allow_vm_block);
163
164 Mutex(Rank rank, const char *name) :
165 Mutex(rank, name, rank > nosafepoint ? false : true) {}
166
167 ~Mutex();
168
169 void lock(); // prints out warning if VM thread blocks
170 void lock(Thread *thread); // overloaded with current thread
171 void unlock();
172 bool is_locked() const { return owner() != nullptr; }
173
174 bool try_lock(); // Like lock(), but unblocking. It returns false instead
175 private:
176 void lock_contended(Thread *thread); // contended slow-path
177 bool try_lock_inner(bool do_rank_checks);
178 public:
179
180 void release_for_safepoint();
181
182 // Lock without safepoint check. Should ONLY be used by safepoint code and other code
183 // that is guaranteed not to block while running inside the VM.
184 void lock_without_safepoint_check();
185 void lock_without_safepoint_check(Thread* self);
186 // A thread should not call this if failure to acquire ownership will blocks its progress
187 bool try_lock_without_rank_check();
188
189 // Current owner - note not MT-safe. Can only be used to guarantee that
190 // the current running thread owns the lock
191 Thread* owner() const { return Atomic::load(&_owner); }
192 void set_owner(Thread* owner) { set_owner_implementation(owner); }
193 bool owned_by_self() const;
194
195 const char *name() const { return _name; }
196
197 void print_on_error(outputStream* st) const;
198 #ifndef PRODUCT
199 void print_on(outputStream* st) const;
200 void print() const;
201 #endif
202 };
203
204 class Monitor : public Mutex {
205 public:
206 Monitor(Rank rank, const char *name, bool allow_vm_block) :
207 Mutex(rank, name, allow_vm_block) {}
208
209 Monitor(Rank rank, const char *name) :
210 Mutex(rank, name) {}
211 // default destructor
212
213 // Wait until monitor is notified (or times out).
214 // Defaults are to make safepoint checks, wait time is forever (i.e.,
215 // zero). Returns true if wait times out; otherwise returns false.
216 bool wait(uint64_t timeout = 0);
217 bool wait_without_safepoint_check(uint64_t timeout = 0);
218 void notify();
219 void notify_all();
220 };
221
222
223 class PaddedMutex : public Mutex {
224 enum {
225 CACHE_LINE_PADDING = (int)DEFAULT_PADDING_SIZE - (int)sizeof(Mutex),
226 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
227 };
228 char _padding[PADDING_LEN];
229 public:
230 PaddedMutex(Rank rank, const char *name, bool allow_vm_block) : Mutex(rank, name, allow_vm_block) {};
231 PaddedMutex(Rank rank, const char *name) : Mutex(rank, name) {};
232 };
233
234 class PaddedMonitor : public Monitor {
235 enum {
236 CACHE_LINE_PADDING = (int)DEFAULT_PADDING_SIZE - (int)sizeof(Monitor),
237 PADDING_LEN = CACHE_LINE_PADDING > 0 ? CACHE_LINE_PADDING : 1
238 };
239 char _padding[PADDING_LEN];
240 public:
241 PaddedMonitor(Rank rank, const char *name, bool allow_vm_block) : Monitor(rank, name, allow_vm_block) {};
242 PaddedMonitor(Rank rank, const char *name) : Monitor(rank, name) {};
243 };
244
245 // RecursiveMutex is a minimal implementation, and has no safety and rank checks that Mutex has.
246 // There are also no checks that the recursive lock is not held when going to Java or to JNI, like
247 // other JVM mutexes have. This should be used only for cases where the alternatives with all the
248 // nice safety features don't work.
249 // Waiting on the RecursiveMutex partipates in the safepoint protocol if the current thread is a Java thread,
250 // (ie. waiting sets JavaThread to blocked)
251 class RecursiveMutex : public CHeapObj<mtThread> {
252 Semaphore _sem;
253 Thread* _owner;
254 int _recursions;
255
256 NONCOPYABLE(RecursiveMutex);
257 public:
258 RecursiveMutex();
259 void lock(Thread* current);
260 void unlock(Thread* current);
261 // For use in asserts
262 bool holds_lock(Thread* current) { return _owner == current; }
263 };
264
265 #endif // SHARE_RUNTIME_MUTEX_HPP