1/*
2 Copyright (c) 2005-2019 Intel Corporation
3
4 Licensed under the Apache License, Version 2.0 (the "License");
5 you may not use this file except in compliance with the License.
6 You may obtain a copy of the License at
7
8 http://www.apache.org/licenses/LICENSE-2.0
9
10 Unless required by applicable law or agreed to in writing, software
11 distributed under the License is distributed on an "AS IS" BASIS,
12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 See the License for the specific language governing permissions and
14 limitations under the License.
15*/
16
17#ifndef __TBB_spin_rw_mutex_H
18#define __TBB_spin_rw_mutex_H
19
20#include "tbb/tbb_stddef.h"
21
22namespace tbb {
23
24//! Fast, unfair, spinning reader-writer lock with backoff and writer-preference
25/** @ingroup synchronization */
26class spin_rw_mutex {
27 //! @cond INTERNAL
28
29 //! Present so that 1.0 headers work with 1.1 dynamic library.
30 static void __TBB_EXPORTED_FUNC internal_itt_releasing(spin_rw_mutex *);
31
32 //! Internal acquire write lock.
33 static bool __TBB_EXPORTED_FUNC internal_acquire_writer(spin_rw_mutex *);
34
35 //! Out of line code for releasing a write lock.
36 /** This code has debug checking and instrumentation for Intel(R) Thread Checker and Intel(R) Thread Profiler. */
37 static void __TBB_EXPORTED_FUNC internal_release_writer(spin_rw_mutex *);
38
39 //! Internal acquire read lock.
40 static void __TBB_EXPORTED_FUNC internal_acquire_reader(spin_rw_mutex *);
41
42 //! Internal upgrade reader to become a writer.
43 static bool __TBB_EXPORTED_FUNC internal_upgrade(spin_rw_mutex *);
44
45 //! Out of line code for downgrading a writer to a reader.
46 /** This code has debug checking and instrumentation for Intel(R) Thread Checker and Intel(R) Thread Profiler. */
47 static void __TBB_EXPORTED_FUNC internal_downgrade(spin_rw_mutex *);
48
49 //! Internal release read lock.
50 static void __TBB_EXPORTED_FUNC internal_release_reader(spin_rw_mutex *);
51
52 //! Internal try_acquire write lock.
53 static bool __TBB_EXPORTED_FUNC internal_try_acquire_writer(spin_rw_mutex *);
54
55 //! Internal try_acquire read lock.
56 static bool __TBB_EXPORTED_FUNC internal_try_acquire_reader(spin_rw_mutex *);
57
58 //! @endcond
59public:
60 //! Construct unacquired mutex.
61 spin_rw_mutex() : state(0) {}
62
63#if TBB_USE_ASSERT
64 //! Destructor asserts if the mutex is acquired, i.e. state is zero.
65 ~spin_rw_mutex() {
66 __TBB_ASSERT( !state, "destruction of an acquired mutex");
67 };
68#endif /* TBB_USE_ASSERT */
69
70 //! The scoped locking pattern
71 /** It helps to avoid the common problem of forgetting to release lock.
72 It also nicely provides the "node" for queuing locks. */
73 class scoped_lock : internal::no_copy {
74 public:
75 //! Construct lock that has not acquired a mutex.
76 /** Equivalent to zero-initialization of *this. */
77 scoped_lock() : mutex(NULL) {}
78
79 //! Construct and acquire lock on given mutex.
80 scoped_lock( spin_rw_mutex& m, bool write = true ) : mutex(NULL) {
81 acquire(m, write);
82 }
83
84 //! Release lock (if lock is held).
85 ~scoped_lock() {
86 if( mutex ) release();
87 }
88
89 //! Acquire lock on given mutex.
90 void acquire( spin_rw_mutex& m, bool write = true ) {
91 __TBB_ASSERT( !mutex, "holding mutex already" );
92 mutex = &m;
93 is_writer = write;
94 if( write ) internal_acquire_writer(mutex);
95 else internal_acquire_reader(mutex);
96 }
97
98 //! Upgrade reader to become a writer.
99 /** Returns whether the upgrade happened without releasing and re-acquiring the lock */
100 bool upgrade_to_writer() {
101 __TBB_ASSERT( mutex, "lock is not acquired" );
102 __TBB_ASSERT( !is_writer, "not a reader" );
103 is_writer = true;
104 return internal_upgrade(mutex);
105 }
106
107 //! Release lock.
108 void release() {
109 __TBB_ASSERT( mutex, "lock is not acquired" );
110 spin_rw_mutex *m = mutex;
111 mutex = NULL;
112 if( is_writer ) {
113#if TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT
114 internal_release_writer(m);
115#else
116 m->state = 0;
117#endif /* TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT */
118 } else {
119 internal_release_reader(m);
120 }
121 };
122
123 //! Downgrade writer to become a reader.
124 bool downgrade_to_reader() {
125 __TBB_ASSERT( mutex, "lock is not acquired" );
126 __TBB_ASSERT( is_writer, "not a writer" );
127#if TBB_USE_THREADING_TOOLS||TBB_USE_ASSERT
128 internal_downgrade(mutex);
129#else
130 mutex->state = 4; // Bit 2 - reader, 00..00100
131#endif
132 is_writer = false;
133 return true;
134 }
135
136 //! Try acquire lock on given mutex.
137 bool try_acquire( spin_rw_mutex& m, bool write = true ) {
138 __TBB_ASSERT( !mutex, "holding mutex already" );
139 bool result;
140 is_writer = write;
141 result = write? internal_try_acquire_writer(&m)
142 : internal_try_acquire_reader(&m);
143 if( result ) mutex = &m;
144 return result;
145 }
146
147 private:
148 //! The pointer to the current mutex that is held, or NULL if no mutex is held.
149 spin_rw_mutex* mutex;
150
151 //! If mutex!=NULL, then is_writer is true if holding a writer lock, false if holding a reader lock.
152 /** Not defined if not holding a lock. */
153 bool is_writer;
154 };
155
156private:
157 typedef uintptr_t state_t;
158 static const state_t WRITER = 1;
159 static const state_t WRITER_PENDING = 2;
160 static const state_t READERS = ~(WRITER | WRITER_PENDING);
161 static const state_t ONE_READER = 4;
162 static const state_t BUSY = WRITER | READERS;
163 /** Bit 0 = writer is holding lock
164 Bit 1 = request by a writer to acquire lock (hint to readers to wait)
165 Bit 2..N = number of readers holding lock */
166 volatile state_t state;
167};
168
169} // namespace tbb
170
171#endif /* __TBB_spin_rw_mutex_H */
172