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_queuing_rw_mutex_H
18#define __TBB_queuing_rw_mutex_H
19
20#include <cstring>
21#include "atomic.h"
22#include "tbb_profiling.h"
23
24namespace tbb {
25
26//! Queuing reader-writer mutex with local-only spinning.
27/** Adapted from Krieger, Stumm, et al. pseudocode at
28 http://www.eecg.toronto.edu/parallel/pubs_abs.html#Krieger_etal_ICPP93
29 @ingroup synchronization */
30class queuing_rw_mutex : internal::mutex_copy_deprecated_and_disabled {
31public:
32 //! Construct unacquired mutex.
33 queuing_rw_mutex() {
34 q_tail = NULL;
35#if TBB_USE_THREADING_TOOLS
36 internal_construct();
37#endif
38 }
39
40 //! Destructor asserts if the mutex is acquired, i.e. q_tail is non-NULL
41 ~queuing_rw_mutex() {
42#if TBB_USE_ASSERT
43 __TBB_ASSERT( !q_tail, "destruction of an acquired mutex");
44#endif
45 }
46
47 //! The scoped locking pattern
48 /** It helps to avoid the common problem of forgetting to release lock.
49 It also nicely provides the "node" for queuing locks. */
50 class scoped_lock: internal::no_copy {
51 //! Initialize fields to mean "no lock held".
52 void initialize() {
53 my_mutex = NULL;
54 my_internal_lock = 0;
55 my_going = 0;
56#if TBB_USE_ASSERT
57 my_state = 0xFF; // Set to invalid state
58 internal::poison_pointer(my_next);
59 internal::poison_pointer(my_prev);
60#endif /* TBB_USE_ASSERT */
61 }
62
63 public:
64 //! Construct lock that has not acquired a mutex.
65 /** Equivalent to zero-initialization of *this. */
66 scoped_lock() {initialize();}
67
68 //! Acquire lock on given mutex.
69 scoped_lock( queuing_rw_mutex& m, bool write=true ) {
70 initialize();
71 acquire(m,write);
72 }
73
74 //! Release lock (if lock is held).
75 ~scoped_lock() {
76 if( my_mutex ) release();
77 }
78
79 //! Acquire lock on given mutex.
80 void acquire( queuing_rw_mutex& m, bool write=true );
81
82 //! Acquire lock on given mutex if free (i.e. non-blocking)
83 bool try_acquire( queuing_rw_mutex& m, bool write=true );
84
85 //! Release lock.
86 void release();
87
88 //! Upgrade reader to become a writer.
89 /** Returns whether the upgrade happened without releasing and re-acquiring the lock */
90 bool upgrade_to_writer();
91
92 //! Downgrade writer to become a reader.
93 bool downgrade_to_reader();
94
95 private:
96 //! The pointer to the mutex owned, or NULL if not holding a mutex.
97 queuing_rw_mutex* my_mutex;
98
99 //! The pointer to the previous and next competitors for a mutex
100 scoped_lock *__TBB_atomic my_prev, *__TBB_atomic my_next;
101
102 typedef unsigned char state_t;
103
104 //! State of the request: reader, writer, active reader, other service states
105 atomic<state_t> my_state;
106
107 //! The local spin-wait variable
108 /** Corresponds to "spin" in the pseudocode but inverted for the sake of zero-initialization */
109 unsigned char __TBB_atomic my_going;
110
111 //! A tiny internal lock
112 unsigned char my_internal_lock;
113
114 //! Acquire the internal lock
115 void acquire_internal_lock();
116
117 //! Try to acquire the internal lock
118 /** Returns true if lock was successfully acquired. */
119 bool try_acquire_internal_lock();
120
121 //! Release the internal lock
122 void release_internal_lock();
123
124 //! Wait for internal lock to be released
125 void wait_for_release_of_internal_lock();
126
127 //! A helper function
128 void unblock_or_wait_on_internal_lock( uintptr_t );
129 };
130
131 void __TBB_EXPORTED_METHOD internal_construct();
132
133 // Mutex traits
134 static const bool is_rw_mutex = true;
135 static const bool is_recursive_mutex = false;
136 static const bool is_fair_mutex = true;
137
138private:
139 //! The last competitor requesting the lock
140 atomic<scoped_lock*> q_tail;
141
142};
143
144__TBB_DEFINE_PROFILING_SET_NAME(queuing_rw_mutex)
145
146} // namespace tbb
147
148#endif /* __TBB_queuing_rw_mutex_H */
149