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Predicate.h
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1 //===-- Predicate.h ---------------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef liblldb_Predicate_h_
10 #define liblldb_Predicate_h_
11 
12 #include <stdint.h>
13 #include <time.h>
14 
15 #include <condition_variable>
16 #include <mutex>
17 
18 #include "lldb/Utility/Timeout.h"
19 #include "lldb/lldb-defines.h"
20 
21 //#define DB_PTHREAD_LOG_EVENTS
22 
23 /// Enumerations for broadcasting.
24 namespace lldb_private {
25 
26 typedef enum {
27  eBroadcastNever, ///< No broadcast will be sent when the value is modified.
28  eBroadcastAlways, ///< Always send a broadcast when the value is modified.
29  eBroadcastOnChange ///< Only broadcast if the value changes when the value is
30  /// modified.
32 
33 /// \class Predicate Predicate.h "lldb/Utility/Predicate.h"
34 /// A C++ wrapper class for providing threaded access to a value of
35 /// type T.
36 ///
37 /// A templatized class that provides multi-threaded access to a value
38 /// of type T. Threads can efficiently wait for bits within T to be set
39 /// or reset, or wait for T to be set to be equal/not equal to a
40 /// specified values.
41 template <class T> class Predicate {
42 public:
43  /// Default constructor.
44  ///
45  /// Initializes the mutex, condition and value with their default
46  /// constructors.
48 
49  /// Construct with initial T value \a initial_value.
50  ///
51  /// Initializes the mutex and condition with their default
52  /// constructors, and initializes the value with \a initial_value.
53  ///
54  /// \param[in] initial_value
55  /// The initial value for our T object.
56  Predicate(T initial_value)
57  : m_value(initial_value), m_mutex(), m_condition() {}
58 
59  /// Destructor.
60  ///
61  /// Destroy the condition, mutex, and T objects.
62  ~Predicate() = default;
63 
64  /// Value get accessor.
65  ///
66  /// Copies the current \a m_value in a thread safe manor and returns
67  /// the copied value.
68  ///
69  /// \return
70  /// A copy of the current value.
71  T GetValue() const {
72  std::lock_guard<std::mutex> guard(m_mutex);
73  T value = m_value;
74  return value;
75  }
76 
77  /// Value set accessor.
78  ///
79  /// Set the contained \a m_value to \a new_value in a thread safe
80  /// way and broadcast if needed.
81  ///
82  /// \param[in] value
83  /// The new value to set.
84  ///
85  /// \param[in] broadcast_type
86  /// A value indicating when and if to broadcast. See the
87  /// PredicateBroadcastType enumeration for details.
88  ///
89  /// \see Predicate::Broadcast()
90  void SetValue(T value, PredicateBroadcastType broadcast_type) {
91  std::lock_guard<std::mutex> guard(m_mutex);
92 #ifdef DB_PTHREAD_LOG_EVENTS
93  printf("%s (value = 0x%8.8x, broadcast_type = %i)\n", __FUNCTION__, value,
94  broadcast_type);
95 #endif
96  const T old_value = m_value;
97  m_value = value;
98 
99  Broadcast(old_value, broadcast_type);
100  }
101 
102  /// Wait for Cond(m_value) to be true.
103  ///
104  /// Waits in a thread safe way for Cond(m_value) to be true. If Cond(m_value)
105  /// is already true, this function will return without waiting.
106  ///
107  /// It is possible for the value to be changed between the time the value is
108  /// set and the time the waiting thread wakes up. If the value no longer
109  /// satisfies the condition when the waiting thread wakes up, it will go back
110  /// into a wait state. It may be necessary for the calling code to use
111  /// additional thread synchronization methods to detect transitory states.
112  ///
113  /// \param[in] Cond
114  /// The condition we want \a m_value satisfy.
115  ///
116  /// \param[in] timeout
117  /// How long to wait for the condition to hold.
118  ///
119  /// \return
120  /// \li m_value if Cond(m_value) is true.
121  /// \li None otherwise (timeout occurred).
122  template <typename C>
123  llvm::Optional<T> WaitFor(C Cond, const Timeout<std::micro> &timeout) {
124  std::unique_lock<std::mutex> lock(m_mutex);
125  auto RealCond = [&] { return Cond(m_value); };
126  if (!timeout) {
127  m_condition.wait(lock, RealCond);
128  return m_value;
129  }
130  if (m_condition.wait_for(lock, *timeout, RealCond))
131  return m_value;
132  return llvm::None;
133  }
134  /// Wait for \a m_value to be equal to \a value.
135  ///
136  /// Waits in a thread safe way for \a m_value to be equal to \a
137  /// value. If \a m_value is already equal to \a value, this
138  /// function will return without waiting.
139  ///
140  /// It is possible for the value to be changed between the time
141  /// the value is set and the time the waiting thread wakes up.
142  /// If the value no longer matches the requested value when the
143  /// waiting thread wakes up, it will go back into a wait state. It
144  /// may be necessary for the calling code to use additional thread
145  /// synchronization methods to detect transitory states.
146  ///
147  /// \param[in] value
148  /// The value we want \a m_value to be equal to.
149  ///
150  /// \param[in] timeout
151  /// How long to wait for the condition to hold.
152  ///
153  /// \return
154  /// \li \b true if the \a m_value is equal to \a value
155  /// \li \b false otherwise (timeout occurred)
156  bool WaitForValueEqualTo(T value,
157  const Timeout<std::micro> &timeout = llvm::None) {
158  return WaitFor([&value](T current) { return value == current; }, timeout) !=
159  llvm::None;
160  }
161 
162  /// Wait for \a m_value to not be equal to \a value.
163  ///
164  /// Waits in a thread safe way for \a m_value to not be equal to \a
165  /// value. If \a m_value is already not equal to \a value, this
166  /// function will return without waiting.
167  ///
168  /// It is possible for the value to be changed between the time
169  /// the value is set and the time the waiting thread wakes up.
170  /// If the value is equal to the test value when the waiting thread
171  /// wakes up, it will go back into a wait state. It may be
172  /// necessary for the calling code to use additional thread
173  /// synchronization methods to detect transitory states.
174  ///
175  /// \param[in] value
176  /// The value we want \a m_value to not be equal to.
177  ///
178  /// \param[in] timeout
179  /// How long to wait for the condition to hold.
180  ///
181  /// \return
182  /// \li m_value if m_value != value
183  /// \li None otherwise (timeout occurred).
184  llvm::Optional<T>
186  const Timeout<std::micro> &timeout = llvm::None) {
187  return WaitFor([&value](T current) { return value != current; }, timeout);
188  }
189 
190 protected:
191  // pthread condition and mutex variable to control access and allow blocking
192  // between the main thread and the spotlight index thread.
193  T m_value; ///< The templatized value T that we are protecting access to
194  mutable std::mutex m_mutex; ///< The mutex to use when accessing the data
195  std::condition_variable m_condition; ///< The pthread condition variable to
196  /// use for signaling that data available
197  /// or changed.
198 
199 private:
200  /// Broadcast if needed.
201  ///
202  /// Check to see if we need to broadcast to our condition variable
203  /// depending on the \a old_value and on the \a broadcast_type.
204  ///
205  /// If \a broadcast_type is eBroadcastNever, no broadcast will be
206  /// sent.
207  ///
208  /// If \a broadcast_type is eBroadcastAlways, the condition variable
209  /// will always be broadcast.
210  ///
211  /// If \a broadcast_type is eBroadcastOnChange, the condition
212  /// variable be broadcast if the owned value changes.
213  void Broadcast(T old_value, PredicateBroadcastType broadcast_type) {
214  bool broadcast =
215  (broadcast_type == eBroadcastAlways) ||
216  ((broadcast_type == eBroadcastOnChange) && old_value != m_value);
217 #ifdef DB_PTHREAD_LOG_EVENTS
218  printf("%s (old_value = 0x%8.8x, broadcast_type = %i) m_value = 0x%8.8x, "
219  "broadcast = %u\n",
220  __FUNCTION__, old_value, broadcast_type, m_value, broadcast);
221 #endif
222  if (broadcast)
223  m_condition.notify_all();
224  }
225 
226  DISALLOW_COPY_AND_ASSIGN(Predicate);
227 };
228 
229 } // namespace lldb_private
230 
231 #endif // liblldb_Predicate_h_
Predicate(T initial_value)
Construct with initial T value initial_value.
Definition: Predicate.h:56
Enumerations for broadcasting.
Definition: SBLaunchInfo.h:14
T GetValue() const
Value get accessor.
Definition: Predicate.h:71
T m_value
The templatized value T that we are protecting access to.
Definition: Predicate.h:193
PredicateBroadcastType
Definition: Predicate.h:26
bool WaitForValueEqualTo(T value, const Timeout< std::micro > &timeout=llvm::None)
Wait for m_value to be equal to value.
Definition: Predicate.h:156
llvm::Optional< T > WaitForValueNotEqualTo(T value, const Timeout< std::micro > &timeout=llvm::None)
Wait for m_value to not be equal to value.
Definition: Predicate.h:185
Always send a broadcast when the value is modified.
Definition: Predicate.h:28
llvm::Optional< T > WaitFor(C Cond, const Timeout< std::micro > &timeout)
Wait for Cond(m_value) to be true.
Definition: Predicate.h:123
~Predicate()=default
Destructor.
Predicate()
Default constructor.
Definition: Predicate.h:47
void SetValue(T value, PredicateBroadcastType broadcast_type)
Value set accessor.
Definition: Predicate.h:90
std::mutex m_mutex
The mutex to use when accessing the data.
Definition: Predicate.h:194
A C++ wrapper class for providing threaded access to a value of type T.
Definition: Predicate.h:41
No broadcast will be sent when the value is modified.
Definition: Predicate.h:27
std::condition_variable m_condition
The pthread condition variable to use for signaling that data available or changed.
Definition: Predicate.h:195
Only broadcast if the value changes when the value is modified.
Definition: Predicate.h:29