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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 LLDB_UTILITY_PREDICATE_H
10 #define LLDB_UTILITY_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 
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.
31 };
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  /// m_value if Cond(m_value) is true, None otherwise (timeout occurred).
121  template <typename C>
122  llvm::Optional<T> WaitFor(C Cond, const Timeout<std::micro> &timeout) {
123  std::unique_lock<std::mutex> lock(m_mutex);
124  auto RealCond = [&] { return Cond(m_value); };
125  if (!timeout) {
126  m_condition.wait(lock, RealCond);
127  return m_value;
128  }
129  if (m_condition.wait_for(lock, *timeout, RealCond))
130  return m_value;
131  return llvm::None;
132  }
133  /// Wait for \a m_value to be equal to \a value.
134  ///
135  /// Waits in a thread safe way for \a m_value to be equal to \a
136  /// value. If \a m_value is already equal to \a value, this
137  /// function will return without waiting.
138  ///
139  /// It is possible for the value to be changed between the time
140  /// the value is set and the time the waiting thread wakes up.
141  /// If the value no longer matches the requested value when the
142  /// waiting thread wakes up, it will go back into a wait state. It
143  /// may be necessary for the calling code to use additional thread
144  /// synchronization methods to detect transitory states.
145  ///
146  /// \param[in] value
147  /// The value we want \a m_value to be equal to.
148  ///
149  /// \param[in] timeout
150  /// How long to wait for the condition to hold.
151  ///
152  /// \return
153  /// true if the \a m_value is equal to \a value, false otherwise (timeout
154  /// occurred).
155  bool WaitForValueEqualTo(T value,
156  const Timeout<std::micro> &timeout = llvm::None) {
157  return WaitFor([&value](T current) { return value == current; }, timeout) !=
158  llvm::None;
159  }
160 
161  /// Wait for \a m_value to not be equal to \a value.
162  ///
163  /// Waits in a thread safe way for \a m_value to not be equal to \a
164  /// value. If \a m_value is already not equal to \a value, this
165  /// function will return without waiting.
166  ///
167  /// It is possible for the value to be changed between the time
168  /// the value is set and the time the waiting thread wakes up.
169  /// If the value is equal to the test value when the waiting thread
170  /// wakes up, it will go back into a wait state. It may be
171  /// necessary for the calling code to use additional thread
172  /// synchronization methods to detect transitory states.
173  ///
174  /// \param[in] value
175  /// The value we want \a m_value to not be equal to.
176  ///
177  /// \param[in] timeout
178  /// How long to wait for the condition to hold.
179  ///
180  /// \return
181  /// m_value if m_value != value, None otherwise (timeout occurred).
182  llvm::Optional<T>
184  const Timeout<std::micro> &timeout = llvm::None) {
185  return WaitFor([&value](T current) { return value != current; }, timeout);
186  }
187 
188 protected:
189  // pthread condition and mutex variable to control access and allow blocking
190  // between the main thread and the spotlight index thread.
191  T m_value; ///< The templatized value T that we are protecting access to
192  mutable std::mutex m_mutex; ///< The mutex to use when accessing the data
193  std::condition_variable m_condition; ///< The pthread condition variable to
194  /// use for signaling that data available
195  /// or changed.
196 
197 private:
198  /// Broadcast if needed.
199  ///
200  /// Check to see if we need to broadcast to our condition variable
201  /// depending on the \a old_value and on the \a broadcast_type.
202  ///
203  /// If \a broadcast_type is eBroadcastNever, no broadcast will be
204  /// sent.
205  ///
206  /// If \a broadcast_type is eBroadcastAlways, the condition variable
207  /// will always be broadcast.
208  ///
209  /// If \a broadcast_type is eBroadcastOnChange, the condition
210  /// variable be broadcast if the owned value changes.
211  void Broadcast(T old_value, PredicateBroadcastType broadcast_type) {
212  bool broadcast =
213  (broadcast_type == eBroadcastAlways) ||
214  ((broadcast_type == eBroadcastOnChange) && old_value != m_value);
215 #ifdef DB_PTHREAD_LOG_EVENTS
216  printf("%s (old_value = 0x%8.8x, broadcast_type = %i) m_value = 0x%8.8x, "
217  "broadcast = %u\n",
218  __FUNCTION__, old_value, broadcast_type, m_value, broadcast);
219 #endif
220  if (broadcast)
221  m_condition.notify_all();
222  }
223 
224  Predicate(const Predicate &) = delete;
225  const Predicate &operator=(const Predicate &) = delete;
226 };
227 
228 } // namespace lldb_private
229 
230 #endif // LLDB_UTILITY_PREDICATE_H
Predicate(T initial_value)
Construct with initial T value initial_value.
Definition: Predicate.h:56
A class that represents a running process on the host machine.
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:191
PredicateBroadcastType
Definition: Predicate.h:26
void Broadcast(T old_value, PredicateBroadcastType broadcast_type)
Broadcast if needed.
Definition: Predicate.h:211
bool WaitForValueEqualTo(T value, const Timeout< std::micro > &timeout=llvm::None)
Wait for m_value to be equal to value.
Definition: Predicate.h:155
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:183
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:122
~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:192
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:193
const Predicate & operator=(const Predicate &)=delete
Only broadcast if the value changes when the value is modified.
Definition: Predicate.h:29