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 26 enum PredicateBroadcastType { 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. Predicate()47 Predicate() : m_value(), m_mutex(), m_condition() {} 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. Predicate(T initial_value)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. GetValue()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() SetValue(T value,PredicateBroadcastType broadcast_type)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> WaitFor(C Cond,const Timeout<std::micro> & timeout)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> 183 WaitForValueNotEqualTo(T value, 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. Broadcast(T old_value,PredicateBroadcastType broadcast_type)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 231