1 files changed, 229 insertions, 0 deletions
diff --git a/lldb/include/lldb/Utility/Predicate.h b/lldb/include/lldb/Utility/Predicate.h
new file mode 100644
index 0000000000000..cbccc3e91a8b2
--- /dev/null
+++ b/lldb/include/lldb/Utility/Predicate.h
@@ -0,0 +1,229 @@
+//===-- Predicate.h ---------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef liblldb_Predicate_h_
+#define liblldb_Predicate_h_
+
+#include <stdint.h>
+#include <time.h>
+
+#include <condition_variable>
+#include <mutex>
+
+#include "lldb/Utility/Timeout.h"
+#include "lldb/lldb-defines.h"
+
+//#define DB_PTHREAD_LOG_EVENTS
+
+/// Enumerations for broadcasting.
+namespace lldb_private {
+
+enum PredicateBroadcastType {
+  eBroadcastNever,   ///< No broadcast will be sent when the value is modified.
+  eBroadcastAlways,  ///< Always send a broadcast when the value is modified.
+  eBroadcastOnChange ///< Only broadcast if the value changes when the value is
+                     /// modified.
+};
+
+/// \class Predicate Predicate.h "lldb/Utility/Predicate.h"
+/// A C++ wrapper class for providing threaded access to a value of
+/// type T.
+///
+/// A templatized class that provides multi-threaded access to a value
+/// of type T. Threads can efficiently wait for bits within T to be set
+/// or reset, or wait for T to be set to be equal/not equal to a
+/// specified values.
+template <class T> class Predicate {
+public:
+  /// Default constructor.
+  ///
+  /// Initializes the mutex, condition and value with their default
+  /// constructors.
+  Predicate() : m_value(), m_mutex(), m_condition() {}
+
+  /// Construct with initial T value \a initial_value.
+  ///
+  /// Initializes the mutex and condition with their default
+  /// constructors, and initializes the value with \a initial_value.
+  ///
+  /// \param[in] initial_value
+  ///     The initial value for our T object.
+  Predicate(T initial_value)
+      : m_value(initial_value), m_mutex(), m_condition() {}
+
+  /// Destructor.
+  ///
+  /// Destroy the condition, mutex, and T objects.
+  ~Predicate() = default;
+
+  /// Value get accessor.
+  ///
+  /// Copies the current \a m_value in a thread safe manor and returns
+  /// the copied value.
+  ///
+  /// \return
+  ///     A copy of the current value.
+  T GetValue() const {
+    std::lock_guard<std::mutex> guard(m_mutex);
+    T value = m_value;
+    return value;
+  }
+
+  /// Value set accessor.
+  ///
+  /// Set the contained \a m_value to \a new_value in a thread safe
+  /// way and broadcast if needed.
+  ///
+  /// \param[in] value
+  ///     The new value to set.
+  ///
+  /// \param[in] broadcast_type
+  ///     A value indicating when and if to broadcast. See the
+  ///     PredicateBroadcastType enumeration for details.
+  ///
+  /// \see Predicate::Broadcast()
+  void SetValue(T value, PredicateBroadcastType broadcast_type) {
+    std::lock_guard<std::mutex> guard(m_mutex);
+#ifdef DB_PTHREAD_LOG_EVENTS
+    printf("%s (value = 0x%8.8x, broadcast_type = %i)\n", __FUNCTION__, value,
+           broadcast_type);
+#endif
+    const T old_value = m_value;
+    m_value = value;
+
+    Broadcast(old_value, broadcast_type);
+  }
+
+  /// Wait for Cond(m_value) to be true.
+  ///
+  /// Waits in a thread safe way for Cond(m_value) to be true. If Cond(m_value)
+  /// is already true, this function will return without waiting.
+  ///
+  /// It is possible for the value to be changed between the time the value is
+  /// set and the time the waiting thread wakes up. If the value no longer
+  /// satisfies the condition when the waiting thread wakes up, it will go back
+  /// into a wait state. It may be necessary for the calling code to use
+  /// additional thread synchronization methods to detect transitory states.
+  ///
+  /// \param[in] Cond
+  ///     The condition we want \a m_value satisfy.
+  ///
+  /// \param[in] timeout
+  ///     How long to wait for the condition to hold.
+  ///
+  /// \return
+  ///     m_value if Cond(m_value) is true, None otherwise (timeout occurred).
+  template <typename C>
+  llvm::Optional<T> WaitFor(C Cond, const Timeout<std::micro> &timeout) {
+    std::unique_lock<std::mutex> lock(m_mutex);
+    auto RealCond = [&] { return Cond(m_value); };
+    if (!timeout) {
+      m_condition.wait(lock, RealCond);
+      return m_value;
+    }
+    if (m_condition.wait_for(lock, *timeout, RealCond))
+      return m_value;
+    return llvm::None;
+  }
+  /// Wait for \a m_value to be equal to \a value.
+  ///
+  /// Waits in a thread safe way for \a m_value to be equal to \a
+  /// value. If \a m_value is already equal to \a value, this
+  /// function will return without waiting.
+  ///
+  /// It is possible for the value to be changed between the time
+  /// the value is set and the time the waiting thread wakes up.
+  /// If the value no longer matches the requested value when the
+  /// waiting thread wakes up, it will go back into a wait state.  It
+  /// may be necessary for the calling code to use additional thread
+  /// synchronization methods to detect transitory states.
+  ///
+  /// \param[in] value
+  ///     The value we want \a m_value to be equal to.
+  ///
+  /// \param[in] timeout
+  ///     How long to wait for the condition to hold.
+  ///
+  /// \return
+  ///     true if the \a m_value is equal to \a value, false otherwise (timeout
+  ///     occurred).
+  bool WaitForValueEqualTo(T value,
+                           const Timeout<std::micro> &timeout = llvm::None) {
+    return WaitFor([&value](T current) { return value == current; }, timeout) !=
+           llvm::None;
+  }
+
+  /// Wait for \a m_value to not be equal to \a value.
+  ///
+  /// Waits in a thread safe way for \a m_value to not be equal to \a
+  /// value. If \a m_value is already not equal to \a value, this
+  /// function will return without waiting.
+  ///
+  /// It is possible for the value to be changed between the time
+  /// the value is set and the time the waiting thread wakes up.
+  /// If the value is equal to the test value when the waiting thread
+  /// wakes up, it will go back into a wait state.  It may be
+  /// necessary for the calling code to use additional thread
+  /// synchronization methods to detect transitory states.
+  ///
+  /// \param[in] value
+  ///     The value we want \a m_value to not be equal to.
+  ///
+  /// \param[in] timeout
+  ///     How long to wait for the condition to hold.
+  ///
+  /// \return
+  ///     m_value if m_value != value, None otherwise (timeout occurred).
+  llvm::Optional<T>
+  WaitForValueNotEqualTo(T value,
+                         const Timeout<std::micro> &timeout = llvm::None) {
+    return WaitFor([&value](T current) { return value != current; }, timeout);
+  }
+
+protected:
+  // pthread condition and mutex variable to control access and allow blocking
+  // between the main thread and the spotlight index thread.
+  T m_value; ///< The templatized value T that we are protecting access to
+  mutable std::mutex m_mutex; ///< The mutex to use when accessing the data
+  std::condition_variable m_condition; ///< The pthread condition variable to
+                                       /// use for signaling that data available
+                                       /// or changed.
+
+private:
+  /// Broadcast if needed.
+  ///
+  /// Check to see if we need to broadcast to our condition variable
+  /// depending on the \a old_value and on the \a broadcast_type.
+  ///
+  /// If \a broadcast_type is eBroadcastNever, no broadcast will be
+  /// sent.
+  ///
+  /// If \a broadcast_type is eBroadcastAlways, the condition variable
+  /// will always be broadcast.
+  ///
+  /// If \a broadcast_type is eBroadcastOnChange, the condition
+  /// variable be broadcast if the owned value changes.
+  void Broadcast(T old_value, PredicateBroadcastType broadcast_type) {
+    bool broadcast =
+        (broadcast_type == eBroadcastAlways) ||
+        ((broadcast_type == eBroadcastOnChange) && old_value != m_value);
+#ifdef DB_PTHREAD_LOG_EVENTS
+    printf("%s (old_value = 0x%8.8x, broadcast_type = %i) m_value = 0x%8.8x, "
+           "broadcast = %u\n",
+           __FUNCTION__, old_value, broadcast_type, m_value, broadcast);
+#endif
+    if (broadcast)
+      m_condition.notify_all();
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(Predicate);
+};
+
+} // namespace lldb_private
+
+#endif // liblldb_Predicate_h_