LimitedHandleResource.h

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// Copyright (c) FIRST and other WPILib contributors.
// Open Source Software; you can modify and/or share it under the terms of
// the WPILib BSD license file in the root directory of this project.
 
#pragma once
 
#include <stdint.h>
 
#include <array>
#include <memory>
 
#include <wpi/mutex.h>
 
#include "HandlesInternal.h"
#include "hal/Types.h"
 
namespace hal {
 
/**
 * The LimitedHandleResource class is a way to track handles. This version
 * allows a limited number of handles that are allocated sequentially.
 *
 * @tparam THandle The Handle Type (Must be typedefed from HAL_Handle)
 * @tparam TStruct The struct type held by this resource
 * @tparam size The number of resources allowed to be allocated
 * @tparam enumValue The type value stored in the handle
 *
 */
template <typename THandle, typename TStruct, int16_t size,
          HAL_HandleEnum enumValue>
class LimitedHandleResource : public HandleBase {
  friend class LimitedHandleResourceTest;
 
 public:
  LimitedHandleResource() = default;
  LimitedHandleResource(const LimitedHandleResource&) = delete;
  LimitedHandleResource& operator=(const LimitedHandleResource&) = delete;
 
  THandle Allocate();
  int16_t GetIndex(THandle handle) {
    return getHandleTypedIndex(handle, enumValue, m_version);
  }
  std::shared_ptr<TStruct> Get(THandle handle);
  void Free(THandle handle);
  void ResetHandles() override;
 
 private:
  std::array<std::shared_ptr<TStruct>, size> m_structures;
  std::array<wpi::mutex, size> m_handleMutexes;
  wpi::mutex m_allocateMutex;
};
 
template <typename THandle, typename TStruct, int16_t size,
          HAL_HandleEnum enumValue>
THandle LimitedHandleResource<THandle, TStruct, size, enumValue>::Allocate() {
  // globally lock to loop through indices
  std::scoped_lock lock(m_allocateMutex);
  for (int16_t i = 0; i < size; i++) {
    if (m_structures[i] == nullptr) {
      // if a false index is found, grab its specific mutex
      // and allocate it.
      std::scoped_lock lock(m_handleMutexes[i]);
      m_structures[i] = std::make_shared<TStruct>();
      return static_cast<THandle>(createHandle(i, enumValue, m_version));
    }
  }
  return HAL_kInvalidHandle;
}
 
template <typename THandle, typename TStruct, int16_t size,
          HAL_HandleEnum enumValue>
std::shared_ptr<TStruct>
LimitedHandleResource<THandle, TStruct, size, enumValue>::Get(THandle handle) {
  // get handle index, and fail early if index out of range or wrong handle
  int16_t index = GetIndex(handle);
  if (index < 0 || index >= size) {
    return nullptr;
  }
  std::scoped_lock lock(m_handleMutexes[index]);
  // return structure. Null will propagate correctly, so no need to manually
  // check.
  return m_structures[index];
}
 
template <typename THandle, typename TStruct, int16_t size,
          HAL_HandleEnum enumValue>
void LimitedHandleResource<THandle, TStruct, size, enumValue>::Free(
    THandle handle) {
  // get handle index, and fail early if index out of range or wrong handle
  int16_t index = GetIndex(handle);
  if (index < 0 || index >= size) {
    return;
  }
  // lock and deallocated handle
  std::scoped_lock allocateLock(m_allocateMutex);
  std::scoped_lock handleLock(m_handleMutexes[index]);
  m_structures[index].reset();
}
 
template <typename THandle, typename TStruct, int16_t size,
          HAL_HandleEnum enumValue>
void LimitedHandleResource<THandle, TStruct, size, enumValue>::ResetHandles() {
  {
    std::scoped_lock allocateLock(m_allocateMutex);
    for (int i = 0; i < size; i++) {
      std::scoped_lock handleLock(m_handleMutexes[i]);
      m_structures[i].reset();
    }
  }
  HandleBase::ResetHandles();
}
}  // namespace hal