Implements Better Error Messages from the HAL (#172)

* Makes the HAL provide a better error message for certain things.

* Makes Java error messages better

* Updates C++ errors.

* Moves handles header folder to HAL directory

hal/include/HAL/handles/DigitalHandleResource.h

@@ -0,0 +1,107 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2016. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <stdint.h>
+
+#include <memory>
+#include <vector>
+
+#include "HAL/Errors.h"
+#include "HAL/Types.h"
+#include "HAL/cpp/priority_mutex.h"
+#include "HAL/handles/HandlesInternal.h"
+
+namespace hal {
+
+/**
+ * The DigitalHandleResource class is a way to track handles. This version
+ * allows a limited number of handles that are allocated by index.
+ * The enum value is seperate, as 2 enum values are allowed per handle
+ * Because they are allocated by index, each individual index holds its own
+ * mutex, which reduces contention heavily.]
+ *
+ * @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
+ *
+ */
+template <typename THandle, typename TStruct, int16_t size>
+class DigitalHandleResource {
+  friend class DigitalHandleResourceTest;
+
+ public:
+  DigitalHandleResource(const DigitalHandleResource&) = delete;
+  DigitalHandleResource operator=(const DigitalHandleResource&) = delete;
+  DigitalHandleResource();
+  ~DigitalHandleResource();
+  THandle Allocate(int16_t index, HAL_HandleEnum enumValue, int32_t* status);
+  std::shared_ptr<TStruct> Get(THandle handle, HAL_HandleEnum enumValue);
+  void Free(THandle handle, HAL_HandleEnum enumValue);
+
+ private:
+  // Dynamic array to shrink HAL file size.
+  std::shared_ptr<TStruct>* m_structures;
+  priority_mutex* m_handleMutexes;
+};
+
+template <typename THandle, typename TStruct, int16_t size>
+DigitalHandleResource<THandle, TStruct, size>::DigitalHandleResource() {
+  m_structures = new std::shared_ptr<TStruct>[size];
+  m_handleMutexes = new priority_mutex[size];
+}
+
+template <typename THandle, typename TStruct, int16_t size>
+DigitalHandleResource<THandle, TStruct, size>::~DigitalHandleResource() {
+  delete[] m_structures;
+  delete[] m_handleMutexes;
+}
+
+template <typename THandle, typename TStruct, int16_t size>
+THandle DigitalHandleResource<THandle, TStruct, size>::Allocate(
+    int16_t index, HAL_HandleEnum enumValue, int32_t* status) {
+  // don't aquire the lock if we can fail early.
+  if (index < 0 || index >= size) {
+    *status = RESOURCE_OUT_OF_RANGE;
+    return HAL_kInvalidHandle;
+  }
+  std::lock_guard<priority_mutex> sync(m_handleMutexes[index]);
+  // check for allocation, otherwise allocate and return a valid handle
+  if (m_structures[index] != nullptr) {
+    *status = RESOURCE_IS_ALLOCATED;
+    return HAL_kInvalidHandle;
+  }
+  m_structures[index] = std::make_shared<TStruct>();
+  return (THandle)hal::createHandle(index, enumValue);
+}
+
+template <typename THandle, typename TStruct, int16_t size>
+std::shared_ptr<TStruct> DigitalHandleResource<THandle, TStruct, size>::Get(
+    THandle handle, HAL_HandleEnum enumValue) {
+  // get handle index, and fail early if index out of range or wrong handle
+  int16_t index = getHandleTypedIndex(handle, enumValue);
+  if (index < 0 || index >= size) {
+    return nullptr;
+  }
+  std::lock_guard<priority_mutex> sync(m_handleMutexes[index]);
+  // return structure. Null will propogate correctly, so no need to manually
+  // check.
+  return m_structures[index];
+}
+
+template <typename THandle, typename TStruct, int16_t size>
+void DigitalHandleResource<THandle, TStruct, size>::Free(
+    THandle handle, HAL_HandleEnum enumValue) {
+  // get handle index, and fail early if index out of range or wrong handle
+  int16_t index = getHandleTypedIndex(handle, enumValue);
+  if (index < 0 || index >= size) return;
+  // lock and deallocated handle
+  std::lock_guard<priority_mutex> sync(m_handleMutexes[index]);
+  m_structures[index].reset();
+}
+}  // namespace hal