allwpilib/wpilibc/wpilibC++/src/Resource.cpp

/*----------------------------------------------------------------------------*/
/* Copyright (c) FIRST 2008. 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 $(WIND_BASE)/WPILib.  */
/*----------------------------------------------------------------------------*/

#include "Resource.h"
#include "WPIErrors.h"
#include "ErrorBase.h"

ReentrantSemaphore Resource::m_createLock;

/**
 * Allocate storage for a new instance of Resource.
 * Allocate a bool array of values that will get initialized to indicate that no
 * resources
 * have been allocated yet. The indicies of the resources are [0 .. elements -
 * 1].
 */
Resource::Resource(uint32_t elements) {
  Synchronized sync(m_createLock);
  m_size = elements;
  m_isAllocated = new bool[m_size];
  for (uint32_t i = 0; i < m_size; i++) {
    m_isAllocated[i] = false;
  }
}

/**
 * Factory method to create a Resource allocation-tracker *if* needed.
 *
 * @param r -- address of the caller's Resource pointer. If *r == NULL, this
 *    will construct a Resource and make *r point to it. If *r != NULL, i.e.
 *    the caller already has a Resource instance, this won't do anything.
 * @param elements -- the number of elements for this Resource allocator to
 *    track, that is, it will allocate resource numbers in the range
 *    [0 .. elements - 1].
 */
/*static*/ void Resource::CreateResourceObject(Resource **r,
                                               uint32_t elements) {
  Synchronized sync(m_createLock);
  if (*r == NULL) {
    *r = new Resource(elements);
  }
}

/**
 * Delete the allocated array or resources.
 * This happens when the module is unloaded (provided it was statically
 * allocated).
 */
Resource::~Resource() { delete[] m_isAllocated; }

/**
 * Allocate a resource.
 * When a resource is requested, mark it allocated. In this case, a free
 * resource value
 * within the range is located and returned after it is marked allocated.
 */
uint32_t Resource::Allocate(const char *resourceDesc) {
  Synchronized sync(m_allocateLock);
  for (uint32_t i = 0; i < m_size; i++) {
    if (!m_isAllocated[i]) {
      m_isAllocated[i] = true;
      return i;
    }
  }
  wpi_setWPIErrorWithContext(NoAvailableResources, resourceDesc);
  return ~0ul;
}

/**
 * Allocate a specific resource value.
 * The user requests a specific resource value, i.e. channel number and it is
 * verified
 * unallocated, then returned.
 */
uint32_t Resource::Allocate(uint32_t index, const char *resourceDesc) {
  Synchronized sync(m_allocateLock);
  if (index >= m_size) {
    wpi_setWPIErrorWithContext(ChannelIndexOutOfRange, resourceDesc);
    return ~0ul;
  }
  if (m_isAllocated[index]) {
    wpi_setWPIErrorWithContext(ResourceAlreadyAllocated, resourceDesc);
    return ~0ul;
  }
  m_isAllocated[index] = true;
  return index;
}

/**
 * Free an allocated resource.
 * After a resource is no longer needed, for example a destructor is called for
 * a channel assignment
 * class, Free will release the resource value so it can be reused somewhere
 * else in the program.
 */
void Resource::Free(uint32_t index) {
  Synchronized sync(m_allocateLock);
  if (index == ~0ul) return;
  if (index >= m_size) {
    wpi_setWPIError(NotAllocated);
    return;
  }
  if (!m_isAllocated[index]) {
    wpi_setWPIError(NotAllocated);
    return;
  }
  m_isAllocated[index] = false;
}