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spark core 2.0 MemoryPool 源代码分析

冯流觞
2023-12-01

MemoryPool管理大小可调的内存区域。 这个类被MemoryManager作为内部使用。

参数是一个MemoryManager实例的一个锁,用于同步。我们特意擦除类型信息,变为Object类型,避免程序错误,因为这个对象应当仅作为同步用。

_poolSize 变量保存当前内存区域的大小。memoryUsed 函数用于已经使用的内存,在子类实现。

/**
 * Manages bookkeeping for an adjustable-sized region of memory. This class is internal to
 * the [[MemoryManager]]. See subclasses for more details.
 *
 * @param lock a [[MemoryManager]] instance, used for synchronization. We purposely erase the type
 *             to `Object` to avoid programming errors, since this object should only be used for
 *             synchronization purposes.
 */
private[memory] abstract class MemoryPool(lock: Object) {

  @GuardedBy("lock")
  private[this] var _poolSize: Long = 0

  /**
   * Returns the current size of the pool, in bytes.
   */
  final def poolSize: Long = lock.synchronized {
    _poolSize
  }

  /**
   * Returns the amount of free memory in the pool, in bytes.
   */
  final def memoryFree: Long = lock.synchronized {
    _poolSize - memoryUsed
  }

  /**
   * Expands the pool by `delta` bytes.
   */
  final def incrementPoolSize(delta: Long): Unit = lock.synchronized {
    require(delta >= 0)
    _poolSize += delta
  }

  /**
   * Shrinks the pool by `delta` bytes.
   */
  final def decrementPoolSize(delta: Long): Unit = lock.synchronized {
    require(delta >= 0)
    require(delta <= _poolSize)
    require(_poolSize - delta >= memoryUsed)
    _poolSize -= delta
  }

  /**
   * Returns the amount of used memory in this pool (in bytes).
   */
  def memoryUsed: Long
}


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