broadcast.R

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

# S4 class representing Broadcast variables

# Hidden environment that holds values for broadcast variables
# This will not be serialized / shipped by default
.broadcastNames <- new.env()
.broadcastValues <- new.env()
.broadcastIdToName <- new.env()

# S4 class that represents a Broadcast variable
#
# Broadcast variables can be created using the broadcast
# function from a \code{SparkContext}.
#
# @rdname broadcast-class
# @seealso broadcast
#
# @param id Id of the backing Spark broadcast variable
setClass("Broadcast", slots = list(id = "character"))

# @rdname broadcast-class
# @param value Value of the broadcast variable
# @param jBroadcastRef reference to the backing Java broadcast object
# @param objName name of broadcasted object
Broadcast <- function(id, value, jBroadcastRef, objName) {
  .broadcastValues[[id]] <- value
  .broadcastNames[[as.character(objName)]] <- jBroadcastRef
  .broadcastIdToName[[id]] <- as.character(objName)
  new("Broadcast", id = id)
}

# @description
# \code{value} can be used to get the value of a broadcast variable inside
# a distributed function.
#
# @param bcast The broadcast variable to get
# @rdname broadcast
setMethod("value",
          signature(bcast = "Broadcast"),
          function(bcast) {
            if (exists(bcast@id, envir = .broadcastValues)) {
              get(bcast@id, envir = .broadcastValues)
            } else {
              NULL
            }
          })

# Internal function to set values of a broadcast variable.
#
# This function is used internally by Spark to set the value of a broadcast
# variable on workers. Not intended for use outside the package.
#
# @rdname broadcast-internal
# @seealso broadcast, value

# @param bcastId The id of broadcast variable to set
# @param value The value to be set
setBroadcastValue <- function(bcastId, value) {
  bcastIdStr <- as.character(bcastId)
  .broadcastValues[[bcastIdStr]] <- value
}

# Helper function to clear the list of broadcast variables we know about
# Should be called when the SparkR JVM backend is shutdown
clearBroadcastVariables <- function() {
  bcasts <- ls(.broadcastNames)
  rm(list = bcasts, envir = .broadcastNames)
}