ARROW-8409: [R] Add R wrappers for getting and setting global CPU thr…

…ead pool capacity

I needed this while running some benchmarks.

Closes #6906 from wesm/ARROW-8409

Lead-authored-by: Wes McKinney <wesm+git@apache.org>
Co-authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Neal Richardson <neal.p.richardson@gmail.com>

r/DESCRIPTION

@@ -61,6 +61,7 @@ Collate:
     'io.R'
     'compression.R'
     'compute.R'
+    'config.R'
     'csv.R'
     'dataset.R'
     'filesystem.R'

r/NAMESPACE

@@ -139,6 +139,7 @@ export(cast_options)
 export(chunked_array)
 export(codec_is_available)
 export(contains)
+export(cpu_count)
 export(dataset_factory)
 export(date32)
 export(date64)
@@ -184,6 +185,7 @@ export(read_table)
 export(read_tsv_arrow)
 export(record_batch)
 export(schema)
+export(set_cpu_count)
 export(starts_with)
 export(string)
 export(struct)

r/R/config.R

@@ -0,0 +1,30 @@
+# 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.
+
+#' Manage the global CPU thread pool in libarrow
+#'
+#' @export
+cpu_count <- function() {
+  GetCpuThreadPoolCapacity()
+}
+
+#' @rdname cpu_count
+#' @param num_threads integer: New number of threads for thread pool
+#' @export
+set_cpu_count <- function(num_threads) {
+  SetCpuThreadPoolCapacity(as.integer(num_threads))
+}

r/_pkgdown.yml

@@ -132,6 +132,9 @@ reference:
   - FileInfo
   - FileStats
   - FileSelector
+- title: Configuration
+  contents:
+  - cpu_count
 - title: Installation helpers
   contents:
   - arrow_available

r/tests/testthat/test-thread-pool.R

@@ -15,12 +15,12 @@
 # specific language governing permissions and limitations
 # under the License.
 
-context("CpuThreadPoolCapacity")
+context("Global Thread Pool")
 
 test_that("can set/get cpu thread pool capacity", {
-  old <- GetCpuThreadPoolCapacity()
-  SetCpuThreadPoolCapacity(19L)
-  expect_equal(GetCpuThreadPoolCapacity(), 19L)
-  SetCpuThreadPoolCapacity(old)
-  expect_equal(GetCpuThreadPoolCapacity(), old)
+  old <- cpu_count()
+  set_cpu_count(19)
+  expect_equal(cpu_count(), 19L)
+  set_cpu_count(old)
+  expect_equal(cpu_count(), old)
 })