Add a push_back() + truncate benchmark test

Author: DavisVaughan

cpp11test/R/cpp11.R

@@ -231,3 +231,7 @@ test_destruction_inner <- function() {
 test_destruction_outer <- function() {
   invisible(.Call(`_cpp11test_test_destruction_outer`))
 }
+
+cpp11_push_and_truncate_ <- function(size_sexp) {
+  .Call(`_cpp11test_cpp11_push_and_truncate_`, size_sexp)
+}

cpp11test/bench/truncate.R

@@ -0,0 +1,17 @@
+pkgload::load_all("cpp11test")
+
+bench::press(len = as.integer(10 ^ (0:6)),
+  {
+    bench::mark(
+      cpp11_push_and_truncate_(len),
+      min_iterations = 100
+    )
+  }
+)
+
+# Longer benchmark, lots of gc
+len <- as.integer(10 ^ 7)
+bench::mark(
+  cpp11_push_and_truncate_(len),
+  min_iterations = 200
+)

cpp11test/src/cpp11.cpp

@@ -438,6 +438,13 @@ extern "C" SEXP _cpp11test_test_destruction_outer() {
     return R_NilValue;
   END_CPP11
 }
+// truncate.cpp
+SEXP cpp11_push_and_truncate_(SEXP size_sexp);
+extern "C" SEXP _cpp11test_cpp11_push_and_truncate_(SEXP size_sexp) {
+  BEGIN_CPP11
+    return cpp11::as_sexp(cpp11_push_and_truncate_(cpp11::as_cpp<cpp11::decay_t<SEXP>>(size_sexp)));
+  END_CPP11
+}
 
 extern "C" {
 /* .Call calls */
@@ -447,6 +454,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"_cpp11test_col_sums",                 (DL_FUNC) &_cpp11test_col_sums,                 1},
     {"_cpp11test_cpp11_add_vec_for_",       (DL_FUNC) &_cpp11test_cpp11_add_vec_for_,       2},
     {"_cpp11test_cpp11_insert_",            (DL_FUNC) &_cpp11test_cpp11_insert_,            1},
+    {"_cpp11test_cpp11_push_and_truncate_", (DL_FUNC) &_cpp11test_cpp11_push_and_truncate_, 1},
     {"_cpp11test_cpp11_release_",           (DL_FUNC) &_cpp11test_cpp11_release_,           1},
     {"_cpp11test_cpp11_safe_",              (DL_FUNC) &_cpp11test_cpp11_safe_,              1},
     {"_cpp11test_data_frame_",              (DL_FUNC) &_cpp11test_data_frame_,              0},

cpp11test/src/truncate.cpp

@@ -0,0 +1,19 @@
+#include "cpp11/doubles.hpp"
+
+[[cpp11::register]] SEXP cpp11_push_and_truncate_(SEXP size_sexp) {
+  R_xlen_t size = INTEGER(size_sexp)[0];
+
+  cpp11::writable::doubles out(size);
+
+  // Fill it
+  for (R_xlen_t i = 0; i < size; ++i) {
+    out.push_back(0);
+  }
+
+  // Push 1 more past the existing capacity,
+  // doubling the capacity
+  out.push_back(0);
+
+  // Truncate back to `size + 1` size and return result.
+  return SEXP(out);
+}