From 824f64845c27f4b305430fc1049339af32561960 Mon Sep 17 00:00:00 2001
From: Nic Crane <thisisnic@gmail.com>
Date: Mon, 13 Jul 2026 08:09:05 +0000
Subject: [PATCH] Delay parallel tasks

---
 r/src/RTasks.cpp     | 8 ++++++--
 r/src/r_task_group.h | 1 +
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/r/src/RTasks.cpp b/r/src/RTasks.cpp
index 5d3a749b6d34..09c5dd630f8e 100644
--- a/r/src/RTasks.cpp
+++ b/r/src/RTasks.cpp
@@ -40,8 +40,11 @@ Status RTasks::Finish() {
     }
   }
 
-  // then wait for the parallel tasks to finish
+  // submit the delayed parallel tasks and wait for them to finish
   if (use_threads_) {
+    for (auto& task : delayed_parallel_tasks_) {
+      parallel_tasks_->Append(std::move(task));
+    }
     status &= parallel_tasks_->Finish();
   }
 
@@ -50,7 +53,7 @@ Status RTasks::Finish() {
 
 void RTasks::Append(bool parallel, RTasks::Task&& task) {
   if (parallel && use_threads_) {
-    parallel_tasks_->Append(std::move(task));
+    delayed_parallel_tasks_.push_back(std::move(task));
   } else {
     delayed_serial_tasks_.push_back(std::move(task));
   }
@@ -58,6 +61,7 @@ void RTasks::Append(bool parallel, RTasks::Task&& task) {
 
 void RTasks::Reset() {
   delayed_serial_tasks_.clear();
+  delayed_parallel_tasks_.clear();
 
   stop_source_.Reset();
   if (use_threads_) {
diff --git a/r/src/r_task_group.h b/r/src/r_task_group.h
index e1c298b27fc3..43c040b9a7c8 100644
--- a/r/src/r_task_group.h
+++ b/r/src/r_task_group.h
@@ -45,6 +45,7 @@ class RTasks {
   StopSource stop_source_;
   std::shared_ptr<arrow::internal::TaskGroup> parallel_tasks_;
   std::vector<Task> delayed_serial_tasks_;
+  std::vector<Task> delayed_parallel_tasks_;
 };
 
 }  // namespace r