1 files changed, 40 insertions, 0 deletions
diff --git a/spec/support/helpers/concurrent_helpers.rb b/spec/support/helpers/concurrent_helpers.rb
new file mode 100644
index 00000000000..4eecc2133e7
--- /dev/null
+++ b/spec/support/helpers/concurrent_helpers.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module ConcurrentHelpers
+  Cancelled = Class.new(StandardError)
+
+  # To test for contention, we may need to run some actions in parallel. This
+  # helper takes an array of blocks and schedules them all on different threads
+  # in a fixed-size thread pool.
+  #
+  # @param [Array[Proc]] blocks
+  # @param [Integer] task_wait_time: time to wait for each task (upper bound on
+  #                                  reasonable task execution time)
+  # @param [Integer] max_concurrency: maximum number of tasks to run at once
+  #
+  def run_parallel(blocks, task_wait_time: 20.seconds, max_concurrency: Concurrent.processor_count - 1)
+    thread_pool = Concurrent::FixedThreadPool.new(
+      [2, max_concurrency].max, { max_queue: blocks.size }
+    )
+    opts = { executor: thread_pool }
+
+    error = Concurrent::MVar.new
+
+    blocks.map { |block| Concurrent::Future.execute(opts, &block) }.each do |future|
+      future.wait(task_wait_time)
+
+      if future.complete?
+        error.put(future.reason) if future.reason && error.empty?
+      else
+        future.cancel
+        error.put(Cancelled.new) if error.empty?
+      end
+    end
+
+    raise error.take if error.full?
+  ensure
+    thread_pool.shutdown
+    thread_pool.wait_for_termination(10)
+    thread_pool.kill if thread_pool.running?
+  end
+end