Y24-120 Part-2 Bug taken link error when creating sequencing batches

app/models/asset_link.rb

@@ -76,4 +76,81 @@
       end
     end
   end
+
+  # Creates an edge between the ancestor and descendant nodes using save.
+  #
+  # This method first attempts to find an existing link between the ancestor
+  # and descendant. If no link is found, it builds a new edge and saves it.
+  # If a link is found, it makes the link an edge and saves it.
+  #
+  # This method is overridden to handle race conditions in finding an
+  # existing link and has_duplicates validation. It also assumes that there
+  # is a unique-together index on ancestor_id and descendant_id columns.
+  #
+  # @param ancestor [Dag::Standard::EndPoint] The ancestor node.
+  # @param descendant [Dag::Standard::EndPoint] The descendant node.
+  # @return [Boolean] Returns true if the edge is successfully created or
+  #   already exists, false otherwise.
+  # @raise [ActiveRecord::RecordNotUnique] Re-raises any exception if it is
+  #   not a constraint violation that involves ancestor_id and descendant_id
+  #   columns.
+  def self.create_edge(ancestor, descendant)
+    # Two processes try to find an existing link.
+    link = find_link(ancestor, descendant)
+    # Either or both may find no link and try to create a new edge.
+    if link.nil?
+      edge = build_edge(ancestor, descendant)
+      result = save_edge_or_handle_error(edge)
+      return result unless result.nil? # Bubble up.
+      # Losing process finds the edge created by the winning process.
+      link = find_link(ancestor, descendant)
+    end
+
+    return if link.nil?
+
+    link.make_direct
+    link.changed? ? link.save : true
+  end
+
+  # Saves the edge between the ancestor and descendant nodes or handles errors.
+  #
+  # @param edge [AssetLink] The edge object containing the errors.
+  # @return [Boolean] Returns true if the edge is successfully saved,
+  #   nil if the error is unique validation or constraint violation,
+  #   false if the error is another validation error.
+  # @raise [ActiveRecord::RecordNotUnique] Re-raises an exception if the
+  #   exception caught is not a unique constraint violation.
+  def self.save_edge_or_handle_error(edge)
+    # Winning process successfully saves the edge (direct link).
+    return true if edge.save
+    # has_duplicate validation may see it for the losing process before
+    # hitting the DB.
+    return false unless unique_validation_error?(edge) # Bubble up.
+    edge.errors.clear # Clear all errors and use the existing link.
+  rescue ActiveRecord::RecordNotUnique => e
+    # Unique constraint violation is triggered for the losing process after
+    # hitting the DB.
+    raise unless unique_violation_error?(edge, e) # Bubble up.
+  end
+
+  # Checks if the validation error includes a specific message indicating a
+  # unique link already exists.
+  #
+  # @param edge [AssetLink] The edge object containing the errors.
+  # @return [Boolean] Returns true if the errors include the message "Link
+  #   already exists between these points", false otherwise.
+  def self.unique_validation_error?(edge)
+    edge.errors[:base].include?('Link already exists between these points')
+  end
+
+  # Checks if the unique constraint violation involves the specified columns.
+  #
+  # @param edge [AssetLink] The edge object containing the column names.
+  # @param exception [ActiveRecord::RecordNotUnique] The exception raised due
+  #   to the unique constraint violation.
+  # @return [Boolean] Returns true if the exception message includes both the
+  #   ancestor and descendant column names, false otherwise.
+  def self.unique_violation_error?(edge, exception)
+    [edge.ancestor_id_column_name, edge.descendant_id_column_name].all? { |col| exception.message.include?(col) }
+  end
 end

db/migrate/20240912000109_add_unique_index_to_asset_links.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+# This migration adds a unique-together index on ancestor_id and descendant_id
+# in order to prevent duplicate links between the same ancestor and descendant
+# labware.
+#
+# Before this migration, the database allowed duplicate asset_links between the
+# same ancestor and descendant labware. Therefore, the migration will fail if
+# there are any duplicate links in the database. To fix this, they must be
+# removed before running the migration using the rake task:
+#
+# bundle exec rake 'support:remove_duplicate_asset_links[csv_file_path]'
+#
+# The rake task will write the removed records into a CSV file that can be used
+# for auditing purposes.
+#
+# Note that the column names in the index name below is used for finding the
+# reason of the database unique constraint violation by the AssetLink model.
+class AddUniqueIndexToAssetLinks < ActiveRecord::Migration[6.1]
+  def change
+    add_index :asset_links,
+              %i[ancestor_id descendant_id],
+              unique: true,
+              name: 'index_asset_links_on_ancestor_id_and_descendant_id'
+  end
+end

db/schema.rb

@@ -115,6 +115,7 @@
     t.integer "count"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["ancestor_id", "descendant_id"], name: "index_asset_links_on_ancestor_id_and_descendant_id", unique: true
     t.index ["ancestor_id", "direct"], name: "index_asset_links_on_ancestor_id_and_direct"
     t.index ["descendant_id", "direct"], name: "index_asset_links_on_descendant_id_and_direct"
   end

spec/models/asset_links_create_edge_spec.rb

@@ -0,0 +1,280 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe AssetLink, type: :model do
+  # rubocop:disable RSpec/InstanceVariable,Metrics/MethodLength,RSpec/ExampleLength,RSpec/MultipleExpectations
+  # Test the overridden create_edge class method.
+  describe '.create_edge' do
+    # Wait for child processes to finish.
+    #
+    # @param pids [Array<Integer>] Process IDs
+    # @raise [Timeout::Error] If a child process does not finish within 10 seconds.
+    # @return [void]
+    def wait_for_child_processes(pids)
+      exits = []
+      pids
+        .each
+        .with_index(1) do |pid, index|
+          Timeout.timeout(10) do
+            _pid, status = Process.wait2(pid)
+            exits << status.exitstatus
+          end
+        rescue Timeout::Error
+          raise StandardError, "parent: Timeout waiting for child#{index} to finish"
+        end
+
+      expect(exits).to eq([0, 0])
+    end
+
+    # Delete created records.
+    after do
+      @ancestor&.destroy
+      @descendant&.destroy
+      @edge&.destroy
+    end
+
+    it 'handles race condition at find_link' do
+      # In this example, the first and second processes are forked from the
+      # main process and they are in race condition to find an existing link
+      # between the ancestor and descendant and create an edge if no link is
+      # found. Both first and second processes finds no link, but the second
+      # process creates the edge first. The first also tries to create the
+      # edge based on the result of the find_link method. Only one link must
+      # be created.
+
+      # Parent
+      ActiveRecord::Base.connection.reconnect!
+      @ancestor = ancestor = create(:labware)
+      @descendant = descendant = create(:labware)
+      ActiveRecord::Base.connection.commit_db_transaction
+
+      # Create a duplex pipe for IPC.
+      first_socket, second_socket = UNIXSocket.pair
+
+      # First child
+      pid1 =
+        fork do
+          ActiveRecord::Base.connection.reconnect!
+
+          find_link_call_count = 0
+          # Patch find_link method
+          allow(described_class).to receive(:find_link).and_wrap_original do |m, *args|
+            find_link_call_count += 1
+            link = m.call(*args)
+            if find_link_call_count == 1
+              expect(link).to be_nil # No link found
+              message = 'paused'
+              first_socket.send(message, 0) # Notify the second child
+              message = 'child1: Timeout waiting for resume message'
+              raise StandardError, message unless first_socket.wait_readable(10)
+              message = 'resume' # Wait for the second child to create the edge
+              first_socket.recv(message.size)
+            elsif find_link_call_count == 2
+              expect(link).not_to be_nil # Found one now
+            end
+            link
+          end
+          described_class.create_edge(ancestor, descendant)
+
+          ActiveRecord::Base.connection.close
+        end
+
+      # Second child
+      pid2 =
+        fork do
+          ActiveRecord::Base.connection.reconnect!
+          message = 'child2: Timeout waiting for paused message'
+          raise StandardError, message unless second_socket.wait_readable(10)
+          message = 'paused' # Wait for the first child to call find_link
+          second_socket.recv(message.size)
+          described_class.create_edge(ancestor, descendant)
+          message = 'resume' # Notify the first child
+          second_socket.send(message, 0)
+          ActiveRecord::Base.connection.close
+        end
+
+      # Parent
+      wait_for_child_processes([pid1, pid2])
+
+      expect(described_class.where(ancestor:, descendant:).count).to eq(1)
+      @edge = edge = described_class.last
+      expect(edge.ancestor).to eq(ancestor)
+      expect(edge.descendant).to eq(descendant)
+      expect(edge.direct).to be_truthy
+      expect(edge.count).to eq(1)
+
+      ActiveRecord::Base.connection.close
+    end
+
+    it 'handles unique validation error' do
+      # In this example, the first and second processes are forked from the
+      # main process. Neither of them finds and existing link between the
+      # ancestor and descendant. Both try to create the edge. One of them
+      # succeeds and the other one fails due to the has_duplicates validation.
+      # Failing process should use the existing link.
+
+      # Parent
+      ActiveRecord::Base.connection.reconnect!
+      @ancestor = ancestor = create(:labware)
+      @descendant = descendant = create(:labware)
+      ActiveRecord::Base.connection.commit_db_transaction
+
+      # Create a duplex pipe for IPC.
+      first_socket, second_socket = UNIXSocket.pair
+
+      # First child
+      pid1 =
+        fork do
+          ActiveRecord::Base.connection.reconnect!
+          find_link_call_count = 0
+          allow(described_class).to receive(:find_link).and_wrap_original do |m, *args|
+            find_link_call_count += 1
+            link = m.call(*args)
+            if find_link_call_count == 1
+              expect(link).to be_nil # No link found
+              message = 'paused' # Notify the second child
+              first_socket.send(message, 0)
+              message = 'child1: Timeout waiting for resume message'
+              raise StandardError, message unless first_socket.wait_readable(10)
+              message = 'resume' # Wait for the second child to create the edge
+              first_socket.recv(message.size)
+            end
+            link
+          end
+
+          # Patch unique_validation_error? method
+          unique_validation_error_return_value = nil
+          allow(described_class).to receive(:unique_validation_error?).and_wrap_original do |m, *args|
+            unique_validation_error_return_value = m.call(*args)
+          end
+
+          result = described_class.create_edge(ancestor, descendant)
+          expect(result).to be_truthy
+          expect(described_class).to have_received(:unique_validation_error?)
+          expect(unique_validation_error_return_value).to be_truthy
+
+          ActiveRecord::Base.connection.close
+        end
+
+      # Second child
+      pid2 =
+        fork do
+          ActiveRecord::Base.connection.reconnect!
+          message = 'child2: Timeout waiting for paused message'
+          raise StandardError, message unless second_socket.wait_readable(10)
+          message = 'paused' # Wait for the first child to call find_link
+          second_socket.recv(message.size)
+          described_class.create_edge(ancestor, descendant)
+          message = 'resume' # Notify the first child
+          second_socket.send(message, 0)
+          ActiveRecord::Base.connection.close
+        end
+
+      # Parent
+      wait_for_child_processes([pid1, pid2])
+
+      expect(described_class.where(ancestor:, descendant:).count).to eq(1)
+      @edge = edge = described_class.last
+      expect(edge.ancestor).to eq(ancestor)
+      expect(edge.descendant).to eq(descendant)
+      expect(edge.direct).to be_truthy
+      expect(edge.count).to eq(1)
+    end
+
+    it 'handles unique constraint violation' do
+      # In this example, the first and second processes are forked from the
+      # main process. Neither of them finds and existing link between the
+      # ancestor and descendant. Both try to create the edge. One of them
+      # succeeds and the other one fails due to the database unique constraint
+      # violation. Failing process should use the existing link.
+
+      # Parent
+      ActiveRecord::Base.connection.reconnect!
+      @ancestor = ancestor = create(:labware)
+      @descendant = descendant = create(:labware)
+      ActiveRecord::Base.connection.commit_db_transaction
+
+      # Create a duplex pipe for IPC.
+      first_socket, second_socket = UNIXSocket.pair
+
+      # First child
+      pid1 =
+        fork do
+          ActiveRecord::Base.connection.reconnect!
+          find_link_call_count = 0
+          allow(described_class).to receive(:find_link).and_wrap_original do |m, *args|
+            find_link_call_count += 1
+            link = m.call(*args)
+            if find_link_call_count == 1
+              expect(link).to be_nil
+              message = 'paused' # Notify the second child
+              first_socket.send(message, 0)
+              message = 'child1: Timeout waiting for resume message'
+              raise StandardError, message unless first_socket.wait_readable(10)
+              message = 'resume' # Wait for the second child to create the edge
+              first_socket.recv(message.size)
+            end
+            link
+          end
+
+          # Patch has_duplicates method.
+          # rubocop:disable RSpec/AnyInstance
+          allow_any_instance_of(Dag::CreateCorrectnessValidator).to receive(:has_duplicates).and_return(false)
+          # rubocop:enable RSpec/AnyInstance
+
+          # Patch save_edge_or_handle_error method.
+          allow(described_class).to receive(:save_edge_or_handle_error).and_wrap_original do |method, *args|
+            edge = args[0]
+            message =
+              "Duplicate entry '#{ancestor.id}-#{descendant.id}' " \
+                "for key 'index_asset_links_on_ancestor_id_and_descendant_id'"
+            exception = ActiveRecord::RecordNotUnique.new(message)
+            allow(edge).to receive(:save).and_raise(exception)
+
+            method.call(*args)
+          end
+
+          # Patch unique_violation_error? method.
+          unique_violation_error_return_value = nil
+          allow(described_class).to receive(:unique_violation_error?).and_wrap_original do |m, *args|
+            unique_violation_error_return_value = m.call(*args)
+          end
+
+          result = described_class.create_edge(ancestor, descendant)
+          expect(result).to be_truthy
+          expect(described_class).to have_received(:unique_violation_error?)
+          expect(unique_violation_error_return_value).to be_truthy
+
+          ActiveRecord::Base.connection.close
+        end
+
+      # Second child
+      pid2 =
+        fork do
+          ActiveRecord::Base.connection.reconnect!
+          message = 'child2: Timeout waiting for paused message'
+          raise StandardError, message unless second_socket.wait_readable(10)
+          message = 'paused' # Wait for the first child to call find_link
+          second_socket.recv(message.size)
+          described_class.create_edge(ancestor, descendant)
+          message = 'resume' # Notify the first child
+          second_socket.send(message, 0)
+          ActiveRecord::Base.connection.close
+        end
+
+      # Parent
+      wait_for_child_processes([pid1, pid2])
+
+      expect(described_class.where(ancestor:, descendant:).count).to eq(1)
+      @edge = edge = described_class.last
+      expect(edge.ancestor).to eq(ancestor)
+      expect(edge.descendant).to eq(descendant)
+      expect(edge.direct).to be_truthy
+      expect(edge.count).to eq(1)
+
+      ActiveRecord::Base.connection.close
+    end
+  end
+  # rubocop:enable RSpec/InstanceVariable,Metrics/MethodLength,RSpec/ExampleLength,RSpec/MultipleExpectations
+end