v0.38 Attempt to reimplement with mutex support for interrupting and resuming during post import. This will have to be tested / validated

gossamer_forums.rb

@@ -1,7 +1,7 @@
 # Federated Computer, Inc.
 # David Sainty <saint@federated.computer>  2024 A.D.
 # Gossamer Threads to Discourse -- Migration-Import Script
-# v0.37.1 Huge move to threaded support for topic-post import; disable topic-post import for current user re-import 202408162130, persistence for exported files
+# v0.38 Attempt to reimplement with mutex support for interrupting and resuming during post import. This will have to be tested / validated
 
 require 'mysql2'
 require 'open-uri'
@@ -965,46 +965,61 @@ class GossamerForumsImporter < ImportScripts::Base
 
   def threaded_topic_import
     # Get list of TOPICS / OP posts, i.e. post ids that have no parent / root id - SELECT post_id FROM gforum_Post WHERE post_root_id = 0;
-    parent_post_ids = execute_query("SELECT post_id FROM gforum_Post WHERE post_root_id = 0")
+    # The query selects post_ids from gforum_Post where post_root_id is 0, meaning these posts are the topic starters (OPs).
+    # It also ensures that we only process posts with a post_id greater than the last processed one, allowing for resumption.
+    parent_post_ids = execute_query("SELECT post_id FROM gforum_Post WHERE post_root_id = 0 AND post_id > #{fetch_highest_processed_post_id} ORDER BY post_id ASC")
 
     parent_post_count = parent_post_ids.count
     batch_size = 100 # Set our batch size for number of posts to import in a single batch
     current_post_batch = 0 # Set our current batch number. This tracks the current batch of posts being processed.
     is_complete = false # Flag to indicate whether the import process is complete.
 
+    # Run until all posts have been processed.
     until is_complete
       # Query in batches, create pool, wait for termination, do it again
-      # SELECT post_id FROM gforum_Post WHERE post_root_id = 0 ORDER BY post_id  
       current_post_batch_max = current_post_batch + batch_size
 
+      ## Static pool size based on number of CPUs
       # pool = Concurrent::FixedThreadPool.new(Concurrent.processor_count) #create thread pool that is bounded by processors avaialable, however play with the number to see what works best
 
-      # Dynamically calculate the pool size based on system load
+      # Dynamically calculate the pool size based on system load to optimise performance
       pool_size = calculate_dynamic_pool_size
-      
-      pool = Concurrent::FixedThreadPool.new(pool_size)
+      pool = Concurrent::FixedThreadPool.new(pool_size)  # Create a thread pool with the calculated size.
 
+      # Process each post in the current batch
       while current_post_batch < current_post_batch_max
-        post_id = parent_post_ids[current_post_batch]
+        post_id = parent_post_ids[current_post_batch]  # Fetch the post_id for the current post
 
         puts "Starting import for post_id #{post_id} in batch #{current_post_batch / batch_size + 1} with #{thread_count} threads"
 
+        # Submit the import job for the current post_id to the thread pool
         pool.post do
           puts "Processing post ID: #{post_id}"
-          topic_import_job(post_id)
+          topic_import_job(post_id)  # Import topic and its replies
         end
 
-        current_post_batch += 1
+        current_post_batch += 1  # Increment, moving to next post in the batch
         break if current_post_batch >= parent_post_count
       end
       
-      pool.shutdown
-      pool.wait_for_termination
+      pool.shutdown  # Initiate thread pool shutdown after all jobs submitted
+      pool.wait_for_termination  # Wait for all threads to finish exec
 
+      # Set when all posts have been processed
       is_complete = true if current_post_batch >= parent_post_count
     end
   end
 
+  # Method to ensure thread-safe updates to highest_processed_post_id
+  def update_highest_processed_post_id_thread_safe(post_id)
+    @highest_processed_mutex ||= Mutex.new
+    @highest_processed_mutex.synchronize do
+      if post_id > fetch_highest_processed_post_id
+        update_highest_processed_post_id(post_id)
+      end
+    end
+  end
+
   # Method to import an entire topic, including its first post and all subsequent replies
   def topic_import_job(post_id)
     #Here is where you can import the entire topic
@@ -1110,10 +1125,6 @@ class GossamerForumsImporter < ImportScripts::Base
         new_url = "https://new/t/#{topic.slug}/#{topic.id}"
         insert_url_mapping(row['post_id'], new_url, unique_title)
   
-        # Update the highest processed post_id in the database
-        puts "Updated highest processed post_id #{post_id}"
-        update_highest_processed_post_id(post_id)
-  
         # Now fetch and import all replies to this topic
         replies = execute_query("SELECT post_id, user_id_fk, post_message, post_time, post_likes FROM gforum_Post WHERE post_root_id = #{post_id} ORDER BY post_time ASC")
   
@@ -1158,15 +1169,17 @@ class GossamerForumsImporter < ImportScripts::Base
             # Handle any attachments associated with the reply
             handle_post_attachments(reply_row['post_id'], post, reply_user_id)
   
-            # Update the highest processed post_id in the database
-            puts "Updated highest processed post_id #{reply_row['post_id']}"
-            update_highest_processed_post_id(reply_row['post_id'])
+            # Update the highest processed post_id in the database (thread-safe)
+            update_highest_processed_post_id_thread_safe(reply_row['post_id'])
   
           rescue ActiveRecord::RecordInvalid => e
             puts "Error importing reply with post_id #{reply_row['post_id']}: #{e.message}"
           end
         end
   
+        # After processing the entire topic, update the highest_processed_post_id to the current topic's post_id (thread-safe)
+        update_highest_processed_post_id_thread_safe(post_id)
+  
       rescue ActiveRecord::RecordInvalid => e
         puts "Error importing topic with post_id #{row['post_id']}: #{e.message}"
       end