Script to reproduce mongo ruby driver's runtime leak

Mongo Runtime Leak

bbrowning@bbrowning-mbp:~/tmp$ jruby mongo_leak.rb 2
Leaked 2 Ruby runtimes in RubyBSONCallback


Uncomment lines 15-16 of mongo_leak.rb and run again


bbrowning@bbrowning-mbp:~/tmp$ jruby mongo_leak.rb 2
Leaked 0 Ruby runtimes in RubyBSONCallback


Attached is a diff showing the same add_finalizer code from mongo_leak.rb but in Java for RubyBSONCallback.java

mongo_leak.rb

require 'mongo'
class Java::OrgJbson::RubyBSONCallback
  field_reader :_runtimeCache
end

NUM_RUNTIMES = (ARGV[0] || 5).to_i
if java.lang.System.getProperty('checking_for_leaks') == 'true'
  document = BSON.serialize(:hello => "world")
  BSON.deserialize(document)
else
  java.lang.System.setProperty('checking_for_leaks', 'true')
  NUM_RUNTIMES.times do
    runtime = org.jruby.Ruby.new_instance
    runtime.load_service.require(__FILE__)
    # runtime.add_finalizer {
    #   Java::OrgJbson.RubyBSONCallback._runtimeCache.remove(runtime)
    # }
    runtime.tear_down(false)
    java.lang.System.gc
  end
  # A few more GCs for good measure
  java.lang.System.gc
  java.lang.System.gc
  num_leaked = Java::OrgJbson.RubyBSONCallback._runtimeCache.size
  puts "Leaked #{num_leaked} Ruby runtimes in RubyBSONCallback"
end

RubyBSONCallback.diff

diff --git a/ext/jbson/src/main/jbson/RubyBSONCallback.java b/ext/jbson/src/main/jbson/RubyBSONCallback.java
index 5c12c27..f5ed7e0 100644
--- a/ext/jbson/src/main/jbson/RubyBSONCallback.java
+++ b/ext/jbson/src/main/jbson/RubyBSONCallback.java
@@ -320,7 +320,7 @@ public class RubyBSONCallback implements BSONCallback {
       return _stack.size() < 1;
     }
 
-    private static HashMap<String, Object> _getRuntimeCache(Ruby runtime) {
+    private static HashMap<String, Object> _getRuntimeCache(final Ruby runtime) {
       // each JRuby runtime may have different objects for these constants,
       // so cache them separately for each runtime
       @SuppressWarnings("unchecked")
@@ -329,6 +329,11 @@ public class RubyBSONCallback implements BSONCallback {
       if(cache == null) {
         cache = new HashMap<String, Object>();
         _runtimeCache.put( runtime, cache );
+        runtime.addFinalizer( new Finalizable() {
+          public void finalize() {
+            _runtimeCache.remove( runtime );
+          }
+        } );
       }
       return cache;
     }