Thread-safety of calling @Bean methods from returned annonymous inner classes

[btiernay]

Is the following test method thread-safe, assuming that this is being called from multiple threads? Sometimes the println statement displays "null"

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import javax.annotation.Resource;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.support.AnnotationConfigContextLoader;

import com.oanda.bi.rm.test.AnnotationConfigTest.Config;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { Config.class }, loader = AnnotationConfigContextLoader.class)
public class AnnotationConfigTest {

    @Resource
    Map<String, Value> map;

    @Test
    public void test() throws InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool( 10 );

        for ( int i = 0; i < 10; i++ ) {
            service.execute( new Runnable() {
                @Override
                public void run() {
                    // Is this thread-safe?
                    Value value = map.get( "value" );

                    // Sometimes null!
                    System.out.println( value.x );
                }
            } );
        }

        service.shutdown();
        service.awaitTermination( 1, TimeUnit.MINUTES );
    }

    public static class Value {
        @Resource
        protected Integer x;
    }

    @Configuration
    public static class Config {

        @Bean
        public Integer x() {
            return 1;
        }

        @Bean
        @Scope("prototype")
        public Value value() {
            return new Value();
        }

        @Bean
        @SuppressWarnings("serial")
        public Map<String, Value> map() {
            // Return a Spring agnostic "bean factory" map
            return Collections.unmodifiableMap( new HashMap<String, Value>() {
                @Override
                public Value get( Object obj ) {
                    String key = (String) obj;

                    if ( key.equals( "value" ) ) {
                        // Create new bean on demand
                        return value();
                    }

                    // Assume other similar branches here...

                    return null;
                }
            } );
        }

    }
}

[btiernay]

Note that if I change Collections.unmodifiableMap to Collections.synchronizedMap the problem seems to go away. This leads me to believe the decorating Spring proxy is not thread safe when used in this way. Thoughts?

[btiernay]

Created https://jira.springsource.org/browse/SPR-9852 to address this issue