Java threading optimizer bug demo

Problem

Adding multiple identical things inside a busy loop causes performance and CPU usage to plummet. Using -Xint increases performance significantly in such case but also increases CPU usage.

Usage

Download the pre-built jar from GitHub or run mvn clean package yourself.

First start the server process:

$ java -Daction=server -jar target/javabug-0.0.1-jar-with-dependencies.jar

Server is expected to stay on the foreground and it must be left on to demonstrate this issue. It won’t terminate on its own. Run the following client commands on separate terminal while server is running.

msgCount=2

$ java -Daction=spam -DmsgCount=2 -jar target/javabug-0.0.1-jar-with-dependencies.jar
[main] INFO com.example.javabug.JavaBug - Target is 127.0.0.1:1601 with 20 threads and 2 messages per batch
Events sent: 30118, total 30118 in 1s (30118 eps)
Events sent: 140546, total 170668 in 2s (85332 eps)
Events sent: 165062, total 335726 in 3s (111908 eps)
Events sent: 165964, total 501694 in 4s (125422 eps)
Events sent: 166208, total 667904 in 5s (133579 eps)

msgCount=2 and interpreted mode

$ java -Xint -Daction=spam -DmsgCount=2 -jar target/javabug-0.0.1-jar-with-dependencies.jar
[main] INFO com.example.javabug.JavaBug - Target is 127.0.0.1:1601 with 20 threads and 2 messages per batch
Events sent: 25326, total 25326 in 1s (25326 eps)
Events sent: 28160, total 53486 in 2s (26743 eps)
Events sent: 29366, total 82852 in 3s (27617 eps)
Events sent: 28964, total 111816 in 4s (27954 eps)
Events sent: 29856, total 141672 in 5s (28334 eps)

msgCount=3

$ java -Daction=spam -DmsgCount=3 -jar target/javabug-0.0.1-jar-with-dependencies.jar
[main] INFO com.example.javabug.JavaBug - Target is 127.0.0.1:1601 with 20 threads and 3 messages per batch
Events sent: 3255, total 3255 in 1s (3255 eps)
Events sent: 1461, total 4716 in 2s (2358 eps)
Events sent: 1464, total 6180 in 3s (2060 eps)
Events sent: 1461, total 7641 in 4s (1910 eps)
Events sent: 1455, total 9096 in 5s (1819 eps)
Events sent: 1461, total 10557 in 6s (1759 eps)

msgCount=3 and interpreted mode

$ java -Xint -Daction=spam -DmsgCount=3 -jar target/javabug-0.0.1-jar-with-dependencies.jar
[main] INFO com.example.javabug.JavaBug - Target is 127.0.0.1:1601 with 20 threads and 3 messages per batch
Events sent: 24876, total 24876 in 1s (24876 eps)
Events sent: 27966, total 52842 in 2s (26421 eps)
Events sent: 25554, total 78396 in 3s (26132 eps)
Events sent: 22275, total 100671 in 4s (25167 eps)
Events sent: 22497, total 123168 in 5s (24633 eps)