About
Exploring Solution Spaces, Keith Ray's blog on Software development and other topics.
Send comments to:
keithray@mac.com
| For Agile Training, eLearning, or Coaching contact: |
| Industrial Logic, Inc. |
| 866-540-8336 (toll free) |
| 510-540-8336 (Berkeley, California) |
| Links |
| xpminifaq |
| Résumé |
| “Adopting XP” Article 2002 (pdf) |
| “ Refactoring” Article 2006 |
| AYE Conference |
| Lucien W. Dupont |
| Elisabeth Hendrickson |
| Johanna Rothman's Managing Product Development |
| Brian Marick's Exploration Through Example |
| Esther Derby's Insights You Can Use |
| Laurent Bossavit's Incipient(thoughts) |
| Dale Emery's Conversations with Dale |
| Martin Fowler's Bliki |
| Creating Passionate Users |
Archives
Subscribe
RSS Exploring Solution Spaces XML
2005.Oct.02 Sun
Fighting Urban Legends about Garbage Collection
Urban performance legends, revisited, by Brian Goetz. Quotes:
The common code path for new Object() in HotSpot 1.4.2 and later is approximately 10 machine instructions ..., whereas the best performing malloc implementations in C require on average between 60 and 100 instructions per call... many real-world C and C++ programs, such as Perl and Ghostscript, spend 20 to 30 percent of their total execution time in malloc and free -- far more than the allocation and garbage collection overhead of a healthy Java application...
... The malloc/free approach deals with blocks of memory one at a time, whereas the garbage collection approach tends to deal with memory management in large batches, yielding more opportunities for optimization...
... you can see why copying collectors enables such fast allocation -- allocating a new object is nothing more than checking to see if there's enough space left in the heap and bumping a pointer if there is. No searching free lists, best-fit, first-fit, lookaside lists -- just grab the first N bytes out of the heap and you're done.
... for most objects, the direct garbage collection cost is -- zero. This is because a copying collector does not need to visit or copy dead objects, only live ones... the vast majority of objects in typical object-oriented programs (between 92 and 98 percent ...) "die young," which means they become garbage shortly after they are allocated, often before the next garbage collection... Therefore, not only is allocation fast, but for most objects, deallocation is free.