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Highly Scalable Java Programming for Multi-Core System

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This is a list of java programming skill which can be used to improve scalability of Java application.

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Highly Scalable Java Programming for Multi-Core System

  1. 1. Highly Scalable Java Programming for Multi-Core System Zhi Gan (ganzhi@gmail.com) http://ganzhi.blogspot.com
  2. 2. Agenda • Software Challenges • Profiling Tools Introduction • Best Practice for Java Programming • Rocket Science: Lock-Free Programming 2
  3. 3. Software challenges • Parallelism – Larger threads per system = more parallelism needed to achieve high utilization – Thread-to-thread affinity (shared code and/or data) • Memory management – Sharing of cache and memory bandwidth across more threads = greater need for memory efficiency – Thread-to-memory affinity (execute thread closest to associated data) • Storage management – Allocate data across DRAM, Disk & Flash according to access frequency and patterns 3
  4. 4. Typical Scalability Curve
  5. 5. The 1st Step: Profiling Parallel Application
  6. 6. Important Profiling Tools • Java Lock Monitor (JLM) – understand the usage of locks in their applications – similar tool: Java Lock Analyzer (JLA) • Multi-core SDK (MSDK) – in-depth analysis of the complete execution stack • AIX Performance Tools – Simple Performance Lock Analysis Tool (SPLAT) – XProfiler – prof, tprof and gprof
  7. 7. Tprof and VPA tool
  8. 8. Java Lock Monitor • %MISS : 100 * SLOW / NONREC • GETS : Lock Entries • NONREC : Non Recursive Gets • SLOW : Non Recursives that Wait • REC : Recursive Gets • TIER2 : SMP: Total try-enter spin loop cnt (middle for 3 tier) • TIER3 : SMP: Total yield spin loop cnt (outer for 3 tier) • %UTIL : 100 * Hold-Time / Total-Time • AVER-HTM : Hold-Time / NONREC
  9. 9. Multi-core SDK Dead Lock View Synchronization View
  10. 10. Best Practice for High Scalable Java Programming
  11. 11. What Is Lock Contention? From JLM tool website
  12. 12. Lock Operation Itself Is Expensive • CAS operations are predominantly used for locking • it takes up a big part of the execution time
  13. 13. Reduce Locking Scope public synchronized void foo1(int k) public void foo2(int k) { { String key = String key = Integer.toString(k); Integer.toString(k); String value = key+"value"; String value = key+"value"; if (null == key){ if (null == key){ return ; return ; }else { }else{ maph.put(key, value); synchronized(this){ } maph.put(key, value); } } } } 25% Execution Time: 16106 Execution Time: 12157 milliseconds milliseconds
  14. 14. Results from JLM report Reduced AVER_HTM
  15. 15. Lock Splitting public synchronized void public void addUser2(String u){ addUser1(String u) { synchronized(users){ users.add(u); users.add(u); } } } public void addQuery2(String q){ public synchronized void synchronized(queries){ addQuery1(String q) { queries.add(q); queries.add(q); } } } Execution Time: 12981 Execution Time: 4797 milliseconds milliseconds 64%
  16. 16. Result from JLM report Reduced lock tries
  17. 17. Lock Striping public synchronized void public void put2(int indx, put1(int indx, String k) { String k) { share[indx] = k; synchronized } (locks[indx%N_LOCKS]) { share[indx] = k; } } Execution Time: 5536 Execution Time: 1857 milliseconds milliseconds 66%
  18. 18. Result from JLM report More locks with less AVER_HTM
  19. 19. Split Hot Points : Scalable Counter – ConcurrentHashMap maintains a independent counter for each segment of hash map, and use a lock for each counter – get global counter by sum all independent counters
  20. 20. Alternatives of Exclusive Lock • Duplicate shared resource if possible • Atomic variables – counter, sequential number generator, head pointer of linked-list • Concurrent container – java.util.concurrent package, Amino lib • Read-Write Lock – java.util.concurrent.locks.ReadWriteLock
  21. 21. Example of AtomicLongArray public synchronized void set1(int private final AtomicLongArray a; idx, long val) { d[idx] = val; public void set2(int idx, long val) { } a.addAndGet(idx, val); } public synchronized long get1(int public long get2(int idx) { idx) { long ret = a.get(idx); return ret; long ret = d[idx]; } return ret; } Execution Time: 23550 Execution Time: 842 milliseconds milliseconds 96%
  22. 22. Using Concurrent Container • java.util.concurrent package – since Java1.5 – ConcurrentHashMap, ConcurrentLinkedQueue, CopyOnWriteArrayList, etc • Amino Lib is another good choice – LockFreeList, LockFreeStack, LockFreeQueue, etc • Thread-safe container • Optimized for common operations • High performance and scalability for multi-core platform • Drawback: without full feature support
  23. 23. Using Immutable and Thread Local data • Immutable data – remain unchanged in its life cycle – always thread-safe • Thread Local data – only be used by a single thread – not shared among different threads – to replace global waiting queue, object pool – used in work-stealing scheduler
  24. 24. Reduce Memory Allocation • JVM: Two level of memory allocation – firstly from thread-local buffer – then from global buffer • Thread-local buffer will be exhausted quickly if frequency of allocation is high • ThreadLocal class may be helpful if temporary object is needed in a loop
  25. 25. Rocket Science: Lock-Free Programming
  26. 26. Using Lock-Free/Wait-Free Algorithm • Lock-Free allow concurrent updates of shared data structures without using any locking mechanisms – solves some of the basic problems associated with using locks in the code – helps create algorithms that show good scalability • Highly scalable and efficient • Amino Lib
  27. 27. Why Lock-Free Often Means Better Scalability? (I) Lock:All threads wait for one Lock free: No wait, but only one can succeed, Other threads need retry
  28. 28. Why Lock-Free Often Means Better Scalability? (II) X X Lock:All threads wait for one Lock free: No wait, but only one can succeed, Other threads often need to retry
  29. 29. Performance of A Lock-Free Stack Picture from: http://www.infoq.com/articles/scalable-java-components
  30. 30. References • Amino Lib – http://amino-cbbs.sourceforge.net/ • MSDK – http://www.alphaworks.ibm.com/tech/msdk • JLA – http://www.alphaworks.ibm.com/tech/jla
  31. 31. Backup

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