Java Threads and Locks

Readings

• Java Language Specification
  • Java Memory Model
• StackOverflow
  • Relationship of reordering & happens-before in java
  • Why setArray() method call required in CopyOnWriteArrayList
  • Java Compiler Reordering
• Wiki
  • Memory model
  • Memory ordering
  • Memory barrier
  • Out of Order Execution
• Happens-Before俗解
• Understanding JIT
• Video
  • Java Memory Model

Memory Reodering

Several mechanisms can produce the reordering. A Just-In-Time(JIT) compiler in a Java Virtual Machine implementation may rearrange code, or the processor. In addition, the memory hierarchy of the architecture on which a Java Virtual Machine implementation is run may make it appear as if code is being reordered.

• Compiler can reorder statements
• Processor can reorder them
• On multi-processor, values not synchronized to global memory
• The memeory model is designed to allow aggressive optimization
• Good for performance