Intro
Task (runnable or callable)
Synchoronus Processing: called in the main thread. Main Thread is blocked till the task processing is finished.
Asynchoronus Processing: main thread delegates to an independe thread via Service/Executor.
Executor (Thread Pool ex: Fixed or Scheduled ) & Service (Lifecycle methods for executor):
– core size, max. number of threads
– work queue
– rejection policy
– thread factory
Each Java thread has 2 stacks ( one native & one java)
resouce thrashing: application is not able to perform due to lack of resources.
How do you size a thread pool?
– benefits are to use many resources like multiple processors & exploit I/O.
– upper bound for a compute intensive task is N or N+1 (num of processors).
– for I/O based activities it is N * target_utilization_rate*(1+(server_time/wait_time))
– Alternate to TP is thread per task and single thread per task type (like in AWT)
– notify() causes fewer context switches than notifyAll(), hard but good to use notify() where u can because of better performance characteristics.
http://www.ibm.com/developerworks/library/j-jtp0730/index.html
http://www.ibm.com/developerworks/java/library/j-jtp05236/index.html
http://www.ibm.com/developerworks/java/library/j-jtp05236/index.html
Handling Blocked methods:
- Blocking Queue: timedpolling as opposed to take which blocks indefinitely. Though easy to implement, responsiveness is poor.
- Convert the task to future by using submit and call cancel on Future. Better responsiveness.
- Post a poision pill
- Interrupt the thread waiting on blocking method! One potential problem is the thread is already stuck on a blocking call. So, invoking another method like shutdown() {which calls interrupt} is also executed on the same thread that is waiting for the blocked method to finish!
Another reason not to interrupt the thread is, it is borrowed from a service and it is not good to make assumption about the borrowed thread’s cancellation policy. or even what task that thread may be running. One exception is for a thread running in standard executor, you can call the “boolean cancel(boolean mayInterrupIfRunning)” with true for the future returned through Executor.submin()
