Java Language Executor, ExecutorService and Thread pools Handle Rejected Execution
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Example
If
- you try to submit tasks to a shutdown Executor or
- the queue is saturated (only possible with bounded ones) and maximum number of Threads has been reached,
RejectedExecutionHandler.rejectedExecution(Runnable, ThreadPoolExecutor) will be called.
The default behavior is that you'll get a RejectedExecutionException thrown at the caller. But there are more predefined behaviors available:
- ThreadPoolExecutor.AbortPolicy (default, will throw REE)
- ThreadPoolExecutor.CallerRunsPolicy (executes task on caller's thread - blocking it)
- ThreadPoolExecutor.DiscardPolicy (silently discard task)
- ThreadPoolExecutor.DiscardOldestPolicy (silently discard oldest task in queue and retry execution of the new task)
You can set them using one of the ThreadPool constructors:
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
RejectedExecutionHandler handler) // <--
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) // <--
You can as well implement your own behavior by extending RejectedExecutionHandler interface:
void rejectedExecution(Runnable r, ThreadPoolExecutor executor)
