package bes.injector;/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
/**
* A pool of worker threads that are shared between all Executors created with it. Each executor is treated as a distinct
* unit, with its own concurrency and task queue limits, but the threads that service the tasks on each executor are
* free to hop between all other executors at will.
*
* To keep producers from incurring unnecessary delays, once an executor is "spun up" (i.e. is processing tasks at a steady
* rate), adding tasks to the executor often involves only placing the task on the work queue and updating the
* task permits (which imposes our max queue length constraints). Only when it cannot be guaranteed the task will be serviced
* promptly does the producer have to signal a thread itself to perform the work.
*
* We do this by scheduling only if there are no 'spinning' workers on this Injector, or if the task queue is full
* (since we have to block in this case anyway)
*
* The worker threads schedule themselves as far as possible: when they are assigned a task, they will attempt to spawn
* a partner worker to service any other work outstanding on the queue (if any); once they have finished the task they
* will either take another (if any remaining) and repeat this, or they will attempt to assign themselves to another executor
* that does have tasks remaining. If both fail, it will enter a non-busy-spinning phase, where it will sleep for a short
* random interval (based upon the number of threads in this mode, so that the total amount of non-sleeping time remains
* approximately fixed regardless of the number of spinning threads), and upon waking up will again try to assign themselves
* an executor with outstanding tasks to perform.
*/
public class Injector
{
// the name assigned to workers in the injector, and the id suffix
final AtomicLong workerId = new AtomicLong();
final AtomicInteger workerCount = new AtomicInteger();
// the collection of executors serviced by this injector
final List<InjectionExecutor> executors = new CopyOnWriteArrayList<>();
// the number of workers currently in a spinning state
final AtomicInteger spinningCount = new AtomicInteger();
// see Worker.maybeStop() - used to self coordinate stopping of threads
final AtomicLong stopCheck = new AtomicLong();
// the collection of threads that are (most likely) in a spinning state - new workers are scheduled from here first
final ConcurrentSkipListMap<Long, Worker> spinning = new ConcurrentSkipListMap<Long, Worker>();
// the collection of threads that have been asked to stop/deschedule - new workers are scheduled from here last
final ConcurrentSkipListMap<Long, Worker> descheduled = new ConcurrentSkipListMap<Long, Worker>();
final ThreadFactory threadFactory;
public Injector(final String poolName)
{
threadFactory = new ThreadFactory()
{
public Thread newThread(Runnable r)
{
Thread thread = new Thread(r, poolName + "-Worker-" + ((Worker) r).workerId);
thread.setDaemon(true);
return thread;
}
};
}
public Injector(ThreadFactory threadFactory)
{
this.threadFactory = threadFactory;
}
void schedule(Work work, boolean internal)
{
// we try to hand-off our work to the spinning queue before the descheduled queue, even though we expect it to be empty
// all we're doing here is hoping to find a worker without work to do, but it doesn't matter too much what we find;
// we atomically set the task so even if this were a collection of all workers it would be safe, and if they are both
// empty we schedule a new thread
Map.Entry<Long, Worker> e;
while (null != (e = spinning.pollFirstEntry()) || null != (e = descheduled.pollFirstEntry()))
if (e.getValue().assign(work, false))
return;
if (!work.isStop())
{
try
{
new Worker(workerId.incrementAndGet(), work, this, threadFactory);
workerCount.incrementAndGet();
}
catch (Throwable t)
{
// the only safe thing to do is to return our permits and
// let the running workers pick up the work when they get a chance
if (work.assigned != null)
{
work.assigned.returnWorkPermit();
work.assigned.returnTaskPermit();
}
if (!internal)
throw t;
Thread thread = Thread.currentThread();
Thread.UncaughtExceptionHandler handler = thread.getUncaughtExceptionHandler();
if (handler != null)
handler.uncaughtException(thread, t);
}
}
}
void maybeStartSpinningWorker(boolean internal)
{
// in general the workers manage spinningCount directly; however if it is zero, we increment it atomically
// ourselves to avoid starting a worker unless we have to
int current = spinningCount.get();
if (current == 0 && spinningCount.compareAndSet(0, 1))
schedule(Work.SPINNING, internal);
}
protected <E extends InjectionExecutor> E addExecutor(E executor)
{
if (executor.injector != null)
throw new IllegalArgumentException("An InjectionExecutor can only be associated with one Injector!");
executor.injector = this;
executors.add(executor);
return executor;
}
public InjectionExecutor newExecutor(int maxWorkers, int maxTasksQueued)
{
InjectionExecutor executor = new InjectionExecutor(maxWorkers, maxTasksQueued);
addExecutor(executor);
return executor;
}
}