tomcat优化jdk原生的线程池

• 为啥要优化

  1、由于tomcat 处理的都是一些网络方面的线程任务，都是IO类型的
  2、JDK原生线程池，当核心线程满了之后往队列里面存放，这样不符合web容器的任务
  3、tomcat修改为，核心线程满了之后，再创建非核心线程。最后再往队列任务里面存放

   

• 优化的手段

  public void execute(Runnable command) {
          if (command == null)
              throw new NullPointerException();
          int c = ctl.get();
          if (workerCountOf(c) < corePoolSize) {
              if (addWorker(command, true))
                  return;
              c = ctl.get();
          }
          if (isRunning(c) && workQueue.offer(command)) {
              int recheck = ctl.get();
              if (! isRunning(recheck) && remove(command))
                  reject(command);
              else if (workerCountOf(recheck) == 0)
                  addWorker(null, false);
          }
          else if (!addWorker(command, false))
              reject(command);
      }

  上述代码中  workQueue.offer(command)  这里的逻辑可以换成，非核心线程未满都返回false。这样就可以创建非核心线程了

队列进行定制为TaskQueue

• TaskQueue核心代码如下

      @Override
      public boolean offer(Runnable o) {
        //we can't do any checks
          if (parent==null) return super.offer(o);
          //we are maxed out on threads, simply queue the object
          if (parent.getPoolSize() == parent.getMaximumPoolSize()) return super.offer(o);
          //we have idle threads, just add it to the queue
          if (parent.getSubmittedCount()<(parent.getPoolSize())) return super.offer(o);
          //if we have less threads than maximum force creation of a new thread
          if (parent.getPoolSize()<parent.getMaximumPoolSize()) return false;
          //if we reached here, we need to add it to the queue
          return super.offer(o);
      }

   

•  tomcat的线程池对象也定制了一下，主要不同点为

    public void execute(Runnable command, long timeout, TimeUnit unit) {
        submittedCount.incrementAndGet();
        try {
            super.execute(command);
        } catch (RejectedExecutionException rx) {
            if (super.getQueue() instanceof TaskQueue) {
                final TaskQueue queue = (TaskQueue)super.getQueue();
                try {
                    if (!queue.force(command, timeout, unit)) {
                        submittedCount.decrementAndGet();
                        throw new RejectedExecutionException("Queue capacity is full.");
                    }
                } catch (InterruptedException x) {
                    submittedCount.decrementAndGet();
                    throw new RejectedExecutionException(x);
                }
            } else {
                submittedCount.decrementAndGet();
                throw rx;
            }
        }
    }
    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        submittedCount.decrementAndGet();
        if (t == null) {
            stopCurrentThreadIfNeeded();
        }
    }

增加了重试功能  ，被拒绝之后，直接强制往队列里面放

备注：变量 submittedCount  是为了统计已经提交到线程池但还没有完成任务的数目    这里变量会在TaskQueue offer方法里面使用，看是否存在空闲的线程