java线程池的提交优先级和执行优先级，execute和submit

深藏阁楼爱情的钟 2022-09-10 10:24 193阅读 0赞

execute 和 submit  
submit和execute 本质上是没有区别的，根据源码所知，submit也是调用了execute()方法，只不过submit是有返回值的。

public Future<?> submit(Runnable task) {
            if (task == null) throw new NullPointerException();
            RunnableFuture<Void> ftask = newTaskFor(task, null);
            execute(ftask);
            return ftask;
        }

submit 提交的优先级 是 核心线程>非核心线程>队列

execute 执行优先级 是 核心线程>队列>非核心线程

//自定义线程池
    ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 20,
            0L, TimeUnit.HOURS,
            new ArrayBlockingQueue<Runnable>(10));

execute 方法源码解析  
1、如果运行的线程数量 小于 corePoolSize 就用核心线程执行  
2、如果核心线程被消耗玩，就放在队列里等待，等核心线程空闲，再来消费队列里的任务  
3、如果核心线程池 和 队列都被消耗完，就会启用非核心线程池  
execute 执行优先级 是 核心线程>队列>非核心线程

public void execute(Runnable command) {
            if (command == null)
                throw new NullPointerException();
            /*
             * Proceed in 3 steps:
             *
             * 1. If fewer than corePoolSize threads are running, try to
             * start a new thread with the given command as its first
             * task.  The call to addWorker atomically checks runState and
             * workerCount, and so prevents false alarms that would add
             * threads when it shouldn't, by returning false.
             *
             * 2. If a task can be successfully queued, then we still need
             * to double-check whether we should have added a thread
             * (because existing ones died since last checking) or that
             * the pool shut down since entry into this method. So we
             * recheck state and if necessary roll back the enqueuing if
             * stopped, or start a new thread if there are none.
             *
             * 3. If we cannot queue task, then we try to add a new
             * thread.  If it fails, we know we are shut down or saturated
             * and so reject the task.
             */
            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);
        }

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