/** * Executes the given task sometime in the future. The task * may execute in a new thread or in an existing pooled thread. * * If the task cannot be submitted for execution, either because this * executor has been shutdown or because its capacity has been reached, * the task is handled by the current {@code RejectedExecutionHandler}. * * @param command the task to execute * @throws RejectedExecutionException at discretion of * {@code RejectedExecutionHandler}, if the task * cannot be accepted for execution * @throws NullPointerException if {@code command} is null */ 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. * 1、如果少于corePoolSize数量的线程正在运行,尝试利用给定的Runnable实例command开启一个新的线程作为它的第一个任务。 * addWorker()方法的调用会对线程池运行状态runState、worker线程数量workerCount进行原子性检测,返回值为启动新线程结果。 * * 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. * 2、如果一个任务可以成功地进入队列,然后我们还需要再次检查(即双份检查)自从进入这个方法后,我们是否应该添加一个线程 * (因为自从上一次检查以来可能存在死亡情况), * 所以我们重新检查状态,如果有必要的话,即线程池已停止,回滚之前的入队操作,或者在没有线程时启动一个新线程。 * * 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. * 3、如果我们不能入列一个任务,那么我们尝试添加一个新线程。 * 如果添加失败,我们知道线程池可能已被关闭或者数量饱和,所以我们会拒绝这个任务。 */ // 获取ctl的值c int c = ctl.get(); // 如果c中有效线程数目小于corePoolSize大小,尝试添加新的worker线程处理任务command: // 从c中获取有效线程数目调用的是workerCountOf()方法, // 添加新的worker线程处理任务command调用的是addWorker()方法, // 线程数的判断利用corePoolSize作为边界约束条件 // 方法返回值是标志添加worker是否成功的标志位,ture表示成功,false表示失败, // 如果为true,则直接返回,否则重新获取ctl的值c if (workerCountOf(c) < corePoolSize) { if (addWorker(command, true)) return; // 添加work线程失败则再次获取ctl的值 c = ctl.get(); } // 根据c判断当前线程池的状态是否为RUNNING状态,即既可以接受新任务,又会处理队列任务的状态, // 并且通过offer()方法,尝试将commond添加到队列workQueue中 // BlockingQueue的offer()方法表示如果可能的话,将参数对象加到BlockingQueue里, // 即如果BlockingQueue可以容纳,则返回true,否则返回false if (isRunning(c) && workQueue.offer(command)) { // 如果当前线程池处于RUNNING状态,且workQueue能够容纳command,并添加成功的话, // 再次获取ctl的值recheck, int recheck = ctl.get(); // 如果当前线程池的状态不是RUNNING,并且从队列workQueue移除command成功的话, // 调用reject()方法拒绝任务command, if (! isRunning(recheck) && remove(command)) reject(command); // 否则如果当前工作线程woker数目为0,尝试添加新的worker线程,但是不携带任务 else if (workerCountOf(recheck) == 0) addWorker(null, false); } // 如果尝试添加新的worker线程处理任务command失败, // 调用reject()方法拒绝任务command,线程数的判断利用maximumPoolSize作为边界约束条件 else if (!addWorker(command, false)) reject(command); } /** * Executes the given task sometime in the future. The task * may execute in a new thread or in an existing pooled thread. * * If the task cannot be submitted for execution, either because this * executor has been shutdown or because its capacity has been reached, * the task is handled by the current {@code RejectedExecutionHandler}. * * @param command the task to execute * @throws RejectedExecutionException at discretion of * {@code RejectedExecutionHandler}, if the task * cannot be accepted for execution * @throws NullPointerException if {@code command} is null */ 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. * 1、如果少于corePoolSize数量的线程正在运行,尝试利用给定的Runnable实例command开启一个新的线程作为它的第一个任务。 * addWorker()方法的调用会对线程池运行状态runState、worker线程数量workerCount进行原子性检测,返回值为启动新线程结果。 * * 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. * 2、如果一个任务可以成功地进入队列,然后我们还需要再次检查(即双份检查)自从进入这个方法后,我们是否应该添加一个线程 * (因为自从上一次检查以来可能存在死亡情况), * 所以我们重新检查状态,如果有必要的话,即线程池已停止,回滚之前的入队操作,或者在没有线程时启动一个新线程。 * * 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. * 3、如果我们不能入列一个任务,那么我们尝试添加一个新线程。 * 如果添加失败,我们知道线程池可能已被关闭或者数量饱和,所以我们会拒绝这个任务。 */ // 获取ctl的值c int c = ctl.get(); // 如果c中有效线程数目小于corePoolSize大小,尝试添加新的worker线程处理任务command: // 从c中获取有效线程数目调用的是workerCountOf()方法, // 添加新的worker线程处理任务command调用的是addWorker()方法, // 线程数的判断利用corePoolSize作为边界约束条件 // 方法返回值是标志添加worker是否成功的标志位,ture表示成功,false表示失败, // 如果为true,则直接返回,否则重新获取ctl的值c if (workerCountOf(c) < corePoolSize) { if (addWorker(command, true)) return; // 添加work线程失败则再次获取ctl的值 c = ctl.get(); } // 根据c判断当前线程池的状态是否为RUNNING状态,即既可以接受新任务,又会处理队列任务的状态, // 并且通过offer()方法,尝试将commond添加到队列workQueue中 // BlockingQueue的offer()方法表示如果可能的话,将参数对象加到BlockingQueue里, // 即如果BlockingQueue可以容纳,则返回true,否则返回false if (isRunning(c) && workQueue.offer(command)) { // 如果当前线程池处于RUNNING状态,且workQueue能够容纳command,并添加成功的话, // 再次获取ctl的值recheck, int recheck = ctl.get(); // 如果当前线程池的状态不是RUNNING,并且从队列workQueue移除command成功的话, // 调用reject()方法拒绝任务command, if (! isRunning(recheck) && remove(command)) reject(command); // 否则如果当前工作线程woker数目为0,尝试添加新的worker线程,但是不携带任务 else if (workerCountOf(recheck) == 0) addWorker(null, false); } // 如果尝试添加新的worker线程处理任务command失败, // 调用reject()方法拒绝任务command,线程数的判断利用maximumPoolSize作为边界约束条件 else if (!addWorker(command, false)) reject(command); }