使用SynchronousQueue的ThreadPoolExecutor拒绝任务，如何避免及确保任务串行执行

如下代码在部分设备上会拒绝第二个任务：

ThreadPoolExecutor exe = new ThreadPoolExecutor(1, 1, 0L, TimeUnit.SECONDS, new SynchronousQueue<>());
Future future = exe.submit(task1);
while (!future.isDone()) {
        // 做一些操作，等待结果
        sleep(1);
}
Future future = exe.submit(task2); // 有时会拒绝该任务

我曾遇到类似未解决的问题。

java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.ExecutorCompletionService$QueueingFuture@8c1e52e[Not completed, task = java.util.concurrent.Executors$RunnableAdapter@6cdbdc4f[Wrapped task = java.util.concurrent.FutureTask@2aa7cf9b[Not completed, task = com.my.example.DatabaseValue$$Lambda$1438/0x0000000840650440@6c918fb6]]] rejected from java.util.concurrent.ThreadPoolExecutor@3aca79dd[Running, pool size = 1, active threads = 0, queued tasks = 0, completed tasks = 592]
    at java.base/java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2055)
    at java.base/java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:825)
    at java.base/java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1355)
    at java.base/java.util.concurrent.ExecutorCompletionService.submit(ExecutorCompletionService.java:184)
...

我无法在自己的设备上复现该问题，但它在其他设备上出现。

现在我改用LinkedBlockingQueue(1)替代SynchronousQueue。此时线程池可提交2个任务，第一个处于活跃状态，第二个进入队列。为防止重复提交，我通过重写ThreadPoolExecutor.beforeExecute、ThreadPoolExecutor.afterExecute并在调用submit前检查无活跃任务来控制。

内容的提问来源于stack exchange，提问作者XorNut