错误描述:
我设置了CountDownLatch对线程的协作做出了一些限制,但是我发现运行一段时间以后便发现定时任务不运行了。
具体代码:
public void sendToCertainWeb() throws IOException, InterruptedException {
List<String> urlList = scheduleplanMapper.getRandomUrlList();
Thread.sleep(6000);
CountDownLatch countDownLatch = new CountDownLatch(20);
for (String s : urlList) {
transportThreadPool.execute(()->{
try {
URL url = new URL(s);
// 打开连接
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
// 设置请求方法为GET
connection.setRequestMethod("GET");
connection.setConnectTimeout(100000);
connection.setReadTimeout(100000);
// 添加自定义的请求头信息
String agent = scheduleplanMapper.getRandomAgent();
connection.addRequestProperty("User-Agent", agent);
connection.addRequestProperty("Accept-Language", "en-US,en;q=0.9");
// 获取服务器返回的状态码
int responseCode = connection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
// 读取服务器返回的数据
BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line;
StringBuilder response = new StringBuilder();
while ((line = reader.readLine()) != null) {
response.append(line);
}
reader.close();
log.info("Right Code: " + responseCode);
} else {
log.error("Error Code: " + responseCode);
}
// 关闭连接
connection.disconnect();
countDownLatch.countDown();
}catch (Exception e){
log.error(JSON.toJSONString(e));
}
});
}
countDownLatch.await();
}
报错以后定时任务不运行了
错误排查:
打印线程日志发现定时任务的线程在第86行代码停着不动了。
正常的线程日志应该是这样的。
查看第86行代码,发现这里并没有唤醒主线程 ,导致线程一直处于运行状态,无法继续下一个任务。
错误的原因是countDownLatch.countDown()并没有放在finally块里因此发生了错误并不会走这块代码,导致线程没有countDown
错误修改:
把countDownLatch.countDown();放在finally代码块里保证一定会进行countDown这个动作
正确代码:
public void sendToCertainWeb() throws IOException, InterruptedException {
List<String> urlList = scheduleplanMapper.getRandomUrlList();
Thread.sleep(6000);
CountDownLatch countDownLatch = new CountDownLatch(20);
for (String s : urlList) {
transportThreadPool.execute(()->{
try {
URL url = new URL(s);
// 打开连接
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
// 设置请求方法为GET
connection.setRequestMethod("GET");
connection.setConnectTimeout(100000);
connection.setReadTimeout(100000);
// 添加自定义的请求头信息
String agent = scheduleplanMapper.getRandomAgent();
connection.addRequestProperty("User-Agent", agent);
connection.addRequestProperty("Accept-Language", "en-US,en;q=0.9");
// 获取服务器返回的状态码
int responseCode = connection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
// 读取服务器返回的数据
BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line;
StringBuilder response = new StringBuilder();
while ((line = reader.readLine()) != null) {
response.append(line);
}
reader.close();
log.info("Right Code: " + responseCode);
} else {
log.error("Error Code: " + responseCode);
}
// 关闭连接
connection.disconnect();
}catch (Exception e){
log.error(JSON.toJSONString(e));
}finally {
countDownLatch.countDown();
}
});
}
countDownLatch.await();
}
错误总结:
我们一般认为线程处于blocked状态的时候线程才是处于阻塞状态,但是这个状态只是对于计算机来说的。对于我们来说,只要业务不执行了,线程就是处于阻塞状态的,因此任何状态下的线程对于业务来说都是阻塞的。 我这个项目是爬虫项目,会去爬取别人网站的数据,有些网站识别爬虫之后不仅会拒绝你访问,还会通过一直不给响应使得你的服务器线程占满,进而导致你的爬虫服务器崩溃。文章来源:https://www.toymoban.com/news/detail-856963.html
参考文章:
未设置超时时间导致线程池资源耗尽,排查过程-CSDN博客文章来源地址https://www.toymoban.com/news/detail-856963.html
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