scheduler | 易学教程

玩转webmagic代码之Scheduler

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> webmagic上线之后，因为灵活性很强，得到了一些爬虫老手的欢迎，但是对于新手来说可能稍微摸不着头脑，我的需求是这样子，什么模块化，什么灵活性，但是看了半天，我也不知道怎么解决我的问题啊？这里先谈谈Scheduler，不单关乎框架，更多是一些爬虫通用的思想，希望对大家有帮助。为什么要有Scheduler 其实Scheduler并非webmagic独创，在scrapy以及其他成熟爬虫中都有类似模块。Scheduler管理了所有待抓取的url，单个爬虫自己是无法控制要抓取什么的，抓什么都由Scheduler决定。这样子最大的好处就是，爬虫本身没有状态，给一个url，处理一个，非常容易进行水平扩展(就是加线程、或者加机器)，而且即使单台爬虫宕机，也不会有什么损失。这跟我们在应用开发中，所说的"服务无状态"的思想是很像的。而相反，如果在单个爬虫线程内部，循环甚至递归的进行抓取，那么这部分工作是无法扩展的，而且宕机之后恢复会很困难。  public interface Scheduler { public void push(Request request, Task task); public Request poll(Task task); }

Does Dart have a scheduler?

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问题 I am looking at dart from server side point of view. Is there a scheduler that can execute isolates at a specific time or X times an hour? I am thinking on the lines of Quartz in the Java world. 回答1: Dart has a few options for delayed and repeating tasks, but I'm not aware of a port of Quartz to Dart (yet... :) Here are the basics: Timer - simply run a function after some delay Future - more robust, composable, functions that return values "in the future" Stream - robust, composable streams

How to set a persistent/regular schedule in Android?

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问题 How can I execute an action (maybe an Intent) on every specified time (e.g. Every day on 5AM)? It has to stay after device reboots, similar to how cron works. I am not sure if I can use AlarmManager for this, or can I? 回答1: If you want it to stay after the device reboots, you have to schedule the alarm after the device reboots. You will need to have the RECEIVE_BOOT_COMPLETED permission in your AndroidManifest.xml <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" /> A

Linux SCHED_OTHER, SCHED_FIFO and SCHED_RR - differences

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问题 Can someone explain the differences between SCHED_OTHER, SCHED_FIFO and SCHED_RR? Thanks 回答1: SCHED_FIFO and SCHED_RR are so called "real-time" policies. They implement the fixed-priority real-time scheduling specified by the POSIX standard. Tasks with these policies preempt every other task, which can thus easily go into starvation (if they don't release the CPU). The difference between SCHED_FIFO and SCHED_RR is that among tasks with the same priority, SCHED_RR performs a round-robin with a

How to execute a method in Asp.net MVC for every 24 hours

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问题 I have method in MVC like public void Sendmails() { //sending mails for every 24 hours. } Can I schedule above method to execute for every 24 hours. I know we can set schedule with sql server agent and windows task scheduler . But due to some issues i want to execute current dll only, is this possible in MVC? 回答1: Possible? Perhaps, with a bit of hacking on invoking tasks and background threads. Reliable? Not in the slightest. A web application is essentially a request-response system. The

Android Process Scheduling

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问题 I am trying to get a better understanding so I can scope the reliability impact from potential interoperability issues when creating an android app/service. I would like to figure out how process priority is determined. The differences in priority between services and activities and if the scheduler treats their priority differently. Basically I'm trying to get a strong understanding of how likely it is that an activity or service is starved by a rogue processes from a different application

Android Process Scheduling

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Python - Start a Function at Given Time

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问题 How can I run a function in Python , at a given time? For example: run_it_at(func, '2012-07-17 15:50:00') and it will run the function func at 2012-07-17 15:50:00. I tried the sched.scheduler, but it didn't start my function. import time as time_module scheduler = sched.scheduler(time_module.time, time_module.sleep) t = time_module.strptime('2012-07-17 15:50:00', '%Y-%m-%d %H:%M:%S') t = time_module.mktime(t) scheduler_e = scheduler.enterabs(t, 1, self.update, ()) What can I do? 回答1: Reading

scheduling task in windows 2008 with powershell

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问题 i want to schedule task in windows 2008 r2 with powershell. i used $username = "BUILTIN\Users" $TaskName = 'kakaka' $t=1 $TaskRun = "$PSHome\powershell.exe Start-Process -FilePath 'C:\v.exe' -ArgumentList '/a' -Verb runas -WindowStyle Normal" $start = (Get-Date).AddMinutes($t).ToString("HH:mm") schtasks /create /ru $username /tn $Taskname /tr $TaskRun /sc once /st $start /f on using above script i got an error "schtasks.exe : ERROR: The task XML contains a value which is incorrectly formatted

AutoSys Job multiple dependencies issue: s(1) & s(2) & s(3)

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问题 I got 4 jobs: 1, 2, 3, 4. 2's condition: s(1); 3's condition: s(2); 4's condition: s(1) & s(2) & s(3) all these jobs are daily jobs the first day is ok. the second day, the 4th job triggered mutilple times : I think when 1 success, and the status of 2 and 3 are still 'success'(the last days status), so the job 4 triggered, then 2 success, triggered again... so is there any solution for this? becase I only want these condition is based on the current day's result. 回答1: This is already answered