semaphore | 易学教程

Name and Unnamed Semaphore

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问题 I'm trying to understand the similarities and differences between named and unnamed semaphore so my google searches yielded me this. I had a question about the wording on the page though, it says: Unnamed semaphores might be usable by more than one process Named semaphores are sharable by several processes Do those two words create any important distinction between those two types of semaphores or are they irrelevant? So so far here's what I have: Similarities -Several processes can do

Mutual exclusion and semaphores

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问题 I am writing a program (for homework) that simulates a unisex bathroom. Only 4 people are allowed at a time and men and woman cannot enter if the other sex is already using the bathroom. My problem is with allowing a max of 4 people in the bathroom. As you can see from the output, only 1 person is getting into the restroom at a time. Here is my code: const int Delayx = 60; int i; int restroom = 0; int Menwaiting = 0; int Womenwaiting = 0; semaphore max_capacity; semaphore woman; semaphore man

Semaphore implementation

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问题 I was wondering if there was a way to implement semaphore in C++ (or C#), any libraries that'd help. I tried using OpenMP but I had no way of actually blocking threads, instead I had to busy wait on 'em which lead to deadlocks if/when I hadn't enough number of threads. So First I'm looking for a some library that would let me block/spawn/kill my threads. Secondly, are there any libraries out there that already implement semaphores? And finally, when I was introduced to the context of

IOS semaphore_wait_trap on main thread causing hang in UI

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问题 I have a long running function inside an asynchronous (serial) worker queue. I know that sometimes this function hangs inside a particular openCV call. For some reason this hang is also causing the main thread to hang. When pausing and entering debug mode I see that there is a call to semaphore_wait_trap() on the main thread (Queue) I can suspend the hanging thread (My worker queue) in debug mode and then this trap goes away and the GUI becomes responsive once again on the phone. After

How to implement event listening in PHP

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问题 here is my problem: I have a script (let's call it comet.php) whic is requsted by an AJAX client script and wait for a change to happen like this: while(no_changes){ usleep(100000); //check for changes } I don't like this too much, it's not very scalable and it's (imho) "bad practice" I would like to improve this behaviour with a semaphore(?) or anyway concurrent programming technique. Can you please give me some tips on how to handle this? (I know, it's not a short answer, but a starting

Python asyncio.semaphore in async-await function

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问题 I am trying to teach myself Python's async functionality. To do so I have built an async web scraper. I would like to limit the total number of connections I have open at once to be a good citizen on servers. I know that semaphore's are a good solution, and the asyncio library has a semaphore class built in. My issue is that Python complains when using yield from in an async function as you are combining yield and await syntax. Below is the exact syntax I am using... import asyncio import

Is there any mutex/semaphore mechanism in shell scripts?

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问题 I'm looking for mutex/semaphore/concurrency mechanism in shell script. Consider following situation: Unless "a" user does not close the shared file, "b" user should not able to open/update it. I'm just wondering how to implement mutex, semaphore, critical sections, etc. in shell scripting. Which is the easiest way to implement locking mechanism [file level] in shell scripting? 回答1: See BashFAQ and ProcessManagment for discussions on file locking in Bash. Tagging your question as shell (only)

ios的线程和同步异步操作

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> ios的线程和同步异步操作 ios的线程和同步异步操作 ios的多线程，同步异步操作，都是我们日常的开发中经常会遇到的问题，本文把常见的ios线程，同步异步的操作进行了整理。代码下载: 我博客中大部分示例代码都上传到了github，地址是：https://github.com/coolnameismy/demo，点击跳转代码下载地址本文代码存放目录是 ThreadAndAsynchronization 如果大家支持，请follow我的github账号，并fork我的项目，有其他问题可以在github上给我留言或者给我发邮件，coolnameismy@hotmail.com，blog的RSS订阅地址：http://liuyanwei.jumppo.com/pages/rss.xml 基础知识 1.线程和进程 ,多线程线程和进程：网上有一大堆很专业的说法，大多数说的都比较复杂，越复杂的解释其实说的越准确和严谨，但是常常会把人弄糊涂。这里我也不去解释了，大多数场景你可以理解为，一个应用程序就是一个进程，而一个进程可以分为多个线程多线程：大多数框架都支持一个进程启多个线程，比如 c#、java、obejctive-c，但是并不是所有的框架都支持，比如flex的框架就不支持多线程。

“The semaphore timeout period has expired” error for USB connection

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问题 I'm getting this error... The semaphore timeout period has expired. On this line... ThePorts.ActivePort1.Open(); ...but I only get it from time to time. When it happens, it happens over and over again. Then the problem goes away, for hours or days, then it comes back. The serial port is a USB with a BlueTooth connected. I think this guy was having a very similar problem, but not in C# Freeze on SerialPort.Open / DeviceIoControl / GetcommState with usbser.sys As best I can estimate, I have

Conditional Variable vs Semaphore

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问题 When should one use a semaphore and when should one use a conditional variable (CondVar) ? 回答1: Locks are used for mutual exclusion. When you want to ensure that a piece of code is atomic, put a lock around it. You could theoretically use a binary semaphore to do this, but that's a special case. Semaphores and condition variables build on top of the mutual exclusion provide by locks and are used for providing synchronized access to shared resources. They can be used for similar purposes. A