deadlock | 易学教程

Why is lockless concurrency such a big deal (in Clojure)?

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问题 I'm told that Clojure has lockless concurrency and that this is Important. I've used a number of languages but didn't realize they were performing locks behind the scenes. Why is this an advantage in Clojure (or in any language that has this feature)? 回答1: I can't speak about Clojure specifically, but ... it means you don't need to wait for someone to be done with something before you can get to work. Which is great. Typically it's achieved with immutable types. If nothing can be modified,

Deadlocks - Will this really help?

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问题 So I've got a query that keeps deadlocking on me. People who know the system well can't figure out why the sproc is deadlocking, but they tell me that I should just add this to it: SET NOCOUNT ON SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED Is this really a valid solution? What does that do? 回答1: SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED This will cause the system to return inconsitent data, including duplicate records and missing records. Read more at Previously committed rows

How to get stack trace of a thread

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问题 I have a multithreaded application. Several messages are coming to the application and are processed in separated threads. For this I am using classes ThreadPoolExecutor and FutureTask from package java.util.concurrent. Occasionally I have some deadlocks in the application. When a deadlock occurs I want to interrupt the blocking thread and I want to log the stack trace of this thread so that I can later resolve the deadlock. Is there any way how can we find the stack trace of a thread outside

Why would SQL Server's SET DEADLOCK_PRIORITY HIGH not be honored?

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问题 I've captured a SQL Server 2012 deadlock graph (using Gail Shaw's query) that shows a process with taskpriority="10" being picked as the deadlock victim over 2 processes with taskpriority="0". My understanding is that the deadlock priority is checked first and lower priority processes will be chosen as the victim. Only when all processes are equal priority will other factors be relevant. Can anyone shed any light on why DEADLOCK_PRIORITY might not be honored? Interestingly, the SET DEADLOCK

use of spin variants in network processing

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问题 I have written a Kernel module that is interacting with net-filter hooks. The net-filter hooks operate in Softirq context. I am accessing a global data structure "Hash Table" from the softirq context as well as from Process context. The process context access is due to a sysctl file being used to modify the contents of the Hash-table. I am using spinlock_irq_save. Is this choice of spin_lock api correct ?? In terms of performance and locking standards. what would happen if an interrupt is

Pthread program deadlocks using condition variables

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问题 What this program is trying to accomplish: This program is supposed to synchronize several threads of "visitors" and "cars". Visitors wander around for a random amount of time until they decide to go on a car ride. If they are first in line for a car ride and a car is available they take a ride, else they must wait till they are first in line or a car comes back. If there are no visitors in line the cars wait in order until a visitor wants to go on a ride. More background info: I remade my

Multiprocessing Queue need Manager?

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问题 Why program A deadlock but program B runs fine? Both uses a queue to pass result between main process and sub-processes. Both wait for all sub-processes to end before retrieving the results from the queue. In the actual program, I need a queue to pass streams of results between steps. This is for working on results when the results are generated and before one of the step completes. Changing the mp.queue in program A to a queue of a mp.Manager would fix the deadlock. But using manager seems

Yet another C# Deadlock Debugging Question

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问题 I have a multi-threaded application build in C# using VS2010 Professional. It's quite a large application and we've experienced the classing GUI cross-threading and deadlock issues before, but in the past month we've noticed the appears to lock up when left idle for around 20-30 minutes. The application is irresponsive and although it will repaint itself when other windows are dragged in front of the application and over it, the GUI still appears to be locked... interstingly (unlike if the

python subprocess deadlock in demonized server

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I'm trying to set up a remote backup server for dar, along these lines . I'd really like to do all the piping with python if possible, but I've asked a separate question about that. Using netcat in subprocess.Popen(cmd, shell=True) , I succeeded in making a differential backup, as in the examples on the dar site. The only two problems are: I don't know how to assign port numbers dynamically this way If I execute the server in the background, it fails. Why? Update: This doesn't seem to be related to netcat; it hangs even without netcat in the mix. Here's my code: from socket import socket, AF

PThread RWLock Deadlocking with Recursive Locks

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问题 I've been working on a small sand-boxed example to help me figure out how to use rwlocks. Everything seems fairly straightforward, however I'm getting deadlocks in my example every once and a while and don't understand why it's happening. I've put the code example on pastebin because it's more than a few lines of code: http://pastebin.org/359203 If you run the example. When it eventually deadlocks the last three print statements will be one of two cases: one: th4: request lock th3: request