locking | 易学教程

What is the correct usage for sqlite on locking or async

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问题 We are using Xamarin to write C# code with SQLite for android and ios. However about how to use sqlite, I seem to have a conceptual misunderstanding: What are the best practices for SQLite on Android? According to the stackoverflow answer it says - one helper and one db connection. Use lock around it to make sure only one thread is accessing sqlite db at any time. My question is - if that is the case - what is the use for async? I tried to use async with synchronized code - and the code gave

Do condition variables still need a mutex if you're changing the checked value atomically?

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问题 Here is the typical way to use a condition variable: // The reader(s) lock(some_mutex); if(protected_by_mutex_var != desired_value) some_condition.wait(some_mutex); unlock(some_mutex); // The writer lock(some_mutex); protected_by_mutex_var = desired_value; unlock(some_mutex); some_condition.notify_all(); But if protected_by_mutex_var is set atomically by say, a compare-and-swap instruction, does the mutex serve any purpose (other than that pthreads and other APIs require you to pass in a

Python 3.2 - GIL - good/bad?

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问题 Python 3.2 ALPHA is out. From the Change Log, it appears the GIL has been entirely rewritten. A few questions: Is having a GIL good or bad? (and why). Is the new GIL better? If so, how? UPDATE : I'm fairly new to Python. So all of this is new to my but I do at least understand that the existence of a GIL with CPython is a huge deal. Question though, why does CPython not just clone the interpreter like Perl does in an attempt to remove the need for the GIL? 回答1: The best explanation I've seen

How to make wordpress blog completely invisible to public [Not Private]

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I want to close a wordpress blog I have from the public and keep it only for myself. I know I can set it to private but it shows an uggly log-in page and I dont want people trying to access it (using random usernames/pass etc) or think that its still open but its for members with accounts or anything like that. I would like the blog to point to a " server not found " for the public and when I am logged in as admin to be able to see my posts and backend aswell as frontend. How can I make this possible? My suggestion would be the following: function is_login_page() { return in_array( $GLOBALS[

Locking tables in Entity Framework

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问题 I have an SQL Database with a table that I would like to lock. I'm using Entity Framework. Basically, there are a number of processes that each want to write to the database concurrently. Each of them wants to update a row in some table. However, I want only one of them to be able to do this at the same time. Is there a way of locking an entire table, such as to prevent anyone from putting new rows or updating rows? Thanks, Christian 回答1: It's not clear to me why you would want this, but if

What strategy to use in Java for hierarchical reentrant read/write locking?

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问题 I'm looking for en efficient system to have a series of read/write locks organized hierarchically to manage access to hierarchically organized resources. If a subtree is locked for write, then no other lock should be able to be obtained in the whole subtree until it is released; similarly, a write lock in a subtree should prevent locking in a parent. Here are the ideas I was contemplating: Use the Apache Commons Transaction . Unforunately, the project hasn't been updated since March 2008 and

Usage of the C# lock keyword

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问题 I post my understanding of C# lock as follows, please help me validate whether or not I get it right. public class TestLock { private object threadLock = new object(); ... public void PrintOne() { lock (threadLock) { // SectionOne } } public void PrintTwo() { lock (threadLock) { // SectionTwo } } ... } Case I> Thread1 and Thread2 simultaneously try to call PrintOne. Since PrintOne is guarded by the instance lock, at any time, only one thread can exclusively enter the SectionOne. Is this

Hand-over-hand locking with Rust

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问题 I'm trying to write an implementation of union-find in Rust. This is famously very simple to implement in languages like C, while still having a complex run time analysis. I'm having trouble getting Rust's mutex semantics to allow iterative hand-over-hand locking. Here's how I got where I am now. First, this is a very simple implementation of part of the structure I want in C: #include <stdlib.h> struct node { struct node * parent; }; struct node * create(struct node * parent) { struct node *

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

Lock and transaction in postgres that should block a query

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问题 Let's assume in SQL window 1 I do: -- query 1 BEGIN TRANSACTION; UPDATE post SET title = 'edited' WHERE id = 1; -- note that there is no explicit commit Then from another window (window 2) I do: -- query 2 SELECT * FROM post WHERE id = 1; I get: 1 | original title Which is fine as the default isolation level is READ COMMITTED and because query 1 is never committed, the change it performs is not readable until I explicitly commit from window 1. In fact if I, in window 1, do: COMMIT TRANSACTION