race-condition

Difference between racearound condition and deadlock

由 孤街浪徒 提交于 2019-11-27 05:04:41
问题 What is the difference between a dead lock and a race around condition in programming terms? 回答1: Think of a race condition using the traditional example. Say you and a friend have an ATM cards for the same bank account. Now suppose the account has $100 in it. Consider what happens when you attempt to withdraw $10 and your friend attempts to withdraw $50 at exactly the same time. Think about what has to happen. The ATM machine must take your input, read what is currently in your account, and

Can node.js code result in race conditions?

由 雨燕双飞 提交于 2019-11-27 04:04:04
问题 From what I read, race conditions occur when different threads try to change a shared variable, which can result in a value that's not possible with any serial order of execution of those threads. But code in node.js runs in a single thread, so, does that mean code written in node.js is free of race conditions? 回答1: Yes. Node.js can run into race conditions as soon as you start sharing resources. I mistakenly also thought you couldn't get race conditions in Node.js because it's single

Ignoring locked row in a MySQL query

由 冷暖自知 提交于 2019-11-27 03:37:45
问题 I have one table that is read at the same time by different threads. Each thread must select 100 rows, execute some tasks on each row (unrelated to the database) then they must delete the selected row from the table. rows are selected using this query: SELECT id FROM table_name FOR UPDATE; My question is: How can I ignore (or skip) rows that were previously locked using a select statement in MySQL ? 回答1: I typically create a process_id column that is default NULL and then have each thread use

Race condition on x86

由 ▼魔方 西西 提交于 2019-11-27 01:53:10
问题 Could someone explain this statement: shared variables x = 0, y = 0 Core 1 Core 2 x = 1; y = 1; r1 = y; r2 = x; How is it possible to have r1 == 0 and r2 == 0 on x86 processors? Source "The Language of Concurrency" by Bartosz Milewski. 回答1: The problem can arise due to optimizations involving reordering of instructions. In other words, both processors can assign r1 and r2 before assigning variables x and y , if they find that this would yield better performance. This can be solved by adding a

Race condition and using Google Analytics Asynchronous (_gaq) synchronously

由 五迷三道 提交于 2019-11-26 22:53:58
问题 I have a website which is using Google Analytics newer asynchronous tracking method (_gaq). The problem I've run into is that I want to institute some specific link tracking and am worried that I will be creating a race condition. Basically, it's a news website so it has headlines which link to stories all over the place. A headline for a story might appear in 3 different places on a page, and appear on hundreds of other pages. Thus, in order to understand how our audience is interacting with

Atomic increment of a counter in django

由 百般思念 提交于 2019-11-26 22:35:39
问题 I'm trying to atomically increment a simple counter in Django. My code looks like this: from models import Counter from django.db import transaction @transaction.commit_on_success def increment_counter(name): counter = Counter.objects.get_or_create(name = name)[0] counter.count += 1 counter.save() If I understand Django correctly, this should wrap the function in a transaction and make the increment atomic. But it doesn't work and there is a race condition in the counter update. How can this

How to make sure there is no race condition in MySQL database when incrementing a field?

由 社会主义新天地 提交于 2019-11-26 21:59:28
How to prevent a race condition in MySQL database when two connections want to update the same record? For example, connection 1 wants to increase "tries" counter. And the second connection wants to do the same. Both connections SELECT the "tries" count, increase the value and both UPDATE "tries" with the increased value. Suddenly "tries" is only "tries+1" instead of being "tries+2", because both connections got the same "tries" and incremented it by one. How to solve this problem? Here's 3 different approaches: Atomic update update table set tries=tries+1 where condition=value; and it will be

C++ memory model and race conditions on char arrays

由 限于喜欢 提交于 2019-11-26 21:03:26
问题 Basically I have trouble understanding this: (from Bjarne FAQ) However, most modern processors cannot read or write a single character, it must read or write a whole word, so the assignment to c really is ``read the word containing c, replace the c part, and write the word back again.'' Since the assignment to b is similar, there are plenty of opportunities for the two threads to clobber each other even though the threads do not (according to their source text) share data! So how can char

Understanding goroutines

由 一曲冷凌霜 提交于 2019-11-26 19:23:34
问题 I'm trying to understand concurrency in Go. In particular, I wrote this thread-unsafe program: package main import "fmt" var x = 1 func inc_x() { //test for { x += 1 } } func main() { go inc_x() for { fmt.Println(x) } } I recognize that I should be using channels to prevent race conditions with x , but that's not the point here. The program prints 1 and then seems to loop forever (without printing anything more). I would expect it to print an infinite list of numbers, possibly skipping some

How to get last inserted row ID from WordPress database?

由 蓝咒 提交于 2019-11-26 19:00:27
问题 My WordPress plugin has a table with a AUTO_INCREMENT primary key field called ID. When a new row is inserted into the table, I'd like to get the ID value of the insertion. The feature is to using AJAX to post data to server to insert into DB. The new row ID is returned in the AJAX response to update client status. It is possible that multiple clients are posting data to server at the same time. So, I have to make sure that each AJAX request get the EXACT new row ID in response. In PHP, there
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