LiteDB: [question] How to prevent race condition?
I am using LiteDB in a web application.
However, I am having this issue: I am storing a list of users, and each user has a data usage number. In each request, the user data usage number is loaded from LiteDB, and is increased. But this is my problem: if the client makes many simultaneous requests, the data usage number will be loaded before it is updated, resulting in an incorrect data usage.
To explain again:
In database: [usage: 20]
request 1:
- thread 1: server loads usage (is
20) - thread 1: does some processsing (adds
10), does not update user in litedb collection yet request 2 (happens during request 1’s data processing): - thread 2: server loads usage (is
20) <-- This is my problem, I want to lock the user so other requests can’t happen until first request processing is done - thread 2: server adds
10 - thread 1 saves user (now usage is
30) - thread 2 saves user (now usage is
30)
the problem is that thread 2 doesn’t wait for thread 1 to finish, and incorrect final value is stored. I am using NancyFx with async/await requests; each request spawns a new thread.
i am using transactions only when saving the value.
thanks
About this issue
- Original URL
- State: closed
- Created 7 years ago
- Comments: 17 (2 by maintainers)
Within the database.
Table: user_locks Fields : Bool write_lock default value off Bool read _lock default value off.
Before processing user data from user table for either read (select) or write (update / insert)
Do check of contents of the values of user_locks table
In structure of example: Table: users Id | username | data… 1| Steve | djdjsjs 2 | John | djdbdbdb 3 | most | dhdjsnsn
Table: user_locks Id | read_lock | write_lock 1 | 0 | 0 2 | 0 | 0 3 | 0 | 0
Program example
To explain again: In database: [usage: 20]
request 1:
litedb collection yet request 2 (happens during request 1’s data processing):
On each of user data in thread do the following: When reading user data Check read_lock If set to true do a wait loop for x. seconds then check again till. read_lock is false Set write_lock to true Read user data. Do processing Set write_lock to false
When writing (saving / updating) Check write_lock Do wait loop till value is false (same as read_lock logic) Set read_lock to true Do update / insert command etc… Set read_lock to false On Jan 6, 2017 2:51 AM, “nictaylr” notifications@github.com wrote: