How to sync in memory data with disk in ASP NET - asp.net-core

Question

In a ASP NET Controller i have a service that returns a list of items.This service serves from the RAM the list to requesters.
The list can also be altered by a special group of users , so everytime it is altered i write the changes to disk and update my RAM from disk. (Reading my own writes this way)
From a JS client when i alter this list , the changes are written correctly on the disk , but when i forward a second request to get my list , i am served a stale list.I need to hit F5 for the client to get the right data.
I do not understand how does the RAM cache lags behind.
You can see in my service below that i have guarded the altering method with a lock.I have also tried without it to no avail.
Service
public class FileService : IADReadWrite {
private const int SIZE = 5;
private const string COMPUTER_FILE = #"computers.txt";
private List<Computer> computers = new List<Computer>();
private readonly object #filelock = new object();
private readonly Computer[] DEFAULT_COMPUTERS_LIST = new Computer[] {
new Computer(id:"W-CZC81371RS",Username:"A"),
new Computer(id:"W-CZC81371RQ",Username:"B"),
};
async Task<Computers> GetComputersAsymc() {
if (this.computers.Count == 0) {
var query = await Fetch();
this.computers = query.ToList();
}
var result = new Computers(this.computers);
return result;
}
public async Task<bool> AddComputerAsync(Computer computer) {
lock (filelock) {
if (this.computers.Any(x => x == computer)) {
return false;
}
this.computers.Add(computer);
File.WriteAllText(COMPUTER_FILE, JsonConvert.SerializeObject(this.computers, Formatting.Indented));
this.computers = JsonConvert.DeserializeObject<List<Computer>>(File.ReadAllText(COMPUTER_FILE));
}
return true;
}
---------------------Helpers --------------------------
private async Task<IEnumerable<Computer>> Fetch() {
if (!File.Exists(COMPUTER_FILE)) {
WriteComputersToDisk();
}
using (FileStream stream = new FileStream(COMPUTER_FILE, FileMode.Open, FileAccess.Read)) {
var raw = await File.ReadAllTextAsync(COMPUTER_FILE);
var comp = JsonConvert.DeserializeObject<List<Computer>>(raw);
return comp;
}
}
private void WriteComputersToDisk() {
var comps = DEFAULT_COMPUTERS_LIST;
var data = JsonConvert.SerializeObject(comps, Formatting.Indented);
File.WriteAllText(COMPUTER_FILE, data);
}
}
Controller
public class MyController:Controller
{
MyController(IADReadWrite service)
{
this.service=service;
}
IADReadWrite service;
[HttpGet]
public async Task<List<Computer>> GetAll()
{
return await service.GetComputersAsync();
}
[HttpPost]
public async Task AddComputer(Computer computer)
{
await service.AddComputerAsync(computer);
}
}
Scenario
Initial list : [0,1]
Client hits controller calling `AddComputer` {2}
I check the file , list is now: [0,1,2]
Client hits controller calling `GetComputers` -> it returns [0,1]
I hit F5 on the browser -> GetComputers gets hit again -> it returns [0,1,2]
P.S
I have not posted the Computer class since it does not matter in this scenario ( It implements IEquateable in case you are wondering if it is failing when i use the == operator.
The last 2 methods deal with the initialization of the Disk file.