private static async Task Write(ProcessingState state)
{
await using var stream = File.Open(Constants.StateFilePath, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Read);
stream.SetLength(0);
await using var reader = new StreamWriter(stream, Encoder);
await reader.WriteAsync(state.ToString());
}
private static async Task <ProcessingState> Read()
{
if (!File.Exists(Constants.StateFilePath))
{
return(new ProcessingState());
}
await using var stream = File.Open(Constants.StateFilePath, FileMode.Open, FileAccess.Read, FileShare.Read);
stream.Seek(0, SeekOrigin.Begin);
using var reader = new StreamReader(stream, Encoder);
var content = await reader.ReadToEndAsync();
return(ProcessingState.FromString(content) ?? new ProcessingState());
}
public async Task <int> GetIndex(NotificationSource source)
{
//multiple requests may try to obtain the new index
//Therefore, to prevent raise conditions, we need to use locking mechanism.
//It will ensure that only one thread obtains new index.
await _lock.WaitAsync();
try
{
var state = await Get();
state.IncrementIndex(source);
await Write(state);
_state = state;
return(state.GetIndex(source));
}
finally
{
_lock.Release();
}
}