json-net-10.cs

JArray largeJson;

// read asynchronously from a file
using (FileStream asyncFileStream = new FileStream(@"large.json", FileMode.Open, FileAccess.Read, FileShare.Read, 4096, true))
{
    largeJson = await JArray.LoadAsync(new JsonTextReader(new StreamReader(asyncFileStream)));
}

JToken user = largeJson.SelectToken("$[?(@.name == 'Woodard Caldwell')]");
user["isActive"] = false;

// write asynchronously to a file
using (FileStream asyncFileStream = new FileStream(@"large.json", FileMode.Open, FileAccess.Write, FileShare.Write, 4096, true))
{
    await largeJson.WriteToAsync(new JsonTextWriter(new StreamWriter(asyncFileStream)));
}