MessageTemplateCache.cs

using System;
using System.Collections;
using Serilog.Events;
using Serilog.Parsing;

#nullable enable
namespace Akka.Logger.Serilog
{
    /// <summary>
    /// Taken directly from Serilog as the cache was internal.
    /// https://github.com/serilog/serilog/blob/master/src/Serilog/Core/Pipeline/MessageTemplateCache.cs
    /// </summary>
    internal class MessageTemplateCache
    {
        private readonly MessageTemplateParser _innerParser;
        private readonly object _templatesLock = new();

        private readonly Hashtable _templates = new();

        private const int MaxCacheItems = 1000;
        private const int MaxCachedTemplateLength = 1024;

        public MessageTemplateCache(MessageTemplateParser innerParser)
        {
            _innerParser = innerParser ?? throw new ArgumentNullException(nameof(innerParser));
        }

        public MessageTemplate Parse(string messageTemplate)
        {
            if (messageTemplate == null) throw new ArgumentNullException(nameof(messageTemplate));

            if (messageTemplate.Length > MaxCachedTemplateLength)
                return _innerParser.Parse(messageTemplate);

            // ReSharper disable once InconsistentlySynchronizedField
            // ignored warning because this is by design
            var result = (MessageTemplate?)_templates[messageTemplate];
            if (result != null)
                return result;

            result = _innerParser.Parse(messageTemplate);

            lock (_templatesLock)
            {
                // Exceeding MaxCacheItems is *not* the sunny day scenario; all we're doing here is preventing out-of-memory
                // conditions when the library is used incorrectly. Correct use (templates, rather than
                // direct message strings) should barely, if ever, overflow this cache.

                // Changing workloads through the lifecycle of an app instance mean we can gain some ground by
                // potentially dropping templates generated only in startup, or only during specific infrequent
                // activities.

                if (_templates.Count == MaxCacheItems)
                    _templates.Clear();

                _templates[messageTemplate] = result;
            }

            return result;
        }
    }
}