[#28] Client: Apply code optimizations

Signed-off-by: Pavel Gross <p.gross@yadro.com>

src/FrostFS.SDK.Client/Pool/SessionCache.cs

@@ -1,23 +1,49 @@
 using System;
-using System.Collections;
+using System.Collections.Concurrent;
 
 namespace FrostFS.SDK.Client;
 
-internal struct SessionCache(ulong sessionExpirationDuration)
+internal sealed class SessionCache(ulong sessionExpirationDuration)
 {
-    internal Hashtable Cache { get; } = [];
+    private ConcurrentDictionary<string, FrostFsSessionToken> _cache { get; } = [];
 
     internal ulong CurrentEpoch { get; set; }
 
     internal ulong TokenDuration { get; set; } = sessionExpirationDuration;
 
+    internal bool Contains(string key)
+    {
+        return _cache.ContainsKey(key);
+    }
+
+    internal bool TryGetValue(string? key, out FrostFsSessionToken? value)
+    {
+        if (key == null)
+        {
+            value = null;
+            return false;
+        }
+
+        var ok = _cache.TryGetValue(key, out value);
+
+        return ok && value != null;
+    }
+
+    internal void SetValue(string? key, FrostFsSessionToken value)
+    {
+        if (key != null)
+        {
+            _cache[key] = value;
+        }
+    }
+
     internal void DeleteByPrefix(string prefix)
     {
-        foreach (var key in Cache.Keys)
+        foreach (var key in _cache.Keys)
         {
-            if (((string)key).StartsWith(prefix, StringComparison.Ordinal))
+            if (key.StartsWith(prefix, StringComparison.Ordinal))
             {
-                Cache.Remove(key);
+                _cache.TryRemove(key, out var _);
             }
         }
     }