Don't lock Cake host object assembly.

src/OmniSharp.Abstractions/Services/IAssemblyLoader.cs

@@ -10,7 +10,7 @@ public interface IAssemblyLoader
 
         IReadOnlyList<Assembly> LoadAllFrom(string folderPath);
 
-        Assembly LoadFrom(string assemblyPath);
+        Assembly LoadFrom(string assemblyPath, bool dontLockAssemblyOnDisk = false);
     }
 
     public static class IAssemblyLoaderExtensions

src/OmniSharp.Cake/CakeProjectSystem.cs

@@ -82,6 +82,7 @@ public void Initalize(IConfiguration configuration)
                         FileName = cakePath,
                         FromDisk = true
                     });
+
                     var project = GetProject(cakeScript, cakePath);
 
                     // add Cake project to workspace
@@ -205,8 +206,15 @@ private ProjectInfo GetProject(CakeScript cakeScript, string filePath)
         {
             var name = Path.GetFileName(filePath);
 
-            var assembly = _assemblyLoader.LoadFrom(cakeScript.Host.AssemblyPath);
-            var hostObjectType = Type.GetType(cakeScript.Host.TypeName, a => assembly, null, true);
+            if (!File.Exists(cakeScript.Host.AssemblyPath))
+            {
+                throw new FileNotFoundException($"Cake is not installed. Path {cakeScript.Host.AssemblyPath} does not exist.");
+            }
+            var hostObjectType = Type.GetType(cakeScript.Host.TypeName, a => _assemblyLoader.LoadFrom(cakeScript.Host.AssemblyPath, dontLockAssemblyOnDisk: true), null, false);
+            if (hostObjectType == null)
+            {
+                throw new InvalidOperationException($"Could not get host object type: {cakeScript.Host.TypeName}.");
+            }
 
             return ProjectInfo.Create(
                 id: ProjectId.CreateNewId(Guid.NewGuid().ToString()),

src/OmniSharp.Host/Services/AssemblyLoader.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.IO;
@@ -9,6 +10,7 @@ namespace OmniSharp.Services
 {
     internal class AssemblyLoader : IAssemblyLoader
     {
+        private static readonly ConcurrentDictionary<string, Assembly> AssemblyCache = new ConcurrentDictionary<string, Assembly>(StringComparer.OrdinalIgnoreCase);
         private readonly ILogger _logger;
 
         public AssemblyLoader(ILoggerFactory loggerFactory)
@@ -59,19 +61,31 @@ public IReadOnlyList<Assembly> LoadAllFrom(string folderPath)
             }
         }
 
-        public Assembly LoadFrom(string assemblyPath)
+        public Assembly LoadFrom(string assemblyPath, bool dontLockAssemblyOnDisk = false)
         {
             if (string.IsNullOrWhiteSpace(assemblyPath)) return null;
 
-            Assembly assembly = null;
-
-            try
+            if (!AssemblyCache.TryGetValue(assemblyPath, out var assembly))
             {
-                assembly = Assembly.LoadFrom(assemblyPath);
-            }
-            catch (Exception ex)
-            {
-                _logger.LogError(ex, $"Failed to load assembly from path: {assemblyPath}");
+                try
+                {
+                    if (dontLockAssemblyOnDisk)
+                    {
+                        var bytes = File.ReadAllBytes(assemblyPath);
+                        assembly = Assembly.Load(bytes);
+                    }
+                    else
+                    {
+                        assembly = Assembly.LoadFrom(assemblyPath);
+                    }
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogError(ex, $"Failed to load assembly from path: {assemblyPath}");
+                    return assembly;
+                }
+
+                AssemblyCache.AddOrUpdate(assemblyPath, assembly, (k, v) => assembly);
             }
 
             _logger.LogTrace($"Assembly loaded from path: {assemblyPath}");