Allow config to define thread count

docs/running_psalm/configuration.md

@@ -396,6 +396,14 @@ Whether or not to allow `require`/`include` calls in your PHP. Defaults to `true
 ```
 Allows you to hard-code a serializer for Psalm to use when caching data. By default, Psalm uses `ext-igbinary` *if* the version is greater than or equal to 2.0.5, otherwise it defaults to PHP's built-in serializer.
 
+#### threads
+```xml
+<psalm
+        threads="[int]"
+>
+```
+Allows you to hard-code a serializer for Psalm to use when caching data. By default, Psalm uses `ext-igbinary` *if* the version is greater than or equal to 2.0.5, otherwise it defaults to PHP's built-in serializer.
+
 
 ## Project settings
 

src/Psalm/Config.php

@@ -563,6 +563,9 @@ class Config
      */
     public $internal_stubs = [];
 
+    /** @var ?int */
+    public $threads;
+
     protected function __construct()
     {
         self::$instance = $this;
@@ -1222,6 +1225,10 @@ private static function fromXmlAndPaths(
             }
         }
 
+        if (isset($config_xml->threads)) {
+            $config->threads = (int)$config_xml->threads;
+        }
+
         return $config;
     }
 

src/Psalm/Internal/Cli/Psalm.php

@@ -249,7 +249,7 @@ public static function run(array $argv): void
             $options['long-progress'] = true;
         }
 
-        $threads = self::detectThreads($options, $in_ci);
+        $threads = self::useThreads($options, $in_ci, $config);
 
         self::emitMacPcreWarning($options, $threads);
 
@@ -1337,4 +1337,15 @@ private static function getHelpText(): string
 
         HELP;
     }
+
+    private static function useThreads(array $options, bool $in_ci, Config $config): int
+    {
+        $threads = self::detectThreads($options, $in_ci);
+
+        if ($config->threads && $config->threads<$threads) {
+            $threads = $config->threads;
+        }
+
+        return $threads;
+    }
 }