ENGCOM-5098: Implement Better Error Handling and Fix Waits on Null PIDs in Parallel SCD Execution magento#22607

 - Merge Pull Request magento#22607 from davidalger/magento2:pcntl-scd-fix-23
 - Merged commits:
   1. 49b3c72
   2. 7631cbc
   3. e1525a8
   4. 8d0a3d8
   5. 2be3105

Author: magento-engcom-team

app/code/Magento/Deploy/Process/Queue.php

@@ -347,6 +347,7 @@ private function isDeployed(Package $package)
                 $result = pcntl_waitpid($pid, $status, WNOHANG);
                 if ($result === $pid) {
                     $package->setState(Package::STATE_COMPLETED);
+                    // phpcs:ignore Magento2.Functions.DiscouragedFunction
                     $exitStatus = pcntl_wexitstatus($status);
 
                     $this->logger->info(
@@ -361,7 +362,9 @@ private function isDeployed(Package $package)
                     // phpcs:ignore Magento2.Functions.DiscouragedFunction
                     return pcntl_wexitstatus($status) === 0;
                 } elseif ($result === -1) {
+                    // phpcs:ignore Magento2.Functions.DiscouragedFunction
                     $errno = pcntl_errno();
+                    // phpcs:ignore Magento2.Functions.DiscouragedFunction
                     $strerror = pcntl_strerror($errno);
 
                     throw new \RuntimeException(
@@ -401,6 +404,7 @@ private function checkTimeout()
      * Protect against zombie process
      *
      * @throws \RuntimeException
+     * @SuppressWarnings(PHPMD.UnusedLocalVariable)
      * @return void
      */
     public function __destruct()
@@ -417,7 +421,9 @@ public function __destruct()
 
             // phpcs:ignore Magento2.Functions.DiscouragedFunction
             if (pcntl_waitpid($pid, $status) === -1) {
+                // phpcs:ignore Magento2.Functions.DiscouragedFunction
                 $errno = pcntl_errno();
+                // phpcs:ignore Magento2.Functions.DiscouragedFunction
                 $strerror = pcntl_strerror($errno);
 
                 throw new \RuntimeException(