Revert "Remove respawn after 50% memory exhaustion during batch proce… (#3952)

* Revert "Remove respawn after 50% memory exhaustion during batch processing. (#3909)"

This reverts commit 92b2359.

* Fixing batch processing if memory limit is reached.

Author: attrib

includes/batch.inc

@@ -52,12 +52,13 @@ class DrushBatchContext extends ArrayObject {
  * Process a Drupal batch by spawning multiple Drush processes.
  *
  * This function will include the correct batch engine for the current
- * major version of Drupal, and will make use of the site-process
- * library to spawn multiple worker threads to handle the processing of
- * the current batch.
+ * major version of Drupal, and will make use of the drush_backend_invoke
+ * system to spawn multiple worker threads to handle the processing of
+ * the current batch, while keeping track of available memory.
  *
  * The batch system will process as many batch sets as possible until
- * the entire batch has been completed.
+ * the entire batch has been completed or half of the available memory
+ * has been used.
  *
  * This function is a drop in replacement for the existing batch_process()
  * function of Drupal.
@@ -195,14 +196,17 @@ function _drush_batch_command($id) {
   if (_drush_batch_worker()) {
     return _drush_batch_finished();
   }
+  else {
+    return ['drush_batch_process_finished' => FALSE];
+  }
 }
 
 
 /**
  * Process batch operations
  *
  * Using the current $batch process each of the operations until the batch
- * has been completed or half of the available memory for the process has been
+ * has been completed or 60% of the available memory for the process has been
  * reached.
  */
 function _drush_batch_worker() {
@@ -278,6 +282,15 @@ function _drush_batch_worker() {
     // At this point, either $current_set contains operations that need to be
     // processed or all sets have been completed.
     $queue = _batch_queue($current_set);
+
+    // If we are in progressive mode, break processing after 60% of memory usage
+    // is reached.
+    if (drush_memory_limit() > 0 && (memory_get_usage() * 1.6) >= drush_memory_limit()) {
+      Drush::logger()->notice(dt("Batch process has consumed in excess of 50% of available memory. Starting new thread"));
+      // Record elapsed wall clock time.
+      $current_set['elapsed'] = round((microtime(TRUE) - $current_set['start']) * 1000, 2);
+      break;
+    }
   }
 
   // Reporting 100% progress will cause the whole batch to be considered