ViewsData::getData() Fiber race condition causes empty cache entries

Problem/Motivation

ViewsData::getData() sets $this->fullyLoaded = TRUE at the beginning of the method (line 221), before data is actually retrieved from cache or rebuilt. This causes a race condition when PHP Fibers are involved.

When a Fiber suspension occurs during hook_views_data() invocation (e.g., due to lazy loading, BigPipe, or other async operations), another Fiber can observe:

• fullyLoaded = TRUE
• allStorage = [] (empty, because the first Fiber hasn't completed yet)

This causes the second Fiber to write an empty cache entry for table-specific views data, which persists and breaks Views functionality for subsequent requests.

This is the same pattern that was fixed in #3553342 (LocalTaskManager Fiber race condition) for Drupal 11.3.2.

Steps to reproduce

1. Set up a multilingual Drupal site with Views using Search API (or any module providing views data via hooks)
2. Clear all caches: drush cr
3. Load a page in language A (e.g., English) that triggers Views data loading
4. Load a page in language B (e.g., German) that uses a View with exposed filters
5. The exposed filter block may disappear or show "broken" handlers

Cache state after reproduction:

                                                                                                                                                                                                                                                                                                 
  views_data:en (main)                              → HAS data ✓                                                                                                                                                                                                                                        
  views_data:de (main)                              → HAS data ✓                                                                                                                                                                                                                                        
  views_data:search_api_index_[name]:en             → HAS data ✓                                                                                                                                                                                                                                        
  views_data:search_api_index_[name]:de             → EMPTY (0 keys) ✗                                                                                                                                                                                                                                  
  

Debug evidence:

Adding debug logging to ViewsData::get() shows:

                                                                                                                                                                                                                                                                                                 
  WRITING EMPTY CACHE for search_api_index_[name]:                                                                                                                                                                                                                                                      
    serviceLang=de, currentLang=de, fullyLoaded=TRUE, allStorageKeys=(empty)                                                                                                                                                                                                                            
  

This "impossible" state (fullyLoaded=TRUE but allStorage empty) occurs because fullyLoaded is set before data is ready, and a Fiber suspension allows concurrent code to see this inconsistent state.

Proposed resolution

Move $this->fullyLoaded = TRUE to after data is obtained, in both code paths (cache hit and cache miss/rebuild).

Before (buggy):

                                                                                                                                                                                                                                                                                                 
  protected function getData() {                                                                                                                                                                                                                                                                        
    $this->fullyLoaded = TRUE;  // BUG: Set before data is ready                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                        
    if ($data = $this->cacheGet($this->baseCid)) {                                                                                                                                                                                                                                                      
      return $data->data;                                                                                                                                                                                                                                                                               
    }                                                                                                                                                                                                                                                                                                   
    else {                                                                                                                                                                                                                                                                                              
      // ... rebuild data ...                                                                                                                                                                                                                                                                           
      return $data;                                                                                                                                                                                                                                                                                     
    }                                                                                                                                                                                                                                                                                                   
  }                                                                                                                                                                                                                                                                                                     
  

After (fixed):

                                                                                                                                                                                                                                                                                                 
  protected function getData() {                                                                                                                                                                                                                                                                        
    // Do NOT set fullyLoaded here - causes Fiber race condition                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                        
    if ($data = $this->cacheGet($this->baseCid)) {                                                                                                                                                                                                                                                      
      $this->fullyLoaded = TRUE;  // Set AFTER data is obtained                                                                                                                                                                                                                                         
      return $data->data;                                                                                                                                                                                                                                                                               
    }                                                                                                                                                                                                                                                                                                   
    else {                                                                                                                                                                                                                                                                                              
      // ... rebuild data ...                                                                                                                                                                                                                                                                           
      $this->cacheSet($this->baseCid, $data);                                                                                                                                                                                                                                                           
      $this->fullyLoaded = TRUE;  // Set AFTER data is rebuilt                                                                                                                                                                                                                                          
      return $data;                                                                                                                                                                                                                                                                                     
    }                                                                                                                                                                                                                                                                                                   
  }                                                                                                                                                                                                                                                                                                     
  

This follows the same fix pattern applied in #3553342 for LocalTaskManager.

Remaining tasks

• Review the proposed fix
• Add test coverage for the Fiber race condition scenario
• Verify fix doesn't introduce performance regression
• Backport consideration for 10.4.x if applicable

User interface changes

None. This is a bug fix that restores expected behavior.

Introduced terminology

None.

API changes

None. The public API of ViewsData remains unchanged.

Data model changes

None.