public Void call() throws Exception {
      synchronized (DiskLruCache.this) {
        if (journalWriter == null) {
          return null; // Closed.
        }
        trimToSize();
        if (journalRebuildRequired()) {
          rebuildJournal();
          redundantOpCount = 0;
        }
      }
      return null;
    }
This cache uses a single background thread to evict entries.
core/src/main/java/com/bumptech/glide/disklrucache/DiskLruCache.java