Issue 6265 - Create shared AdblockEngine instance in AdblockWebView in background

libadblockplus-android/src/org/adblockplus/libadblockplus/android/AdblockEngineProvider.java

Index: libadblockplus-android/src/org/adblockplus/libadblockplus/android/AdblockEngineProvider.java
diff --git a/libadblockplus-android/src/org/adblockplus/libadblockplus/android/AdblockEngineProvider.java b/libadblockplus-android/src/org/adblockplus/libadblockplus/android/AdblockEngineProvider.java
index a48f06e478904d861e20debb9a7d3fad12c90814..c5a80d945df434cb51209e706b5b97c26b57500b 100644
--- a/libadblockplus-android/src/org/adblockplus/libadblockplus/android/AdblockEngineProvider.java
+++ b/libadblockplus-android/src/org/adblockplus/libadblockplus/android/AdblockEngineProvider.java
@@ -19,8 +19,36 @@ package org.adblockplus.libadblockplus.android;
 
 public interface AdblockEngineProvider
 {
+  /**
+   * Register AdblockEngine client
+   * @param asynchronous If `true` engines will be created in background thread without locking of
+   *                     current thread. Use waitForReady() before getEngine() later.
+   *                     If `false` locks current thread.
+   * @return if a new instance is allocated
+   */
   boolean retain(boolean asynchronous);
+
+  /**
+   * Wait until everything is ready (used for `retain(true)`)
+   * Warning: locks current thread
+   */
   void waitForReady();
-  AdblockEngine getAdblockEngine();
+
+  /**
+   * Return AdblockEngine instance
+   * @return AdblockEngine instance. Can be `null` is not yet retained or already released
+   */
+  AdblockEngine getEngine();
+
+  /**
+   * Unregister AdblockEngine client
+   * @return `true` if the last instance is destroyed
+   */
   boolean release();
+
+  /**
+   * Get registered clients count
+   * @return registered clients count
+   */
+  int getCounter();
 }