content: /*
   * Copyright (C) 2010 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.android.layoutlib.bridge.impl;
  
  import com.android.internal.annotations.GuardedBy;
  import com.android.layoutlib.bridge.util.Debug;
  import com.android.layoutlib.bridge.util.SparseWeakArray;
  
  import android.annotation.Nullable;
  import android.util.SparseArray;
  
  import java.io.PrintStream;
  import java.lang.ref.WeakReference;
  import java.util.HashSet;
  import java.util.LinkedList;
  import java.util.Set;
  import java.util.WeakHashMap;
  import java.util.concurrent.atomic.AtomicLong;
  
  import libcore.util.NativeAllocationRegistry_Delegate;
  
  /**
   * Manages native delegates.
   *
   * This is used in conjunction with layoublib_create: certain Android java classes are mere
   * wrappers around a heavily native based implementation, and we need a way to run these classes
   * in our Android Studio rendering framework without bringing all the native code from the Android
   * platform.
   *
   * Thus we instruct layoutlib_create to modify the bytecode of these classes to replace their
   * native methods by "delegate calls".
   *
   * For example, a native method android.graphics.Matrix.init(...) will actually become
   * a call to android.graphics.Matrix_Delegate.init(...).
   *
   * The Android java classes that use native code uses an int (Java side) to reference native
   * objects. This int is generally directly the pointer to the C structure counterpart.
   * Typically a creation method will return such an int, and then this int will be passed later
   * to a Java method to identify the C object to manipulate.
   *
   * Since we cannot use the Java object reference as the int directly, DelegateManager manages the
   * int -> Delegate class link.
   *
   * Native methods usually always have the int as parameters. The first thing the delegate method
   * will do is call {@link #getDelegate(long)} to get the Java object matching the int.
   *
   * Typical native init methods are returning a new int back to the Java class, so
   * {@link #addNewDelegate(Object)} does the same.
   *
   * The JNI references are counted, so we do the same through a {@link WeakReference}. Because
   * the Java object needs to count as a reference (even though it only holds an int), we use the
   * following mechanism:
   *
   * - {@link #addNewDelegate(Object)} and {@link #removeJavaReferenceFor(long)} adds and removes
   *   the delegate to/from a set. This set holds the reference and prevents the GC from reclaiming
   *   the delegate.
   *
   * - {@link #addNewDelegate(Object)} also adds the delegate to a {@link SparseArray} that holds a
   *   {@link WeakReference} to the delegate. This allows the delegate to be deleted automatically
   *   when nothing references it. This means that any class that holds a delegate (except for the
   *   Java main class) must not use the int but the Delegate class instead. The integers must
   *   only be used in the API between the main Java class and the Delegate.
   *
   * @param <T> the delegate class to manage
   */
  public final class DelegateManager<T> {
      private static final SparseWeakArray<Object> sDelegates = new SparseWeakArray<>();
      /** Set used to store delegates when their main object holds a reference to them.
       * This is to ensure that the WeakReference in the SparseWeakArray doesn't get GC'ed
       * @see #addNewDelegate(Object)
       * @see #removeJavaReferenceFor(long)
       */
      private static final Set<Object> sJavaReferences = new HashSet<>();
      private static final AtomicLong sDelegateCounter = new AtomicLong(1);
      /**
       * Tracks "native" allocations. This means that we know of the object in the Java side and we
       * can attach the delegate lifecycle to the lifecycle of the Java object. If the Java object
       * is disposed, it means we can get rid of the delegate allocation.
       * Ideally, we would use a {@link WeakHashMap} but we do not control the equals() method of the
       * referents so we can not safely rely on them.
       */
      private static final LinkedList<NativeAllocationHolder> sNativeAllocations = new LinkedList<>();
      /**
       * Map that allows to do a quick lookup of delegates that have been marked as native
       * allocations.
       * This allows us to quickly check if, when a manual dispose happens, there is work we have
       * to do.
       */
      @GuardedBy("sNativeAllocations")
      private static final WeakHashMap<Object, WeakReference<NativeAllocationHolder>>
              sNativeAllocationsReferences = new WeakHashMap<>();
      /**
       * Counter of the number of native allocations. We use this counter to trigger the collection
       * of unlinked references in the sNativeAllocations list. We do not need to do this process
       * on every allocation so only run it every 50 allocations.
       */
      @GuardedBy("sNativeAllocations")
      private static long sNativeAllocationsCount = 0;
  
      @SuppressWarnings("FieldCanBeLocal")
      private final Class<T> mClass;
  
      public DelegateManager(Class<T> theClass) {
          mClass = theClass;
      }
  
      public synchronized static void dump(PrintStream out) {
          for (Object reference : sJavaReferences) {
              int idx = sDelegates.indexOfValue(reference);
              out.printf("[%d] %s\n", sDelegates.keyAt(idx), reference.getClass().getSimpleName());
          }
          out.printf("\nTotal number of objects: %d\n", sJavaReferences.size());
      }
  
      /**
       * Returns the delegate from the given native int.
       * <p>
       * If the int is zero, then this will always return null.
       * <p>
       * If the int is non zero and the delegate is not found, this will throw an assert.
       *
       * @param native_object the native int.
       * @return the delegate or null if not found.
       */
      @Nullable
      public T getDelegate(long native_object) {
          if (native_object > 0) {
              Object delegate;
              synchronized (DelegateManager.class) {
                  delegate = sDelegates.get(native_object);
              }
  
              if (Debug.DEBUG) {
                  if (delegate == null) {
                      System.err.println("Unknown " + mClass.getSimpleName() + " with int " +
                              native_object);
                  }
              }
  
              assert delegate != null;
              //noinspection unchecked
              return (T)delegate;
          }
          return null;
      }
  
      /**
       * Adds a delegate to the manager and returns the native int used to identify it.
       * @param newDelegate the delegate to add
       * @return a unique native int to identify the delegate
       */
      public long addNewDelegate(T newDelegate) {
          long native_object = sDelegateCounter.getAndIncrement();
          synchronized (DelegateManager.class) {
              sDelegates.put(native_object, newDelegate);
              // Only for development: assert !sJavaReferences.contains(newDelegate);
              sJavaReferences.add(newDelegate);
          }
  
          if (Debug.DEBUG) {
              System.out.println(
                      "New " + mClass.getSimpleName() + " " +
                              "with int " +
                              native_object);
          }
  
          return native_object;
      }
  
      /**
       * Removes the main reference on the given delegate.
       * @param native_object the native integer representing the delegate.
       */
      public void removeJavaReferenceFor(long native_object) {
          synchronized (DelegateManager.class) {
              T delegate = getDelegate(native_object);
  
              if (Debug.DEBUG) {
                  System.out.println("Removing main Java ref on " + mClass.getSimpleName() +
                          " with int " + native_object);
              }
  
              if (!sJavaReferences.remove(delegate)) {
                  // We didn't have any strong references to the delegate so it might be tracked by
                  // the native allocations tracker. If so, we want to remove that reference to
                  // make it available to collect ASAP.
                  synchronized (sNativeAllocations) {
                      WeakReference<NativeAllocationHolder> holderRef = sNativeAllocationsReferences.get(delegate);
                      NativeAllocationHolder holder = holderRef.get();
                      if (holder != null) {
                          // We only null the referred delegate. We do not spend the time in finding
                          // the holder in the list and removing it since the "garbage collection" in
                          // markAsNativeAllocation will do it for us.
                          holder.mReferred = null;
                      }
                  }
              }
          }
      }
  
      /**
       * This method marks the given native_object as a native allocation of the passed referent.
       * This means that the lifecycle of the native_object can now be attached to the referent and
       * if the referent is disposed, we can safely dispose the delegate.
       * This method is called by the {@link NativeAllocationRegistry_Delegate} and allows the
       * DelegateManager to remove the strong reference to the delegate.
       */
      public void markAsNativeAllocation(Object referent, long native_object) {
          NativeAllocationHolder holder;
          synchronized (DelegateManager.class) {
              T delegate = getDelegate(native_object);
              if (Debug.DEBUG) {
                  if (delegate == null) {
                      System.err.println("Unknown " + mClass.getSimpleName() + " with int " +
                              native_object);
                  }
                  else {
                      System.err.println("Marking element as native " + native_object);
                  }
              }
  
              assert delegate != null;
              if (sJavaReferences.remove(delegate)) {
                  // We had a strong reference, move to the native allocation tracker.
                  holder = new NativeAllocationHolder(referent, delegate);
              }
              else {
                  holder = null;
              }
          }
  
          if (holder != null) {
              synchronized (sNativeAllocations) {
                  sNativeAllocations.add(holder);
                  // The value references the key in this case but we use a WeakReference value.
                  sNativeAllocationsReferences.put(holder.mReferred, new WeakReference<>(holder));
  
                  if (++sNativeAllocationsCount % 50 == 0) {
                      // Do garbage collection
                      boolean collected = sNativeAllocations.removeIf(e -> e.mReferent.get() == null);
                      if (Debug.DEBUG && collected) {
                          System.err.println("Elements collected");
                      }
                  }
              }
          }
      }
  
      private static class NativeAllocationHolder {
          private final WeakReference<Object> mReferent;
          // The referred object is not null so we can null them on demand
          private Object mReferred;
  
          private NativeAllocationHolder(Object referent, Object referred) {
              mReferent = new WeakReference<>(referent);
              mReferred = referred;
          }
      }
  }
  