Implement destroy() for all ImapElement classes.

- This is to make sure we're not touching any ImapResponse that's
  already been destroyed.

- I didn't add "is it already destroyed?" check to them
  (except for ImapTempFileLiteral), because it can be costly.
  Just let NPE be thrown.

Change-Id: Idc7b88c4844727922841cbad8a106bf781181d45

src/com/android/email/mail/store/imap/ImapElement.java

@@ -48,6 +48,11 @@ public abstract class ImapElement {
      * is out of range.
      */
     public static final ImapElement NONE = new ImapElement() {
+        @Override public void destroy() {
+            // Don't call super.destroy().
+            // It's a shared object.  We don't want the mDestroyed to be set on this.
+        }
+
         @Override public boolean isList() {
             return false;
         }
@@ -66,15 +71,31 @@ public abstract class ImapElement {
         }
     };
 
+    private boolean mDestroyed = false;
+
     public abstract boolean isList();
 
     public abstract boolean isString();
 
+    protected boolean isDestroyed() {
+        return mDestroyed;
+    }
+
     /**
      * Clean up the resources used by the instance.
      * It's for removing a temp file used by {@link ImapTempFileLiteral}.
      */
     public void destroy() {
+        mDestroyed = true;
+    }
+
+    /**
+     * Throws {@link RuntimeException} if it's already destroyed.
+     */
+    protected final void checkNotDestroyed() {
+        if (mDestroyed) {
+            throw new RuntimeException("Already destroyed");
+        }
     }
 
     /**

src/com/android/email/mail/store/imap/ImapList.java

@@ -26,12 +26,17 @@ public class ImapList extends ImapElement {
      * {@link ImapList} representing an empty list.
      */
     public static final ImapList EMPTY = new ImapList() {
+        @Override public void destroy() {
+            // Don't call super.destroy().
+            // It's a shared object.  We don't want the mDestroyed to be set on this.
+        }
+
         @Override void add(ImapElement e) {
             throw new RuntimeException();
         }
     };
 
-    private final ArrayList<ImapElement> mList = new ArrayList<ImapElement>();
+    private ArrayList<ImapElement> mList = new ArrayList<ImapElement>();
 
     /* package */ void add(ImapElement e) {
         if (e == null) {
@@ -164,9 +169,13 @@ public class ImapList extends ImapElement {
 
     @Override
     public void destroy() {
-        for (ImapElement e : mList) {
-            e.destroy();
+        if (mList != null) {
+            for (ImapElement e : mList) {
+                e.destroy();
+            }
+            mList = null;
         }
+        super.destroy();
     }
 
     @Override

src/com/android/email/mail/store/imap/ImapMemoryLiteral.java

@@ -30,7 +30,7 @@ import java.io.InputStream;
  * Subclass of {@link ImapString} used for literals backed by an in-memory byte array.
  */
 public class ImapMemoryLiteral extends ImapString {
-    private final byte[] mData;
+    private byte[] mData;
 
     /* package */ ImapMemoryLiteral(FixedLengthInputStream in) throws IOException {
         // We could use ByteArrayOutputStream and IOUtils.copy, but it'd perform an unnecessary
@@ -49,6 +49,12 @@ public class ImapMemoryLiteral extends ImapString {
         }
     }
 
+    @Override
+    public void destroy() {
+        mData = null;
+        super.destroy();
+    }
+
     @Override
     public String getString() {
         return Utility.fromAscii(mData);

src/com/android/email/mail/store/imap/ImapSimpleString.java

@@ -25,12 +25,18 @@ import java.io.InputStream;
  * Subclass of {@link ImapString} used for non literals.
  */
 public class ImapSimpleString extends ImapString {
-    private final String mString;
+    private String mString;
 
     /* package */  ImapSimpleString(String string) {
         mString = (string != null) ? string : "";
     }
 
+    @Override
+    public void destroy() {
+        mString = null;
+        super.destroy();
+    }
+
     @Override
     public String getString() {
         return mString;

src/com/android/email/mail/store/imap/ImapString.java

@@ -38,6 +38,11 @@ public abstract class ImapString extends ImapElement {
     private static final byte[] EMPTY_BYTES = new byte[0];
 
     public static final ImapString EMPTY = new ImapString() {
+        @Override public void destroy() {
+            // Don't call super.destroy().
+            // It's a shared object.  We don't want the mDestroyed to be set on this.
+        }
+
         @Override public String getString() {
             return "";
         }

src/com/android/email/mail/store/imap/ImapTempFileLiteral.java

@@ -37,8 +37,6 @@ import java.io.OutputStream;
  * Subclass of {@link ImapString} used for literals backed by a temp file.
  */
 public class ImapTempFileLiteral extends ImapString {
-    private boolean mDestroyed = false;
-
     /* package for test */ final File mFile;
 
     /** Size is purely for toString() */
@@ -71,12 +69,6 @@ public class ImapTempFileLiteral extends ImapString {
         }
     }
 
-    private void checkNotDestroyed() {
-        if (mDestroyed) {
-            throw new RuntimeException("Already destroyed");
-        }
-    }
-
     @Override
     public InputStream getAsStream() {
         checkNotDestroyed();
@@ -105,12 +97,14 @@ public class ImapTempFileLiteral extends ImapString {
     @Override
     public void destroy() {
         try {
-            if (!mDestroyed && mFile.exists()) {
+            if (!isDestroyed() && mFile.exists()) {
                 mFile.delete();
             }
-        } finally {
-            mDestroyed = true;
+        } catch (RuntimeException re) {
+            // Just log and ignore.
+            Log.w(Email.LOG_TAG, "Failed to remove temp file: " + re.getMessage());
         }
+        super.destroy();
     }
 
     @Override