ConcurrentModificationException即使在使用synchronized时也是如此(ConcurrentModificationException even when using synchronized)

 我有两个线程：第一个是渲染线程，第二个线程是我处理UI操作的主线程。 
 
 我收到以下错误： 
 
 java.util.ConcurrentModificationException at java.util.AbstractList$SimpleListIterator.next(AbstractList.java:95) at com.convekta.android.chessboard.ChessBoard.renderGamerPieces(ChessBoard.java:424) at com.convekta.android.chessboard.ChessBoard.render(ChessBoard.java:162) at com.convekta.android.chessboard.ChessDrawThread.run(ChessDrawThread.java:41) 
 
 ConcurrentModification异常的常见原因是迭代列表的更改，但我只在renderGamerPieces函数中读取它。 mGamerPieces可能改变的唯一地方是loadPosition方法，但loadPosition和renderGamerPieces都在synchronized块内调用 
 
 也许我不明白的东西..那么这个错误可能会出现怎么样？ 
 
 我的代码： 
 
private final List<DrawablePiece> mGamerPieces = new ArrayList<DrawablePiece>();
private final Object mGamerPiecesLock = new Object();

public void loadPosition(byte[] pieces, byte[] places) {
        synchronized (mGamerPiecesLock) {
            mPicked = null;
            mGamerPieces.clear();
            for (int i = 0; i < pieces.length; i++) {
                byte p = GamerUtils.UncastleRook(pieces[i]);
                if (p != GamerPieces.EMPTY) {
                    byte pl = places[i];
                    if (pl <= GAME_BOARDSIZE)
                        mGamerPieces.add(new DrawablePiece(p,
                                GamerUtils.columnByCell(pl), GamerUtils.rowByCell(pl,
                                        true)));
                }
            }
        }
    }

public void renderGamerPieces(Canvas canvas) {
    ...
    Rect r = new Rect(0, 0, mCellSize, mCellSize);
    List<DrawablePiece> over = new ArrayList<DrawablePiece>();

    for (DrawablePiece d : mGamerPieces) {
        if (d.isFloating()) {
            over.add(d);
        } else {
            r.offsetTo(invert(d.getBoardCol()) * mCellSize,
                    invert(d.getBoardRow()) * mCellSize);
            r.offset(mBoardRegion.left, mBoardRegion.top);
            Bitmap pic = mPieceFactory.getBitmapPiece(d.getPiece(),
                    mCellSize);
            if (null != pic)
                canvas.drawBitmap(pic, null, r, null);
        }
    }
    ...
 }

public void render(Canvas canvas) {
        ...
        synchronized (mGamerPiecesLock) {
            renderGamerPieces(canvas);
        }
        ...
}
 
 谢谢你的评论！ 我将整理我的代码 - 在renderGamerPieces添加同步块，并检查可以从另一个同步块调用loadPosition 。 

I have two threads: first one is an render thread, the second thread is the main thread in which I handle UI actions.
 
I get the following error: 
 
java.util.ConcurrentModificationException at java.util.AbstractList$SimpleListIterator.next(AbstractList.java:95) at com.convekta.android.chessboard.ChessBoard.renderGamerPieces(ChessBoard.java:424) at com.convekta.android.chessboard.ChessBoard.render(ChessBoard.java:162) at com.convekta.android.chessboard.ChessDrawThread.run(ChessDrawThread.java:41)
 
The usual reason of ConcurrentModification exception is changing of iterated list, but I only read it in renderGamerPieces function. The only place where mGamerPieces may change is loadPosition method, but both loadPosition and renderGamerPieces are called inside synchronized blocks
 
Maybe I didn't understand something.. So how this error may appear?
 
My code:
 
private final List<DrawablePiece> mGamerPieces = new ArrayList<DrawablePiece>();
private final Object mGamerPiecesLock = new Object();

public void loadPosition(byte[] pieces, byte[] places) {
        synchronized (mGamerPiecesLock) {
            mPicked = null;
            mGamerPieces.clear();
            for (int i = 0; i < pieces.length; i++) {
                byte p = GamerUtils.UncastleRook(pieces[i]);
                if (p != GamerPieces.EMPTY) {
                    byte pl = places[i];
                    if (pl <= GAME_BOARDSIZE)
                        mGamerPieces.add(new DrawablePiece(p,
                                GamerUtils.columnByCell(pl), GamerUtils.rowByCell(pl,
                                        true)));
                }
            }
        }
    }

public void renderGamerPieces(Canvas canvas) {
    ...
    Rect r = new Rect(0, 0, mCellSize, mCellSize);
    List<DrawablePiece> over = new ArrayList<DrawablePiece>();

    for (DrawablePiece d : mGamerPieces) {
        if (d.isFloating()) {
            over.add(d);
        } else {
            r.offsetTo(invert(d.getBoardCol()) * mCellSize,
                    invert(d.getBoardRow()) * mCellSize);
            r.offset(mBoardRegion.left, mBoardRegion.top);
            Bitmap pic = mPieceFactory.getBitmapPiece(d.getPiece(),
                    mCellSize);
            if (null != pic)
                canvas.drawBitmap(pic, null, r, null);
        }
    }
    ...
 }

public void render(Canvas canvas) {
        ...
        synchronized (mGamerPiecesLock) {
            renderGamerPieces(canvas);
        }
        ...
}
 
Thank you for comments! I will tidy up my code - add synchronization block in renderGamerPieces, and check can loadPosition be called from another synchronized block.

原文：https://stackoverflow.com/questions/26544241