Java线程并发读写

Question

I have a arraylist which store data i received and transmit asynchronously over bluetooth.

I have a write thread and a read thread to access the arraylist. I am trying to simulate bluetooth echo (The bluetooth is to echo back everything i send).

private class ReadThread extends Thread {
@Override
public void run() {
    super.run();
        while(!isInterrupted()) {

            try {
                byte[] buffer = new byte[64];
                if (mInputStream == null) return;
                size = mInputStream.read(buffer);
                if (size == 64) {
                    if (bufferList.isEmpty()){
                        Log.i("AOK Fail","Nothing to AOK");
                    }

                    if (compareByte(buffer,bufferList.get(0) == true) // Compare data in this 2 byte array
                          bufferList.remove(0);
                }
            } catch (IOException e) {
            e.printStackTrace();
            return;
        }
    }
}
}

private class WriteThread extends Thread {
    @Override
    public void run() {
    super.run();
    while(!isInterrupted()) {

        try {
            count++;
            if (bufferList.isEmpty() == false && count < 3){    
                write(bufferList.get(0));       
                count = 0;
            }else{
                // Drop data after 3 fail attempt
                bufferList.remove(0);
                count=0;
            }               

            Thread.sleep(500);
        } catch (IOException e) {
            e.printStackTrace();
            return;
        }
    }
}
}

On button pressed i will send data . It works fine if i transmit slowly. However it fails when i start to click rapidly (queue data for transmission). Once i received a AOK Fail message . All remaining data will all be AOK Fail even newly add data. Why is that so

If it is a threading issue shouldn't it be resolve after all data is transmitted ?

Answer 1

This bufferList variable is a thread safe object? like an array blocking list or something? If not you may be having some problems trying to add/remove itens simultaneously.

This would cause an exception in the producer Thread, nothing else would be transmitted you'd get the "Nothing to AOk" log.

Answer 2

It's not very clear how this code works because it does not include some details:

• How are you feeding bufferList and which is its type? Maybe the ArrayList you mentioned in your question? ArrayList is not thread safe see ArrayList documentation for Android .
• What write method does?
• What compareByte method does? It seems obvious, but it will be good to take a look at the code, you know, just in case (also you are missing a bracket).
• Where is the count var you are using inside WriteThread class declared? Are you incrementing count value outside this code? If that's true, you may be removing all contents from bufferList variable when count >= 3 (else block). And if you do this, the first part of your bufferList.isEmpty() == false && count < 3 condition can be false at some time because your bufferList will be empty; then you will execute the else block, trying to remove an element from an empty ArrayList, your code will throw an IndexOutOfBoudsException (see the ArrayList remove method documentation ) and your WriteThread will be aborted.