java线程安全访问arraylist:两个生产者一个消费者。锁定对象足够了吗?
我有两个线程可以产生价值并将其添加到arraylist中, 其他线程可以访问它来读取值
我的问题是,生产者可以在消费者使用数据的同时访问列表
这是我的代码:
public class CommandTree
{
Lock lock = new ReentrantLock();
ArrayList<Command> cmdToSend = null;
JSONObject sendCmdMap;
public CommandTree(JSONObject sendCmdMap)
{
this.cmdToSend = new ArrayList<Command>();
this.sendCmdMap = sendCmdMap;
}
private synchronized void addMacroCmd(String macro, int fmt, int tgt, int sid,int count,JSONArray sli,String paramName,JSONObject params,int function)
{
boolean check = false;
int i = 0;
lock.lock();
try
{
for(i=0; i<cmdToSend.size(); i++)
{
if(cmdToSend.get(i).getMacroName().equalsIgnoreCase(macro))
{
check = true;
break;
}
}
if(check == false)
{
cmdToSend.add(new Command(macro,fmt,tgt,sid,count,function,sli));
}
if(paramName != null)
{
if(check)
cmdToSend.get(i).setParameter(paramName,params);
else
cmdToSend.get(cmdToSend.size()-1).setParameter(paramName,params);
}
}
finally
{
lock.unlock();
}
}
private void addParameter(String macro,int fmt, int tgt, int sid,int count,JSONArray sli,String paramName,JSONObject params,int function)
{
lock.lock();
try
{
this.addMacroCmd(macro, fmt, tgt, sid, count,sli, paramName,params,function);
}
finally
{
lock.unlock();
}
}
public int getSize()
{
return cmdToSend.size();
}
public void reset()
{
lock.lock();
try
{
cmdToSend.clear();
}
finally
{
lock.unlock();
}
}
/*
public Command getNextCommandInLoop()
{
return cmdToSend.;
}
*/
public Command getNextCommand(int i)
{
Command result;
lock.lock();
try
{
result = cmdToSend.get(i);
}
finally
{
lock.unlock();
}
return result;
}
public synchronized boolean populateCommandTree(String i,String target) throws JSONException
{
JSONObject tgtCmd = (JSONObject) sendCmdMap.get(target);
JSONObject cmdObject;
Iterator<String> iter = tgtCmd.keys();
while (iter.hasNext())
{
String key = iter.next();
if(key.equalsIgnoreCase(i))
{
//it is a general commands
JSONObject macro = (JSONObject)tgtCmd.opt(key);
cmdObject = (JSONObject) macro.opt("cmd");
addMacroCmd(key,cmdObject.optInt("fmt"),cmdObject.optInt("tgt"),cmdObject.optInt("sid"),cmdObject.optInt("count"),cmdObject.optJSONArray("sli"),null,null,macro.optInt("function"));
return true;
}
else
{
//It is a parameter, we have to search its general command
cmdObject = (JSONObject)tgtCmd.opt(key);
if(cmdObject == null)
{
continue;
}
JSONObject parameter = cmdObject.optJSONObject("Parameter");
if( parameter == null)
{
//There isn't the requested command, we iterate on the next one
continue;
}
else
{
if(((JSONObject) parameter).optJSONObject(i) != null)
{
JSONObject cmdStructure = (JSONObject)cmdObject.opt("cmd");
//We have found the command, save it in commandSendCache
addMacroCmd(key,cmdStructure.optInt("fmt"),cmdStructure.optInt("tgt"),cmdStructure.optInt("sid"),cmdStructure.optInt("count"),cmdStructure.optJSONArray("sli"),i,parameter.optJSONObject(i),cmdObject.optInt("function"));
return true;//(JSONObject)tgtCmd.opt(key);
}
else
{
continue;
}
}
}
}
return false;
}}
我读了一些关于那个案子的帖子,但我不太明白。我想用这种方式发布我的代码,这样我可以更好地理解
另一个问题是,一个生产者是一个UI线程,我担心如果有问题,停止UI线程一段时间
我还想过使用ConcurrentLinkedQueue,因为有时我需要在列表上循环,我总是从第一个位置提取值,但使用ConcurrentLinkedQueue,我不知道如何实现循环,以及如何实现addMacroCmd方法
在我的例子中,我想使用lock对象和ArrayList
你有什么建议吗?我想以更好的方式学习并发性,但对我来说并不容易:(
编辑:以下是添加和删除命令的代码部分:
public synchronized void readSensorData(String[] sensor, String target)
{
cmdTree.reset();
for(int i=0;i<sensor.length;i++)
{
try
{
cmdTree.populateCommandTree(sensor[i],target);
}
catch (JSONException e)
{
}
}
writeExecutor.execute(this.writeCommandTree);
}
/**
*
* @param i
* @param target
* @return
* @throws JSONException when the command requested doesn't exists
*/
private ByteArrayOutputStream f = new ByteArrayOutputStream();
ExecutorService writeExecutor = Executors.newSingleThreadExecutor();
Semaphore mutex = new Semaphore(0);
volatile boolean diagnostic = false;
volatile int index = 0;
Runnable writeCommandTree = new Runnable()
{
@Override
public void run()
{
while(index < cmdTree.getSize())
{
writeCmd();
try
{
mutex.acquire();
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
sendAnswerBroadcast("answer", answer);
answer = new JSONObject();
index = 0;
}
};
当收到新的响应时,互斥锁被释放
Addictional information :
The readSensorData() is called when button on the ux (UI Thread) is pressed and in same case from other Thread B. WriteCommandTree is only execute in the executor (Other Thread C).
I change the name of getnextcommand into getcommand - getcommand(int i) is called in the callback of the response (sometime is in other thread (i'm forget to that function ...) and in writecmd inside writecommandtree - getsize in the writecommandTree in the thread C
# 1 楼答案
您可以使用blockingQueue实现同样的功能。请参阅关于blockingQueue的简单教程:http://tutorials.jenkov.com/java-util-concurrent/blockingqueue.html