Thread Safety and Shared Resources

I have been reading that code that is safe to call by multiple threads simultaneously is called thread safe. If a piece of code is thread safe, then it contains no race conditions. Race condition only occur when multiple threads update shared resources. Therefore it is important to know what resources Java threads share when executing.

I have a class as below;

public class ClassA

JSONObject data = new JSONObject();

public void methodA(Map<?, ?> resultMap, String Url)

try
data.put("request_id", resultMap.get("request_id"));
data.put("account", resultMap.get("account"));

postToCallBackUrl.sendToCallBackUrl(data, Url, resultMap);

catch (JSONException e)

logger.error(e);




public void methodB(Map<?, ?> resultMap, String Url)

try
data.put("request_id", resultMap.get("request_id"));
data.put("name", resultMap.get("name"));

postToCallBackUrl.sendToCallBackUrl(data, Url, resultMap);

catch (JSONException e)

logger.error(e);






My question is on the usage of JSONObject data = new JSONObject(), is it thread safe as currently declared?

JSONObject data = new JSONObject()

Or do I need to declare it in every method?

The data in all the methods is passed to another class postToCallBackUrl and a specific method sendToCallBackUrl(data, Url, resultMap).

postToCallBackUrl

sendToCallBackUrl(data, Url, resultMap)

Anyone advice?

1 Answer
1

This looks wildly thread-unsafe. The javadoc for JSONObject explicitly states that the class is not thread safe. Since data can be accessed from the methods without any sort of synchronization, this is not a safe usage.

JSONObject

data

But the code doesn't even look safe for one thread to use, because state from one method invocation affects other method invocations.

Yes, create a new JSONObject as a local variable in the methods. It then becomes thread safe by confinement, and you retain no state between method invocations.

JSONObject

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