我正在编写多线程程序，该程序可以同时从多个用户访问，并且该程序必须避免竞争条件。
代码/多线程:
public class DataProcessor implements Serializable, Runnable {
private static final long serialVersionUID = 1L;
public DataProcessor() {
}
@Override
public void run() {
process();
}
private void process() {
int iSize = 5;
for (int iCounter = 0; iCounter < iSize; iCounter++) {
DataKey objDataKey = new DataKey();
ArrayList<String> list = //..fetch data method ()
HashMap<String, String> hmPQdata = //..fetch data method ()
SendNForgotHelperThread helperThread = new SendNForgotHelperThread(objDataKey, list, hmPQdata);
Thread t = new Thread(helperThread);
t.start();
}
}
class SendNForgotHelperThread implements Runnable {
private ArrayList<String> list;
private HashMap<String, String> hmPQdata;
private DataKey objDataKey;
public SendNForgotHelperThread(DataKey objDataKey, ArrayList<String> list, HashMap<String, String> hmPQdata) {
this.list = list;
this.hmPQdata = hmPQdata;
this.objDataKey = objDataKey;
}
@Override
public void run() {
try {
// Option 1 : synchronized method - SendNForgotHelperThread class object locking
DataCollector objDataSenderM = new DataCollector();
objDataSenderM.synchronizedMethodStore(this.objDataKey, this.list, this.hmPQdata);
// Option 2 : synchronized block - SendNForgotHelperThread class object locking
synchronized (this) {
DataCollector objDataSender = new DataCollector();
objDataSender.store(this.objDataKey, this.list, this.hmPQdata);
}
// Option 3 : Class level locking
synchronized (SendNForgotHelperThread.class) {
DataCollector objDataSender = new DataCollector();
objDataSender.store(this.objDataKey, this.list, this.hmPQdata);
}
} catch (Exception iex) {
System.out.println("Exception in thread: " + iex.getMessage());
}
}
}
class DataCollector {
public void store(DataKey objDataKey, ArrayList<String> list, HashMap<String, String> hmPQdata) {
HashMap<String, String> retrivedValue = (HashMap<String, String>) MemCacheUtil
.retrieveFromMemCache(objDataKey.getKey());
retrivedValue.putAll(hmPQdata);
MemCacheUtil.addToMemCache(objDataKey.getKey(), retrivedValue, "expTime value");
// Sending data in queue
sendDataToQueue(objDataKey, list, hmPQdata);
}
synchronized void synchronizedMethodStore(DataKey objDataKey, ArrayList<String> list,
HashMap<String, String> hmPQdata) {
store(objDataKey, list, hmPQdata);
}
}
class DataKey {
private String key;
public String getKey() {
return key;
}
public void setKey(String key) {
this.key = key;
}
}
public void sendDataToQueue(DataKey objDataKey, ArrayList<String> list, HashMap<String, String> hmPQdata) {
// sending data to queue
}
}
用户 1:
public class UserA {
public static void main(String[] args) {
DataProcessor objDataProcessor = new DataProcessor();
Thread thProcessorThread = new Thread(objDataProcessor, "PROCESSOR");
thProcessorThread.start();
}
}
用户 2:
public class UserB {
public static void main(String[] args) {
DataProcessor objDataProcessor = new DataProcessor();
Thread thProcessorThread = new Thread(objDataProcessor, "PROCESSOR");
thProcessorThread.start();
}
}
用户A和B将同时调用DataProcessor线程。 很明显，选项 1 和 2 将面临竞争条件，因为它们锁定该类的对象/自类对象锁定，而选项 3 将提供类级别的锁定 - 如果多个用户同时访问该程序，则选项 3 将提供减慢应用程序的速度并且多线程的整个目的都会被折腾下去。
有人可以建议阅读有关如何处理这种情况的文章吗？
编辑:
任何人都可以帮助处理 SendNForgotHelperThread 线程对象上的竞争条件 - 该线程从循环中调用，并且为每个循环启动新线程 SendNForgotHelperThread 。
最佳答案
您将 DataProcessor 的两个不同实例传递给类 UserA 和 UserB 中的线程，如果您启动这些主要方法，它将运行正常。您的应用程序中不会出现竞争条件。
要发生竞争条件，您必须传递共享对象，即多个线程对同一对象进行操作，并且共享对象应该具有字段/属性以在多个线程之间共享
DataProcessor objDataProcessor = new DataProcessor();
Thread thProcessorThread1 = new Thread(objDataProcessor, "PROCESSOR-1");
thProcessorThread1.start();
Thread thProcessorThread2 = new Thread(objDataProcessor, "PROCESSOR-2");
thProcessorThread2.start();
关于Java线程: Multithreading - Race condition，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37763319/