并发访问@Lock(LockType.WRITE)方法 [英] Concurrent access to a @Lock(LockType.WRITE) method
问题描述
我想完成什么:
我有一个JMS队列,我想异步地从该队列中获取元素并发送到打印机。这个打印机是非常具体和笨的,所以它不能排队在它或缓冲任何东西。我必须在本打印机上按顺序执行5个步骤,排队的电子元件的步骤不能与另一个元素的步骤重叠。对于每个步骤,打印机将在成功时返回1,而在失败时打印机将返回另一个数字。
I have a JMS queue and I want to asynchronously get elements from that queue and send to a Printer. This printer is very specific and dumb so it can't queue on it's on or buffer anything at all. I must perform 5 steps in sequence on this printer and the steps of a queued elemet must not overlap the steps of another element. For each step the printer will return 1 on success and another number on failure.
当前的实现是一个具有 onMessage 方法调用的MDB来自Singleton ejb的@Lock(LockType.WRITE)方法。
The current implementation is an MDB with an onMessage method call to a @Lock(LockType.WRITE) method from a Singleton ejb.
MDB:
@MessageDriven(activationConfig = {
@ActivationConfigProperty(propertyName = "destinationLookup",
propertyValue = "jms/MyQueue"),
@ActivationConfigProperty(propertyName = "destinationType",
propertyValue = "javax.jms.Queue")})
public class SimpleMessageBean implements MessageListener {
@Resource
private MessageDrivenContext mdc;
static final Logger logger = Logger.getLogger("SimpleMessageBean");
@EJB
private Print print;
public SimpleMessageBean() {
}
@Override
public void onMessage(Message inMessage) {
try {
if (inMessage instanceof TextMessage) {
logger.log(Level.INFO, "MESSAGE BEAN: Message received: {0}", inMessage.getBody(String.class));
String params[] = ((TextMessage) inMessage).getText().split("\\s+");
print.doStuff(params[0], params[1]);
} else {
logger.log(Level.WARNING,"Error")
}
} catch (Exception e) {
logger.log(Level.SEVERE, "Rollback Happening: {0}", e.toString());
mdc.setRollbackOnly();
}
}
单身人士:
@ConcurrencyManagement(ConcurrencyManagementType.CONTAINER)
@Startup
@Singleton
@AccessTimeout(value = 120000)
public class Print {
static final Logger logger = Logger.getLogger("SimpleMessageBean");
public Print() {
}
@Lock(LockType.WRITE)
public void doStuff(String cpf, String value) throws Exception{
try{
int return;
return = Bematech.AbreCupom(cpf);
System.out.println("Stage0 = " + return);
return = Bematech.VendeItem("111112", "Parking", "FF", "hours", "1", 2, value, "%", "00,00");
System.out.println("Stage1 = " + return);
return = Bematech.IniciaFechamentoCupom("D", "%", "00,00");
System.out.println("Stage2 = " + return);
return = Bematech.EfetuaFormaPagamento("Dinheiro", value);
System.out.println("Stage3 = " + return);
return = Bematech.TerminaFechamentoCupom("Thankyou ofr your support");
System.out.println("Stage4 = " + return);
}catch ( Exception MensagemErro ){
throw MensagemErro;
}
}
我预计这个实现从队列中接收数据并在doStuff()方法被锁定的同时打印一个元素,AKA:
I expected this implementation to receive the data from the queue and print it one element at a time as the doStuff() method is locked, AKA:
Stage0=1
Stage1=1
Stage2=1
Stage3=1
Stage4=1
Stage0=1
Stage1=1
Stage2=1
Stage3=1
Stage4=1
Stage0=1
...
但是有时候(似乎是随机的,但是当几个消息一次排队时它会更频繁地发生)我得到两个并发访问打印方法:
But sometimes (seems to be random but it happens more often when several messages are queued at once) i get two concurrent access to the print method:
Stage0=1
Stage1=1
Stage0=1
Stage2=1
Stage1=1
Stage3=1
Stage2=1
...
从什么是打印我可以看到2个元素重叠在打印机访问。
From what is being print I can see that 2 elements are overlapping in the printer access.
有用的信息:
Java EE 7.
Glassfish 4-0 。
不使用JBOSS。
Java EE 7. Glassfish 4-0. Not Using JBOSS.
任何想法为什么会发生这种情况?
Any ideas why this is happening?
推荐答案
同步关键字解决了我的问题。没有找到原始代码出错了。
Synchronized keyword solved my problem. Did not find out what was wrong with original code.
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