[jira] [Created] (SCB-1006) Support SagaEnd Callback invocation

[Willem Jiang (JIRA)]

Willem Jiang created SCB-1006:
---------------------------------

             Summary: Support SagaEnd Callback invocation
                 Key: SCB-1006
                 URL: https://issues.apache.org/jira/browse/SCB-1006
             Project: Apache ServiceComb
          Issue Type: Improvement
          Components: Saga
            Reporter: Willem Jiang


Here is the use case for using the lock to provide the isolation in Saga. 
We just want to release this lock after the saga invocation is finished. Here 
is the code snippet for it.  method2 wraps the Saga event to release the lock. 
{code}
@SagaStart
void doSagaTx() {
   doLocalTx1();
   doLocalTx1();
}

@Compensable(timeout=5, compensationMethod="cancelLocalTx1")
void doLocalTx1(){
   ...
}

void cancelLocalTx1(){
   ....
}

@Compensable(timeout=5, compensationMethod="cancelLocalTx2")
void doLocalTx2(){
   ...
}

void cancelLocalTx2(){
   ....
}

void method2() {
   Lock resourceLock = getResourceLock();
   if (resourceLock.tryLock()) {
    try {

        doSagaTx();
    } finally {
        resourceLock.release();
    }
   } else {
     // Resource was locked
   }
}
{code}

But, this method is not good enough, as if there are something wrong inside of 
the Saga transaction, we need to wait for a while to let the transaction 
coordinator to finish the  compensation invocation before release the resource 
lock. 
If ServiceComb saga can provide a callback when the saga transaction is 
finished, it could save lots of my time. The code just like this.

{code}
@SagaStart(endMethod="sagaTxEnd")
void doSagaTx(resourceLock) {
   doLocalTx1();
   doLocalTx1();
}

void sagaTxEnd(resourceLock){
   resourceLock.release();
}

@Compensable(timeout=5, compensationMethod="cancelLocalTx1")
void doLocalTx1(){
   ...
}

void cancelLocalTx1(){
   ....
}

@Compensable(timeout=5, compensationMethod="cancelLocalTx2")
void doLocalTx2(){
   ...
}

void cancelLocalTx2(){
   ....
}

void method2() {
   Lock resourceLock = getResourceLock();
   if (resourceLock.tryLock()) {
    doSagaTx(resourceLock);
   } else {
     // Resource was locked
   }
}
{code}



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