com.gemstone.gemfire.cache.execute

Interface ResultCollector<T,S>

public interface ResultCollector<T,S>

Defines the interface for a container that gathers results from function execution.
GemFire provides a default implementation for ResultCollector. Applications can choose to implement their own custom ResultCollector. A custom ResultCollector facilitates result sorting or aggregation. Aggregation functions like sum, minimum, maximum and average can also be applied to the result using a custom ResultCollector. Results arrive as they are sent using the ResultSender.sendResult(Object) and can be used as they arrive. To indicate that all results have been received endResults() is called.

Example:

  Region region ; 
  Set keySet = Collections.singleton("myKey");
  Function multiGetFunction ;
  Object args ;
  ResultCollector rc = FunctionService.onRegion(region)
                                      .withArgs(args)
                                      .withFilter(keySet)
                                      .withCollector(new MyCustomResultCollector())
                                      .execute(multiGetFunction.getId());
  Application can do something else here before retrieving the result
  Or it can have some logic in {addResult(DistributedMember, Object) to use the partial results.
  If it wants to see all the results it can use 
  Object functionResult = rc.getResult();
  or
  Object functionResult = rc.getResult(timeout,TimeUnit);
  depending on if it wants to wait for all the results or wait for a timeout period.
 

GemFire provides default implementation of ResultCollector which collects results in Arraylist. There is no need to provide a synchronization mechanism in the user implementations of ResultCollector

Since:

6.0

Method Summary

Methods

Modifier and Type	Method and Description
void	addResult(DistributedMember memberID, T resultOfSingleExecution) Method used to feed result to the ResultCollector.
void	clearResults() GemFire will invoke this method before re-executing function (in case of Function Execution HA).
void	endResults() GemFire will invoke this method when function execution has completed and all results for the execution have been obtained and added to the ResultCollector Unless the ResultCollector has received last result from all the executing nodes, it keeps waiting for more results to come.
S	getResult() Method used to pull results from the ResultCollector.
S	getResult(long timeout, TimeUnit unit) Method used to pull results from the ResultCollector.

Method Detail

getResult

S getResult()
            throws FunctionException

Method used to pull results from the ResultCollector. It returns the result of function execution, potentially blocking until all the results are available has been called.

Returns:

the result

Throws:

FunctionException - if result retrieval fails

Since:

6.0

getResult

S getResult(long timeout,
          TimeUnit unit)
            throws FunctionException,
                   InterruptedException

Method used to pull results from the ResultCollector. It returns the result of function execution, blocking for the timeout period until all the results are available. If all the results are not received in provided time a FunctionException is thrown.

Parameters:

timeout - the maximum time to wait

unit - the time unit of the timeout argument

Returns:

the result

Throws:

FunctionException - if result retrieval fails within timeout provided

InterruptedException - if the current thread was interrupted while waiting

Since:

6.0

addResult

void addResult(DistributedMember memberID,
             T resultOfSingleExecution)

Method used to feed result to the ResultCollector. It adds a single function execution result to the ResultCollector It is invoked every time a result is sent using ResultSender.

Parameters:

resultOfSingleExecution -

memberID - DistributedMember ID to which result belongs

Since:

6.0

endResults

void endResults()

GemFire will invoke this method when function execution has completed and all results for the execution have been obtained and added to the ResultCollector Unless the ResultCollector has received last result from all the executing nodes, it keeps waiting for more results to come.

Since:

6.0

See Also:

ResultSender.lastResult(Object)

clearResults

void clearResults()

GemFire will invoke this method before re-executing function (in case of Function Execution HA). This is to clear the previous execution results from the result collector

Since:

6.5