Programming to Get Function Results

The client may use the default result collector. If the client needs special results handling, code a custom ResultsCollector implementation to replace the default. Use the Execution::withCollector method to define the custom collector.

Note: This section applies only to functions that return results.

To program your client to get the results from a function, use the result collector returned from the function execution, like this:

ResultCollectorPtr rc = FunctionService::onRegion(region)
                    ->withArgs(args)
                    ->withFilter(keySet)
                    ->withCollector(new MyCustomResultCollector())
                    .execute(Function);
CacheableVectorPtr functionResult = rc.getResult();

The getResult methods of the default result collector block until all results are received, then return the full result set.

To handle the results in a custom manner:

  1. Write a class that implements the ResultCollector interface to handle the results in a custom manner. The methods are of two types: one handles data and information from GemFire and populates the results set, while the other returns the compiled results to the calling application:
    • addResult is called when results arrive from the Function methods. Use addResult to add a single result to the ResultCollector.
    • endResults is called to signal the end of all results from the function execution.
    • getResult is available to your executing application (the one that calls Execution.execute) to retrieve the results. This may block until all results are available.
    • clearResults is called to clear partial results from the results collector. This is used only for highly available onRegion functions where the calling application waits for the results. If the call fails, before GemFire retries the execution, it calls clearResults to ready the instance for a clean set of results.
  2. Use the Execution object in your executing member to call withCollector, passing your custom collector, as shown in the example above.