Provided is an apparatus, method and computer program product for executing an aggregation method in an integration environment comprising: issuing, in response to receiving an input message from a requesting application, a first control signal, using, in response to receiving the first control signal, a single logical thread to: generate an entry associated with an in-memory data structure, wherein the entry comprises: an aggregation identifier associated with the input message and a response identifier associated with a response message associated with a target application; update, in response to receiving the response message from the target application, the entry with the response message; and add the updated entry to the in-memory data structure.