Each request received from the server is processed in a new Smalltalk process, which implies that multiple requests may be being processed concurrently within an image. If this causes a problem because the processing your part does is not Smalltalk process reentrant, the transactionMustBeSerialzed method can be implemented on your part to return true. The WSI server ensures that at most one Web Connection part that answers false to transactionMustBeSerialized is running at a time.