Coupled Processes (Semantics)

In addition to strong (Volume 1, page 419) and weak (60) process coupling patterns we also have another variant that we call semantic coupling. Some processes (not necessarily from the same vendor) cooperate to provide certain functionality. The cooperation might not involve trackable and visible inter-process communication such as (A)LPC/RPC or pipes but involve events, shared memory and other possible mechanisms not explicitly visible when we look at memory dumps. In many cases, after finding problems in one or several processes from a semantic group we also look at the remaining processes from that group to see if there are some anomalies there as well. The one example I encounter often can be generalized as follows: we have an ALPC wait chain ProcessA -> ProcessB <-> ProcessC (not necessarily a deadlock) but the crucial piece of functionality is also implemented in ProcessD. Sometimes ProcessD is healthy and the problem resides in ProcessC or ProcessB, and sometimes, when we look at ProcessD we find evidence of an earlier problem pattern there so the focus of recommendations shifts to one of ProcessD modules.