Implementing cause-effect tracking

In order to implement the unifying concept of cause-effect relationship preservation, we need to give access to the cause-effect structure to the processes.

We call asynchronous history such structure, which is an irreflexive partial ordering of sessions.

Each process knows how certain sessions, among those to which the process has participated, are placed with respect to the asynchronous history.

Such knowledge is represented by a single integer value, that we call level, that is attached

• to each session we want to track with respect to cause-effect preservation and
• to the current session.

The algorithm used to generate the level of a new session is simple: just take the maximum of all the levels of the processes that engage in the new session.

If processes decide to include the new session in the cause-effect preservation mechanism, the level is further incremented by one. We say that they trigger a global event.

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