OS Foundations and Process Model

Trace identity, parenthood, exit and reaping. A syscall privilege transition can return to the same process.

Separate the lifecycle events

Fork creates a child identity; exec replaces a program image. Exit leaves zombie bookkeeping; wait reaps a zombie child. The simulator models fork/exit/wait, not scheduling or exec.

Adopt living and zombie children

Create2 under1; create3/4 under2; exit3; exit2. 2 is zombie under1; 3 is zombie under1; 4 remains live under1. Wait(1) returns2 then3, then-1. Never leave an exited child attached to a subsequently removed parent.

Maintain both directions

Each child parent field and its parent child-set must agree. Adoption updates the child, the old parent and init. Wait removes one PID from the table and parent set. PID reuse is outside this model.

Predict before coding

Create2/3 under1; exit3 then2. What are two waits, Fork(2), then Fork(1)? Explain PID selection versus exit order; revisit the answer in the lesson.