Advanced · Module 6 · Lesson 2 of 10
Process Synchronization: wait, waitpid, and Zombie Reaping
Synchronize parent and child lifecycles, parse termination status codes, eliminate PID table exhaustion from zombie processes, and implement non-blocking reaping loops.
By the end you can
- Block execution or poll child process state transitions using wait and waitpid
- Decode child exit statuses and terminating signals using POSIX status macros
- Explain kernel process table retention, zombie states, and init/systemd reparenting
- Construct non-blocking reaping loops using WNOHANG to prevent process table exhaustion
Builds on Process Lifecycle: fork, execve, and Address Space Duplication.
01 · A question first
Why does a child process that has already finished running and freed all its memory continue to occupy a slot in the operating system process table? And how can a rogue parent process that never calls wait() bring an entire multi-user Linux server to a halt?
Make a guess before you read on.
02 · The idea
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What's inside
- Start with the problem
- How the idea works
- Why it is correct
- What it costs
- Pitfalls and variations
- Where it is used
03 · Practice
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