Implement Shared Memory for Fast IPC

Fast Bulk IPC

Shared memory maps the same physical pages into multiple address spaces. After setup, processes communicate with loads and stores, not per-byte syscalls. Throughput beats pipes for large buffers.

shmget/shmat Flow

SysV style:

• shmget(key, size, IPC_CREAT) creates segment
• shmat attaches at OS-chosen or fixed VA
• shmdt detaches; shmctl(IPC_RMID) removes id

For example, a 4 MB frame buffer attached in producer and consumer avoids copying through kernel buffers on every frame.

Why This Matters in Production

PostgreSQL's shared buffer pool and Chrome's GPU compositor both rely on SysV or POSIX shared memory for exactly the reason this task highlights: zero-copy access is dramatically faster than message-passing IPC for large, frequently-touched data. The task's warning about missing synchronization is a real operational hazard too, since orphaned shmget segments that outlive their creating process are a well-known source of production memory leaks, which is why ipcs/ipcrm exist as cleanup tools.

Debugging Checklist

Before you call the implementation done, walk failure modes on purpose. Test empty structures, single-element edge cases, maximum concurrency, and errno paths that must not crash the program. OS code usually fails in production when happy-path tests pass but invariants break under contention or memory pressure.

Implementation Notes

Keep structures small and name fields after kernel counterparts when possible. That lets you read man pages and kernel source side by side while you work. Print observable events during development; remove noisy logs once tests pass reliably.

For This Exercise

You will create a segment, attach in parent and child after fork, and exchange a structured message. The task asks you to measure latency vs an equivalent pipe transfer.