Advanced · Module 6 · Lesson 6 of 10
POSIX Shared Memory: shm_open and Mapped Regions
Establish high-speed zero-copy IPC channels using shm_open, size shared memory segments with ftruncate, map pages with mmap, and clean up with shm_unlink.
By the end you can
- Create and open POSIX shared memory objects with shm_open and mode permissions
- Configure shared segment byte capacity using ftruncate
- Map shared memory objects across unrelated processes using mmap with MAP_SHARED
- Manage shared object lifecycles and unlink /dev/shm entries with shm_unlink
Builds on Inter-Process Streams: Anonymous Pipes and Named FIFOs.
01 · A question first
Why do pipes and sockets copy every byte twice through kernel memory buffers, while POSIX shared memory lets independent processes exchange gigabytes of structured data at the raw memory-bus speed of RAM? The secret lies in mapping identical physical RAM frames into disparate virtual address spaces.
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
- Complete Multi-Process Example
- Why it is correct
- What it costs
- Pitfalls and variations
- Where it is used
03 · Practice
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