Day57 - POSIX Message Queue IPC¶

Date¶

2026-05-18

Topics¶

POSIX message queue IPC
mq_open()
mq_send()
mq_receive()
mq_attr
message priority
blocking queue
non-blocking queue
mq_notify()
epoll + mqueue
timerfd integration
signalfd integration

Implemented¶

Basic POSIX mqueue IPC¶

Implemented:

independent sender
independent receiver
queue creation/open
blocking receive
message transmission

Queue Attribute Management¶

Explored:

mq_maxmsg
mq_msgsize
mq_curmsgs
mq_flags

Observed:

mq_receive() buffer size must >= mq_msgsize

Priority Queue¶

Implemented message priority.

Verified:

higher priority dequeued first
FIFO ordering inside same priority

Blocking Queue Behavior¶

Verified:

queue full -> mq_send() blocks
queue empty -> mq_receive() blocks

Non-Blocking Queue¶

Implemented:

O_NONBLOCK

Observed:

EAGAIN when queue full
EAGAIN when queue empty

mq_notify()¶

Implemented:

SIGEV_SIGNAL

notification.

Learned:

empty -> non-empty transition
one-shot registration
re-arm logic
queue drain pattern

epoll Integration¶

Integrated:

mqueue fd
timerfd
signalfd

into one epoll loop.

timerfd¶

Used timerfd for:

periodic queue statistics
mq_curmsgs monitoring

signalfd¶

Used signalfd for:

SIGINT
SIGTERM

graceful shutdown handling.

Key Learnings¶

POSIX Message Queue¶

Kernel-managed IPC:

synchronized by kernel
message-oriented
priority-aware

Linux Event Architecture¶

Compared:

mq_notify()

vs

epoll

POSIX vs Linux Style¶

mq_notify()¶

POSIX async notification model.

epoll¶

Linux fd readiness model.

Unified Event Loop¶

Final architecture:

epoll
 ├── mqueue
 ├── timerfd
 └── signalfd

This demonstrates modern Linux userspace middleware architecture.

Result¶

Successfully implemented a complete Linux POSIX message queue IPC demo with:

blocking/non-blocking operation
priority queue
async notification
epoll integration
timerfd/signalfd integration
unified Linux event loop