add read me

Author: tarcisiozf

README.md

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+# IPC queue
+
+This is a study on how to do create a queue via IPC (inter-process communication).
+
+Please take a look at the examples of [producer](./producer.c) and [consumer](./consumer.c)
+
+## Design
+
+There are two main components that can be used independently:
+
+**SharedMem** 
+
+exposes an interface to share memory among processes, 
+it uses [MMAP](https://en.wikipedia.org/wiki/Mmap) under the hood, and pre-allocates space that will be used.
+
+---
+
+**SharedQueue** 
+
+It uses the shared memory to create a ring buffer in the available space.
+Each message has a sequence number, that is prepended to the front on the message like a header, so we can keep track when reading.
+
+The messages for this implementation have a fixed size, this way we can have O(1) access to memory by calculating the memory offset. 
+This has some downsides if your domain has variable-length messages, but this could be easily implemented by modifying the queue and adding the message size into the header.
+
+Due to each process being responsible for managing its own sequence number we end up having a lock-free, single-producer, multi-consumer model.
+This is heavily inspired by [LMAX's Disruptor](https://lmax-exchange.github.io/disruptor/).
+
+Be aware that due to the ring buffer reuse of space some  messages can be lost if the consumer is lagging (not ingesting messages fast enough).
+This has to be measured for your use case and can be solved by increasing the buffer size of the shared memory. 
+
+---
+
+Warning: those components can act as writer/reader (or producer/consumer) but never both simultaneously.
+
+## How to run
+
+Just run `make` and then start the `./producer` and `./consumer` in different terminals.
+
+## Improvements
+
+I'm not a C expert, and I'm sure this code can be improved a lot
+
+This is just for demonstration purposes; thus, there are lots of cases that are not covered, some examples: 
+* trying to write to a read-only resources and so on
+* try to change initiate more than once (writer becomes a reader)
+
+Feel free to contribute.
+
+---
+
+Shout-out to @apuxbt for sharing some snippets that inspired me