I have a single producer, single consumer problem which (I believe) can be solved using a circular/ring buffer.
I have a micro-controller running a RTOS, with an ISR(Interrupt Service Routine) handling UART (Serial port) interrupts. When the UART raises an interrupt, the ISR posts the received characters into the circular buffer. In another RTOS task (called packet_handler), I am reading from this circular buffer and running a state machine to decode the packet. A valid packet has 64 bytes including all the framing bytes.
The UART operates at 115200, and a packet arrives every 10ms. The packet_handler runs every 10ms. However, this handler may sometimes get delayed by the scheduler due to another higher priority task executing.
If I use an arbitrarily large circular buffer, there are no packet drops. But how to determine the optimal circular buffer size in this case? At least theoretically. How is this decision of buffer size made in practice?
Currently, I am detecting overrun of the buffer through some instrumentation functions and then increasing the buffer size to reduce packet loss.
While all of the above answers are correct and throws light on the issue, this page summarizes all the factors to be considered while choosing the size of a ring buffer.
Some queuing models can be used to theoretically analyze the problem at hand and find out the suitable size of ring buffer.
A more pragmatic approach is to start with a large buffer, then find out the maximum used buffer size in real test case (this process is called watermarking) and use this figure in the final code.