PyCSP provides a CSP (Communicating Sequential Processes) based library for Python, where CSP processes can be executed as threads, operating system processes or greenlets. The main drawback of using threads and processes is that they limit the number of CSP processes that a program can use due to operating system restrictions and memory and synchronisation overheads. This overhead is reduced when using greenlets, but requires the use of an external library. aPyCSP is an experimental implementation of PyCSP that uses recent support for coroutines in Python and the asyncio library. This paper explores two implementation approaches for aPyCSP where the most recent version is shorter, simpler to read and understand and supports more functionality than the original version, including generic channel support and input and output guards. We believe some of the identified implementation techniques can be useful for other CSP libraries. The aPyCSP implementation is also faster and uses less memory per CSP process, allowing us to scale to 15 million processes on a computer with 64 GB memory.
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