On Wednesday, 6 November 2019 14:21:22 GMT Maarten ter Huurne wrote:
On Wednesday, 6 November 2019 07:19:56 CET Waqar Khan wrote:
Hi, So, I am writing a twisted server. This server spawn multiple child processes using reactor spawnProcess that initializes a process protocol.
Now, each of the childprocess receives some REST requests. Each process has a dict that acts as cache. Now, I want to share dict across processes. In general, python has SharedMemoryManager in multiprocessing module which would have helped. https://docs.python.org/3/library/multiprocessing.shared_memory.html#m ultiprocessing.managers.SharedMemoryManager.SharedMemory But since I am using twisted internal process implementation, how do I share this dict across the processes so that all the processes use this common cache?
Keeping a dictionary in SharedMemoryManager seems far from trivial. I don't think you can allocate arbitrary Python objects in the shared memory and even if you could, you would run into problems when one process mutates the dictionary while another is looking up something or also mutating it.
It could in theory work if you implement a custom lock-less dictionary, but that would be a lot of work and hard to get right. Also having shared memory mutations be synced between multiple CPU cores could degrade performance, since keeping core-local CPU caches in sync is expensive.
Would it be an option to have only one process accept the REST requests, check whether the result is in the cache and only distribute work to the other processes if you get a cache miss? Typically the case where an answer is cached is pretty fast, so perhaps you don't need multiple processes to handle incoming requests.
We have used a couple of ways to cache. 1. Use a singleton process to hold the cache and ask it, via IPC, for answers from the other process. 2. have a cache in each process Barry
Bye, Maarten
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