On 31 Aug 2015 at 2:33, Andreas Schäfer wrote:
1. Should Boost.AFIO be accepted into Boost? Please state all conditions for acceptance explicity.
I vote no. For acceptance I'd expect a library that outperforms "naive" OpenMP code.
I will place a wager with you for €100 right now that nobody will EVER implement an asynchronous file i/o library on Linux < 4.0 which beats OpenMP. Linux currently does not provide the facilities to do better.
Also, the design should be greatly simplified.
AFIO is a simple design which keeps close to the bare metal in order to expose the underlying systems file system concurrency guarantees. If you want even more simple, ASIO provides a simple asynchronous file i/o library. I think you'll find it delivers you no useful benefit.
3. What is your evaluation of the implementation?
I tried to assess the library's performance as IMHO (and the library's documentation) performance is the major motivation for using AFIO. The code failed to compile with Intel's C++ compiler icpc[2]. With g++ 4.9.3 the code compiled, but segfaulted when traversing a Linux 4.1.6 source tree[3].
The library's documentation clearly specifies that the compilers tested are GCC >= 4.8, clang >= 3.3 and VS2015. Any other compiler is not supported. As to why you saw a segfault when traversing a Linux source tree (was it with find regex in files?), I am sorry this occurred. I would suggest to use the find regex in files binary compiled using Boost.Build rather than any custom build and see if it happens there too. If it does, open an issue on github please.
The code (and the naive OpenMP implementation provided in the documentation) completed successfully on a Boost.AFIO source tree, but the OpenMP code (~600 MB/s) was significantly faster than the AFIO code (~270 MB/s), see [4]. Test system: Intel Core i7-3610QM, Samsung EVO 1TB SSD, Linux 4.1.5. (I can provide further details if necessary.) All of this does not positively impress me.
You have highly unrealistic expectations. On Linux there is no useful async backend, so AFIO emulates async using a thread pool and the normal synchronous APIs. It goes without saying that will always be slower than OpenMP using the same APIs. It can never be faster. What AFIO provides is a *portable* API for async file system and file i/o. It provides the least benefit on Linux of any of the platforms, but that is not AFIO's fault. When Linux does provide a decent async file i/o implementation, I'll add a backend and you'll see a corresponding benefit. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/