> On Dec 21, 2020, at 4:33 PM, Mike Schinkel <m...@newclarity.net> wrote: > >> On Dec 17, 2020, at 11:30 AM, Aaron Piotrowski <aa...@trowski.com> wrote: >> >> Hello everyone! >> >> I would like to introduce an RFC for adding full-stack fibers to PHP: >> https://wiki.php.net/rfc/fibers >> >> Fibers are primarily used to implement green-threads or coroutines for >> asynchronous I/O. Fibers are similar to threads, except fibers exist within >> a single thread and require cooperative scheduling of the fibers by the >> process. Since fibers do not require a full CPU context switch, they are >> lightweight and more performant than multi-processing or threading for >> awaiting I/O. >> >> An implementation as an extension is at https://github.com/amphp/ext-fiber >> >> Fibers are a complex feature. The RFC contains many examples and links to >> code using fibers to help explain and demonstrate what is possible, however >> I’m certain many more questions and concerns will arise. Looking forward to >> feedback and discussion. >> > > This is interesting, and potentially very useful. > > I am curious about how you propose access to shared memory across fibers? > What will happen if two fibers try to update a $GLOBALS variable at the same > time? Or a property of the same object? How will developers manage that? > > -Mike > > P.S. Have you considered concurrency functionality like in GoLang[1] e.g. > channels, where the mantra is "Do not communicate by sharing memory; instead, > share memory by communicating?" > > [1] > https://medium.com/@thejasbabu/concurrency-in-go-e4a61ec96491#:~:text=Do%20not%20communicate%20by%20sharing,race%20conditions%2C%20memory%20management%20etc > > <https://medium.com/@thejasbabu/concurrency-in-go-e4a61ec96491#:~:text=Do%20not%20communicate%20by%20sharing,race%20conditions%2C%20memory%20management%20etc>.
Hi Mike, Fibers do not change the single-threaded nature of PHP. Only a single fiber can be running at one time, so memory cannot be modified simultaneously. There are synchronization issues when writing asynchronous code using either stackless or stackful coroutines, as anyone who has worked with AMPHP or ReactPHP can tell you. Multiple fibers (coroutines, green-threads, whatever you want to call them) will interleave execution. Multiple interleaved fibers can change object state between pausing and resuming, which I'm guessing is more to what you were concerned about, rather than literal simultaneous modification that can occur with threads. The RFC does not provide tools to synchronize memory access, as these can be implemented in user space. Fibers don't provide the entire API, just the "bare-metal" API needed to implement various styles of concurrency in user space code. AMPHP provides synchronization tools such as mutexes, semaphores, parcels, and channels in https://github.com/amphp/sync <https://github.com/amphp/sync> and https://github.com/amphp/parallel <https://github.com/amphp/parallel>. Other libraries could provide similar tools, though perhaps with a different approach. We too like the Go-style of concurrency and look to emulate it in AMPHP v3. Cheers, Aaron Piotrowski
