On Tue, Oct 27, 2020 at 8:29 AM Alon Zakai <[email protected]> wrote:
> > As a hacky workaround, you could always provide your own memory by > setting `Module['wasmMemory']` before loading the generated JS and then set > the memory flag to shared using `wasm-dis + edit + wasm-as`. Obviously not > ideal but maybe good for experimenting. > > I don't think that will work now that the Memory is not imported anymore > in a normal build. You'd need to also mod the wasm to import the memory, > and change the JS a little as well. > We haven't made the switch yet I don't think (although I would like to change that!). Its only STANDALONE_WASM I believe that creates and exports its memory from the wasm module. The normal build still creates the memory object in JS. > > But I agree building with pthreads enabled, but not actually using any > pthreads APIs, seems like a good solution here. There may be a minor code > size cost, is the only downside I can think of. > > On Tue, Oct 27, 2020 at 6:19 AM 'Sam Clegg' via emscripten-discuss < > [email protected]> wrote: > >> This certainly seems like a reasonable setup. >> >> My first reaction would be why not just build with `USE_PTHREADS=1`? >> This is the canonical way to tell emscripten to use shared memory. If >> you don't actually start any threads I'm not sure what costs it has. What >> "extra complexity of the WebAssembly threading model" are you referring to >> here? >> >> If there are indeed significant costs to running single threaded programs >> built with `USE_PTHREADS=1` then we can look into adding a separate option >> for using shared memory, but I think it will be tricky to persuade the >> linker wasm-ld to accept both shared memory, and object files build for >> non-shared memory. >> >> As a hacky workaround, you could always provide your own memory by >> setting `Module['wasmMemory']` before loading the generated JS and then set >> the memory flag to shared using `wasm-dis + edit + wasm-as`. Obviously not >> ideal but maybe good for experimenting. >> >> cheers, >> sam >> >> On Tue, Oct 27, 2020 at 12:27 AM Soeren Balko <[email protected]> >> wrote: >> >>> I've been running into an issue with Emscripten, where I cannot use a >>> shared WebAssembly.Memory (ie., backed by a SharedArrayBuffer) in a >>> single-threaded build. The rationale for this is to be able to use the >>> Emscripten heap as a shared state with other workers / the UI thread. >>> Specifically, it would allow us to directly copy data to the heap in other >>> threads, avoiding to copy data. >>> >>> Our scenario looks like this: >>> (1) We run a (single-threaded) WebAssembly module in a worker in a >>> long-running synchronous call; >>> (2) From within the synchronous call stack, the wasm module calls into >>> JS to dispatch some work to the UI thread; >>> (3) We currently COPY the data from the WebAssembly.Memory heap to a >>> separate SharedArrayBuffer, which we then postMessage to the main thread. >>> (4) The worker then uses a wait/notify pattern to block the Emscripten >>> call stack until the UI thread has passed back a result on the >>> SharedArrayBuffer >>> (5) The UI thread can meanwhile perform some asynchronous work (eg., >>> IndexedDB, etc.) and store the response in the SharedArrayBuffer, then >>> notify the waiting worker. >>> (6) The waiting worker then has to COPY the result from the >>> SharedArrayBuffer back onto the Emscripten heap and return. >>> >>> In effect, we're performing two (expensive) copies. If the Emscripten >>> heap was using a SharedArrayBuffer, we could trivially share that with the >>> UI thread and merely pass offsets on the heap around. >>> >>> So in summary, are there any plans to supporting an SAB-backed >>> WebAssembly.Memory for scenarios like these? I understand that a >>> multi-threaded build could accomplish this. However, the extra complexity >>> of the WebAssembly threading model (especially when running the WebAssembly >>> module inside a worker) is not really acceptable in this case. >>> >>> Soeren >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "emscripten-discuss" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/emscripten-discuss/283659cd-4e07-4913-a185-e4e9495f8d12n%40googlegroups.com >>> <https://groups.google.com/d/msgid/emscripten-discuss/283659cd-4e07-4913-a185-e4e9495f8d12n%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "emscripten-discuss" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/emscripten-discuss/CAL_va2_82PfYNs7%3DFHXfobPDQKt23Rg6nx3AhkhrFfbiJzTVoQ%40mail.gmail.com >> <https://groups.google.com/d/msgid/emscripten-discuss/CAL_va2_82PfYNs7%3DFHXfobPDQKt23Rg6nx3AhkhrFfbiJzTVoQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "emscripten-discuss" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/emscripten-discuss/CAEX4NpQy6trmUWddtGCmZMNseKxBm%2B6xiVwSQpUzL2YagJgNPw%40mail.gmail.com > <https://groups.google.com/d/msgid/emscripten-discuss/CAEX4NpQy6trmUWddtGCmZMNseKxBm%2B6xiVwSQpUzL2YagJgNPw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. 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