52 lines
2.5 KiB
C
52 lines
2.5 KiB
C
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/*
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* nanosleep_yield.c — make a MAIN-THREAD nanosleep() YIELD to the JS event loop via
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* Asyncify instead of busy-spinning, so on-demand pthread-Worker creation can complete
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* WITHOUT editing KiCad.
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*
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* THE PROBLEM (the "non-warm thread" deadlock): once KiCad's thread pool has consumed all
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* the pre-warmed Workers (-sPTHREAD_POOL_SIZE), a later raw std::thread (the raytracer)
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* must spawn a NEW Worker on demand. Finalizing it needs the main thread's event loop to
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* run the new-Worker 'loaded' -> 'run' handshake. KiCad's join is a sleep_for() busy-wait
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* -> nanosleep -> emscripten_thread_sleep, which busy-spins and NEVER returns to the JS
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* event loop, so the new Worker never starts -> deadlock.
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*
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* THE FIX: the only main-thread primitive that returns to the event loop is an Asyncify
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* unwind (emscripten_sleep). This provides a nanosleep that, ON THE MAIN THREAD, yields via
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* an EM_ASYNC_JS await (= emscripten_sleep semantics; __asyncjs__* is already in the
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* post-link asyncify-imports). The unmodified sleep_for busy-wait then pumps the loop, the
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* Worker handshake completes, and on-demand creation works with no KiCad edit.
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*
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* MECHANISM: a STRONG definition of nanosleep here SHADOWS musl's archive member — the
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* linker only pulls musl's nanosleep.o if the symbol is left undefined, and ours defines it.
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* (-Wl,--wrap=nanosleep is not an option here — it crashes wasm-ld with a SIGSEGV in
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* lld::wasm::ImportSection::addImport.) On a pthread worker we fall back to
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* emscripten_thread_sleep (the real underlying blocking sleep — workers may block).
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*
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* SCOPE: only the main browser thread yields; only it must never block the event loop.
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*/
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#include <emscripten/emscripten.h>
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#include <emscripten/threading.h>
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#include <time.h>
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/* EM_ASYNC_JS integrates with Asyncify automatically (binaryen instruments every caller). */
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EM_ASYNC_JS( void, __wasm_main_thread_yield_ms, ( double ms ), {
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await new Promise( function( resolve ) { setTimeout( resolve, ms ); } );
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} );
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int nanosleep( const struct timespec* req, struct timespec* rem )
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{
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if( req )
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{
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double ms = (double) req->tv_sec * 1000.0 + (double) req->tv_nsec / 1.0e6;
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if( emscripten_is_main_runtime_thread() )
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__wasm_main_thread_yield_ms( ms ); /* yield -> event loop runs -> Worker boots */
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else
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emscripten_thread_sleep( ms ); /* worker: real blocking sleep */
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}
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if( rem )
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{
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rem->tv_sec = 0;
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rem->tv_nsec = 0;
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}
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return 0;
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}
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