Never run callbacks synchronously in emscripten_dlopen

[sbc100]

Having sometimes-syncrinous callbacks is a bad idea, and it was actually causing real issues with the emscripten_dlopen_promice API.

This introduced a new emscripten_queue_microtask API to match the long standing web API (also available in node).
See https://developer.mozilla.org/en-US/docs/Web/API/Window/queueMicrotask

See #24461 and pyodide/pyodide#5610 (comment)

[ryanking13]

Thanks for fixing this! I tested this patch in my Pyodide PR that use emscripten_dlopen and I get the following error during the build

cache:INFO: generating system library: sysroot/lib/wasm32-emscripten/pic/libc.a... (this will be cached in "/src/emsdk/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libc.a" for subsequent builds)
../../../system/lib/libc/dynlink.c:635:5: error: call to undeclared function 'emscripten_queue_microtask'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  635 |     emscripten_queue_microtask(run_success_callback, d);

Interestingly, adding #include <emscripten/eventloop.h> in dynlink.c doesn't seem to fix the issue. So I don't really understand the error...

Full cmdline was

/src/emsdk/emsdk/upstream/emscripten/emcc -c -O2 -Wall -fno-unroll-loops -std=c99 -D_XOPEN_SOURCE=700 -Wno-unused-result -Os -fno-inline-functions -fno-builtin -Wno-ignored-attributes -Wno-macro-redefined -Wno-shift-op-parentheses -Wno-string-plus-int -Wno-missing-braces -Wno-logical-op-parentheses -Wno-bitwise-op-parentheses -Wno-unused-but-set-variable -Wno-unused-variable -Wno-unused-label -Wno-pointer-sign -g -sSTRICT -Werror -sRELOCATABLE -DEMSCRIPTEN_DYNAMIC_LINKING -ffile-prefix-map=/src/emsdk/emsdk/upstream/emscripten=/emsdk/emscripten -ffile-prefix-map=../../..=/emsdk/emscripten -fdebug-compilation-dir=/emsdk/emscripten -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc/musl/src/internal -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc/musl/src/include -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc/musl/include -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc -I/src/emsdk/emsdk/upstream/emscripten/system/lib/pthread -DNDEBUG ../../../system/lib/libc/pthread_sigmask.c ../../../system/lib/libc/raise.c ../../../system/lib/libc/sigaction.c ../../../system/lib/libc/sigtimedwait.c ../../../system/lib/libc/wasi-helpers.c ../../../system/lib/libc/system.c ../../../system/lib/libc/dynlink.c ../../../system/lib/pthread/thread_profiler.c ../../../system/lib/libc/compat/__synccall.c ../../../system/lib/libc/compat/aligned_alloc.c ../../../system/lib/libc/compat/strlwr.c ../../../system/lib/libc/compat/strtol_l.c ../../../system/lib/libc/compat/strupr.c

[sbc100]

Thanks for fixing this! I tested this patch in my Pyodide PR that use emscripten_dlopen and I get the following error during the build

cache:INFO: generating system library: sysroot/lib/wasm32-emscripten/pic/libc.a... (this will be cached in "/src/emsdk/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/pic/libc.a" for subsequent builds)
../../../system/lib/libc/dynlink.c:635:5: error: call to undeclared function 'emscripten_queue_microtask'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  635 |     emscripten_queue_microtask(run_success_callback, d);

Interestingly, adding #include <emscripten/eventloop.h> in dynlink.c doesn't seem to fix the issue. So I don't really understand the error...

Full cmdline was

/src/emsdk/emsdk/upstream/emscripten/emcc -c -O2 -Wall -fno-unroll-loops -std=c99 -D_XOPEN_SOURCE=700 -Wno-unused-result -Os -fno-inline-functions -fno-builtin -Wno-ignored-attributes -Wno-macro-redefined -Wno-shift-op-parentheses -Wno-string-plus-int -Wno-missing-braces -Wno-logical-op-parentheses -Wno-bitwise-op-parentheses -Wno-unused-but-set-variable -Wno-unused-variable -Wno-unused-label -Wno-pointer-sign -g -sSTRICT -Werror -sRELOCATABLE -DEMSCRIPTEN_DYNAMIC_LINKING -ffile-prefix-map=/src/emsdk/emsdk/upstream/emscripten=/emsdk/emscripten -ffile-prefix-map=../../..=/emsdk/emscripten -fdebug-compilation-dir=/emsdk/emscripten -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc/musl/src/internal -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc/musl/src/include -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc/musl/include -I/src/emsdk/emsdk/upstream/emscripten/system/lib/libc -I/src/emsdk/emsdk/upstream/emscripten/system/lib/pthread -DNDEBUG ../../../system/lib/libc/pthread_sigmask.c ../../../system/lib/libc/raise.c ../../../system/lib/libc/sigaction.c ../../../system/lib/libc/sigtimedwait.c ../../../system/lib/libc/wasi-helpers.c ../../../system/lib/libc/system.c ../../../system/lib/libc/dynlink.c ../../../system/lib/pthread/thread_profiler.c ../../../system/lib/libc/compat/__synccall.c ../../../system/lib/libc/compat/aligned_alloc.c ../../../system/lib/libc/compat/strlwr.c ../../../system/lib/libc/compat/strtol_l.c ../../../system/lib/libc/compat/strupr.c

Likely the sysroot would need updating to get the header file.

You can use ./embuilder build sysroot --force to do that.