Emscripten: Move the Qt event loop off the JS main thread

...so that spawning and joining new threads works now and we no longer need a
hardcoded -sPTHREAD_POOL_SIZE of pre-spawned threads (see
b84ef4d67eaf9f9fd7fd700ca05339cb0cdff742 "Adapt comphelper::ThreadPool to
Emscripten's threading needs"; lets keep MAX_CONCURRENCY capped at 4, at least
for now, though).

This requires
<167b08844d>
"Minimal support for Emscripten -sPROXY_TO_PTHREAD=1" and
<c722a25630>
"Implement QWasmCursor::changeCursor for Emscripten PROXY_TO_PTHREAD case" (see
TODOs there).

Change-Id: I8cea827bd7786e3c9fd9401b4b2bef9d3ec00d5a
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/171758
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>
Tested-by: Jenkins

desktop/Executable_soffice_bin.mk

@@ -63,6 +63,7 @@ $(call gb_Executable_get_linktarget_target,soffice_bin): \
 
 $(eval $(call gb_Executable_add_ldflags,soffice_bin,\
 	-s EXPORTED_FUNCTIONS=@$(gb_CustomTarget_workdir)/desktop/soffice_bin-emscripten-exports/exports -Wl$(COMMA)--whole-archive $(call gb_StaticLibrary_get_target,unoembind) -Wl$(COMMA)--no-whole-archive \
+	-sPROXY_TO_PTHREAD=1 -sOFFSCREENCANVAS_SUPPORT=1 -sOFFSCREENCANVASES_TO_PTHREAD=\#qtcanvas \
 ))
 ifeq ($(ENABLE_QT6),TRUE)
 $(eval $(call gb_Executable_add_ldflags,soffice_bin, \

solenv/gbuild/platform/EMSCRIPTEN_INTEL_GCC.mk

@@ -15,7 +15,7 @@ gb_EMSCRIPTEN_CPPFLAGS := -pthread -s USE_PTHREADS=1 -D_LARGEFILE64_SOURCE -D_LA
 gb_EMSCRIPTEN_LDFLAGS := $(gb_EMSCRIPTEN_CPPFLAGS)
 
 # Initial memory size and worker thread pool
-gb_EMSCRIPTEN_LDFLAGS += -s TOTAL_MEMORY=1GB -s PTHREAD_POOL_SIZE=6
+gb_EMSCRIPTEN_LDFLAGS += -s TOTAL_MEMORY=1GB
 
 # To keep the link time (and memory) down, prevent all rewriting options from wasm-emscripten-finalize
 # See emscripten.py, finalize_wasm, modify_wasm = True

static/README.wasm.md

@@ -64,11 +64,14 @@ With "-opensource -confirm-license" you agree to the open source license.
 
     git clone https://github.com/allotropia/qt5.git
     cd qt5
-    git checkout v5.15.2+wasm
+    git checkout 5.15.2+wasm
     ./init-repository --module-subset=qtbase
     ./configure -opensource -confirm-license -xplatform wasm-emscripten -feature-thread -prefix <whatever> QMAKE_CFLAGS+=-sSUPPORT_LONGJMP=wasm QMAKE_CXXFLAGS+=-sSUPPORT_LONGJMP=wasm
     make -j<CORES> module-qtbase
 
+Note that `5.15.2+wasm` is a branch that is expected to contain further fixes as they become
+necessary.
+
 Do not include `-fwasm-exceptions` in the above `QMAKE_CXXFLAGS`, see
 <https://emscripten.org/docs/api_reference/emscripten.h.html#c.emscripten_set_main_loop> "Note:
 Currently, using the new Wasm exception handling and simulate_infinite_loop == true at the same time

static/emscripten/environment.js

@@ -5,3 +5,4 @@ Module.preRun.push(function() {
     ENV.MAX_CONCURRENCY = '4';
     ENV.SAL_LOG = "+WARN"
 });
+Module.ignoreApplicationExit = true;