Adapt comphelper::ThreadPool to Emscripten's threading needs

...by keeping the worker threads around by default instead of joining and later
re-spawning them; see 5b1df7709d75c6dd993da5a272e7e37e55a70174 "Document the
Emscripten threads issue".  But lets be cautious and change the bJoin default
only for Emscripten.

Also, cap the thread pool size to MAX_CONCURRENCY=4 and increase to
-sPTHREAD_POOL_SIZE=6.  In an experimental setup where the Emscripten build
starts up with the start center rather than a Writer document, that is just
enough to cover the thread-spawning needs when executing the start center
window's paint task:  Four threads for the comphelper::ThreadPool (used from
within drawinglayer::convertToBitmapEx -> ... ->
BitmapBasicMorphologyFilter::filter), and one each for
configmgr::Components::WriteThread (see e8358d0a0f7c2c4b1ccf800fe9ec8a7f2bf7066a
"Keep around a single configmgr::Components::WriteThread instance") and
salhelper::TimerManager.

Change-Id: I5b1d0e9dc09f05fb3b679c8dc1c38ee45c61c0f8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/171004
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>
Tested-by: Jenkins

1 files changed, 7 insertions, 1 deletions

diff --git a/include/comphelper/threadpool.hxx b/include/comphelper/threadpool.hxx
index 84f9dc9284f6..0b2ebc8ac9e6 100644
--- a/include/comphelper/threadpool.hxx
+++ b/include/comphelper/threadpool.hxx
@@ -67,7 +67,13 @@ public:
     /** Wait until all queued tasks associated with the tag are completed
         @param  bJoin - if set call joinThreadsIfIdle() at the end
     */
-    void        waitUntilDone(const std::shared_ptr<ThreadTaskTag>&, bool bJoin = true);
+    void        waitUntilDone(const std::shared_ptr<ThreadTaskTag>&, bool bJoin =
+#if defined EMSCRIPTEN
+                                                                     false
+#else
+                                                                     true
+#endif
+                             );
 
     /// join all threads if there are no tasks presently.
     void        joinThreadsIfIdle();