back to elementary options used in Isabelle2015 for jdk-7 -- none of the intermediate experiments for jdk-8 improved reactivity on particular dual-CPU system, but the problem seems to be absent on common single-CPU systems;
--- a/etc/settings Sat Jan 23 11:52:48 2016 +0100
+++ b/etc/settings Sat Jan 23 23:50:54 2016 +0100
@@ -14,7 +14,7 @@
ISABELLE_SCALA_BUILD_OPTIONS="-encoding UTF-8 -nowarn -target:jvm-1.7 -Xmax-classfile-name 130"
-ISABELLE_JAVA_SYSTEM_OPTIONS="-server -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -Dfile.encoding=UTF-8 -Disabelle.threads=0"
+ISABELLE_JAVA_SYSTEM_OPTIONS="-server -Dfile.encoding=UTF-8 -Disabelle.threads=0"
classpath "$ISABELLE_HOME/lib/classes/Pure.jar"