8254912: ZGC: Change ZCollectionInterval type to double

Reviewed-by: pliden, ayang

Author: stefank

src/hotspot/share/gc/z/zDirector.cpp

@@ -48,7 +48,7 @@ void ZDirector::sample_allocation_rate() const {
 }
 
 bool ZDirector::rule_timer() const {
-  if (ZCollectionInterval == 0) {
+  if (ZCollectionInterval <= 0) {
     // Rule disabled
     return false;
   }
@@ -57,7 +57,7 @@ bool ZDirector::rule_timer() const {
   const double time_since_last_gc = ZStatCycle::time_since_last();
   const double time_until_gc = ZCollectionInterval - time_since_last_gc;
 
-  log_debug(gc, director)("Rule: Timer, Interval: %us, TimeUntilGC: %.3fs",
+  log_debug(gc, director)("Rule: Timer, Interval: %.3fs, TimeUntilGC: %.3fs",
                           ZCollectionInterval, time_until_gc);
 
   return time_until_gc <= 0;

src/hotspot/share/gc/z/z_globals.hpp

@@ -42,7 +42,7 @@
           "Maximum number of bytes allocated for mark stacks")              \
           range(32*M, 1024*G)                                               \
                                                                             \
-  product(uint, ZCollectionInterval, 0,                                     \
+  product(double, ZCollectionInterval, 0,                                   \
           "Force GC at a fixed time interval (in seconds)")                 \
                                                                             \
   product(bool, ZProactive, true,                                           \