[GR-3590] Process::CLOCK_REALTIME has microsecond precision on Java 9+

PullRequest: truffleruby/2410

Author: bjfish

spec/ruby/core/time/shared/now.rb

@@ -19,15 +19,15 @@
   end
 
   it "has at least microsecond precision" do
-    times = []
-    10_000.times do
-      times << Time.now.nsec
-    end
-
     # The clock should not be less accurate than expected (times should
     # not all be a multiple of the next precision up, assuming precisions
     # are multiples of ten.)
     expected = 1_000
-    times.select { |t| t % (expected * 10) == 0  }.size.should_not == times.size
+    t = 0
+    10_000.times.find do
+      t = Time.now.nsec
+      t % (expected * 10) != 0
+    end
+    (t % (expected * 10)).should != 0
   end
 end

spec/tags/core/time/now_tags.txt

@@ -1 +1 @@
-fails:Time.now has at least microsecond precision
+java8:Time.now has at least microsecond precision

spec/truffleruby.mspec

@@ -1,3 +1,5 @@
+# truffleruby_primitives: true
+
 require 'rbconfig'
 
 # Inherit from the default configuration
@@ -123,6 +125,10 @@ class MSpecScript
     excludes << 'arm64'
   end
 
+  if defined?(::TruffleRuby) and Primitive.vm_java_version <= 8
+    excludes << 'java8'
+  end
+
   # All specs, excluding specs needing C-extensions support.
   set :files, get(:command_line) + get(:language) + get(:core) + get(:library) + get(:truffle) + get(:security)
 

src/main/java/org/truffleruby/core/ProcessNodes.java

@@ -19,6 +19,8 @@
 
 import sun.misc.Signal;
 
+import java.time.Instant;
+
 @CoreModule(value = "Process", isClass = true)
 public abstract class ProcessNodes {
 
@@ -33,13 +35,14 @@ protected long nanoTime() {
 
     }
 
-    @Primitive(name = "process_time_currenttimemillis")
-    public abstract static class ProcessTimeCurrentTimeMillisNode extends PrimitiveArrayArgumentsNode {
+    @Primitive(name = "process_time_instant")
+    public abstract static class ProcessTimeInstantNode extends PrimitiveArrayArgumentsNode {
 
         @TruffleBoundary
         @Specialization
-        protected long currentTimeMillis() {
-            return System.currentTimeMillis();
+        protected long instant() {
+            final Instant now = Instant.now();
+            return (now.getEpochSecond() * 1_000_000_000L) + now.getNano();
         }
 
     }

src/main/java/org/truffleruby/core/VMPrimitiveNodes.java

@@ -531,4 +531,24 @@ protected Object shouldNotReachHere(Object message,
 
     }
 
+    @Primitive(name = "vm_java_version")
+    public abstract static class VMJavaVersionNode extends PrimitiveArrayArgumentsNode {
+
+        private static final int JAVA_SPECIFICATION_VERSION = getJavaSpecificationVersion();
+
+        private static int getJavaSpecificationVersion() {
+            String value = System.getProperty("java.specification.version");
+            if (value.startsWith("1.")) {
+                value = value.substring(2);
+            }
+            return Integer.parseInt(value);
+        }
+
+        @Specialization
+        protected int javaVersion() {
+            return JAVA_SPECIFICATION_VERSION;
+        }
+
+    }
+
 }

src/main/ruby/truffleruby/core/process.rb

@@ -112,7 +112,8 @@ def self.clock_getres(id, unit=:float_second)
                :CLOCK_BASED_CLOCK_PROCESS_CPUTIME_ID
             1_000
           when CLOCK_REALTIME
-            1_000_000
+            # https://bugs.openjdk.java.net/browse/JDK-8068730
+            Primitive.vm_java_version >= 9 ? 1000 : 1_000_000
           when :TIMES_BASED_CLOCK_MONOTONIC,
                :TIMES_BASED_CLOCK_PROCESS_CPUTIME_ID
             10_000_000
@@ -156,7 +157,7 @@ def self.clock_gettime(id, unit=:float_second)
 
     case id
     when CLOCK_REALTIME
-      time = Primitive.process_time_currenttimemillis * 1_000_000
+      time = Primitive.process_time_instant
     when CLOCK_MONOTONIC
       time = Primitive.process_time_nanotime
     else