[GR-19220] Make Process.clock_gettime(Process::CLOCK_MONOTONIC) simpler (#2394)

PullRequest: truffleruby/2834

Author: eregon

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

@@ -27,7 +27,6 @@ public abstract class ProcessNodes {
     @Primitive(name = "process_time_nanotime")
     public abstract static class ProcessTimeNanoTimeNode extends PrimitiveArrayArgumentsNode {
 
-        @TruffleBoundary
         @Specialization
         protected long nanoTime() {
             return System.nanoTime();

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

@@ -156,10 +156,10 @@ def self.clock_gettime(id, unit=:float_second)
     end
 
     case id
+    when CLOCK_MONOTONIC # most common clock id
+      time = Primitive.process_time_nanotime
     when CLOCK_REALTIME
       time = Primitive.process_time_instant
-    when CLOCK_MONOTONIC
-      time = Primitive.process_time_nanotime
     else
       time = Truffle::POSIX.truffleposix_clock_gettime(id)
       Errno.handle if time == 0
@@ -169,21 +169,21 @@ def self.clock_gettime(id, unit=:float_second)
   end
 
   def self.nanoseconds_to_unit(nanoseconds, unit)
-    case unit
+    case unit # ordered by expected frequency
+    when :float_second, nil
+      nanoseconds / 1e9
     when :nanosecond
       nanoseconds
     when :microsecond
       nanoseconds / 1_000
-    when :millisecond
-      nanoseconds / 1_000_000
-    when :second
-      nanoseconds / 1_000_000_000
     when :float_microsecond
       nanoseconds / 1e3
     when :float_millisecond
       nanoseconds / 1e6
-    when :float_second, nil
-      nanoseconds / 1e9
+    when :second
+      nanoseconds / 1_000_000_000
+    when :millisecond
+      nanoseconds / 1_000_000
     else
       raise ArgumentError, "unexpected unit: #{unit}"
     end