process.c: Use getrusage(2) in Process.times

if getrusage(2) is available, to improve precision of Process.times and
its user like lib/benchmark.rb.

On macOS, since getrusage(2) has better precision than times(3),
they are much improved like:

* Before

Process.times
=> #<struct Process::Tms utime=0.56, stime=0.35, cutime=0.04, cstime=0.03>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.340000   0.310000   0.650000 (  0.674025)

* After

Process.times
=> #<struct Process::Tms utime=0.561899, stime=0.35076, cutime=0.046483, cstime=0.038929>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.343223   0.310037   0.653260 (  0.674025)

On Linux, since struct rusage from getrusage(2) is used instead of struct tms
from times(2), they are slightly improved like:

* Before

Process.times
=> #<struct Process::Tms utime=0.43, stime=0.11, cutime=0.0, cstime=0.0>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.120000   0.040000   0.170000 (  0.171621)

* After

Process.times
=> #<struct Process::Tms utime=0.432, stime=0.116, cutime=0.0, cstime=0.0>

puts Benchmark.measure { "a" * 1_000_000_000 }
  0.124000   0.048000   0.172000 (  0.171621)

[ruby-dev:49471] [Feature #11952]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58935 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -59,6 +59,10 @@ with all sufficient information, see the ChangeLog file or Redmine
     of #coerce. Return nil in #coerce if the coercion is impossible.
     [Feature #7688]
 
+* Process
+
+  * Precision of Process.times is improved if getrusage(2) exists. [Feature #11952]
+
 * Range
   * Range#initialize no longer rescue exceptions when comparing begin and
     end with #<=> and raise a "bad value for range" ArgumentError

process.c

@@ -6887,15 +6887,26 @@ get_clk_tck(void)
 VALUE
 rb_proc_times(VALUE obj)
 {
+    VALUE utime, stime, cutime, cstime, ret;
+#if defined(RUSAGE_SELF) && defined(RUSAGE_CHILDREN)
+    struct rusage usage_s, usage_c;
+
+    if (getrusage(RUSAGE_SELF, &usage_s) != 0 || getrusage(RUSAGE_CHILDREN, &usage_c) != 0)
+	rb_sys_fail("getrusage");
+    utime = DBL2NUM((double)usage_s.ru_utime.tv_sec + (double)usage_s.ru_utime.tv_usec/1e6);
+    stime = DBL2NUM((double)usage_s.ru_stime.tv_sec + (double)usage_s.ru_stime.tv_usec/1e6);
+    cutime = DBL2NUM((double)usage_c.ru_utime.tv_sec + (double)usage_c.ru_utime.tv_usec/1e6);
+    cstime = DBL2NUM((double)usage_c.ru_stime.tv_sec + (double)usage_c.ru_stime.tv_usec/1e6);
+#else
     const double hertz = get_clk_tck();
     struct tms buf;
-    VALUE utime, stime, cutime, cstime, ret;
 
     times(&buf);
     utime = DBL2NUM(buf.tms_utime / hertz);
     stime = DBL2NUM(buf.tms_stime / hertz);
     cutime = DBL2NUM(buf.tms_cutime / hertz);
     cstime = DBL2NUM(buf.tms_cstime / hertz);
+#endif
     ret = rb_struct_new(rb_cProcessTms, utime, stime, cutime, cstime);
     RB_GC_GUARD(utime);
     RB_GC_GUARD(stime);