process.c (waitpid_wait): do not set ECHILD prematurely

It is possible to have both MJIT and normal child processes
alive, so we cannot set ECHILD based on such a guess.  We can
still elide waitpid(PID <= 0) calls if we have callers in
vm->waiting_pids, however.

For specs, ensure Process.waitall does not leak MJIT
PIDs to Rubyspace.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63764 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

process.c

@@ -1074,12 +1074,6 @@ waitpid_wait(struct waitpid_state *w)
     }
     else if (w->options & WNOHANG) {
         w->cond = 0;
-
-        /* MJIT must be waiting, but don't tell Ruby callers about it */
-        if (w->pid < 0 && !list_empty(&vm->waiting_pids)) {
-            w->ret = -1;
-            w->errnum = ECHILD;
-        }
     }
     else {
         w->cond = rb_sleep_cond_get(w->ec);

spec/mspec/lib/mspec/guards/feature.rb

@@ -39,3 +39,9 @@ end
 def with_feature(*features, &block)
   FeatureGuard.new(*features).run_if(:with_feature, &block)
 end
+
+MSpecEnv.class_eval do
+  def without_feature(*features, &block)
+    FeatureGuard.new(*features).run_unless(:without_feature, &block)
+  end
+end

spec/ruby/core/process/wait2_spec.rb

@@ -4,11 +4,19 @@ describe "Process.wait2" do
   before :all do
     # HACK: this kludge is temporarily necessary because some
     # misbehaving spec somewhere else does not clear processes
+    # Note: background processes are unavoidable with MJIT,
+    # but we shouldn't reap them from Ruby-space
     begin
       Process.wait(-1, Process::WNOHANG)
+      without_feature :mjit do
         $stderr.puts "Leaked process before wait2 specs! Waiting for it"
+      end
       leaked = Process.waitall
-      $stderr.puts "leaked before wait2 specs: #{leaked}"
+      $stderr.puts "leaked before wait2 specs: #{leaked}" unless leaked.empty?
+      with_feature :mjit do
+        # Ruby-space should not see PIDs used by mjit
+        leaked.should be_empty
+      end
     rescue Errno::ECHILD # No child processes
     rescue NotImplementedError
     end

spec/ruby/core/process/wait_spec.rb

@@ -8,6 +8,10 @@ describe "Process.wait" do
     begin
       leaked = Process.waitall
       puts "leaked before wait specs: #{leaked}" unless leaked.empty?
+      with_feature :mjit do
+        # Ruby-space should not see PIDs used by mjit
+        leaked.should be_empty
+      end
     rescue NotImplementedError
     end
   end