runtime: remove untyped allocation of ParFor

Now it's two allocations. I don't see much downside to that,
since the two pieces were in different cache lines anyway.

Rename 'conservative' to 'cgo_conservative_type' and make
clear that _cgo_allocate is the only allowed user.

This depends on CL 141490043, which removes the other
use of conservative (in defer).

LGTM=dvyukov, iant
R=khr, dvyukov, iant
CC=golang-codereviews, rlh
https://golang.org/cl/139610043

1 files changed, 8 insertions, 0 deletions

diff --git a/src/runtime/runtime.go b/src/runtime/runtime.go
index d4f7c64a52..dbaea45a66 100644
--- a/src/runtime/runtime.go
+++ b/src/runtime/runtime.go
@@ -39,3 +39,11 @@ func tickspersecond() int64 {
 func makeStringSlice(n int) []string {
 	return make([]string, n)
 }
+
+// TODO: Move to parfor.go when parfor.c becomes parfor.go.
+func parforalloc(nthrmax uint32) *parfor {
+	return &parfor{
+		thr:     &make([]parforthread, nthrmax)[0],
+		nthrmax: nthrmax,
+	}
+}