runtime: eliminate parfor ctx field

Prior to the conversion of the runtime to Go, this void* was
necessary to get closure information in to C callbacks.  There
are no more C callbacks and parfor is perfectly capable of
invoking a Go closure now, so eliminate ctx and all of its
unsafe-ness.  (Plus, the runtime currently doesn't use ctx for
anything.)

Change-Id: I39fc53b7dd3d7f660710abc76b0d831bfc6296d8
Reviewed-on: https://go-review.googlesource.com/3395Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

src/runtime/export_test.go

@@ -41,7 +41,6 @@ type ParFor struct {
 	Nthr   uint32
 	thrseq uint32
 	Cnt    uint32
-	Ctx    *byte
 	wait   bool
 }
 
@@ -53,9 +52,9 @@ func NewParFor(nthrmax uint32) *ParFor {
 	return desc
 }
 
-func ParForSetup(desc *ParFor, nthr, n uint32, ctx *byte, wait bool, body func(*ParFor, uint32)) {
+func ParForSetup(desc *ParFor, nthr, n uint32, wait bool, body func(*ParFor, uint32)) {
 	systemstack(func() {
-		parforsetup((*parfor)(unsafe.Pointer(desc)), nthr, n, unsafe.Pointer(ctx), wait,
+		parforsetup((*parfor)(unsafe.Pointer(desc)), nthr, n, wait,
 			*(*func(*parfor, uint32))(unsafe.Pointer(&body)))
 	})
 }

src/runtime/mgc.go

@@ -1490,7 +1490,7 @@ func gcscan_m() {
 	work.ndone = 0
 	work.nproc = 1 // For now do not do this in parallel.
 	//	ackgcphase is not needed since we are not scanning running goroutines.
-	parforsetup(work.markfor, work.nproc, uint32(_RootCount+local_allglen), nil, false, markroot)
+	parforsetup(work.markfor, work.nproc, uint32(_RootCount+local_allglen), false, markroot)
 	parfordo(work.markfor)
 
 	lock(&allglock)
@@ -1588,7 +1588,7 @@ func gc(start_time int64, eagersweep bool) {
 		traceGCScanStart()
 	}
 
-	parforsetup(work.markfor, work.nproc, uint32(_RootCount+allglen), nil, false, markroot)
+	parforsetup(work.markfor, work.nproc, uint32(_RootCount+allglen), false, markroot)
 	if work.nproc > 1 {
 		noteclear(&work.alldone)
 		helpgc(int32(work.nproc))

src/runtime/parfor.go

@@ -15,7 +15,6 @@ type parfor struct {
 	nthr   uint32         // total number of threads
 	thrseq uint32         // thread id sequencer
 	cnt    uint32         // iteration space [0, cnt)
-	ctx    unsafe.Pointer // arbitrary user context
 	wait   bool           // if true, wait while all threads finish processing,
 	// otherwise parfor may return while other threads are still working
 
@@ -58,9 +57,7 @@ func parforalloc(nthrmax uint32) *parfor {
 // If wait is false, parfordo may return when there is a small amount
 // of work left, under the assumption that another thread has that
 // work well in hand.
-// The opaque user context ctx is recorded as desc.ctx and can be used by body.
-// TODO(austin): Remove ctx in favor of using a closure for body.
-func parforsetup(desc *parfor, nthr, n uint32, ctx unsafe.Pointer, wait bool, body func(*parfor, uint32)) {
+func parforsetup(desc *parfor, nthr, n uint32, wait bool, body func(*parfor, uint32)) {
 	if desc == nil || nthr == 0 || nthr > uint32(len(desc.thr)) || body == nil {
 		print("desc=", desc, " nthr=", nthr, " count=", n, " body=", body, "\n")
 		throw("parfor: invalid args")
@@ -71,7 +68,6 @@ func parforsetup(desc *parfor, nthr, n uint32, ctx unsafe.Pointer, wait bool, bo
 	desc.nthr = nthr
 	desc.thrseq = 0
 	desc.cnt = n
-	desc.ctx = ctx
 	desc.wait = wait
 	desc.nsteal = 0
 	desc.nstealcnt = 0

src/runtime/parfor_test.go

@@ -10,11 +10,8 @@ package runtime_test
 import (
 	. "runtime"
 	"testing"
-	"unsafe"
 )
 
-var gdata []uint64
-
 // Simple serial sanity test for parallelfor.
 func TestParFor(t *testing.T) {
 	const P = 1
@@ -24,12 +21,7 @@ func TestParFor(t *testing.T) {
 		data[i] = i
 	}
 	desc := NewParFor(P)
-	// Avoid making func a closure: parfor cannot invoke them.
-	// Since it doesn't happen in the C code, it's not worth doing
-	// just for the test.
-	gdata = data
-	ParForSetup(desc, P, N, nil, true, func(desc *ParFor, i uint32) {
-		data := gdata
+	ParForSetup(desc, P, N, true, func(desc *ParFor, i uint32) {
 		data[i] = data[i]*data[i] + 1
 	})
 	ParForDo(desc)
@@ -49,9 +41,8 @@ func TestParFor2(t *testing.T) {
 		data[i] = i
 	}
 	desc := NewParFor(P)
-	ParForSetup(desc, P, N, (*byte)(unsafe.Pointer(&data)), false, func(desc *ParFor, i uint32) {
-		d := *(*[]uint64)(unsafe.Pointer(desc.Ctx))
-		d[i] = d[i]*d[i] + 1
+	ParForSetup(desc, P, N, false, func(desc *ParFor, i uint32) {
+		data[i] = data[i]*data[i] + 1
 	})
 	for p := 0; p < P; p++ {
 		ParForDo(desc)
@@ -70,7 +61,7 @@ func TestParForSetup(t *testing.T) {
 	desc := NewParFor(P)
 	for n := uint32(0); n < N; n++ {
 		for p := uint32(1); p <= P; p++ {
-			ParForSetup(desc, p, n, nil, true, func(desc *ParFor, i uint32) {})
+			ParForSetup(desc, p, n, true, func(desc *ParFor, i uint32) {})
 			sum := uint32(0)
 			size0 := uint32(0)
 			end0 := uint32(0)
@@ -113,9 +104,7 @@ func TestParForParallel(t *testing.T) {
 	P := GOMAXPROCS(-1)
 	c := make(chan bool, P)
 	desc := NewParFor(uint32(P))
-	gdata = data
-	ParForSetup(desc, uint32(P), uint32(N), nil, false, func(desc *ParFor, i uint32) {
-		data := gdata
+	ParForSetup(desc, uint32(P), uint32(N), false, func(desc *ParFor, i uint32) {
 		data[i] = data[i]*data[i] + 1
 	})
 	for p := 1; p < P; p++ {