runtime: add network polling support into scheduler

This is a part of the bigger change that moves network poller into runtime:
https://golang.org/cl/7326051/

R=golang-dev, bradfitz, mikioh.mikioh, rsc
CC=golang-dev
https://golang.org/cl/7448048

src/pkg/runtime/netpoll_stub.c

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build windows
+
+#include "runtime.h"
+
+// Polls for ready network connections.
+// Returns list of goroutines that become runnable.
+G*
+runtime·netpoll(bool block)
+{
+	// Implementation for platforms that do not support
+	// integrated network poller.
+	USED(block);
+	return nil;
+}

src/pkg/runtime/proc.c

@@ -49,6 +49,7 @@ struct Sched {
 	Note	stopnote;
 	uint32	sysmonwait;
 	Note	sysmonnote;
+	uint64	lastpoll;
 
 	int32	profilehz;	// cpu profiling rate
 };
@@ -107,6 +108,7 @@ static void globrunqput(G*);
 static G* globrunqget(P*);
 static P* pidleget(void);
 static void pidleput(P*);
+static void injectglist(G*);
 
 // The bootstrap sequence is:
 //
@@ -135,6 +137,7 @@ runtime·schedinit(void)
 	// so that we don't need to call malloc when we crash.
 	// runtime·findfunc(0);
 
+	runtime·sched.lastpoll = runtime·nanotime();
 	procs = 1;
 	p = runtime·getenv("GOMAXPROCS");
 	if(p != nil && (n = runtime·atoi(p)) > 0) {
@@ -391,8 +394,11 @@ runtime·starttheworld(void)
 {
 	P *p, *p1;
 	M *mp;
+	G *gp;
 	bool add;
 
+	gp = runtime·netpoll(false);  // non-blocking
+	injectglist(gp);
 	add = needaddgcproc();
 	runtime·lock(&runtime·sched);
 	if(newprocs) {
@@ -976,7 +982,7 @@ execute(G *gp)
 }
 
 // Finds a runnable goroutine to execute.
-// Tries to steal from other P's and get g from global queue.
+// Tries to steal from other P's, get g from global queue, poll network.
 static G*
 findrunnable(void)
 {
@@ -1001,6 +1007,13 @@ top:
 		if(gp)
 			return gp;
 	}
+	// poll network
+	gp = runtime·netpoll(false);  // non-blocking
+	if(gp) {
+		injectglist(gp->schedlink);
+		gp->status = Grunnable;
+		return gp;
+	}
 	// If number of spinning M's >= number of busy P's, block.
 	// This is necessary to prevent excessive CPU consumption
 	// when GOMAXPROCS>>1 but the program parallelism is low.
@@ -1055,10 +1068,54 @@ stop:
 			break;
 		}
 	}
+	// poll network
+	if(runtime·xchg64(&runtime·sched.lastpoll, 0) != 0) {
+		if(m->p)
+			runtime·throw("findrunnable: netpoll with p");
+		if(m->spinning)
+			runtime·throw("findrunnable: netpoll with spinning");
+		gp = runtime·netpoll(true);  // block until new work is available
+		runtime·atomicstore64(&runtime·sched.lastpoll, runtime·nanotime());
+		if(gp) {
+			runtime·lock(&runtime·sched);
+			p = pidleget();
+			runtime·unlock(&runtime·sched);
+			if(p) {
+				acquirep(p);
+				injectglist(gp->schedlink);
+				gp->status = Grunnable;
+				return gp;
+			}
+			injectglist(gp);
+		}
+	}
 	stopm();
 	goto top;
 }
 
+// Injects the list of runnable G's into the scheduler.
+// Can run concurrently with GC.
+static void
+injectglist(G *glist)
+{
+	int32 n;
+	G *gp;
+
+	if(glist == nil)
+		return;
+	runtime·lock(&runtime·sched);
+	for(n = 0; glist; n++) {
+		gp = glist;
+		glist = gp->schedlink;
+		gp->status = Grunnable;
+		globrunqput(gp);
+	}
+	runtime·unlock(&runtime·sched);
+
+	for(; n && runtime·sched.npidle; n--)
+		startm(nil, false);
+}
+
 // One round of scheduler: find a runnable goroutine and execute it.
 // Never returns.
 static void
@@ -1916,6 +1973,8 @@ static void
 sysmon(void)
 {
 	uint32 idle, delay;
+	int64 now, lastpoll;
+	G *gp;
 	uint32 ticks[MaxGomaxprocs];
 
 	idle = 0;  // how many cycles in succession we had not wokeup somebody
@@ -1940,6 +1999,14 @@ sysmon(void)
 			} else
 				runtime·unlock(&runtime·sched);
 		}
+		// poll network if not polled for more than 10ms
+		lastpoll = runtime·atomicload64(&runtime·sched.lastpoll);
+		now = runtime·nanotime();
+		if(lastpoll != 0 && lastpoll + 10*1000*1000 > now) {
+			gp = runtime·netpoll(false);  // non-blocking
+			injectglist(gp);
+		}
+		// retake P's blocked in syscalls
 		if(retake(ticks))
 			idle = 0;
 		else

src/pkg/runtime/runtime.h

@@ -767,6 +767,7 @@ void	runtime·blockevent(int64, int32);
 extern int64 runtime·blockprofilerate;
 void	runtime·addtimer(Timer*);
 bool	runtime·deltimer(Timer*);
+G*	runtime·netpoll(bool);
 
 #pragma	varargck	argpos	runtime·printf	1
 #pragma	varargck	type	"d"	int32
@@ -968,5 +969,5 @@ extern uint64 ·neginf;
 
 enum
 {
-	UseSpanType = 1,
+	UseSpanType = 0,
 };