runtime: run goroutines during init

Fixes #583.
Fixes #1776.
Fixes #2001.
Fixes #2112.

R=golang-dev, bradfitz, r, gri
CC=golang-dev
https://golang.org/cl/5265044

doc/go_spec.html

@@ -5109,12 +5109,6 @@ unspecified results  if <code>A</code>'s initializer calls a function defined
 in another package that refers to <code>B</code>.
 </p>
 <p>
-Initialization code may contain "go" statements, but the functions
-they invoke do not begin execution until initialization of the entire
-program is complete. Therefore, all initialization code is run in a single
-goroutine.
-</p>
-<p>
 An <code>init</code> function cannot be referred to from anywhere
 in a program. In particular, <code>init</code> cannot be called explicitly,
 nor can a pointer to <code>init</code> be assigned to a function variable.

src/pkg/runtime/386/asm.s

@@ -92,7 +92,6 @@ ok:
 
 TEXT runtime·mainstart(SB),7,$0
 	CALL	main·init(SB)
-	CALL	runtime·initdone(SB)
 	CALL	main·main(SB)
 	PUSHL	$0
 	CALL	runtime·exit(SB)

src/pkg/runtime/amd64/asm.s

@@ -74,7 +74,6 @@ ok:
 
 TEXT runtime·mainstart(SB),7,$0
 	CALL	main·init(SB)
-	CALL	runtime·initdone(SB)
 	CALL	main·main(SB)
 	PUSHQ	$0
 	CALL	runtime·exit(SB)

src/pkg/runtime/arm/asm.s

@@ -63,7 +63,6 @@ TEXT _rt0_arm(SB),7,$-4
 
 TEXT runtime·mainstart(SB),7,$4
 	BL	main·init(SB)
-	BL	runtime·initdone(SB)
 	EOR	R0, R0
 	MOVW	R0, 0(R13)
 	BL	main·main(SB)

src/pkg/runtime/proc.c

@@ -71,7 +71,6 @@ struct Sched {
 
 	volatile uint32 atomic;	// atomic scheduling word (see below)
 
-	int32 predawn;		// running initialization, don't run new g's.
 	int32 profilehz;	// cpu profiling rate
 
 	Note	stopped;	// one g can set waitstop and wait here for m's to stop
@@ -202,8 +201,8 @@ runtime·schedinit(void)
 	}
 	setmcpumax(runtime·gomaxprocs);
 	runtime·singleproc = runtime·gomaxprocs == 1;
-	runtime·sched.predawn = 1;
 
+	mstats.enablegc = 1;
 	m->nomemprof--;
 }
 
@@ -227,22 +226,6 @@ schedunlock(void)
 		runtime·notewakeup(&m->havenextg);
 }
 
-// Called after main·init_function; main·main will be called on return.
-void
-runtime·initdone(void)
-{
-	// Let's go.
-	runtime·sched.predawn = 0;
-	mstats.enablegc = 1;
-
-	// If main·init_function started other goroutines,
-	// kick off new m's to handle them, like ready
-	// would have, had it not been pre-dawn.
-	schedlock();
-	matchmg();
-	schedunlock();
-}
-
 void
 runtime·goexit(void)
 {
@@ -467,7 +450,6 @@ readylocked(G *g)
 	g->status = Grunnable;
 
 	gput(g);
-	if(!runtime·sched.predawn)
 	matchmg();
 }
 
@@ -793,9 +775,6 @@ schedule(G *gp)
 
 	schedlock();
 	if(gp != nil) {
-		if(runtime·sched.predawn)
-			runtime·throw("init rescheduling");
-
 		// Just finished running gp.
 		gp->m = nil;
 		runtime·sched.grunning--;
@@ -893,9 +872,6 @@ runtime·entersyscall(void)
 {
 	uint32 v;
 
-	if(runtime·sched.predawn)
-		return;
-
 	// Leave SP around for gc and traceback.
 	runtime·gosave(&g->sched);
 	g->gcsp = g->sched.sp;
@@ -947,9 +923,6 @@ runtime·exitsyscall(void)
 {
 	uint32 v;
 
-	if(runtime·sched.predawn)
-		return;
-
 	// Fast path.
 	// If we can do the mcpu++ bookkeeping and
 	// find that we still have mcpu <= mcpumax, then we can
@@ -1513,8 +1486,6 @@ runtime·Gosched(void)
 void
 runtime·LockOSThread(void)
 {
-	if(runtime·sched.predawn)
-		runtime·throw("cannot wire during init");
 	m->lockedg = g;
 	g->lockedm = m;
 }

test/init1.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2011 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.
+
+// Test that goroutines and garbage collection run during init.
+
+package main
+
+import "runtime"
+
+var x []byte
+
+func init() {
+	c := make(chan int)
+	go send(c)
+	<-c
+	
+	const chunk = 1<<20
+	runtime.UpdateMemStats()
+	sys := runtime.MemStats.Sys	
+	b := make([]byte, chunk)
+	for i := range b {
+		b[i] = byte(i%10 + '0')
+	}
+	s := string(b)
+	for i := 0; i < 1000; i++ {
+		x = []byte(s)
+	}
+	runtime.UpdateMemStats()
+	sys1 := runtime.MemStats.Sys
+	if sys1-sys > chunk*50 {
+		println("allocated 1000 chunks of", chunk, "and used ", sys1-sys, "memory")
+	}
+}
+
+func send(c chan int) {
+	c <- 1
+}
+
+func main() {
+}
+