runtime: decentralize sweep termination and mark transition

This moves all of GC initialization, sweep termination, and the
transition to concurrent marking in to the off->mark transition
function. This means it's now handled on the goroutine that detected
the state exit condition.

As a result, malloc no longer needs to Gosched() at the beginning of
the GC cycle to prevent over-allocation while the GC is starting up
because it will now *help* the GC to start up. The Gosched hack is
still necessary during GC shutdown (this is easy to test by enabling
gctrace and hitting Ctrl-S to block the gctrace output).

At this point, the GC coordinator still handles later phases. This
requires a small tweak to how we start the GC coordinator. Currently,
starting the GC coordinator is best-effort and may fail if the
coordinator is about to park from the previous cycle but hasn't yet.
We fix this by replacing the park/ready to wake up the coordinator
with a semaphore. This is temporary since the coordinator will be
going away in a few commits.

Updates #11970.

Change-Id: I2c6a11c91e72dfbc59c2d8e7c66146dee9a444fe
Reviewed-on: https://go-review.googlesource.com/16357
Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index 230849609f..45ebe712ba 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -737,7 +737,7 @@ func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
 	if shouldhelpgc && gcShouldStart(false) {
 		gcStart(gcBackgroundMode, false)
 	} else if shouldhelpgc && bggc.working != 0 && gcBlackenEnabled == 0 {
-		// The GC is starting up or shutting down, so we can't
+		// The GC shutting down, so we can't
 		// assist, but we also can't allocate unabated. Slow
 		// down this G's allocation and help the GC stay
 		// scheduled by yielding.