runtime: move per-P timers state into its own struct

Continuing conversion from C to Go, introduce type timers
encapsulating all timer heap state, with methods for operations.
This should at least be easier to think about, instead of having
these fields strewn through the P struct. It should also be easier
to test.

I am skeptical about the pair of atomic int64 deadlines:
I think there are missed wakeups lurking.
Having the code in an abstracted API should make it easier
to reason through and fix if needed.

[This is one CL in a refactoring stack making very small changes
in each step, so that any subtle bugs that we miss can be more
easily pinpointed to a small change.]

Change-Id: If5ea3e0b946ca14076f44c85cbb4feb9eddb4f95
Reviewed-on: https://go-review.googlesource.com/c/go/+/564132
Reviewed-by: Austin Clements <austin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>

1 files changed, 2 insertions, 27 deletions

diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 248f489da5..985c1ffab4 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -708,16 +708,6 @@ type p struct {
 
 	palloc persistentAlloc // per-P to avoid mutex
 
-	// The when field of the first entry on the timer heap.
-	// This is 0 if the timer heap is empty.
-	timer0When atomic.Int64
-
-	// The earliest known nextwhen field of a timer with
-	// timerModifiedEarlier status. Because the timer may have been
-	// modified again, there need not be any timer with this value.
-	// This is 0 if there are no timerModifiedEarlier timers.
-	timerModifiedEarliest atomic.Int64
-
 	// Per-P GC state
 	gcAssistTime         int64 // Nanoseconds in assistAlloc
 	gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic)
@@ -751,23 +741,8 @@ type p struct {
 	// writing any stats. Its value is even when not, odd when it is.
 	statsSeq atomic.Uint32
 
-	// Lock for timers. We normally access the timers while running
-	// on this P, but the scheduler can also do it from a different P.
-	timersLock mutex
-
-	// Actions to take at some time. This is used to implement the
-	// standard library's time package.
-	// Must hold timersLock to access.
-	timers []*timer
-
-	// Number of timers in P's heap.
-	numTimers atomic.Uint32
-
-	// Number of timerDeleted timers in P's heap.
-	deletedTimers atomic.Uint32
-
-	// Race context used while executing timer functions.
-	timerRaceCtx uintptr
+	// Timer heap.
+	timers timers
 
 	// maxStackScanDelta accumulates the amount of stack space held by
 	// live goroutines (i.e. those eligible for stack scanning).