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runtime: merge timerNoStatus into timerRemoved

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For historical reasons, we have to treat a zero timer as
the same as an initialized timer that was stopped (removed).
The two states are already treated mostly identically.
Merge them.

This is part of a larger simplification of the state set.

[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: I9c3aeb8f92bafb18c47489c1ec20a7b87ac5cd9c
Reviewed-on: https://go-review.googlesource.com/c/go/+/564122
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
This commit is contained in:
Russ Cox 2024-02-14 11:56:59 -05:00
parent 3be36e9b20
commit ed0ad591d3
1 changed files with 12 additions and 21 deletions
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33
src/runtime/time.go
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@ -73,7 +73,6 @@ type timer struct {
// deltimer:
// timerWaiting -> timerModifying -> timerDeleted
// timerModified -> timerModifying -> timerDeleted
// timerNoStatus -> do nothing
// timerDeleted -> do nothing
// timerRemoved -> do nothing
// timerRunning -> wait until status changes
@ -81,7 +80,6 @@ type timer struct {
// modtimer:
// timerWaiting -> timerModifying -> timerModified
// timerModified -> timerModifying -> timerModified
// timerNoStatus -> timerModifying -> timerWaiting
// timerRemoved -> timerModifying -> timerWaiting
// timerDeleted -> timerModifying -> timerModified
// timerRunning -> wait until status changes
@ -90,9 +88,9 @@ type timer struct {
// timerDeleted -> timerModifying -> timerRemoved
// timerModified -> timerModifying -> timerWaiting
// runtimer (looks in P's timer heap):
// timerNoStatus -> panic: uninitialized timer
// timerRemoved -> panic: uninitialized timer
// timerWaiting -> timerWaiting or
// timerWaiting -> timerRunning -> timerNoStatus or
// timerWaiting -> timerRunning -> timerRemoved or
// timerWaiting -> timerRunning -> timerWaiting
// timerModifying -> wait until status changes
// timerModified -> timerModifying -> timerWaiting
@ -101,8 +99,9 @@ type timer struct {
// Values for the timer status field.
const (
// Timer has no status set yet.
timerNoStatus = iota
// Timer has no status set yet or is removed from the heap.
// Must be zero value; see issue 21874.
timerRemoved = iota
// Waiting for timer to fire.
// The timer is in some P's heap.
@ -116,10 +115,6 @@ const (
// It should not be run, but it is still in some P's heap.
timerDeleted
// The timer has been stopped.
// It is not in any P's heap.
timerRemoved
// The timer is being modified.
// The timer will only have this status briefly.
timerModifying
@ -183,7 +178,7 @@ func startTimer(t *timer) {
if raceenabled {
racerelease(unsafe.Pointer(t))
}
if t.status.Load() != timerNoStatus {
if t.status.Load() != 0 {
throw("startTimer called with initialized timer")
}
resettimer(t, t.when)
@ -278,10 +273,6 @@ func deltimer(t *timer) bool {
// The timer is being run or modified, by a different P.
// Wait for it to complete.
osyield()
case timerNoStatus:
// Removing timer that was never added or
// has already been run. Also see issue 21874.
return false
default:
badTimer()
}
@ -326,7 +317,7 @@ func modtimer(t *timer, when, period int64, f func(any, uintptr), arg any, seq u
throw("timer period must be non-negative")
}
status := uint32(timerNoStatus)
status := uint32(timerRemoved)
wasRemoved := false
var pending bool
var mp *m
@ -342,7 +333,7 @@ loop:
break loop
}
releasem(mp)
case timerNoStatus, timerRemoved:
case timerRemoved:
// Prevent preemption while the timer is in timerModifying.
// This could lead to a self-deadlock. See #38070.
mp = acquirem()
@ -536,7 +527,7 @@ func moveTimers(pp *p, timers []*timer) {
case timerModifying:
// Loop until the modification is complete.
osyield()
case timerNoStatus, timerRemoved:
case timerRemoved:
// We should not see these status values in a timers heap.
badTimer()
case timerRunning:
@ -604,7 +595,7 @@ func adjusttimers(pp *p, now int64, force bool) {
badTimer()
}
}
case timerNoStatus, timerRunning, timerRemoved:
case timerRunning, timerRemoved:
badTimer()
case timerWaiting:
// OK, nothing to do.
@ -762,7 +753,7 @@ func runtimer(pp *p, now int64) int64 {
// Wait for modification to complete.
osyield()
case timerNoStatus, timerRemoved:
case timerRemoved:
// Should not see a new or inactive timer on the heap.
badTimer()
case timerRunning:
@ -808,7 +799,7 @@ func runOneTimer(pp *p, t *timer, now int64) {
} else {
// Remove from heap.
dodeltimer0(pp)
if !t.status.CompareAndSwap(timerRunning, timerNoStatus) {
if !t.status.CompareAndSwap(timerRunning, timerRemoved) {
badTimer()
}
}