From 7a177114df3e26f4362378e907a869c4fbbf38b7 Mon Sep 17 00:00:00 2001
From: Rhys Hiltner <rhys.hiltner@gmail.com>
Date: Fri, 14 Mar 2025 12:38:34 -0700
Subject: [PATCH] runtime: commit to spinbitmutex GOEXPERIMENT
Use the "spinbit" mutex implementation always (including on platforms
that need to emulate atomic.Xchg8), and delete the prior "tristate"
implementations.
The exception is GOARCH=wasm, where the Go runtime does not use multiple
threads.
For #68578
Change-Id: Ifc29bbfa05071d776c23a19ae185891a03a82417
Reviewed-on: https://go-review.googlesource.com/c/go/+/658456
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---
src/internal/buildcfg/exp.go | 3 -
.../goexperiment/exp_spinbitmutex_off.go | 8 -
.../goexperiment/exp_spinbitmutex_on.go | 8 -
src/internal/goexperiment/flags.go | 4 -
src/runtime/lock_futex_tristate.go | 138 ----------------
src/runtime/lock_sema_tristate.go | 148 ------------------
src/runtime/lock_spinbit.go | 2 +-
src/runtime/runtime2.go | 7 +-
8 files changed, 4 insertions(+), 314 deletions(-)
delete mode 100644 src/internal/goexperiment/exp_spinbitmutex_off.go
delete mode 100644 src/internal/goexperiment/exp_spinbitmutex_on.go
delete mode 100644 src/runtime/lock_futex_tristate.go
delete mode 100644 src/runtime/lock_sema_tristate.go
diff --git a/src/internal/buildcfg/exp.go b/src/internal/buildcfg/exp.go
index ccdf465ffbb..e36ec08a5b0 100644
--- a/src/internal/buildcfg/exp.go
+++ b/src/internal/buildcfg/exp.go
@@ -67,8 +67,6 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
regabiSupported = true
}
- haveThreads := goarch != "wasm"
-
// Older versions (anything before V16) of dsymutil don't handle
// the .debug_rnglists section in DWARF5. See
// https://github.com/golang/go/issues/26379#issuecomment-2677068742
@@ -85,7 +83,6 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
RegabiArgs: regabiSupported,
AliasTypeParams: true,
SwissMap: true,
- SpinbitMutex: haveThreads,
SyncHashTrieMap: true,
Dwarf5: dwarf5Supported,
}
diff --git a/src/internal/goexperiment/exp_spinbitmutex_off.go b/src/internal/goexperiment/exp_spinbitmutex_off.go
deleted file mode 100644
index 776b0dc77ff..00000000000
--- a/src/internal/goexperiment/exp_spinbitmutex_off.go
+++ /dev/null
@@ -1,8 +0,0 @@
-// Code generated by mkconsts.go. DO NOT EDIT.
-
-//go:build !goexperiment.spinbitmutex
-
-package goexperiment
-
-const SpinbitMutex = false
-const SpinbitMutexInt = 0
diff --git a/src/internal/goexperiment/exp_spinbitmutex_on.go b/src/internal/goexperiment/exp_spinbitmutex_on.go
deleted file mode 100644
index 8468030c769..00000000000
--- a/src/internal/goexperiment/exp_spinbitmutex_on.go
+++ /dev/null
@@ -1,8 +0,0 @@
-// Code generated by mkconsts.go. DO NOT EDIT.
-
-//go:build goexperiment.spinbitmutex
-
-package goexperiment
-
-const SpinbitMutex = true
-const SpinbitMutexInt = 1
diff --git a/src/internal/goexperiment/flags.go b/src/internal/goexperiment/flags.go
index 271fdc2b3cf..0961764bee6 100644
--- a/src/internal/goexperiment/flags.go
+++ b/src/internal/goexperiment/flags.go
@@ -115,10 +115,6 @@ type Flags struct {
// SwissMap enables the SwissTable-based map implementation.
SwissMap bool
- // SpinbitMutex enables the new "spinbit" mutex implementation on supported
- // platforms. See https://go.dev/issue/68578.
- SpinbitMutex bool
-
// SyncHashTrieMap enables the HashTrieMap sync.Map implementation.
SyncHashTrieMap bool
diff --git a/src/runtime/lock_futex_tristate.go b/src/runtime/lock_futex_tristate.go
deleted file mode 100644
index b7df18c86c0..00000000000
--- a/src/runtime/lock_futex_tristate.go
+++ /dev/null
@@ -1,138 +0,0 @@
-// 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.
-
-//go:build (dragonfly || freebsd || linux) && !goexperiment.spinbitmutex
-
-package runtime
-
-import (
- "internal/runtime/atomic"
-)
-
-// This implementation depends on OS-specific implementations of
-//
-// futexsleep(addr *uint32, val uint32, ns int64)
-// Atomically,
-// if *addr == val { sleep }
-// Might be woken up spuriously; that's allowed.
-// Don't sleep longer than ns; ns < 0 means forever.
-//
-// futexwakeup(addr *uint32, cnt uint32)
-// If any procs are sleeping on addr, wake up at most cnt.
-
-const (
- mutex_unlocked = 0
- mutex_locked = 1
- mutex_sleeping = 2
-
- active_spin = 4
- active_spin_cnt = 30
- passive_spin = 1
-)
-
-// Possible lock states are mutex_unlocked, mutex_locked and mutex_sleeping.
-// mutex_sleeping means that there is presumably at least one sleeping thread.
-// Note that there can be spinning threads during all states - they do not
-// affect mutex's state.
-
-type mWaitList struct{}
-
-func lockVerifyMSize() {}
-
-func mutexContended(l *mutex) bool {
- return atomic.Load(key32(&l.key)) > mutex_locked
-}
-
-func lock(l *mutex) {
- lockWithRank(l, getLockRank(l))
-}
-
-func lock2(l *mutex) {
- gp := getg()
-
- if gp.m.locks < 0 {
- throw("runtime·lock: lock count")
- }
- gp.m.locks++
-
- // Speculative grab for lock.
- v := atomic.Xchg(key32(&l.key), mutex_locked)
- if v == mutex_unlocked {
- return
- }
-
- // wait is either MUTEX_LOCKED or MUTEX_SLEEPING
- // depending on whether there is a thread sleeping
- // on this mutex. If we ever change l->key from
- // MUTEX_SLEEPING to some other value, we must be
- // careful to change it back to MUTEX_SLEEPING before
- // returning, to ensure that the sleeping thread gets
- // its wakeup call.
- wait := v
-
- timer := &lockTimer{lock: l}
- timer.begin()
- // On uniprocessors, no point spinning.
- // On multiprocessors, spin for ACTIVE_SPIN attempts.
- spin := 0
- if ncpu > 1 {
- spin = active_spin
- }
- for {
- // Try for lock, spinning.
- for i := 0; i < spin; i++ {
- for l.key == mutex_unlocked {
- if atomic.Cas(key32(&l.key), mutex_unlocked, wait) {
- timer.end()
- return
- }
- }
- procyield(active_spin_cnt)
- }
-
- // Try for lock, rescheduling.
- for i := 0; i < passive_spin; i++ {
- for l.key == mutex_unlocked {
- if atomic.Cas(key32(&l.key), mutex_unlocked, wait) {
- timer.end()
- return
- }
- }
- osyield()
- }
-
- // Sleep.
- v = atomic.Xchg(key32(&l.key), mutex_sleeping)
- if v == mutex_unlocked {
- timer.end()
- return
- }
- wait = mutex_sleeping
- futexsleep(key32(&l.key), mutex_sleeping, -1)
- }
-}
-
-func unlock(l *mutex) {
- unlockWithRank(l)
-}
-
-func unlock2(l *mutex) {
- v := atomic.Xchg(key32(&l.key), mutex_unlocked)
- if v == mutex_unlocked {
- throw("unlock of unlocked lock")
- }
- if v == mutex_sleeping {
- futexwakeup(key32(&l.key), 1)
- }
-
- gp := getg()
- gp.m.mLockProfile.recordUnlock(l)
- gp.m.locks--
- if gp.m.locks < 0 {
- throw("runtime·unlock: lock count")
- }
- if gp.m.locks == 0 && gp.preempt { // restore the preemption request in case we've cleared it in newstack
- gp.stackguard0 = stackPreempt
- }
-}
diff --git a/src/runtime/lock_sema_tristate.go b/src/runtime/lock_sema_tristate.go
deleted file mode 100644
index 4375791d46f..00000000000
--- a/src/runtime/lock_sema_tristate.go
+++ /dev/null
@@ -1,148 +0,0 @@
-// 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.
-
-//go:build (aix || darwin || netbsd || openbsd || plan9 || solaris || windows) && !goexperiment.spinbitmutex
-
-package runtime
-
-import (
- "internal/runtime/atomic"
- "unsafe"
-)
-
-// This implementation depends on OS-specific implementations of
-//
-// func semacreate(mp *m)
-// Create a semaphore for mp, if it does not already have one.
-//
-// func semasleep(ns int64) int32
-// If ns < 0, acquire m's semaphore and return 0.
-// If ns >= 0, try to acquire m's semaphore for at most ns nanoseconds.
-// Return 0 if the semaphore was acquired, -1 if interrupted or timed out.
-//
-// func semawakeup(mp *m)
-// Wake up mp, which is or will soon be sleeping on its semaphore.
-const (
- active_spin = 4
- active_spin_cnt = 30
- passive_spin = 1
-)
-
-// mWaitList is part of the M struct, and holds the list of Ms that are waiting
-// for a particular runtime.mutex.
-//
-// When an M is unable to immediately obtain a lock, it adds itself to the list
-// of Ms waiting for the lock. It does that via this struct's next field,
-// forming a singly-linked list with the mutex's key field pointing to the head
-// of the list.
-type mWaitList struct {
- next muintptr // next m waiting for lock
-}
-
-func lockVerifyMSize() {}
-
-func mutexContended(l *mutex) bool {
- return atomic.Loaduintptr(&l.key) > locked
-}
-
-func lock(l *mutex) {
- lockWithRank(l, getLockRank(l))
-}
-
-func lock2(l *mutex) {
- gp := getg()
- if gp.m.locks < 0 {
- throw("runtime·lock: lock count")
- }
- gp.m.locks++
-
- // Speculative grab for lock.
- if atomic.Casuintptr(&l.key, 0, locked) {
- return
- }
- semacreate(gp.m)
-
- timer := &lockTimer{lock: l}
- timer.begin()
- // On uniprocessor's, no point spinning.
- // On multiprocessors, spin for ACTIVE_SPIN attempts.
- spin := 0
- if ncpu > 1 {
- spin = active_spin
- }
-Loop:
- for i := 0; ; i++ {
- v := atomic.Loaduintptr(&l.key)
- if v&locked == 0 {
- // Unlocked. Try to lock.
- if atomic.Casuintptr(&l.key, v, v|locked) {
- timer.end()
- return
- }
- i = 0
- }
- if i < spin {
- procyield(active_spin_cnt)
- } else if i < spin+passive_spin {
- osyield()
- } else {
- // Someone else has it.
- // l.key points to a linked list of M's waiting
- // for this lock, chained through m.mWaitList.next.
- // Queue this M.
- for {
- gp.m.mWaitList.next = muintptr(v &^ locked)
- if atomic.Casuintptr(&l.key, v, uintptr(unsafe.Pointer(gp.m))|locked) {
- break
- }
- v = atomic.Loaduintptr(&l.key)
- if v&locked == 0 {
- continue Loop
- }
- }
- if v&locked != 0 {
- // Queued. Wait.
- semasleep(-1)
- i = 0
- }
- }
- }
-}
-
-func unlock(l *mutex) {
- unlockWithRank(l)
-}
-
-// We might not be holding a p in this code.
-//
-//go:nowritebarrier
-func unlock2(l *mutex) {
- gp := getg()
- var mp *m
- for {
- v := atomic.Loaduintptr(&l.key)
- if v == locked {
- if atomic.Casuintptr(&l.key, locked, 0) {
- break
- }
- } else {
- // Other M's are waiting for the lock.
- // Dequeue an M.
- mp = muintptr(v &^ locked).ptr()
- if atomic.Casuintptr(&l.key, v, uintptr(mp.mWaitList.next)) {
- // Dequeued an M. Wake it.
- semawakeup(mp) // no use of mp after this point; it's awake
- break
- }
- }
- }
- gp.m.mLockProfile.recordUnlock(l)
- gp.m.locks--
- if gp.m.locks < 0 {
- throw("runtime·unlock: lock count")
- }
- if gp.m.locks == 0 && gp.preempt { // restore the preemption request in case we've cleared it in newstack
- gp.stackguard0 = stackPreempt
- }
-}
diff --git a/src/runtime/lock_spinbit.go b/src/runtime/lock_spinbit.go
index 7b7bc651ad9..9bca4bd8243 100644
--- a/src/runtime/lock_spinbit.go
+++ b/src/runtime/lock_spinbit.go
@@ -2,7 +2,7 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-//go:build (aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || plan9 || solaris || windows) && goexperiment.spinbitmutex
+//go:build !wasm
package runtime
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 27d14b890bd..f7371c450bd 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -8,7 +8,6 @@ import (
"internal/abi"
"internal/chacha8rand"
"internal/goarch"
- "internal/goexperiment"
"internal/runtime/atomic"
"internal/runtime/sys"
"unsafe"
@@ -628,9 +627,9 @@ type mPadded struct {
// Size the runtime.m structure so it fits in the 2048-byte size class, and
// not in the next-smallest (1792-byte) size class. That leaves the 11 low
- // bits of muintptr values available for flags, as required for
- // GOEXPERIMENT=spinbitmutex.
- _ [goexperiment.SpinbitMutexInt * (2048 - mallocHeaderSize - mRedZoneSize - unsafe.Sizeof(m{}))]byte
+ // bits of muintptr values available for flags, as required by
+ // lock_spinbit.go.
+ _ [(1 - goarch.IsWasm) * (2048 - mallocHeaderSize - mRedZoneSize - unsafe.Sizeof(m{}))]byte
}
type p struct {
--
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