func lock(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)
// 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) {
return
}
i = 0
}
if i < spin {
procyield(active_spin_cnt)
} else if i < spin+passive_spin {
osyield()
} else {
// Someone else has it.
// l->waitm points to a linked list of M's waiting
// for this lock, chained through m->nextwaitm.
// Queue this M.
for {
gp.m.nextwaitm = 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
}
}
}
}
// block returns the spans in the i'th block of buffer b. block is
// safe to call concurrently with push.
func (b *gcSweepBuf) block(i int) []*mspan {
// Perform bounds check before loading spine address since
// push ensures the allocated length is at least spineLen.
if i < 0 || uintptr(i) >= atomic.Loaduintptr(&b.spineLen) {
throw("block index out of range")
}
// Get block i.
spine := atomic.Loadp(unsafe.Pointer(&b.spine))
blockp := add(spine, sys.PtrSize*uintptr(i))
block := (*gcSweepBlock)(atomic.Loadp(blockp))
// Slice the block if necessary.
cursor := uintptr(atomic.Load(&b.index))
top, bottom := cursor/gcSweepBlockEntries, cursor%gcSweepBlockEntries
var spans []*mspan
if uintptr(i) < top {
spans = block.spans[:]
} else {
spans = block.spans[:bottom]
}
// push may have reserved a slot but not filled it yet, so
// trim away unused entries.
for len(spans) > 0 && spans[len(spans)-1] == nil {
spans = spans[:len(spans)-1]
}
return spans
}
//go:nowritebarrier
// We might not be holding a p in this code.
func unlock(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 = (*m)(unsafe.Pointer(v &^ locked))
if atomic.Casuintptr(&l.key, v, mp.nextwaitm) {
// Dequeued an M. Wake it.
semawakeup(mp)
break
}
}
}
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
}
}
// lockextra locks the extra list and returns the list head.
// The caller must unlock the list by storing a new list head
// to extram. If nilokay is true, then lockextra will
// return a nil list head if that's what it finds. If nilokay is false,
// lockextra will keep waiting until the list head is no longer nil.
//go:nosplit
func lockextra(nilokay bool) *m {
const locked = 1
incr := false
for {
old := atomic.Loaduintptr(&extram)
if old == locked {
yield := osyield
yield()
continue
}
if old == 0 && !nilokay {
if !incr {
// Add 1 to the number of threads
// waiting for an M.
// This is cleared by newextram.
atomic.Xadd(&extraMWaiters, 1)
incr = true
}
usleep(1)
continue
}
if atomic.Casuintptr(&extram, old, locked) {
return (*m)(unsafe.Pointer(old))
}
yield := osyield
yield()
continue
}
}
// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
// some miscellany) and initializes scanning-related state.
//
// The caller must have call gcCopySpans().
//
// The world must be stopped.
//
//go:nowritebarrier
func gcMarkRootPrepare() {
// Compute how many data and BSS root blocks there are.
nBlocks := func(bytes uintptr) int {
return int((bytes + rootBlockBytes - 1) / rootBlockBytes)
}
work.nDataRoots = 0
work.nBSSRoots = 0
// Only scan globals once per cycle; preferably concurrently.
if !work.markrootDone {
for datap := &firstmoduledata; datap != nil; datap = datap.next {
nDataRoots := nBlocks(datap.edata - datap.data)
if nDataRoots > work.nDataRoots {
work.nDataRoots = nDataRoots
}
}
for datap := &firstmoduledata; datap != nil; datap = datap.next {
nBSSRoots := nBlocks(datap.ebss - datap.bss)
if nBSSRoots > work.nBSSRoots {
work.nBSSRoots = nBSSRoots
}
}
}
if !work.markrootDone {
// On the first markroot, we need to scan span roots.
// In concurrent GC, this happens during concurrent
// mark and we depend on addfinalizer to ensure the
// above invariants for objects that get finalizers
// after concurrent mark. In STW GC, this will happen
// during mark termination.
work.nSpanRoots = (len(work.spans) + rootBlockSpans - 1) / rootBlockSpans
// On the first markroot, we need to scan all Gs. Gs
// may be created after this point, but it's okay that
// we ignore them because they begin life without any
// roots, so there's nothing to scan, and any roots
// they create during the concurrent phase will be
// scanned during mark termination. During mark
// termination, allglen isn't changing, so we'll scan
// all Gs.
work.nStackRoots = int(atomic.Loaduintptr(&allglen))
work.nRescanRoots = 0
} else {
// We've already scanned span roots and kept the scan
// up-to-date during concurrent mark.
work.nSpanRoots = 0
// On the second pass of markroot, we're just scanning
// dirty stacks. It's safe to access rescan since the
// world is stopped.
work.nStackRoots = 0
work.nRescanRoots = len(work.rescan.list)
}
work.markrootNext = 0
work.markrootJobs = uint32(fixedRootCount + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots + work.nRescanRoots)
}
func notewakeup(n *note) {
var v uintptr
for {
v = atomic.Loaduintptr(&n.key)
if atomic.Casuintptr(&n.key, v, locked) {
break
}
}
// Successfully set waitm to locked.
// What was it before?
switch {
case v == 0:
// Nothing was waiting. Done.
case v == locked:
// Two notewakeups! Not allowed.
throw("notewakeup - double wakeup")
default:
// Must be the waiting m. Wake it up.
semawakeup((*m)(unsafe.Pointer(v)))
}
}
func profileloop1(param uintptr) uint32 {
stdcall2(_SetThreadPriority, currentThread, _THREAD_PRIORITY_HIGHEST)
for {
stdcall2(_WaitForSingleObject, profiletimer, _INFINITE)
first := (*m)(atomic.Loadp(unsafe.Pointer(&allm)))
for mp := first; mp != nil; mp = mp.alllink {
thread := atomic.Loaduintptr(&mp.thread)
// Do not profile threads blocked on Notes,
// this includes idle worker threads,
// idle timer thread, idle heap scavenger, etc.
if thread == 0 || mp.profilehz == 0 || mp.blocked {
continue
}
stdcall1(_SuspendThread, thread)
if mp.profilehz != 0 && !mp.blocked {
profilem(mp)
}
stdcall1(_ResumeThread, thread)
}
}
}
// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
// some miscellany) and initializes scanning-related state.
//
// The caller must have call gcCopySpans().
//
//go:nowritebarrier
func gcMarkRootPrepare() {
// Compute how many data and BSS root blocks there are.
nBlocks := func(bytes uintptr) int {
return int((bytes + rootBlockBytes - 1) / rootBlockBytes)
}
work.nDataRoots = 0
for datap := &firstmoduledata; datap != nil; datap = datap.next {
nDataRoots := nBlocks(datap.edata - datap.data)
if nDataRoots > work.nDataRoots {
work.nDataRoots = nDataRoots
}
}
work.nBSSRoots = 0
for datap := &firstmoduledata; datap != nil; datap = datap.next {
nBSSRoots := nBlocks(datap.ebss - datap.bss)
if nBSSRoots > work.nBSSRoots {
work.nBSSRoots = nBSSRoots
}
}
// Compute number of span roots.
work.nSpanRoots = (len(work.spans) + rootBlockSpans - 1) / rootBlockSpans
// Snapshot of allglen. During concurrent scan, we just need
// to be consistent about how many markroot jobs we create and
// how many Gs we check. Gs may be created after this point,
// but it's okay that we ignore them because they begin life
// without any roots, so there's nothing to scan, and any
// roots they create during the concurrent phase will be
// scanned during mark termination. During mark termination,
// allglen isn't changing, so we'll scan all Gs.
work.nStackRoots = int(atomic.Loaduintptr(&allglen))
work.markrootNext = 0
work.markrootJobs = uint32(fixedRootCount + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots)
}
// gcMarkRootPrepare queues root scanning jobs (stacks, globals, and
// some miscellany) and initializes scanning-related state.
//
// The caller must have call gcCopySpans().
//
// The world must be stopped.
//
//go:nowritebarrier
func gcMarkRootPrepare() {
if gcphase == _GCmarktermination {
work.nFlushCacheRoots = int(gomaxprocs)
} else {
work.nFlushCacheRoots = 0
}
// Compute how many data and BSS root blocks there are.
nBlocks := func(bytes uintptr) int {
return int((bytes + rootBlockBytes - 1) / rootBlockBytes)
}
work.nDataRoots = 0
work.nBSSRoots = 0
// Only scan globals once per cycle; preferably concurrently.
if !work.markrootDone {
for _, datap := range activeModules() {
nDataRoots := nBlocks(datap.edata - datap.data)
if nDataRoots > work.nDataRoots {
work.nDataRoots = nDataRoots
}
}
for _, datap := range activeModules() {
nBSSRoots := nBlocks(datap.ebss - datap.bss)
if nBSSRoots > work.nBSSRoots {
work.nBSSRoots = nBSSRoots
}
}
}
if !work.markrootDone {
// On the first markroot, we need to scan span roots.
// In concurrent GC, this happens during concurrent
// mark and we depend on addfinalizer to ensure the
// above invariants for objects that get finalizers
// after concurrent mark. In STW GC, this will happen
// during mark termination.
//
// We're only interested in scanning the in-use spans,
// which will all be swept at this point. More spans
// may be added to this list during concurrent GC, but
// we only care about spans that were allocated before
// this mark phase.
work.nSpanRoots = mheap_.sweepSpans[mheap_.sweepgen/2%2].numBlocks()
// On the first markroot, we need to scan all Gs. Gs
// may be created after this point, but it's okay that
// we ignore them because they begin life without any
// roots, so there's nothing to scan, and any roots
// they create during the concurrent phase will be
// scanned during mark termination. During mark
// termination, allglen isn't changing, so we'll scan
// all Gs.
work.nStackRoots = int(atomic.Loaduintptr(&allglen))
work.nRescanRoots = 0
} else {
// We've already scanned span roots and kept the scan
// up-to-date during concurrent mark.
work.nSpanRoots = 0
// On the second pass of markroot, we're just scanning
// dirty stacks. It's safe to access rescan since the
// world is stopped.
work.nStackRoots = 0
work.nRescanRoots = len(work.rescan.list)
}
work.markrootNext = 0
work.markrootJobs = uint32(fixedRootCount + work.nFlushCacheRoots + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots + work.nRescanRoots)
}
// push adds span s to buffer b. push is safe to call concurrently
// with other push operations, but NOT to call concurrently with pop.
func (b *gcSweepBuf) push(s *mspan) {
// Obtain our slot.
cursor := uintptr(atomic.Xadd(&b.index, +1) - 1)
top, bottom := cursor/gcSweepBlockEntries, cursor%gcSweepBlockEntries
// Do we need to add a block?
spineLen := atomic.Loaduintptr(&b.spineLen)
var block *gcSweepBlock
retry:
if top < spineLen {
spine := atomic.Loadp(unsafe.Pointer(&b.spine))
blockp := add(spine, sys.PtrSize*top)
block = (*gcSweepBlock)(atomic.Loadp(blockp))
} else {
// Add a new block to the spine, potentially growing
// the spine.
lock(&b.spineLock)
// spineLen cannot change until we release the lock,
// but may have changed while we were waiting.
spineLen = atomic.Loaduintptr(&b.spineLen)
if top < spineLen {
unlock(&b.spineLock)
goto retry
}
if spineLen == b.spineCap {
// Grow the spine.
newCap := b.spineCap * 2
if newCap == 0 {
newCap = gcSweepBufInitSpineCap
}
newSpine := persistentalloc(newCap*sys.PtrSize, sys.CacheLineSize, &memstats.gc_sys)
if b.spineCap != 0 {
// Blocks are allocated off-heap, so
// no write barriers.
memmove(newSpine, b.spine, b.spineCap*sys.PtrSize)
}
// Spine is allocated off-heap, so no write barrier.
atomic.StorepNoWB(unsafe.Pointer(&b.spine), newSpine)
b.spineCap = newCap
// We can't immediately free the old spine
// since a concurrent push with a lower index
// could still be reading from it. We let it
// leak because even a 1TB heap would waste
// less than 2MB of memory on old spines. If
// this is a problem, we could free old spines
// during STW.
}
// Allocate a new block and add it to the spine.
block = (*gcSweepBlock)(persistentalloc(unsafe.Sizeof(gcSweepBlock{}), sys.CacheLineSize, &memstats.gc_sys))
blockp := add(b.spine, sys.PtrSize*top)
// Blocks are allocated off-heap, so no write barrier.
atomic.StorepNoWB(blockp, unsafe.Pointer(block))
atomic.Storeuintptr(&b.spineLen, spineLen+1)
unlock(&b.spineLock)
}
// We have a block. Insert the span.
block.spans[bottom] = s
}
// Called from runtime·morestack when more stack is needed.
// Allocate larger stack and relocate to new stack.
// Stack growth is multiplicative, for constant amortized cost.
//
// g->atomicstatus will be Grunning or Gscanrunning upon entry.
// If the GC is trying to stop this g then it will set preemptscan to true.
func newstack() {
thisg := getg()
// TODO: double check all gp. shouldn't be getg().
if thisg.m.morebuf.g.ptr().stackguard0 == stackFork {
throw("stack growth after fork")
}
if thisg.m.morebuf.g.ptr() != thisg.m.curg {
print("runtime: newstack called from g=", hex(thisg.m.morebuf.g), "\n"+"\tm=", thisg.m, " m->curg=", thisg.m.curg, " m->g0=", thisg.m.g0, " m->gsignal=", thisg.m.gsignal, "\n")
morebuf := thisg.m.morebuf
traceback(morebuf.pc, morebuf.sp, morebuf.lr, morebuf.g.ptr())
throw("runtime: wrong goroutine in newstack")
}
if thisg.m.curg.throwsplit {
gp := thisg.m.curg
// Update syscallsp, syscallpc in case traceback uses them.
morebuf := thisg.m.morebuf
gp.syscallsp = morebuf.sp
gp.syscallpc = morebuf.pc
print("runtime: newstack sp=", hex(gp.sched.sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
traceback(morebuf.pc, morebuf.sp, morebuf.lr, gp)
throw("runtime: stack split at bad time")
}
gp := thisg.m.curg
morebuf := thisg.m.morebuf
thisg.m.morebuf.pc = 0
thisg.m.morebuf.lr = 0
thisg.m.morebuf.sp = 0
thisg.m.morebuf.g = 0
rewindmorestack(&gp.sched)
// NOTE: stackguard0 may change underfoot, if another thread
// is about to try to preempt gp. Read it just once and use that same
// value now and below.
preempt := atomic.Loaduintptr(&gp.stackguard0) == stackPreempt
// Be conservative about where we preempt.
// We are interested in preempting user Go code, not runtime code.
// If we're holding locks, mallocing, or preemption is disabled, don't
// preempt.
// This check is very early in newstack so that even the status change
// from Grunning to Gwaiting and back doesn't happen in this case.
// That status change by itself can be viewed as a small preemption,
// because the GC might change Gwaiting to Gscanwaiting, and then
// this goroutine has to wait for the GC to finish before continuing.
// If the GC is in some way dependent on this goroutine (for example,
// it needs a lock held by the goroutine), that small preemption turns
// into a real deadlock.
if preempt {
if thisg.m.locks != 0 || thisg.m.mallocing != 0 || thisg.m.preemptoff != "" || thisg.m.p.ptr().status != _Prunning {
// Let the goroutine keep running for now.
// gp->preempt is set, so it will be preempted next time.
gp.stackguard0 = gp.stack.lo + _StackGuard
gogo(&gp.sched) // never return
}
}
if gp.stack.lo == 0 {
throw("missing stack in newstack")
}
sp := gp.sched.sp
if sys.ArchFamily == sys.AMD64 || sys.ArchFamily == sys.I386 {
// The call to morestack cost a word.
sp -= sys.PtrSize
}
if stackDebug >= 1 || sp < gp.stack.lo {
print("runtime: newstack sp=", hex(sp), " stack=[", hex(gp.stack.lo), ", ", hex(gp.stack.hi), "]\n",
"\tmorebuf={pc:", hex(morebuf.pc), " sp:", hex(morebuf.sp), " lr:", hex(morebuf.lr), "}\n",
"\tsched={pc:", hex(gp.sched.pc), " sp:", hex(gp.sched.sp), " lr:", hex(gp.sched.lr), " ctxt:", gp.sched.ctxt, "}\n")
}
if sp < gp.stack.lo {
print("runtime: gp=", gp, ", gp->status=", hex(readgstatus(gp)), "\n ")
print("runtime: split stack overflow: ", hex(sp), " < ", hex(gp.stack.lo), "\n")
throw("runtime: split stack overflow")
}
if gp.sched.ctxt != nil {
// morestack wrote sched.ctxt on its way in here,
// without a write barrier. Run the write barrier now.
// It is not possible to be preempted between then
// and now, so it's okay.
writebarrierptr_nostore((*uintptr)(unsafe.Pointer(&gp.sched.ctxt)), uintptr(gp.sched.ctxt))
}
if preempt {
if gp == thisg.m.g0 {
throw("runtime: preempt g0")
}
if thisg.m.p == 0 && thisg.m.locks == 0 {
throw("runtime: g is running but p is not")
}
// Synchronize with scang.
casgstatus(gp, _Grunning, _Gwaiting)
if gp.preemptscan {
for !castogscanstatus(gp, _Gwaiting, _Gscanwaiting) {
// Likely to be racing with the GC as
// it sees a _Gwaiting and does the
// stack scan. If so, gcworkdone will
// be set and gcphasework will simply
// return.
}
if !gp.gcscandone {
// gcw is safe because we're on the
// system stack.
gcw := &gp.m.p.ptr().gcw
scanstack(gp, gcw)
if gcBlackenPromptly {
gcw.dispose()
}
gp.gcscandone = true
}
gp.preemptscan = false
gp.preempt = false
casfrom_Gscanstatus(gp, _Gscanwaiting, _Gwaiting)
// This clears gcscanvalid.
casgstatus(gp, _Gwaiting, _Grunning)
gp.stackguard0 = gp.stack.lo + _StackGuard
gogo(&gp.sched) // never return
}
// Act like goroutine called runtime.Gosched.
casgstatus(gp, _Gwaiting, _Grunning)
gopreempt_m(gp) // never return
}
// Allocate a bigger segment and move the stack.
oldsize := int(gp.stackAlloc)
newsize := oldsize * 2
if uintptr(newsize) > maxstacksize {
print("runtime: goroutine stack exceeds ", maxstacksize, "-byte limit\n")
throw("stack overflow")
}
// The goroutine must be executing in order to call newstack,
// so it must be Grunning (or Gscanrunning).
casgstatus(gp, _Grunning, _Gcopystack)
// The concurrent GC will not scan the stack while we are doing the copy since
// the gp is in a Gcopystack status.
copystack(gp, uintptr(newsize), true)
if stackDebug >= 1 {
print("stack grow done\n")
}
casgstatus(gp, _Gcopystack, _Grunning)
gogo(&gp.sched)
}
//go:nosplit
func notetsleep_internal(n *note, ns int64, gp *g, deadline int64) bool {
// gp and deadline are logically local variables, but they are written
// as parameters so that the stack space they require is charged
// to the caller.
// This reduces the nosplit footprint of notetsleep_internal.
gp = getg()
// Register for wakeup on n->waitm.
if !atomic.Casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
// Must be locked (got wakeup).
if n.key != locked {
throw("notetsleep - waitm out of sync")
}
return true
}
if ns < 0 {
// Queued. Sleep.
gp.m.blocked = true
semasleep(-1)
gp.m.blocked = false
return true
}
deadline = nanotime() + ns
for {
// Registered. Sleep.
gp.m.blocked = true
if semasleep(ns) >= 0 {
gp.m.blocked = false
// Acquired semaphore, semawakeup unregistered us.
// Done.
return true
}
gp.m.blocked = false
// Interrupted or timed out. Still registered. Semaphore not acquired.
ns = deadline - nanotime()
if ns <= 0 {
break
}
// Deadline hasn't arrived. Keep sleeping.
}
// Deadline arrived. Still registered. Semaphore not acquired.
// Want to give up and return, but have to unregister first,
// so that any notewakeup racing with the return does not
// try to grant us the semaphore when we don't expect it.
for {
v := atomic.Loaduintptr(&n.key)
switch v {
case uintptr(unsafe.Pointer(gp.m)):
// No wakeup yet; unregister if possible.
if atomic.Casuintptr(&n.key, v, 0) {
return false
}
case locked:
// Wakeup happened so semaphore is available.
// Grab it to avoid getting out of sync.
gp.m.blocked = true
if semasleep(-1) < 0 {
throw("runtime: unable to acquire - semaphore out of sync")
}
gp.m.blocked = false
return true
default:
throw("runtime: unexpected waitm - semaphore out of sync")
}
}
}