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runtime: don't publish new itab table before growth is finished

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This change could improve the hit rate on itabTable during growth.

While we are here patch comments to refer to existing functions.

Change-Id: I76f81c860a3d6107e077e7e3932550858a8b7651
Reviewed-on: https://go-review.googlesource.com/55912
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Marvin Stenger 2017-08-16 03:39:13 +02:00 committed by Daniel Martí
parent 526f3420c2
commit d30f99647a
1 changed files with 16 additions and 12 deletions
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28
src/runtime/iface.go
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@ -49,7 +49,7 @@ func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
// First, look in the existing table to see if we can find the itab we need.
// This is by far the most common case, so do it without locks.
// Use atomic to ensure we see any previous writes done by the thread
// that updates the itabTable field (with atomic.Storep in addItab).
// that updates the itabTable field (with atomic.Storep in itabAdd).
t := (*itabTableType)(atomic.Loadp(unsafe.Pointer(&itabTable)))
if m = t.find(inter, typ); m != nil {
goto finish
@ -85,7 +85,7 @@ finish:
panic(&TypeAssertionError{concreteString: typ.string(), assertedString: inter.typ.string(), missingMethod: m.init()})
}
// itabFind finds the given interface/type pair in t.
// find finds the given interface/type pair in t.
// Returns nil if the given interface/type pair isn't present.
func (t *itabTableType) find(inter *interfacetype, typ *_type) *itab {
// Implemented using quadratic probing.
@ -115,31 +115,34 @@ func (t *itabTableType) find(inter *interfacetype, typ *_type) *itab {
func itabAdd(m *itab) {
t := itabTable
if t.count >= 3*(t.size/4) { // 75% load factor
// Grow hash table. Use an atomic write: see comment in getitab.
// Grow hash table.
// t2 = new(itabTableType) + some additional entries
// We lie and tell malloc we want pointer-free memory because
// all the pointed-to values are not in the heap.
t2 := (*itabTableType)(mallocgc((2+2*t.size)*sys.PtrSize, nil, true))
t2.size = t.size * 2
atomicstorep(unsafe.Pointer(&itabTable), unsafe.Pointer(t2))
// Copy over entries.
// Note: while copying, other threads may look for an itab and
// fail to find it. That's ok, they will then try to get the itab lock
// and as a consequence wait until this copying is complete.
for i := uintptr(0); i < t.size; i++ {
if m2 := *(**itab)(add(unsafe.Pointer(&t.entries), i*sys.PtrSize)); m2 != nil {
itabAdd(m2)
}
}
if itabTable.count != t.count {
iterate_itabs(t2.add)
if t2.count != t.count {
throw("mismatched count during itab table copy")
}
// Publish new hash table. Use an atomic write: see comment in getitab.
atomicstorep(unsafe.Pointer(&itabTable), unsafe.Pointer(t2))
// Adopt the new table as our own.
t = itabTable
// Note: the old table can be GC'ed here.
}
// See comment in itabFind about the probe sequence.
t.add(m)
}
// add adds the given itab to itab table t.
// itabLock must be held.
func (t *itabTableType) add(m *itab) {
// See comment in find about the probe sequence.
// Insert new itab in the first empty spot in the probe sequence.
mask := t.size - 1
h := itabHashFunc(m.inter, m._type) & mask
@ -602,7 +605,8 @@ func reflect_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
}
func iterate_itabs(fn func(*itab)) {
// Note: only runs during stop the world, so no locks/atomics needed.
// Note: only runs during stop the world or with itabLock held,
// so no other locks/atomics needed.
t := itabTable
for i := uintptr(0); i < t.size; i++ {
m := *(**itab)(add(unsafe.Pointer(&t.entries), i*sys.PtrSize))