src/runtime/iface.go - go - Git at Google

 // Copyright 2014 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.

 package runtime

 import (
 	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
 )

 const (
 	hashSize = 1009
 )

 var (
 	ifaceLock mutex // lock for accessing hash
 	hash      [hashSize]*itab
 )

 func itabhash(inter *interfacetype, typ *_type) uint32 {
 	// compiler has provided some good hash codes for us.
 	h := inter.typ.hash
 	h += 17 * typ.hash
 	// TODO(rsc): h += 23 * x.mhash ?
 	return h % hashSize
 }

 func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
 	if len(inter.mhdr) == 0 {
 		throw("internal error - misuse of itab")
 	}

 	// easy case
 	if typ.tflag&tflagUncommon == 0 {
 		if canfail {
 			return nil
 		}
 		name := inter.typ.nameOff(inter.mhdr[0].name)
 		panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), name.name()})
 	}

 	h := itabhash(inter, typ)

 	// look twice - once without lock, once with.
 	// common case will be no lock contention.
 	var m *itab
 	var locked int
 	for locked = 0; locked < 2; locked++ {
 		if locked != 0 {
 			lock(&ifaceLock)
 		}
 		for m = (*itab)(atomic.Loadp(unsafe.Pointer(&hash[h]))); m != nil; m = m.link {
 			if m.inter == inter && m._type == typ {
 				if m.bad != 0 {
 					if !canfail {
 						// this can only happen if the conversion
 						// was already done once using the , ok form
 						// and we have a cached negative result.
 						// the cached result doesn't record which
 						// interface function was missing, so try
 						// adding the itab again, which will throw an error.
 						additab(m, locked != 0, false)
 					}
 					m = nil
 				}
 				if locked != 0 {
 					unlock(&ifaceLock)
 				}
 				return m
 			}
 		}
 	}

 	m = (*itab)(persistentalloc(unsafe.Sizeof(itab{})+uintptr(len(inter.mhdr)-1)*sys.PtrSize, 0, &memstats.other_sys))
 	m.inter = inter
 	m._type = typ
 	additab(m, true, canfail)
 	unlock(&ifaceLock)
 	if m.bad != 0 {
 		return nil
 	}
 	return m
 }

 func additab(m *itab, locked, canfail bool) {
 	inter := m.inter
 	typ := m._type
 	x := typ.uncommon()

 	// both inter and typ have method sorted by name,
 	// and interface names are unique,
 	// so can iterate over both in lock step;
 	// the loop is O(ni+nt) not O(ni*nt).
 	ni := len(inter.mhdr)
 	nt := int(x.mcount)
 	xmhdr := (*[1 << 16]method)(add(unsafe.Pointer(x), uintptr(x.moff)))[:nt:nt]
 	j := 0
 	for k := 0; k < ni; k++ {
 		i := &inter.mhdr[k]
 		itype := inter.typ.typeOff(i.ityp)
 		name := inter.typ.nameOff(i.name)
 		iname := name.name()
 		ipkg := name.pkgPath()
 		if ipkg == "" {
 			ipkg = inter.pkgpath.name()
 		}
 		for ; j < nt; j++ {
 			t := &xmhdr[j]
 			tname := typ.nameOff(t.name)
 			if typ.typeOff(t.mtyp) == itype && tname.name() == iname {
 				pkgPath := tname.pkgPath()
 				if pkgPath == "" {
 					pkgPath = typ.nameOff(x.pkgpath).name()
 				}
 				if tname.isExported() || pkgPath == ipkg {
 					if m != nil {
 						ifn := typ.textOff(t.ifn)
 						*(*unsafe.Pointer)(add(unsafe.Pointer(&m.fun[0]), uintptr(k)*sys.PtrSize)) = ifn
 					}
 					goto nextimethod
 				}
 			}
 		}
 		// didn't find method
 		if !canfail {
 			if locked {
 				unlock(&ifaceLock)
 			}
 			panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), iname})
 		}
 		m.bad = 1
 		break
 	nextimethod:
 	}
 	if !locked {
 		throw("invalid itab locking")
 	}
 	h := itabhash(inter, typ)
 	m.link = hash[h]
 	m.inhash = 1
 	atomicstorep(unsafe.Pointer(&hash[h]), unsafe.Pointer(m))
 }

 func itabsinit() {
 	lock(&ifaceLock)
 	for _, md := range activeModules() {
 		for _, i := range md.itablinks {
 			// itablinks is a slice of pointers to the itabs used in this
 			// module. A given itab may be used in more than one module
 			// and thanks to the way global symbol resolution works, the
 			// pointed-to itab may already have been inserted into the
 			// global 'hash'.
 			if i.inhash == 0 {
 				additab(i, true, false)
 			}
 		}
 	}
 	unlock(&ifaceLock)
 }

 // panicdottype is called when doing an i.(T) conversion and the conversion fails.
 // have = the dynamic type we have.
 // want = the static type we're trying to convert to.
 // iface = the static type we're converting from.
 func panicdottype(have, want, iface *_type) {
 	haveString := ""
 	if have != nil {
 		haveString = have.string()
 	}
 	panic(&TypeAssertionError{iface.string(), haveString, want.string(), ""})
 }

 // panicnildottype is called when doing a i.(T) conversion and the interface i is nil.
 // want = the static type we're trying to convert to.
 func panicnildottype(want *_type) {
 	panic(&TypeAssertionError{"", "", want.string(), ""})
 	// TODO: Add the static type we're converting from as well.
 	// It might generate a better error message.
 	// Just to match other nil conversion errors, we don't for now.
 }

 // The conv and assert functions below do very similar things.
 // The convXXX functions are guaranteed by the compiler to succeed.
 // The assertXXX functions may fail (either panicking or returning false,
 // depending on whether they are 1-result or 2-result).
 // The convXXX functions succeed on a nil input, whereas the assertXXX
 // functions fail on a nil input.

 func convT2E(t *_type, elem unsafe.Pointer) (e eface) {
 	if raceenabled {
 		raceReadObjectPC(t, elem, getcallerpc(unsafe.Pointer(&t)), funcPC(convT2E))
 	}
 	if msanenabled {
 		msanread(elem, t.size)
 	}
 	if isDirectIface(t) {
 		// This case is implemented directly by the compiler.
 		throw("direct convT2E")
 	}
 	x := newobject(t)
 	// TODO: We allocate a zeroed object only to overwrite it with
 	// actual data. Figure out how to avoid zeroing. Also below in convT2I.
 	typedmemmove(t, x, elem)
 	e._type = t
 	e.data = x
 	return
 }

 func convT2I(tab *itab, elem unsafe.Pointer) (i iface) {
 	t := tab._type
 	if raceenabled {
 		raceReadObjectPC(t, elem, getcallerpc(unsafe.Pointer(&tab)), funcPC(convT2I))
 	}
 	if msanenabled {
 		msanread(elem, t.size)
 	}
 	if isDirectIface(t) {
 		// This case is implemented directly by the compiler.
 		throw("direct convT2I")
 	}
 	x := newobject(t)
 	typedmemmove(t, x, elem)
 	i.tab = tab
 	i.data = x
 	return
 }

 func convI2I(inter *interfacetype, i iface) (r iface) {
 	tab := i.tab
 	if tab == nil {
 		return
 	}
 	if tab.inter == inter {
 		r.tab = tab
 		r.data = i.data
 		return
 	}
 	r.tab = getitab(inter, tab._type, false)
 	r.data = i.data
 	return
 }

 func assertI2I(inter *interfacetype, i iface) (r iface) {
 	tab := i.tab
 	if tab == nil {
 		// explicit conversions require non-nil interface value.
 		panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
 	}
 	if tab.inter == inter {
 		r.tab = tab
 		r.data = i.data
 		return
 	}
 	r.tab = getitab(inter, tab._type, false)
 	r.data = i.data
 	return
 }

 func assertI2I2(inter *interfacetype, i iface) (r iface, b bool) {
 	tab := i.tab
 	if tab == nil {
 		return
 	}
 	if tab.inter != inter {
 		tab = getitab(inter, tab._type, true)
 		if tab == nil {
 			return
 		}
 	}
 	r.tab = tab
 	r.data = i.data
 	b = true
 	return
 }

 func assertE2I(inter *interfacetype, e eface) (r iface) {
 	t := e._type
 	if t == nil {
 		// explicit conversions require non-nil interface value.
 		panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
 	}
 	r.tab = getitab(inter, t, false)
 	r.data = e.data
 	return
 }

 func assertE2I2(inter *interfacetype, e eface) (r iface, b bool) {
 	t := e._type
 	if t == nil {
 		return
 	}
 	tab := getitab(inter, t, true)
 	if tab == nil {
 		return
 	}
 	r.tab = tab
 	r.data = e.data
 	b = true
 	return
 }

 //go:linkname reflect_ifaceE2I reflect.ifaceE2I
 func reflect_ifaceE2I(inter *interfacetype, e eface, dst *iface) {
 	*dst = assertE2I(inter, e)
 }

 func iterate_itabs(fn func(*itab)) {
 	for _, h := range &hash {
 		for ; h != nil; h = h.link {
 			fn(h)
 		}
 	}
 }
	// Copyright 2014 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.

	package runtime

	import (
	"runtime/internal/atomic"
	"runtime/internal/sys"
	"unsafe"
	)

	const (
	hashSize = 1009
	)

	var (
	ifaceLock mutex // lock for accessing hash
	hash [hashSize]*itab
	)

	func itabhash(inter interfacetype, typ _type) uint32 {
	// compiler has provided some good hash codes for us.
	h := inter.typ.hash
	h += 17 * typ.hash
	// TODO(rsc): h += 23 * x.mhash ?
	return h % hashSize
	}

	func getitab(inter interfacetype, typ _type, canfail bool) *itab {
	if len(inter.mhdr) == 0 {
	throw("internal error - misuse of itab")
	}

	// easy case
	if typ.tflag&tflagUncommon == 0 {
	if canfail {
	return nil
	}
	name := inter.typ.nameOff(inter.mhdr[0].name)
	panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), name.name()})
	}

	h := itabhash(inter, typ)

	// look twice - once without lock, once with.
	// common case will be no lock contention.
	var m *itab
	var locked int
	for locked = 0; locked < 2; locked++ {
	if locked != 0 {
	lock(&ifaceLock)
	}
	for m = (*itab)(atomic.Loadp(unsafe.Pointer(&hash[h]))); m != nil; m = m.link {
	if m.inter == inter && m._type == typ {
	if m.bad != 0 {
	if !canfail {
	// this can only happen if the conversion
	// was already done once using the , ok form
	// and we have a cached negative result.
	// the cached result doesn't record which
	// interface function was missing, so try
	// adding the itab again, which will throw an error.
	additab(m, locked != 0, false)
	}
	m = nil
	}
	if locked != 0 {
	unlock(&ifaceLock)
	}
	return m
	}
	}
	}

	m = (itab)(persistentalloc(unsafe.Sizeof(itab{})+uintptr(len(inter.mhdr)-1)sys.PtrSize, 0, &memstats.other_sys))
	m.inter = inter
	m._type = typ
	additab(m, true, canfail)
	unlock(&ifaceLock)
	if m.bad != 0 {
	return nil
	}
	return m
	}

	func additab(m *itab, locked, canfail bool) {
	inter := m.inter
	typ := m._type
	x := typ.uncommon()

	// both inter and typ have method sorted by name,
	// and interface names are unique,
	// so can iterate over both in lock step;
	// the loop is O(ni+nt) not O(ni*nt).
	ni := len(inter.mhdr)
	nt := int(x.mcount)
	xmhdr := (*[1 << 16]method)(add(unsafe.Pointer(x), uintptr(x.moff)))[:nt:nt]
	j := 0
	for k := 0; k < ni; k++ {
	i := &inter.mhdr[k]
	itype := inter.typ.typeOff(i.ityp)
	name := inter.typ.nameOff(i.name)
	iname := name.name()
	ipkg := name.pkgPath()
	if ipkg == "" {
	ipkg = inter.pkgpath.name()
	}
	for ; j < nt; j++ {
	t := &xmhdr[j]
	tname := typ.nameOff(t.name)
	if typ.typeOff(t.mtyp) == itype && tname.name() == iname {
	pkgPath := tname.pkgPath()
	if pkgPath == "" {
	pkgPath = typ.nameOff(x.pkgpath).name()
	}
	if tname.isExported() \|\| pkgPath == ipkg {
	if m != nil {
	ifn := typ.textOff(t.ifn)
	(unsafe.Pointer)(add(unsafe.Pointer(&m.fun[0]), uintptr(k)*sys.PtrSize)) = ifn
	}
	goto nextimethod
	}
	}
	}
	// didn't find method
	if !canfail {
	if locked {
	unlock(&ifaceLock)
	}
	panic(&TypeAssertionError{"", typ.string(), inter.typ.string(), iname})
	}
	m.bad = 1
	break
	nextimethod:
	}
	if !locked {
	throw("invalid itab locking")
	}
	h := itabhash(inter, typ)
	m.link = hash[h]
	m.inhash = 1
	atomicstorep(unsafe.Pointer(&hash[h]), unsafe.Pointer(m))
	}

	func itabsinit() {
	lock(&ifaceLock)
	for _, md := range activeModules() {
	for _, i := range md.itablinks {
	// itablinks is a slice of pointers to the itabs used in this
	// module. A given itab may be used in more than one module
	// and thanks to the way global symbol resolution works, the
	// pointed-to itab may already have been inserted into the
	// global 'hash'.
	if i.inhash == 0 {
	additab(i, true, false)
	}
	}
	}
	unlock(&ifaceLock)
	}

	// panicdottype is called when doing an i.(T) conversion and the conversion fails.
	// have = the dynamic type we have.
	// want = the static type we're trying to convert to.
	// iface = the static type we're converting from.
	func panicdottype(have, want, iface *_type) {
	haveString := ""
	if have != nil {
	haveString = have.string()
	}
	panic(&TypeAssertionError{iface.string(), haveString, want.string(), ""})
	}

	// panicnildottype is called when doing a i.(T) conversion and the interface i is nil.
	// want = the static type we're trying to convert to.
	func panicnildottype(want *_type) {
	panic(&TypeAssertionError{"", "", want.string(), ""})
	// TODO: Add the static type we're converting from as well.
	// It might generate a better error message.
	// Just to match other nil conversion errors, we don't for now.
	}

	// The conv and assert functions below do very similar things.
	// The convXXX functions are guaranteed by the compiler to succeed.
	// The assertXXX functions may fail (either panicking or returning false,
	// depending on whether they are 1-result or 2-result).
	// The convXXX functions succeed on a nil input, whereas the assertXXX
	// functions fail on a nil input.

	func convT2E(t *_type, elem unsafe.Pointer) (e eface) {
	if raceenabled {
	raceReadObjectPC(t, elem, getcallerpc(unsafe.Pointer(&t)), funcPC(convT2E))
	}
	if msanenabled {
	msanread(elem, t.size)
	}
	if isDirectIface(t) {
	// This case is implemented directly by the compiler.
	throw("direct convT2E")
	}
	x := newobject(t)
	// TODO: We allocate a zeroed object only to overwrite it with
	// actual data. Figure out how to avoid zeroing. Also below in convT2I.
	typedmemmove(t, x, elem)
	e._type = t
	e.data = x
	return
	}

	func convT2I(tab *itab, elem unsafe.Pointer) (i iface) {
	t := tab._type
	if raceenabled {
	raceReadObjectPC(t, elem, getcallerpc(unsafe.Pointer(&tab)), funcPC(convT2I))
	}
	if msanenabled {
	msanread(elem, t.size)
	}
	if isDirectIface(t) {
	// This case is implemented directly by the compiler.
	throw("direct convT2I")
	}
	x := newobject(t)
	typedmemmove(t, x, elem)
	i.tab = tab
	i.data = x
	return
	}

	func convI2I(inter *interfacetype, i iface) (r iface) {
	tab := i.tab
	if tab == nil {
	return
	}
	if tab.inter == inter {
	r.tab = tab
	r.data = i.data
	return
	}
	r.tab = getitab(inter, tab._type, false)
	r.data = i.data
	return
	}

	func assertI2I(inter *interfacetype, i iface) (r iface) {
	tab := i.tab
	if tab == nil {
	// explicit conversions require non-nil interface value.
	panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
	}
	if tab.inter == inter {
	r.tab = tab
	r.data = i.data
	return
	}
	r.tab = getitab(inter, tab._type, false)
	r.data = i.data
	return
	}

	func assertI2I2(inter *interfacetype, i iface) (r iface, b bool) {
	tab := i.tab
	if tab == nil {
	return
	}
	if tab.inter != inter {
	tab = getitab(inter, tab._type, true)
	if tab == nil {
	return
	}
	}
	r.tab = tab
	r.data = i.data
	b = true
	return
	}

	func assertE2I(inter *interfacetype, e eface) (r iface) {
	t := e._type
	if t == nil {
	// explicit conversions require non-nil interface value.
	panic(&TypeAssertionError{"", "", inter.typ.string(), ""})
	}
	r.tab = getitab(inter, t, false)
	r.data = e.data
	return
	}

	func assertE2I2(inter *interfacetype, e eface) (r iface, b bool) {
	t := e._type
	if t == nil {
	return
	}
	tab := getitab(inter, t, true)
	if tab == nil {
	return
	}
	r.tab = tab
	r.data = e.data
	b = true
	return
	}

	//go:linkname reflect_ifaceE2I reflect.ifaceE2I
	func reflect_ifaceE2I(inter interfacetype, e eface, dst iface) {
	*dst = assertE2I(inter, e)
	}

	func iterate_itabs(fn func(*itab)) {
	for _, h := range &hash {
	for ; h != nil; h = h.link {
	fn(h)
	}
	}
	}