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runtime: allocate map element zero values for reflect-created types on demand

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Preallocating them in reflect means that
(1) if you say _ = PtrTo(ArrayOf(1000000000, reflect.TypeOf(byte(0)))), you just allocated 1GB of data
(2) if you say it again, that's *another* GB of data.

The only use of t.zero in the runtime is for map elements.
Delay the allocation until the creation of a map with that element type,
and share the zeros.

The one downside of the shared zero is that it's not garbage collected,
but it's also never written, so the OS should be able to handle it fairly
efficiently.

Change-Id: I56b098a091abf3ac0945de28ebef9a6c08e76614
Reviewed-on: https://go-review.googlesource.com/10111
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Russ Cox 2015-05-14 17:27:04 -04:00
parent 65c4d7beab
commit 7e26a2d9a8
2 changed files with 48 additions and 9 deletions
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9
src/reflect/type.go
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@ -1087,7 +1087,6 @@ func (t *rtype) ptrTo() *rtype {
p.uncommonType = nil
p.ptrToThis = nil
p.zero = unsafe.Pointer(&make([]byte, p.size)[0])
p.elem = t
ptrMap.m[t] = p
@ -1467,7 +1466,6 @@ func ChanOf(dir ChanDir, t Type) Type {
ch.elem = typ
ch.uncommonType = nil
ch.ptrToThis = nil
ch.zero = unsafe.Pointer(&make([]byte, ch.size)[0])
return cachePut(ckey, &ch.rtype)
}
@ -1530,7 +1528,6 @@ func MapOf(key, elem Type) Type {
mt.reflexivekey = isReflexive(ktyp)
mt.uncommonType = nil
mt.ptrToThis = nil
mt.zero = unsafe.Pointer(&make([]byte, mt.size)[0])
return cachePut(ckey, &mt.rtype)
}
@ -1610,7 +1607,6 @@ func FuncOf(in, out []Type, variadic bool) Type {
ft.string = &str
ft.uncommonType = nil
ft.ptrToThis = nil
ft.zero = unsafe.Pointer(&make([]byte, ft.size)[0])
funcLookupCache.m[hash] = append(funcLookupCache.m[hash], &ft.rtype)
return ft
@ -1857,7 +1853,6 @@ func SliceOf(t Type) Type {
slice.elem = typ
slice.uncommonType = nil
slice.ptrToThis = nil
slice.zero = unsafe.Pointer(&make([]byte, slice.size)[0])
return cachePut(ckey, &slice.rtype)
}
@ -1913,10 +1908,6 @@ func ArrayOf(count int, elem Type) Type {
array.fieldAlign = typ.fieldAlign
array.uncommonType = nil
array.ptrToThis = nil
if array.size > 0 {
zero := make([]byte, array.size)
array.zero = unsafe.Pointer(&zero[0])
}
array.len = uintptr(count)
array.slice = slice.(*rtype)