// 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
// This file contains the implementation of Go's map type.
//
// A map is just a hash table. The data is arranged
// into an array of buckets. Each bucket contains up to
// 8 key/elem pairs. The low-order bits of the hash are
// used to select a bucket. Each bucket contains a few
// high-order bits of each hash to distinguish the entries
// within a single bucket.
//
// If more than 8 keys hash to a bucket, we chain on
// extra buckets.
//
// When the hashtable grows, we allocate a new array
// of buckets twice as big. Buckets are incrementally
// copied from the old bucket array to the new bucket array.
//
// Map iterators walk through the array of buckets and
// return the keys in walk order (bucket #, then overflow
// chain order, then bucket index). To maintain iteration
// semantics, we never move keys within their bucket (if
// we did, keys might be returned 0 or 2 times). When
// growing the table, iterators remain iterating through the
// old table and must check the new table if the bucket
// they are iterating through has been moved ("evacuated")
// to the new table.
// Picking loadFactor: too large and we have lots of overflow
// buckets, too small and we waste a lot of space. I wrote
// a simple program to check some stats for different loads:
// (64-bit, 8 byte keys and elems)
// loadFactor %overflow bytes/entry hitprobe missprobe
// 4.00 2.13 20.77 3.00 4.00
// 4.50 4.05 17.30 3.25 4.50
// 5.00 6.85 14.77 3.50 5.00
// 5.50 10.55 12.94 3.75 5.50
// 6.00 15.27 11.67 4.00 6.00
// 6.50 20.90 10.79 4.25 6.50
// 7.00 27.14 10.15 4.50 7.00
// 7.50 34.03 9.73 4.75 7.50
// 8.00 41.10 9.40 5.00 8.00
//
// %overflow = percentage of buckets which have an overflow bucket
// bytes/entry = overhead bytes used per key/elem pair
// hitprobe = # of entries to check when looking up a present key
// missprobe = # of entries to check when looking up an absent key
//
// Keep in mind this data is for maximally loaded tables, i.e. just
// before the table grows. Typical tables will be somewhat less loaded.
import (
"runtime/internal/atomic"
"runtime/internal/math"
"runtime/internal/sys"
"unsafe"
)
const (
// Maximum number of key/elem pairs a bucket can hold.
bucketCntBits = 3
bucketCnt = 1 << bucketCntBits
// Maximum average load of a bucket that triggers growth is 6.5.
// Represent as loadFactorNum/loadFactorDen, to allow integer math.
loadFactorNum = 13
loadFactorDen = 2
// Maximum key or elem size to keep inline (instead of mallocing per element).
// Must fit in a uint8.
// Fast versions cannot handle big elems - the cutoff size for
// fast versions in cmd/compile/internal/gc/walk.go must be at most this elem.
maxKeySize = 128
maxElemSize = 128
// data offset should be the size of the bmap struct, but needs to be
// aligned correctly. For amd64p32 this means 64-bit alignment
// even though pointers are 32 bit.
dataOffset = unsafe.Offsetof(struct {
b bmap
v int64
}{}.v)
// Possible tophash values. We reserve a few possibilities for special marks.
// Each bucket (including its overflow buckets, if any) will have either all or none of its
// entries in the evacuated* states (except during the evacuate() method, which only happens
// during map writes and thus no one else can observe the map during that time).
emptyRest = 0 // this cell is empty, and there are no more non-empty cells at higher indexes or overflows.
emptyOne = 1 // this cell is empty
evacuatedX = 2 // key/elem is valid. Entry has been evacuated to first half of larger table.
evacuatedY = 3 // same as above, but evacuated to second half of larger table.
evacuatedEmpty = 4 // cell is empty, bucket is evacuated.
minTopHash = 5 // minimum tophash for a normal filled cell.
// flags
iterator = 1 // there may be an iterator using buckets
oldIterator = 2 // there may be an iterator using oldbuckets
hashWriting = 4 // a goroutine is writing to the map
sameSizeGrow = 8 // the current map growth is to a new map of the same size
// sentinel bucket ID for iterator checks
noCheck = 1<<(8*sys.PtrSize) - 1
)
// isEmpty reports whether the given tophash array entry represents an empty bucket entry.
func isEmpty(x uint8) bool {
return x <= emptyOne
}
// A header for a Go map.
type hmap struct {
// Note: the format of the hmap is also encoded in cmd/compile/internal/gc/reflect.go.
// Make sure this stays in sync with the compiler's definition.
count int // # live cells == size of map. Must be first (used by len() builtin)
flags uint8
B uint8 // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
hash0 uint32 // hash seed
buckets unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
nevacuate uintptr // progress counter for evacuation (buckets less than this have been evacuated)
extra *mapextra // optional fields
}
// mapextra holds fields that are not present on all maps.
type mapextra struct {
// If both key and elem do not contain pointers and are inline, then we mark bucket
// type as containing no pointers. This avoids scanning such maps.
// However, bmap.overflow is a pointer. In order to keep overflow buckets
// alive, we store pointers to all overflow buckets in hmap.extra.overflow and hmap.extra.oldoverflow.
// overflow and oldoverflow are only used if key and elem do not contain pointers.
// overflow contains overflow buckets for hmap.buckets.
// oldoverflow contains overflow buckets for hmap.oldbuckets.
// The indirection allows to store a pointer to the slice in hiter.
overflow *[]*bmap
oldoverflow *[]*bmap
// nextOverflow holds a pointer to a free overflow bucket.
nextOverflow *bmap
}
// A bucket for a Go map.
type bmap struct {
// tophash generally contains the top byte of the hash value
// for each key in this bucket. If tophash[0] < minTopHash,
// tophash[0] is a bucket evacuation state instead.
tophash [bucketCnt]uint8
// Followed by bucketCnt keys and then bucketCnt elems.
// NOTE: packing all the keys together and then all the elems together makes the
// code a bit more complicated than alternating key/elem/key/elem/... but it allows
// us to eliminate padding which would be needed for, e.g., map[int64]int8.
// Followed by an overflow pointer.
}
// A hash iteration structure.
// If you modify hiter, also change cmd/compile/internal/gc/reflect.go to indicate
// the layout of this structure.
type hiter struct {
key unsafe.Pointer // Must be in first position. Write nil to indicate iteration end (see cmd/compile/internal/gc/range.go).
elem unsafe.Pointer // Must be in second position (see cmd/compile/internal/gc/range.go).
t *maptype
h *hmap
buckets unsafe.Pointer // bucket ptr at hash_iter initialization time
bptr *bmap // current bucket
overflow *[]*bmap // keeps overflow buckets of hmap.buckets alive
oldoverflow *[]*bmap // keeps overflow buckets of hmap.oldbuckets alive
startBucket uintptr // bucket iteration started at
offset uint8 // intra-bucket offset to start from during iteration (should be big enough to hold bucketCnt-1)
wrapped bool // already wrapped around from end of bucket array to beginning
B uint8
i uint8
bucket uintptr
checkBucket uintptr
}
// bucketShift returns 1<<b, optimized for code generation.
func bucketShift(b uint8) uintptr {
// Masking the shift amount allows overflow checks to be elided.
return uintptr(1) << (b & (sys.PtrSize*8 - 1))
}
// bucketMask returns 1<<b - 1, optimized for code generation.
func bucketMask(b uint8) uintptr {
return bucketShift(b) - 1
}
// tophash calculates the tophash value for hash.
func tophash(hash uintptr) uint8 {
top := uint8(hash >> (sys.PtrSize*8 - 8))
if top < minTopHash {
top += minTopHash
}
return top
}
func evacuated(b *bmap) bool {
h := b.tophash[0]
return h > emptyOne && h < minTopHash
}
func (b *bmap) overflow(t *maptype) *bmap {
return *(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-sys.PtrSize))
}
func (b *bmap) setoverflow(t *maptype, ovf *bmap) {
*(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-sys.PtrSize)) = ovf
}
func (b *bmap) keys() unsafe.Pointer {
return add(unsafe.Pointer(b), dataOffset)
}
// incrnoverflow increments h.noverflow.
// noverflow counts the number of overflow buckets.
// This is used to trigger same-size map growth.
// See also tooManyOverflowBuckets.
// To keep hmap small, noverflow is a uint16.
// When there are few buckets, noverflow is an exact count.
// When there are many buckets, noverflow is an approximate count.
func (h *hmap) incrnoverflow() {
// We trigger same-size map growth if there are
// as many overflow buckets as buckets.
// We need to be able to count to 1<<h.B.
if h.B < 16 {
h.noverflow++
return
}
// Increment with probability 1/(1<<(h.B-15)).
// When we reach 1<<15 - 1, we will have approximately
// as many overflow buckets as buckets.
mask := uint32(1)<<(h.B-15) - 1
// Example: if h.B == 18, then mask == 7,
// and fastrand & 7 == 0 with probability 1/8.
if fastrand()&mask == 0 {
h.noverflow++
}
}
func (h *hmap) newoverflow(t *maptype, b *bmap) *bmap {
var ovf *bmap
if h.extra != nil && h.extra.nextOverflow != nil {
// We have preallocated overflow buckets available.
// See makeBucketArray for more details.
ovf = h.extra.nextOverflow
if ovf.overflow(t) == nil {
// We're not at the end of the preallocated overflow buckets. Bump the pointer.
h.extra.nextOverflow = (*bmap)(add(unsafe.Pointer(ovf), uintptr(t.bucketsize)))
} else {
// This is the last preallocated overflow bucket.
// Reset the overflow pointer on this bucket,
// which was set to a non-nil sentinel value.
ovf.setoverflow(t, nil)
h.extra.nextOverflow = nil
}
} else {
ovf = (*bmap)(newobject(t.bucket))
}
h.incrnoverflow()
if t.bucket.ptrdata == 0 {
h.createOverflow()
*h.extra.overflow = append(*h.extra.overflow, ovf)
}
b.setoverflow(t, ovf)
return ovf
}
func (h *hmap) createOverflow() {
if h.extra == nil {
h.extra = new(mapextra)
}
if h.extra.overflow == nil {
h.extra.overflow = new([]*bmap)
}
}
func makemap64(t *maptype, hint int64, h *hmap) *hmap {
if int64(int(hint)) != hint {
hint = 0
}
return makemap(t, int(hint), h)
}
// makemap_small implements Go map creation for make(map[k]v) and
// make(map[k]v, hint) when hint is known to be at most bucketCnt
// at compile time and the map needs to be allocated on the heap.
func makemap_small() *hmap {
h := new(hmap)
h.hash0 = fastrand()
return h
}
// makemap implements Go map creation for make(map[k]v, hint).
// If the compiler has determined that the map or the first bucket
// can be created on the stack, h and/or bucket may be non-nil.
// If h != nil, the map can be created directly in h.
// If h.buckets != nil, bucket pointed to can be used as the first bucket.
func makemap(t *maptype, hint int, h *hmap) *hmap {
mem, overflow := math.MulUintptr(uintptr(hint), t.bucket.size)
if overflow || mem > maxAlloc {
hint = 0
}
// initialize Hmap
if h == nil {
h = new(hmap)
}
h.hash0 = fastrand()
// Find the size parameter B which will hold the requested # of elements.
// For hint < 0 overLoadFactor returns false since hint < bucketCnt.
B := uint8(0)
for overLoadFactor(hint, B) {
B++
}
h.B = B
// allocate initial hash table
// if B == 0, the buckets field is allocated lazily later (in mapassign)
// If hint is large zeroing this memory could take a while.
if h.B != 0 {
var nextOverflow *bmap
h.buckets, nextOverflow = makeBucketArray(t, h.B, nil)
if nextOverflow != nil {
h.extra = new(mapextra)
h.extra.nextOverflow = nextOverflow
}
}
return h
}
// makeBucketArray initializes a backing array for map buckets.
// 1<<b is the minimum number of buckets to allocate.
// dirtyalloc should either be nil or a bucket array previously
// allocated by makeBucketArray with the same t and b parameters.
// If dirtyalloc is nil a new backing array will be alloced and
// otherwise dirtyalloc will be cleared and reused as backing array.
func makeBucketArray(t *maptype, b uint8, dirtyalloc unsafe.Pointer) (buckets unsafe.Pointer, nextOverflow *bmap) {
base := bucketShift(b)
nbuckets := base
// For small b, overflow buckets are unlikely.
// Avoid the overhead of the calculation.
if b >= 4 {
// Add on the estimated number of overflow buckets
// required to insert the median number of elements
// used with this value of b.
nbuckets += bucketShift(b - 4)
sz := t.bucket.size * nbuckets
up := roundupsize(sz)
if up != sz {
nbuckets = up / t.bucket.size
}
}
if dirtyalloc == nil {
buckets = newarray(t.bucket, int(nbuckets))
} else {
// dirtyalloc was previously generated by
// the above newarray(t.bucket, int(nbuckets))
// but may not be empty.
buckets = dirtyalloc
size := t.bucket.size * nbuckets
if t.bucket.ptrdata != 0 {
memclrHasPointers(buckets, size)
} else {
memclrNoHeapPointers(buckets, size)
}
}
if base != nbuckets {
// We preallocated some overflow buckets.
// To keep the overhead of tracking these overflow buckets to a minimum,
// we use the convention that if a preallocated overflow bucket's overflow
// pointer is nil, then there are more available by bumping the pointer.
// We need a safe non-nil pointer for the last overflow bucket; just use buckets.
nextOverflow = (*bmap)(add(buckets, base*uintptr(t.bucketsize)))
last := (*bmap)(add(buckets, (nbuckets-1)*uintptr(t.bucketsize)))
last.setoverflow(t, (*bmap)(buckets))
}
return buckets, nextOverflow
}
// mapaccess1 returns a pointer to h[key]. Never returns nil, instead
// it will return a reference to the zero object for the elem type if
// the key is not in the map.
// NOTE: The returned pointer may keep the whole map live, so don't
// hold onto it for very long.
func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
if raceenabled && h != nil {
callerpc := getcallerpc()
pc := funcPC(mapaccess1)
racereadpc(unsafe.Pointer(h), callerpc, pc)
raceReadObjectPC(t.key, key, callerpc, pc)
}
if msanenabled && h != nil {
msanread(key, t.key.size)
}
if h == nil || h.count == 0 {
if t.hashMightPanic() {
t.hasher(key, 0) // see issue 23734
}
return unsafe.Pointer(&zeroVal[0])
}
if h.flags&hashWriting != 0 {
throw("concurrent map read and map write")
}
hash := t.hasher(key, uintptr(h.hash0))
m := bucketMask(h.B)
b := (*bmap)(add(h.buckets, (hash&m)*uintptr(t.bucketsize)))
if c := h.oldbuckets; c != nil {
if !h.sameSizeGrow() {
// There used to be half as many buckets; mask down one more power of two.
m >>= 1
}
oldb := (*bmap)(add(c, (hash&m)*uintptr(t.bucketsize)))
if !evacuated(oldb) {
b = oldb
}
}
top := tophash(hash)
bucketloop:
for ; b != nil; b = b.overflow(t) {
for i := uintptr(0); i < bucketCnt; i++ {
if b.tophash[i] != top {
if b.tophash[i] == emptyRest {
break bucketloop
}
continue
}
k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
if t.indirectkey() {
k = *((*unsafe.Pointer)(k))
}
if t.key.equal(key, k) {
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
if t.indirectelem() {
e = *((*unsafe.Pointer)(e))
}
return e
}
}
}
return unsafe.Pointer(&zeroVal[0])
}
func mapaccess2(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, bool) {
if raceenabled && h != nil {
callerpc := getcallerpc()
pc := funcPC(mapaccess2)
racereadpc(unsafe.Pointer(h), callerpc, pc)
raceReadObjectPC(t.key, key, callerpc, pc)
}
if msanenabled && h != nil {
msanread(key, t.key.size)
}
if h == nil || h.count == 0 {
if t.hashMightPanic() {
t.hasher(key, 0) // see issue 23734
}
return unsafe.Pointer(&zeroVal[0]), false
}
if h.flags&hashWriting != 0 {
throw("concurrent map read and map write")
}
hash := t.hasher(key, uintptr(h.hash0))
m := bucketMask(h.B)
b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + (hash&m)*uintptr(t.bucketsize)))
if c := h.oldbuckets; c != nil {
if !h.sameSizeGrow() {
// There used to be half as many buckets; mask down one more power of two.
m >>= 1
}
oldb := (*bmap)(unsafe.Pointer(uintptr(c) + (hash&m)*uintptr(t.bucketsize)))
if !evacuated(oldb) {
b = oldb
}
}
top := tophash(hash)
bucketloop:
for ; b != nil; b = b.overflow(t) {
for i := uintptr(0); i < bucketCnt; i++ {
if b.tophash[i] != top {
if b.tophash[i] == emptyRest {
break bucketloop
}
continue
}
k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
if t.indirectkey() {
k = *((*unsafe.Pointer)(k))
}
if t.key.equal(key, k) {
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
if t.indirectelem() {
e = *((*unsafe.Pointer)(e))
}
return e, true
}
}
}
return unsafe.Pointer(&zeroVal[0]), false
}
// returns both key and elem. Used by map iterator
func mapaccessK(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, unsafe.Pointer) {
if h == nil || h.count == 0 {
return nil, nil
}
hash := t.hasher(key, uintptr(h.hash0))
m := bucketMask(h.B)
b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + (hash&m)*uintptr(t.bucketsize)))
if c := h.oldbuckets; c != nil {
if !h.sameSizeGrow() {
// There used to be half as many buckets; mask down one more power of two.
m >>= 1
}
oldb := (*bmap)(unsafe.Pointer(uintptr(c) + (hash&m)*uintptr(t.bucketsize)))
if !evacuated(oldb) {
b = oldb
}
}
top := tophash(hash)
bucketloop:
for ; b != nil; b = b.overflow(t) {
for i := uintptr(0); i < bucketCnt; i++ {
if b.tophash[i] != top {
if b.tophash[i] == emptyRest {
break bucketloop
}
continue
}
k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
if t.indirectkey() {
k = *((*unsafe.Pointer)(k))
}
if t.key.equal(key, k) {
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
if t.indirectelem() {
e = *((*unsafe.Pointer)(e))
}
return k, e
}
}
}
return nil, nil
}
func mapaccess1_fat(t *maptype, h *hmap, key, zero unsafe.Pointer) unsafe.Pointer {
e := mapaccess1(t, h, key)
if e == unsafe.Pointer(&zeroVal[0]) {
return zero
}
return e
}
func mapaccess2_fat(t *maptype, h *hmap, key, zero unsafe.Pointer) (unsafe.Pointer, bool) {
e := mapaccess1(t, h, key)
if e == unsafe.Pointer(&zeroVal[0]) {
return zero, false
}
return e, true
}
// Like mapaccess, but allocates a slot for the key if it is not present in the map.
func mapassign(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
if h == nil {
panic(plainError("assignment to entry in nil map"))
}
if raceenabled {
callerpc := getcallerpc()
pc := funcPC(mapassign)
racewritepc(unsafe.Pointer(h), callerpc, pc)
raceReadObjectPC(t.key, key, callerpc, pc)
}
if msanenabled {
msanread(key, t.key.size)
}
if h.flags&hashWriting != 0 {
throw("concurrent map writes")
}
hash := t.hasher(key, uintptr(h.hash0))
// Set hashWriting after calling t.hasher, since t.hasher may panic,
// in which case we have not actually done a write.
h.flags ^= hashWriting
if h.buckets == nil {
h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
}
again:
bucket := hash & bucketMask(h.B)
if h.growing() {
growWork(t, h, bucket)
}
b := (*bmap)(add(h.buckets, bucket*uintptr(t.bucketsize)))
top := tophash(hash)
var inserti *uint8
var insertk unsafe.Pointer
var elem unsafe.Pointer
bucketloop:
for {
for i := uintptr(0); i < bucketCnt; i++ {
if b.tophash[i] != top {
if isEmpty(b.tophash[i]) && inserti == nil {
inserti = &b.tophash[i]
insertk = add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
elem = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
}
if b.tophash[i] == emptyRest {
break bucketloop
}
continue
}
k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
if t.indirectkey() {
k = *((*unsafe.Pointer)(k))
}
if !t.key.equal(key, k) {
continue
}
// already have a mapping for key. Update it.
if t.needkeyupdate() {
typedmemmove(t.key, k, key)
}
elem = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
goto done
}
ovf := b.overflow(t)
if ovf == nil {
break
}
b = ovf
}
// Did not find mapping for key. Allocate new cell & add entry.
// If we hit the max load factor or we have too many overflow buckets,
// and we're not already in the middle of growing, start growing.
if !h.growing() && (overLoadFactor(h.count+1, h.B) || tooManyOverflowBuckets(h.noverflow, h.B)) {
hashGrow(t, h)
goto again // Growing the table invalidates everything, so try again
}
if inserti == nil {
// The current bucket and all the overflow buckets connected to it are full, allocate a new one.
newb := h.newoverflow(t, b)
inserti = &newb.tophash[0]
insertk = add(unsafe.Pointer(newb), dataOffset)
elem = add(insertk, bucketCnt*uintptr(t.keysize))
}
// store new key/elem at insert position
if t.indirectkey() {
kmem := newobject(t.key)
*(*unsafe.Pointer)(insertk) = kmem
insertk = kmem
}
if t.indirectelem() {
vmem := newobject(t.elem)
*(*unsafe.Pointer)(elem) = vmem
}
typedmemmove(t.key, insertk, key)
*inserti = top
h.count++
done:
if h.flags&hashWriting == 0 {
throw("concurrent map writes")
}
h.flags &^= hashWriting
if t.indirectelem() {
elem = *((*unsafe.Pointer)(elem))
}
return elem
}
func mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
if raceenabled && h != nil {
callerpc := getcallerpc()
pc := funcPC(mapdelete)
racewritepc(unsafe.Pointer(h), callerpc, pc)
raceReadObjectPC(t.key, key, callerpc, pc)
}
if msanenabled && h != nil {
msanread(key, t.key.size)
}
if h == nil || h.count == 0 {
if t.hashMightPanic() {
t.hasher(key, 0) // see issue 23734
}
return
}
if h.flags&hashWriting != 0 {
throw("concurrent map writes")
}
hash := t.hasher(key, uintptr(h.hash0))
// Set hashWriting after calling t.hasher, since t.hasher may panic,
// in which case we have not actually done a write (delete).
h.flags ^= hashWriting
bucket := hash & bucketMask(h.B)
if h.growing() {
growWork(t, h, bucket)
}
b := (*bmap)(add(h.buckets, bucket*uintptr(t.bucketsize)))
bOrig := b
top := tophash(hash)
search:
for ; b != nil; b = b.overflow(t) {
for i := uintptr(0); i < bucketCnt; i++ {
if b.tophash[i] != top {
if b.tophash[i] == emptyRest {
break search
}
continue
}
k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
k2 := k
if t.indirectkey() {
k2 = *((*unsafe.Pointer)(k2))
}
if !t.key.equal(key, k2) {
continue
}
// Only clear key if there are pointers in it.
if t.indirectkey() {
*(*unsafe.Pointer)(k) = nil
} else if t.key.ptrdata != 0 {
memclrHasPointers(k, t.key.size)
}
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
if t.indirectelem() {
*(*unsafe.Pointer)(e) = nil
} else if t.elem.ptrdata != 0 {
memclrHasPointers(e, t.elem.size)
} else {
memclrNoHeapPointers(e, t.elem.size)
}
b.tophash[i] = emptyOne
// If the bucket now ends in a bunch of emptyOne states,
// change those to emptyRest states.
// It would be nice to make this a separate function, but
// for loops are not currently inlineable.
if i == bucketCnt-1 {
if b.overflow(t) != nil && b.overflow(t).tophash[0] != emptyRest {
goto notLast
}
} else {
if b.tophash[i+1] != emptyRest {
goto notLast
}
}
for {
b.tophash[i] = emptyRest
if i == 0 {
if b == bOrig {
break // beginning of initial bucket, we're done.
}
// Find previous bucket, continue at its last entry.
c := b
for b = bOrig; b.overflow(t) != c; b = b.overflow(t) {
}
i = bucketCnt - 1
} else {
i--
}
if b.tophash[i] != emptyOne {
break
}
}
notLast:
h.count--
// Reset the hash seed to make it more difficult for attackers to
// repeatedly trigger hash collisions. See issue 25237.
if h.count == 0 {
h.hash0 = fastrand()
}
break search
}
}
if h.flags&hashWriting == 0 {
throw("concurrent map writes")
}
h.flags &^= hashWriting
}
// mapiterinit initializes the hiter struct used for ranging over maps.
// The hiter struct pointed to by 'it' is allocated on the stack
// by the compilers order pass or on the heap by reflect_mapiterinit.
// Both need to have zeroed hiter since the struct contains pointers.
func mapiterinit(t *maptype, h *hmap, it *hiter) {
if raceenabled && h != nil {
callerpc := getcallerpc()
racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiterinit))
}
if h == nil || h.count == 0 {
return
}
if unsafe.Sizeof(hiter{})/sys.PtrSize != 12 {
throw("hash_iter size incorrect") // see cmd/compile/internal/gc/reflect.go
}
it.t = t
it.h = h
// grab snapshot of bucket state
it.B = h.B
it.buckets = h.buckets
if t.bucket.ptrdata == 0 {
// Allocate the current slice and remember pointers to both current and old.
// This preserves all relevant overflow buckets alive even if
// the table grows and/or overflow buckets are added to the table
// while we are iterating.
h.createOverflow()
it.overflow = h.extra.overflow
it.oldoverflow = h.extra.oldoverflow
}
// decide where to start
r := uintptr(fastrand())
if h.B > 31-bucketCntBits {
r += uintptr(fastrand()) << 31
}
it.startBucket = r & bucketMask(h.B)
it.offset = uint8(r >> h.B & (bucketCnt - 1))
// iterator state
it.bucket = it.startBucket
// Remember we have an iterator.
// Can run concurrently with another mapiterinit().
if old := h.flags; old&(iterator|oldIterator) != iterator|oldIterator {
atomic.Or8(&h.flags, iterator|oldIterator)
}
mapiternext(it)
}
func mapiternext(it *hiter) {
h := it.h
if raceenabled {
callerpc := getcallerpc()
racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiternext))
}
if h.flags&hashWriting != 0 {
throw("concurrent map iteration and map write")
}
t := it.t
bucket := it.bucket
b := it.bptr
i := it.i
checkBucket := it.checkBucket
next:
if b == nil {
if bucket == it.startBucket && it.wrapped {
// end of iteration
it.key = nil
it.elem = nil
return
}
if h.growing() && it.B == h.B {
// Iterator was started in the middle of a grow, and the grow isn't done yet.
// If the bucket we're looking at hasn't been filled in yet (i.e. the old
// bucket hasn't been evacuated) then we need to iterate through the old
// bucket and only return the ones that will be migrated to this bucket.
oldbucket := bucket & it.h.oldbucketmask()
b = (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
if !evacuated(b) {
checkBucket = bucket
} else {
b = (*bmap)(add(it.buckets, bucket*uintptr(t.bucketsize)))
checkBucket = noCheck
}
} else {
b = (*bmap)(add(it.buckets, bucket*uintptr(t.bucketsize)))
checkBucket = noCheck
}
bucket++
if bucket == bucketShift(it.B) {
bucket = 0
it.wrapped = true
}
i = 0
}
for ; i < bucketCnt; i++ {
offi := (i + it.offset) & (bucketCnt - 1)
if isEmpty(b.tophash[offi]) || b.tophash[offi] == evacuatedEmpty {
// TODO: emptyRest is hard to use here, as we start iterating
// in the middle of a bucket. It's feasible, just tricky.
continue
}
k := add(unsafe.Pointer(b), dataOffset+uintptr(offi)*uintptr(t.keysize))
if t.indirectkey() {
k = *((*unsafe.Pointer)(k))
}
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+uintptr(offi)*uintptr(t.elemsize))
if checkBucket != noCheck && !h.sameSizeGrow() {
// Special case: iterator was started during a grow to a larger size
// and the grow is not done yet. We're working on a bucket whose
// oldbucket has not been evacuated yet. Or at least, it wasn't
// evacuated when we started the bucket. So we're iterating
// through the oldbucket, skipping any keys that will go
// to the other new bucket (each oldbucket expands to two
// buckets during a grow).
if t.reflexivekey() || t.key.equal(k, k) {
// If the item in the oldbucket is not destined for
// the current new bucket in the iteration, skip it.
hash := t.hasher(k, uintptr(h.hash0))
if hash&bucketMask(it.B) != checkBucket {
continue
}
} else {
// Hash isn't repeatable if k != k (NaNs). We need a
// repeatable and randomish choice of which direction
// to send NaNs during evacuation. We'll use the low
// bit of tophash to decide which way NaNs go.
// NOTE: this case is why we need two evacuate tophash
// values, evacuatedX and evacuatedY, that differ in
// their low bit.
if checkBucket>>(it.B-1) != uintptr(b.tophash[offi]&1) {
continue
}
}
}
if (b.tophash[offi] != evacuatedX && b.tophash[offi] != evacuatedY) ||
!(t.reflexivekey() || t.key.equal(k, k)) {
// This is the golden data, we can return it.
// OR
// key!=key, so the entry can't be deleted or updated, so we can just return it.
// That's lucky for us because when key!=key we can't look it up successfully.
it.key = k
if t.indirectelem() {
e = *((*unsafe.Pointer)(e))
}
it.elem = e
} else {
// The hash table has grown since the iterator was started.
// The golden data for this key is now somewhere else.
// Check the current hash table for the data.
// This code handles the case where the key
// has been deleted, updated, or deleted and reinserted.
// NOTE: we need to regrab the key as it has potentially been
// updated to an equal() but not identical key (e.g. +0.0 vs -0.0).
rk, re := mapaccessK(t, h, k)
if rk == nil {
continue // key has been deleted
}
it.key = rk
it.elem = re
}
it.bucket = bucket
if it.bptr != b { // avoid unnecessary write barrier; see issue 14921
it.bptr = b
}
it.i = i + 1
it.checkBucket = checkBucket
return
}
b = b.overflow(t)
i = 0
goto next
}
// mapclear deletes all keys from a map.
func mapclear(t *maptype, h *hmap) {
if raceenabled && h != nil {
callerpc := getcallerpc()
pc := funcPC(mapclear)
racewritepc(unsafe.Pointer(h), callerpc, pc)
}
if h == nil || h.count == 0 {
return
}
if h.flags&hashWriting != 0 {
throw("concurrent map writes")
}
h.flags ^= hashWriting
h.flags &^= sameSizeGrow
h.oldbuckets = nil
h.nevacuate = 0
h.noverflow = 0
h.count = 0
// Reset the hash seed to make it more difficult for attackers to
// repeatedly trigger hash collisions. See issue 25237.
h.hash0 = fastrand()
// Keep the mapextra allocation but clear any extra information.
if h.extra != nil {
*h.extra = mapextra{}
}
// makeBucketArray clears the memory pointed to by h.buckets
// and recovers any overflow buckets by generating them
// as if h.buckets was newly alloced.
_, nextOverflow := makeBucketArray(t, h.B, h.buckets)
if nextOverflow != nil {
// If overflow buckets are created then h.extra
// will have been allocated during initial bucket creation.
h.extra.nextOverflow = nextOverflow
}
if h.flags&hashWriting == 0 {
throw("concurrent map writes")
}
h.flags &^= hashWriting
}
func hashGrow(t *maptype, h *hmap) {
// If we've hit the load factor, get bigger.
// Otherwise, there are too many overflow buckets,
// so keep the same number of buckets and "grow" laterally.
bigger := uint8(1)
if !overLoadFactor(h.count+1, h.B) {
bigger = 0
h.flags |= sameSizeGrow
}
oldbuckets := h.buckets
newbuckets, nextOverflow := makeBucketArray(t, h.B+bigger, nil)
flags := h.flags &^ (iterator | oldIterator)
if h.flags&iterator != 0 {
flags |= oldIterator
}
// commit the grow (atomic wrt gc)
h.B += bigger
h.flags = flags
h.oldbuckets = oldbuckets
h.buckets = newbuckets
h.nevacuate = 0
h.noverflow = 0
if h.extra != nil && h.extra.overflow != nil {
// Promote current overflow buckets to the old generation.
if h.extra.oldoverflow != nil {
throw("oldoverflow is not nil")
}
h.extra.oldoverflow = h.extra.overflow
h.extra.overflow = nil
}
if nextOverflow != nil {
if h.extra == nil {
h.extra = new(mapextra)
}
h.extra.nextOverflow = nextOverflow
}
// the actual copying of the hash table data is done incrementally
// by growWork() and evacuate().
}
// overLoadFactor reports whether count items placed in 1<<B buckets is over loadFactor.
func overLoadFactor(count int, B uint8) bool {
return count > bucketCnt && uintptr(count) > loadFactorNum*(bucketShift(B)/loadFactorDen)
}
// tooManyOverflowBuckets reports whether noverflow buckets is too many for a map with 1<<B buckets.
// Note that most of these overflow buckets must be in sparse use;
// if use was dense, then we'd have already triggered regular map growth.
func tooManyOverflowBuckets(noverflow uint16, B uint8) bool {
// If the threshold is too low, we do extraneous work.
// If the threshold is too high, maps that grow and shrink can hold on to lots of unused memory.
// "too many" means (approximately) as many overflow buckets as regular buckets.
// See incrnoverflow for more details.
if B > 15 {
B = 15
}
// The compiler doesn't see here that B < 16; mask B to generate shorter shift code.
return noverflow >= uint16(1)<<(B&15)
}
// growing reports whether h is growing. The growth may be to the same size or bigger.
func (h *hmap) growing() bool {
return h.oldbuckets != nil
}
// sameSizeGrow reports whether the current growth is to a map of the same size.
func (h *hmap) sameSizeGrow() bool {
return h.flags&sameSizeGrow != 0
}
// noldbuckets calculates the number of buckets prior to the current map growth.
func (h *hmap) noldbuckets() uintptr {
oldB := h.B
if !h.sameSizeGrow() {
oldB--
}
return bucketShift(oldB)
}
// oldbucketmask provides a mask that can be applied to calculate n % noldbuckets().
func (h *hmap) oldbucketmask() uintptr {
return h.noldbuckets() - 1
}
func growWork(t *maptype, h *hmap, bucket uintptr) {
// make sure we evacuate the oldbucket corresponding
// to the bucket we're about to use
evacuate(t, h, bucket&h.oldbucketmask())
// evacuate one more oldbucket to make progress on growing
if h.growing() {
evacuate(t, h, h.nevacuate)
}
}
func bucketEvacuated(t *maptype, h *hmap, bucket uintptr) bool {
b := (*bmap)(add(h.oldbuckets, bucket*uintptr(t.bucketsize)))
return evacuated(b)
}
// evacDst is an evacuation destination.
type evacDst struct {
b *bmap // current destination bucket
i int // key/elem index into b
k unsafe.Pointer // pointer to current key storage
e unsafe.Pointer // pointer to current elem storage
}
func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
b := (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
newbit := h.noldbuckets()
if !evacuated(b) {
// TODO: reuse overflow buckets instead of using new ones, if there
// is no iterator using the old buckets. (If !oldIterator.)
// xy contains the x and y (low and high) evacuation destinations.
var xy [2]evacDst
x := &xy[0]
x.b = (*bmap)(add(h.buckets, oldbucket*uintptr(t.bucketsize)))
x.k = add(unsafe.Pointer(x.b), dataOffset)
x.e = add(x.k, bucketCnt*uintptr(t.keysize))
if !h.sameSizeGrow() {
// Only calculate y pointers if we're growing bigger.
// Otherwise GC can see bad pointers.
y := &xy[1]
y.b = (*bmap)(add(h.buckets, (oldbucket+newbit)*uintptr(t.bucketsize)))
y.k = add(unsafe.Pointer(y.b), dataOffset)
y.e = add(y.k, bucketCnt*uintptr(t.keysize))
}
for ; b != nil; b = b.overflow(t) {
k := add(unsafe.Pointer(b), dataOffset)
e := add(k, bucketCnt*uintptr(t.keysize))
for i := 0; i < bucketCnt; i, k, e = i+1, add(k, uintptr(t.keysize)), add(e, uintptr(t.elemsize)) {
top := b.tophash[i]
if isEmpty(top) {
b.tophash[i] = evacuatedEmpty
continue
}
if top < minTopHash {
throw("bad map state")
}
k2 := k
if t.indirectkey() {
k2 = *((*unsafe.Pointer)(k2))
}
var useY uint8
if !h.sameSizeGrow() {
// Compute hash to make our evacuation decision (whether we need
// to send this key/elem to bucket x or bucket y).
hash := t.hasher(k2, uintptr(h.hash0))
if h.flags&iterator != 0 && !t.reflexivekey() && !t.key.equal(k2, k2) {
// If key != key (NaNs), then the hash could be (and probably
// will be) entirely different from the old hash. Moreover,
// it isn't reproducible. Reproducibility is required in the
// presence of iterators, as our evacuation decision must
// match whatever decision the iterator made.
// Fortunately, we have the freedom to send these keys either
// way. Also, tophash is meaningless for these kinds of keys.
// We let the low bit of tophash drive the evacuation decision.
// We recompute a new random tophash for the next level so
// these keys will get evenly distributed across all buckets
// after multiple grows.
useY = top & 1
top = tophash(hash)
} else {
if hash&newbit != 0 {
useY = 1
}
}
}
if evacuatedX+1 != evacuatedY || evacuatedX^1 != evacuatedY {
throw("bad evacuatedN")
}
b.tophash[i] = evacuatedX + useY // evacuatedX + 1 == evacuatedY
dst := &xy[useY] // evacuation destination
if dst.i == bucketCnt {
dst.b = h.newoverflow(t, dst.b)
dst.i = 0
dst.k = add(unsafe.Pointer(dst.b), dataOffset)
dst.e = add(dst.k, bucketCnt*uintptr(t.keysize))
}
dst.b.tophash[dst.i&(bucketCnt-1)] = top // mask dst.i as an optimization, to avoid a bounds check
if t.indirectkey() {
*(*unsafe.Pointer)(dst.k) = k2 // copy pointer
} else {
typedmemmove(t.key, dst.k, k) // copy elem
}
if t.indirectelem() {
*(*unsafe.Pointer)(dst.e) = *(*unsafe.Pointer)(e)
} else {
typedmemmove(t.elem, dst.e, e)
}
dst.i++
// These updates might push these pointers past the end of the
// key or elem arrays. That's ok, as we have the overflow pointer
// at the end of the bucket to protect against pointing past the
// end of the bucket.
dst.k = add(dst.k, uintptr(t.keysize))
dst.e = add(dst.e, uintptr(t.elemsize))
}
}
// Unlink the overflow buckets & clear key/elem to help GC.
if h.flags&oldIterator == 0 && t.bucket.ptrdata != 0 {
b := add(h.oldbuckets, oldbucket*uintptr(t.bucketsize))
// Preserve b.tophash because the evacuation
// state is maintained there.
ptr := add(b, dataOffset)
n := uintptr(t.bucketsize) - dataOffset
memclrHasPointers(ptr, n)
}
}
if oldbucket == h.nevacuate {
advanceEvacuationMark(h, t, newbit)
}
}
func advanceEvacuationMark(h *hmap, t *maptype, newbit uintptr) {
h.nevacuate++
// Experiments suggest that 1024 is overkill by at least an order of magnitude.
// Put it in there as a safeguard anyway, to ensure O(1) behavior.
stop := h.nevacuate + 1024
if stop > newbit {
stop = newbit
}
for h.nevacuate != stop && bucketEvacuated(t, h, h.nevacuate) {
h.nevacuate++
}
if h.nevacuate == newbit { // newbit == # of oldbuckets
// Growing is all done. Free old main bucket array.
h.oldbuckets = nil
// Can discard old overflow buckets as well.
// If they are still referenced by an iterator,
// then the iterator holds a pointers to the slice.
if h.extra != nil {
h.extra.oldoverflow = nil
}
h.flags &^= sameSizeGrow
}
}
// Reflect stubs. Called from ../reflect/asm_*.s
//go:linkname reflect_makemap reflect.makemap
func reflect_makemap(t *maptype, cap int) *hmap {
// Check invariants and reflects math.
if t.key.equal == nil {
throw("runtime.reflect_makemap: unsupported map key type")
}
if t.key.size > maxKeySize && (!t.indirectkey() || t.keysize != uint8(sys.PtrSize)) ||
t.key.size <= maxKeySize && (t.indirectkey() || t.keysize != uint8(t.key.size)) {
throw("key size wrong")
}
if t.elem.size > maxElemSize && (!t.indirectelem() || t.elemsize != uint8(sys.PtrSize)) ||
t.elem.size <= maxElemSize && (t.indirectelem() || t.elemsize != uint8(t.elem.size)) {
throw("elem size wrong")
}
if t.key.align > bucketCnt {
throw("key align too big")
}
if t.elem.align > bucketCnt {
throw("elem align too big")
}
if t.key.size%uintptr(t.key.align) != 0 {
throw("key size not a multiple of key align")
}
if t.elem.size%uintptr(t.elem.align) != 0 {
throw("elem size not a multiple of elem align")
}
if bucketCnt < 8 {
throw("bucketsize too small for proper alignment")
}
if dataOffset%uintptr(t.key.align) != 0 {
throw("need padding in bucket (key)")
}
if dataOffset%uintptr(t.elem.align) != 0 {
throw("need padding in bucket (elem)")
}
return makemap(t, cap, nil)
}
//go:linkname reflect_mapaccess reflect.mapaccess
func reflect_mapaccess(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
elem, ok := mapaccess2(t, h, key)
if !ok {
// reflect wants nil for a missing element
elem = nil
}
return elem
}
//go:linkname reflect_mapassign reflect.mapassign
func reflect_mapassign(t *maptype, h *hmap, key unsafe.Pointer, elem unsafe.Pointer) {
p := mapassign(t, h, key)
typedmemmove(t.elem, p, elem)
}
//go:linkname reflect_mapdelete reflect.mapdelete
func reflect_mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
mapdelete(t, h, key)
}
//go:linkname reflect_mapiterinit reflect.mapiterinit
func reflect_mapiterinit(t *maptype, h *hmap) *hiter {
it := new(hiter)
mapiterinit(t, h, it)
return it
}
//go:linkname reflect_mapiternext reflect.mapiternext
func reflect_mapiternext(it *hiter) {
mapiternext(it)
}
//go:linkname reflect_mapiterkey reflect.mapiterkey
func reflect_mapiterkey(it *hiter) unsafe.Pointer {
return it.key
}
//go:linkname reflect_mapiterelem reflect.mapiterelem
func reflect_mapiterelem(it *hiter) unsafe.Pointer {
return it.elem
}
//go:linkname reflect_maplen reflect.maplen
func reflect_maplen(h *hmap) int {
if h == nil {
return 0
}
if raceenabled {
callerpc := getcallerpc()
racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
}
return h.count
}
//go:linkname reflectlite_maplen internal/reflectlite.maplen
func reflectlite_maplen(h *hmap) int {
if h == nil {
return 0
}
if raceenabled {
callerpc := getcallerpc()
racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
}
return h.count
}
const maxZero = 1024 // must match value in reflect/value.go:maxZero cmd/compile/internal/gc/walk.go:zeroValSize
var zeroVal [maxZero]byte
 |
The pages are generated with Golds v0.4.2. (GOOS=darwin GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
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