【Golang1.20源码阅读】runtime/map.go

// 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.
// 此文件包含Go的映射类型的实现。
// 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.
// 地图只是一个散列表。数据被排列成一组桶。每个存储桶最多包含8对key/elem。散列的低位用于选择一个桶。
// 每个bucket包含每个hash的几个高阶位，以区分单个bucket中的条目。

// If more than 8 keys hash to a bucket, we chain on
// extra buckets.
// 如果一个bucket散列了8个以上的密钥，我们会在额外的bucket上进行连锁。
// 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.
// 当哈希表增长时，我们会分配一个两倍大的新bucket数组。bucket是从旧bucket数组增量复制到新bucket数组的。

// 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.
// 映射迭代器遍历bucket数组，并按遍历顺序返回键（bucket#，然后是溢出链顺序，然后是bucket索引）。
// 为了维护迭代语义，我们从不在它们的bucket中移动键（如果这样做，键可能会被返回0或2次）。
// 在扩展表时，迭代器保持在旧表中迭代，并且必须检查新表是否已将其迭代的bucket移动（“抽空”）到新表中。

// 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:
// 拣选装载系数：太大，我们有很多溢流桶，太小，我们浪费了很多空间。我写了一个简单的程序来检查不同负载的一些统计数据：
// (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 具有溢出存储桶的存储桶百分比
// bytes/entry = overhead bytes used per key/elem pair 每个key/elem对使用的开销字节
// hitprobe    = # of entries to check when looking up a present key 查找当前密钥时要检查的条目数
// missprobe   = # of entries to check when looking up an absent key 查找缺少的密钥时要检查的条目数
//
// Keep in mind this data is for maximally loaded tables, i.e. just
// before the table grows. Typical tables will be somewhat less loaded.
// 请记住，这些数据适用于最大加载的表，即在表增长之前。典型的表格会稍微少加载一些。

import (
	"internal/abi"
	"internal/goarch"
	"runtime/internal/atomic"
	"runtime/internal/math"
	"unsafe"
)

const (
	// Maximum number of key/elem pairs a bucket can hold. 存储桶可容纳的最大key/elem对数。
	bucketCntBits = 3
	bucketCnt     = 1 << bucketCntBits

	// Maximum average load of a bucket that triggers growth is 6.5. 触发增长的铲斗的最大平均负载为6.5。
	// Represent as loadFactorNum/loadFactorDen, to allow integer math. 表示为loadFactorNum/loadFactorDen，以允许进行整数运算。
	loadFactorNum = 13
	loadFactorDen = 2

	// Maximum key or elem size to keep inline (instead of mallocing per element). 保持内联的最大键或elem大小（而不是对每个元素进行mallocing）。
	// Must fit in a uint8. 必须符合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.
	// 快速版本无法处理大的elem-cmd/compile/internal/gc/walk.go中快速版本的截止大小最多只能是这个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.
	// 数据偏移量应该是bmap结构的大小，但需要正确对齐。对于amd64p32，这意味着64位对齐，即使指针是32位。
	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).
	// 可能的tophash值。我们保留了一些特殊标记的可能性。每个bucket（包括其溢出bucket，如果有的话）的所有条目都将处于抽空*状态（除了在evacuate（）方法期间，该方法只在映射写入期间发生，因此在此期间没有其他人可以观察到映射）。
	// emptyRest=0//此单元格为空，并且在较高索引或溢出时不再有非空单元格。
	emptyRest      = 0 // this cell is empty, and there are no more non-empty cells at higher indexes or overflows. 此单元格为空，在较高的索引或溢出处不再有非空单元格。
	emptyOne       = 1 // this cell is empty 此单元格为空
	evacuatedX     = 2 // key/elem is valid.  Entry has been evacuated to first half of larger table. key/elem有效。入口已疏散到较大桌子的前半部分。
	evacuatedY     = 3 // same as above, but evacuated to second half of larger table. 和上面一样，但疏散到较大桌子的后半部分。
	evacuatedEmpty = 4 // cell is empty, bucket is evacuated. cell是空的，桶被排空了。
	minTopHash     = 5 // minimum tophash for a normal filled cell. 正常填充cell的最小tophash。

	// flags
	iterator     = 1 // there may be an iterator using buckets 可能存在使用bucket的迭代器
	oldIterator  = 2 // there may be an iterator using oldbuckets 可能存在使用旧桶的迭代器
	hashWriting  = 4 // a goroutine is writing to the map 一个goroutine正在写map
	sameSizeGrow = 8 // the current map growth is to a new map of the same size 当前地图的增长是到一个相同大小的新map

	// sentinel bucket ID for iterator checks 用于迭代器检查的sentinel bucket ID
	noCheck = 1<<(8*goarch.PtrSize) - 1
)

// isEmpty reports whether the given tophash array entry represents an empty bucket entry.
// isEmpty报告给定的tophash数组条目是否表示空的bucket条目。
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/reflectdata/reflect.go.
	// 注意：hmap的格式也编码在cmd/compile/internal/reflectdata/relect.go中。
	// Make sure this stays in sync with the compiler's definition.  请确保这与编译器的定义保持同步。
	// count-元素数目
	count     int // # live cells == size of map.  Must be first (used by len() builtin)
	//flags 字段标志map的状态, 如map当前正在被遍历或正在被写入
	flags     uint8
	// 哈希桶数目以2为底的对数
	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items) 铲斗数量的log_2（最多可容纳负载系数*2^B个项）
	// noverflow 是溢出桶的数目, 这个数值不是恒定精确的
	noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details 溢流桶的大致数量；详见incrnoverflow
	hash0     uint32 // hash seed

	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0. 2^B桶阵列。如果count==0，则可以为零。
	// oldbuckets 是当桶扩容时指向旧桶的指针
	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing 前一个大小为一半的bucket数组，仅在增长时为非零
	// nevacuate 是当桶进行调整时指示的搬迁进度, 小于此地址的 buckets 是以前搬迁完毕的哈希桶
	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated) 疏散进度计数器（已疏散少于此数量的铲斗）
	// mapextra 则是溢出桶的变量
	extra *mapextra // optional fields 可选字段
}

// mapextra holds fields that are not present on all maps.
//mapextra包含并非所有map上都存在的字段。
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.
	// 如果key和elem都不包含指针并且是内联的，那么我们将bucket类型标记为不包含指针。这样可以避免扫描此类map。但是，bmap.overflow是一个指针。
	// 为了使溢出存储桶保持活动状态，我们将指向所有溢出存储桶的指针存储在hmanp.extra.overflow和hmanp.extra.oldoverflow中。
	// 只有当key和elem不包含指针时，才会使用overflow和oldoverflow。overflow包含用于hmap.oldbucket的溢出bucket。
	// oldoverflow包含hmap.ordbucket的溢流bucket。 间接寻址允许在hiter中存储指向切片的指针。
	overflow    *[]*bmap
	oldoverflow *[]*bmap

	// nextOverflow holds a pointer to a free overflow bucket. nextOverflow保存一个指向空闲溢出存储桶的指针
	nextOverflow *bmap
}

// A bucket for a Go map.Go map的桶。
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通常包含该bucket中每个键的哈希值的顶部字节。如果tophash[0]＜minTopHash，则tophash[0]为bucket疏散状态。
	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.
	// 然后是bucketCnt键，然后是buketCnt elems。注意：将所有密钥打包在一起，然后将所有elem打包在一起会使代码比交替使用key/elem/key/elem/更复杂。
	// 但它允许我们消除例如map[int64]int8所需的填充。后面跟一个溢出指针。
}

// A hash iteration structure.
// If you modify hiter, also change cmd/compile/internal/reflectdata/reflect.go
// and reflect/value.go to match the layout of this structure.
// 散列迭代结构。
// 如果修改hiter，还可以更改cmd/compile/internal/reflectdata/reflect.go和reflect/value.go以匹配此结构的布局。
type hiter struct {
	// 必须处于第一位置。写nil表示迭代结束（请参阅cmd/compile/internal/walk/range.go）。
	key         unsafe.Pointer // Must be in first position.  Write nil to indicate iteration end (see cmd/compile/internal/walk/range.go).
	// 必须位于第二个位置（请参阅cmd/compile/internal/walk/range.go）。
	elem        unsafe.Pointer // Must be in second position (see cmd/compile/internal/walk/range.go).
	t           *maptype
	h           *hmap
	// hash_iter初始化时的bucket ptr
	buckets     unsafe.Pointer // bucket ptr at hash_iter initialization time
	bptr        *bmap          // current bucket 当前桶
	overflow    *[]*bmap       // keeps overflow buckets of hmap.buckets alive 保持溢出的hmap.buckets的活力
	oldoverflow *[]*bmap       // keeps overflow buckets of hmap.oldbuckets alive 保持溢出的hmap.oldbucket的活力
	startBucket uintptr        // bucket iteration started at bucket迭代开始位置
	offset      uint8          // intra-bucket offset to start from during iteration (should be big enough to hold bucketCnt-1) 迭代期间要开始的桶内偏移（应该足够大以容纳桶Cnt-1）
	wrapped     bool           // already wrapped around from end of bucket array to beginning 已经从bucket数组的末尾绕到了开头
	B           uint8
	i           uint8
	bucket      uintptr
	checkBucket uintptr
}

// bucketShift returns 1<<b, optimized for code generation.
// bucketShift返回1<<b，针对代码生成进行了优化。
func bucketShift(b uint8) uintptr {
	// Masking the shift amount allows overflow checks to be elided.
	//屏蔽偏移量可以消除溢出检查。
	return uintptr(1) << (b & (goarch.PtrSize*8 - 1))
}

// bucketMask returns 1<<b - 1, optimized for code generation.
//bucketMask返回1<<b-1，针对代码生成进行了优化。
func bucketMask(b uint8) uintptr {
	return bucketShift(b) - 1
}

// tophash calculates the tophash value for hash.
//tophash计算hash的tophash值。
func tophash(hash uintptr) uint8 {
	top := uint8(hash >> (goarch.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)-goarch.PtrSize))
}

func (b *bmap) setoverflow(t *maptype, ovf *bmap) {
	*(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-goarch.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.
// incrnoverflow递增h.noverflow。noverflow统计溢出存储桶的数量。这是用来触发相同大小的map增长。
// 另请参阅tooManyOverflowBuckets。为了保持hmap较小，noverflow是一个uint16。当桶很少时，noverflow是一个精确的计数。
// 当有许多桶时，noverflow是一个近似计数。
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.
	// 如果溢出的bucket和bucket一样多，我们就会触发相同大小的map增长。我们需要能够计数到1。
	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.
	// 以概率1/（1<<（h.B-15））递增。当我们达到1<<15-1时，我们将有大约与桶一样多的溢出桶。
	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.
		// 我们有预先分配的可用溢出存储桶。有关更多详细信息，请参阅makeBucketArray。
		ovf = h.extra.nextOverflow
		if ovf.overflow(t) == nil {
			// We're not at the end of the preallocated overflow buckets. Bump the pointer.
			// //我们还没有到预先分配的溢出存储桶的末尾。碰撞指针。
			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.
			// 这是最后一个预先分配的溢出存储桶。重置此存储桶上的溢出指针，该指针已设置为非nil sentinel值。
			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.
// makemap_small为make（map[k]v）和make（map/k]v，hint）实现Go映射创建，当编译时已知hint最多为bucketCnt，并且需要在堆上分配映射时。
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.
// makemap实现了make的Go映射创建（map[k]v，hint）。如果编译器已经确定可以在堆栈上创建map或第一个bucket，则h和/或bucket可以是非nil。
// 如果h！=nil，则可以直接在h中创建映射。如果h.buckets！=nil，指向的bucket可以用作第一个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 初始化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.
	// 查找大小参数B，该参数将包含请求的元素数。对于提示＜0，overLoadFactor返回false，因为提示＜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.
	// 分配初始哈希表如果B==0，buckets字段稍后会延迟分配（在mapassign中）如果提示很大，则归零此内存可能需要一段时间。
	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.
// makeBucketArray初始化map桶的后备数组。1<<b是要分配的最小存储桶数。
// dirtyalloc应该是nil，或者是makeBucketArray以前使用相同的t和b参数分配的bucket数组。
// 如果dirtyalloc为nil，则将分配一个新的备份阵列，否则dirtyallok将被清除并重新用作备份阵列。
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.
	// 对于小b，不太可能溢出bucket。避免计算的开销。
	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.
		// 加上所需的溢出桶的估计数量，以插入与该值b一起使用的元素的中值数量。
		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.
		//dirtyalloc以前是由上面的newarray（t.bucket，int（nbuckets））生成的，但可能不为空。
		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.
		// 我们预先分配了一些溢出存储桶。为了将跟踪这些溢出存储桶的开销降至最低，我们使用了这样一种约定，即如果预分配的溢出存储桶中的溢出指针为零，
		// 则通过碰撞指针可以获得更多可用的溢出指针。我们需要一个安全的非零指针用于最后一个溢出桶；只用水桶。
		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.
// mapaccess1返回一个指向h[key]的指针。从不返回nil，相反，如果键不在映射中，它将返回对elem类型的zero对象的引用。
// 注意：返回的指针可能会使整个地图保持活动状态，所以不要长时间保持它。
func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
	if raceenabled && h != nil {
		callerpc := getcallerpc()
		pc := abi.FuncPCABIInternal(mapaccess1)
		racereadpc(unsafe.Pointer(h), callerpc, pc)
		raceReadObjectPC(t.key, key, callerpc, pc)
	}
	if msanenabled && h != nil {
		msanread(key, t.key.size)
	}
	if asanenabled && h != nil {
		asanread(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 {
		fatal("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.
			//过去有一半的水桶；掩盖二次幂的一次幂
			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 := abi.FuncPCABIInternal(mapaccess2)
		racereadpc(unsafe.Pointer(h), callerpc, pc)
		raceReadObjectPC(t.key, key, callerpc, pc)
	}
	if msanenabled && h != nil {
		msanread(key, t.key.size)
	}
	if asanenabled && h != nil {
		asanread(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 {
		fatal("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, true
			}
		}
	}
	return unsafe.Pointer(&zeroVal[0]), false
}

// returns both key and elem. Used by map iterator.
//返回key和elem。由映射迭代器使用。
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)(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 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.
//类似于mapaccess，但如果密钥不在映射中，则为其分配一个插槽。
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 := abi.FuncPCABIInternal(mapassign)
		racewritepc(unsafe.Pointer(h), callerpc, pc)
		raceReadObjectPC(t.key, key, callerpc, pc)
	}
	if msanenabled {
		msanread(key, t.key.size)
	}
	if asanenabled {
		asanread(key, t.key.size)
	}
	if h.flags&hashWriting != 0 {
		fatal("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.
	// 在调用t.hasher之后设置hashWriting，因为t.hasher可能会死机，在这种情况下，我们实际上还没有进行写入。
	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.
			//已经具有键的映射。更新它。
			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.
	// 找不到键的映射。分配新单元格并添加条目。如果我们达到了最大负载因子，或者我们有太多的溢出桶，而我们还没有处于增长之中，那么就开始增长。
	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 增大表会使所有内容无效，请重试
	}

	if inserti == nil {
		// The current bucket and all the overflow buckets connected to it are full, allocate a new one.
		//当前bucket和与其连接的所有溢出bucket都已满，请分配一个新的bucket。
		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
	//将新key/eem存储在插入位置
	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 {
		fatal("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 := abi.FuncPCABIInternal(mapdelete)
		racewritepc(unsafe.Pointer(h), callerpc, pc)
		raceReadObjectPC(t.key, key, callerpc, pc)
	}
	if msanenabled && h != nil {
		msanread(key, t.key.size)
	}
	if asanenabled && h != nil {
		asanread(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 {
		fatal("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).
	// 在调用t.hasher之后设置hashWriting，因为t.hasher可能会死机，在这种情况下，我们实际上还没有进行写入（删除）。
	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.
			// 只有当键中有指针时才清除键。
			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.
			//如果bucket现在以一堆emptyOne状态结束，请将这些状态更改为emptyRest状态。将其作为一个单独的函数会很好，但for循环目前不可内联。
			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. 开始最初的桶，我们完成了。
					}
					// Find previous bucket, continue at its last entry. 找到上一个bucket，在其最后一个条目处继续。
					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.
			//重置哈希种子，使攻击者更难重复触发哈希冲突。见第25237期。
			if h.count == 0 {
				h.hash0 = fastrand()
			}
			break search
		}
	}

	if h.flags&hashWriting == 0 {
		fatal("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.
// mapiterinit初始化用于对映射进行测距的hiter结构。“it”指向的hiter结构由编译器order pass在堆栈上分配，
// 或由reflect_mapiterinit在堆上分配。由于结构包含指针，因此两者都需要具有零hiter。
func mapiterinit(t *maptype, h *hmap, it *hiter) {
	if raceenabled && h != nil {
		callerpc := getcallerpc()
		racereadpc(unsafe.Pointer(h), callerpc, abi.FuncPCABIInternal(mapiterinit))
	}

	it.t = t
	if h == nil || h.count == 0 {
		return
	}

	if unsafe.Sizeof(hiter{})/goarch.PtrSize != 12 {
		throw("hash_iter size incorrect") // see cmd/compile/internal/reflectdata/reflect.go
	}
	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.
		// 分配当前切片并记住指向当前和旧切片的指针。
		// 这将保持所有相关的溢出存储桶处于活动状态，即使在我们迭代时表增长和/或溢出存储桶添加到表中也是如此。
		h.createOverflow()
		it.overflow = h.extra.overflow
		it.oldoverflow = h.extra.oldoverflow
	}

	// decide where to start
	//决定从哪里开始
	var r uintptr
	if h.B > 31-bucketCntBits {
		r = uintptr(fastrand64())
	} else {
		r = uintptr(fastrand())
	}
	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().
	//记住我们有一个迭代器。可以与另一个mapiteinit（）同时运行。
	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, abi.FuncPCABIInternal(mapiternext))
	}
	if h.flags&hashWriting != 0 {
		fatal("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.
			// 迭代程序是在增长过程中启动的，但增长尚未完成。如果我们正在查看的bucket尚未填充（即，旧bucket尚未排空），
			// 那么我们需要遍历旧bucket，只返回将迁移到此bucket的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.
			// TODO:emptyRest在这里很难使用，因为我们开始在桶的中间迭代。这是可行的，只是很棘手。
			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).
			// 特殊情况：迭代器是在增长到更大的大小时启动的，但尚未完成增长。我们正在处理一个旧桶还没有被疏散的桶。
			// 或者至少，当我们启动水桶时，它没有被疏散。因此，我们遍历旧bucket，跳过任何将进入另一个新bucket的键（在增长过程中，每个旧bucket扩展到两个bucket）。
			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.
				// 如果旧存储桶中的项目不是迭代中当前新存储桶的目标，请跳过它。
				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.
				// 如果k！=，则哈希不可重复k（NaNs）。我们需要一个可重复和随机的选择，在疏散期间向哪个方向发送NaN。
				// 我们将使用tophash的低位来决定NaN的走向。注意：这种情况就是为什么我们需要两个抽空tophash值，抽空X和抽空Y，它们的低位不同。
				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.
			// 这是黄金数据，我们可以将其返回。OR键=key，所以条目不能被删除或更新，所以我们可以直接返回它。这对我们来说很幸运，因为当key=密钥我们无法成功查找。
			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).
			// 自迭代器启动以来，哈希表一直在增长。这个密钥的黄金数据现在在其他地方。请检查当前哈希表中的数据。
			// 此代码处理密钥已被删除、更新或删除并重新插入的情况。注意：我们需要重新标记密钥，因为它可能已更新为equal（），但不是相同的密钥（例如+0.0与-0.0）。
			rk, re := mapaccessK(t, h, k)
			if rk == nil {
				continue // key has been deleted //密钥已被删除
			}
			it.key = rk
			it.elem = re
		}
		it.bucket = bucket
		if it.bptr != b { // avoid unnecessary write barrier; see issue 14921
			// 避免不必要的写入障碍；见第14921期
			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.
// 避免不必要的写入障碍；见第14921期
func mapclear(t *maptype, h *hmap) {
	if raceenabled && h != nil {
		callerpc := getcallerpc()
		pc := abi.FuncPCABIInternal(mapclear)
		racewritepc(unsafe.Pointer(h), callerpc, pc)
	}

	if h == nil || h.count == 0 {
		return
	}

	if h.flags&hashWriting != 0 {
		fatal("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.
	// 重置哈希种子，使攻击者更难重复触发哈希冲突。见第25237期。
	h.hash0 = fastrand()

	// Keep the mapextra allocation but clear any extra information.
	// 保留地图额外分配，但清除任何额外信息。
	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.
	//makeBucketArray清除h.buckets指向的内存，并通过生成溢出的bucket来恢复溢出的buckets，就像h.buckets是新分配的一样。
	_, 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.
		// 如果创建了溢出存储桶，则在初始存储桶创建期间将分配h.extra。
		h.extra.nextOverflow = nextOverflow
	}

	if h.flags&hashWriting == 0 {
		fatal("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.
	//如果我们已经达到了负载系数，就做大。否则，溢出的桶太多，所以保持相同的桶数并横向“增长”。
	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.
		//将当前溢出存储桶升级到旧一代。
		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().
	//哈希表数据的实际复制是通过growWork（）和evacuate（）增量完成的。
}

// overLoadFactor reports whether count items placed in 1<<B buckets is over loadFactor.
// overLoadFactor报告放置在1<<B存储桶中的计数项目是否为overLoadFactor。
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.
// tooManyOverflowBuckets报告noverflow bucket对于具有1<<B bucket的映射是否太多。
// 请注意，这些溢出存储桶中的大多数必须稀疏使用；如果使用密集，那么我们已经触发了地图的定期增长。
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.
	//如果阈值太低，我们就做无关的工作。如果阈值太高，则增长和收缩的映射可能会保留大量未使用的内存。“过多”是指（大约）与常规桶一样多的溢出桶。请参阅incrnoverflow了解更多详细信息。
	if B > 15 {
		B = 15
	}
	// The compiler doesn't see here that B < 16; mask B to generate shorter shift code.
	//编译器在这里看不到B<16；掩码B以生成较短的移位码。
	return noverflow >= uint16(1)<<(B&15)
}

// growing reports whether h is growing. The growth may be to the same size or bigger.
//growing报告h是否在增长。增长的规模可能相同，也可能更大。
func (h *hmap) growing() bool {
	return h.oldbuckets != nil
}

// sameSizeGrow reports whether the current growth is to a map of the same size.
//sameSizeGrow报告当前增长是否为相同大小的映射。
func (h *hmap) sameSizeGrow() bool {
	return h.flags&sameSizeGrow != 0
}

// noldbuckets calculates the number of buckets prior to the current map growth.
//noldbuckets计算当前map增长之前的存储桶数量。
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().
//oldbucketmask提供了一个掩码，可用于计算n%noldBucket（）。
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
	//确保我们疏散与我们将要使用的桶相对应的旧桶
	evacuate(t, h, bucket&h.oldbucketmask())

	// evacuate one more oldbucket to make progress on growing
	//再疏散一个oldbucket，在成长上取得进展
	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.
//evacDst是一个疏散目的地。
type evacDst struct {
	b *bmap          // current destination bucket 当前目标存储桶
	i int            // key/elem index into b key/elem索引到b
	k unsafe.Pointer // pointer to current key storage 指向当前密钥存储的指针
	e unsafe.Pointer // pointer to current elem storage 指向当前elem存储的指针
}

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.)
		// TODO:如果没有使用旧存储桶的迭代器，则重用溢出存储桶，而不是使用新存储桶。（如果！oldIterator。）
		// xy contains the x and y (low and high) evacuation destinations.
		// xy包含x和y（低和高）疏散目的地。
		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.
			// 只有当我们变得更大时才计算y指针。否则GC可能会看到错误的指针。
			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).
					// 计算hash以做出疏散决定（我们是否需要将此密钥/elem发送到bucket x或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.
						// If key！=密钥（NaNs），则哈希可能（并且可能）与旧哈希完全不同。此外，它不可复制。迭代器存在时需要再现性，
						// 因为我们的疏散决策必须与迭代器做出的任何决策相匹配。幸运的是，我们可以任意发送这些密钥。
						// 此外，tophash对于这些类型的密钥是没有意义的。我们让低层次的tophash来推动疏散决定。
						// 我们为下一级重新计算一个新的随机tophash，这样这些密钥在多次增长后将均匀分布在所有桶中。
						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 掩码dst.i作为优化，以避免边界检查
				if t.indirectkey() {
					*(*unsafe.Pointer)(dst.k) = k2 // copy pointer 复制指针
				} else {
					typedmemmove(t.key, dst.k, k) // copy elem 复制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.
				// 这些更新可能会将这些指针推到键或elem数组的末尾。这没关系，因为我们在bucket的末尾有溢出指针，以防止指针超过bucket的结尾。
				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. 取消链接溢出存储桶并清除key/elem以帮助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.
			// 保留b.tophash，因为那里保持着疏散状态。
			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.
	// 实验表明，1024至少高估了一个数量级。无论如何，把它放在那里作为一种保护措施，以确保O（1）行为。
	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. 成长就是一切。释放旧的主存储桶阵列。
		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.
		// 也可以丢弃旧的溢出桶。如果它们仍然被迭代器引用，那么迭代器会保存一个指向切片的指针。
		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. 检查不变量并反映math。
	if t.key.equal == nil {
		throw("runtime.reflect_makemap: unsupported map key type")
	}
	if t.key.size > maxKeySize && (!t.indirectkey() || t.keysize != uint8(goarch.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(goarch.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 reflect对缺少的元素要零
		elem = nil
	}
	return elem
}

//go:linkname reflect_mapaccess_faststr reflect.mapaccess_faststr
func reflect_mapaccess_faststr(t *maptype, h *hmap, key string) unsafe.Pointer {
	elem, ok := mapaccess2_faststr(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_mapassign_faststr reflect.mapassign_faststr
func reflect_mapassign_faststr(t *maptype, h *hmap, key string, elem unsafe.Pointer) {
	p := mapassign_faststr(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_mapdelete_faststr reflect.mapdelete_faststr
func reflect_mapdelete_faststr(t *maptype, h *hmap, key string) {
	mapdelete_faststr(t, h, key)
}

//go:linkname reflect_mapiterinit reflect.mapiterinit
func reflect_mapiterinit(t *maptype, h *hmap, it *hiter) {
	mapiterinit(t, h, 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, abi.FuncPCABIInternal(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, abi.FuncPCABIInternal(reflect_maplen))
	}
	return h.count
}
// 必须与reflect/value.go:maxZero cmd/compile/internal/gc/walk.go:zeroValSize中的值匹配
const maxZero = 1024 // must match value in reflect/value.go:maxZero cmd/compile/internal/gc/walk.go:zeroValSize
var zeroVal [maxZero]byte