Go语言源码map类型解读，你知道为什么go的map打印是无序的吗？

func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer
func mapaccess2(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, bool) 

func mapaccess2(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, bool) {
	if h == nil || h.count == 0 {
		if t.hashMightPanic() {
			t.hasher(key, 0) // see issue 23734
		}
		return unsafe.Pointer(&zeroVal[0]), false
	}
  // 如果map正在写入中 panic
	if h.flags&hashWriting != 0 {
		throw("concurrent map read and map write")
	}
	hash := t.hasher(key, uintptr(h.hash0))
	m := bucketMask(h.B)
  // 通过低地址获得桶的地址
	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)))
    // 如果老桶没有迁移完 则在老桶里面查找
		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
			}
      // 找到了 获取key的地址
			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
      // 如果 key 是一个地址的话 还原地址对应值
			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
			}
		}
	}
  
  // 未找到  返回零值
	return unsafe.Pointer(&zeroVal[0]), false

func mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
	
	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))

  // 在之后调用 是因为调用hasher
  // 在这种情况下 实际上我们并未执行写入（删除）操作
	h.flags ^= hashWriting

	bucket := hash & bucketMask(h.B)
  // 查看 map 是不是正在扩容，等扩容完 
	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
}