Brother Lian Blockchain technology training share the Go Language source code interpretation map

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When iterate the entire map, it is safe to use delete. This is not the same as C + +, C + + at the time of delete, will cause the whole tree to change, so you can not delete the elements in the iteration.

Then why Golang map is safe, from the source point of view, Golang map uses the concept of barrels, elements are hash to the bucket storage, each bucket preset is stored eight kv, and in the head has a uint8 TOPHASH[8] structure, Stores the high eight bits of each key (that is, hash (key)» (64-8)), and if the position is not placed on the element, there is a special flag empty. When inserting deletes, the first comparison is whether the uint8 is equal to the hash (key). Of course, buckets also utilize the overflow pointer, which can grow infinitely, like a linked list.

Therefore, the For loop is actually iterating over each bucket, judging each uint8 position, and deleting the operation is not the actual memset, but the position of the corresponding Tophash is set to empty. Therefore, it is safe to use delete during the map process of the iteration Golang.

struct HMAP

{

Uintgo count;  # Live Cells = = size of map. Must is first (used by Len () builtin)

UInt32 flags;

UInt32 Hash0; Hash seed

Uint8 B; Log_2 of # of buckets (can hold up to LOAD * 2^b items)

Uint8 keysize; Key size in bytes

Uint8 valuesize; Value Size in bytes

UInt16 bucketsize; Bucket size in bytes

BYTE *buckets; Array of 2^b Buckets. May is nil if count==0.

BYTE *oldbuckets; Previous bucket array of half the size, Non-nil only when growing

UIntPtr nevacuate; Progress counter for evacuation (buckets less than this has been evacuated)

};

typedef struct Bucket bucket;

struct Bucket

{

Uint8 Tophash[bucketsize]; Top 8 bits of hash of each entry (0 = empty)

Bucket *overflow; Overflow bucket, if any

BYTE data[1]; Bucketsize keys followed by bucketsize values

};

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