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runtime: detect hash map collision problems 

This can only happen if the hash function we're using is getting
far more than it's fair share of collisions, but that has happened
to us repeatedly as we've expanded the allowed use cases for
hash tables (issue 1544, issue 2609, issue 2630, issue 2883, issue 3695).
Maybe this will help the next time we try something new.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6306083
This commit is contained in:
Russ Cox 2012-06-24 19:47:50 -04:00
parent 35c3afdb62
commit bca01cd0bf
1 changed files with 6 additions and 2 deletions
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8
src/pkg/runtime/hashmap.c
View File

@ -416,8 +416,12 @@ hash_insert_internal (MapType *t, struct hash_subtable **pst, int32 flags, hash_
*pres = ins_e->data;
return (1);
}
assert (e_hash != hash || (flags & HASH_REHASH) == 0);
hash += (e_hash == hash); /* adjust hash if it collides */
if (e_hash == hash) { /* adjust hash if it collides */
assert ((flags & HASH_REHASH) == 0);
hash++;
if ((hash & HASH_MASK) == HASH_SUBHASH)
runtime·throw("runtime: map hash collision overflow");
}
ins_e = HASH_OFFSET (ins_e, elemsize);
ins_i++;
if (e_hash <= hash) { /* set e to insertion point */