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libctf, hash: improve insertion of existing keys into dynhashes

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Right now, if you insert a key/value pair into a dynhash, the old slot's
key is freed and the new one always assigned.  This seemed sane to me
when I wrote it, but I got it wrong time and time again.  It's much
less confusing to free the key passed in: if a key-freeing function
was passed, you are asserting that the dynhash owns the key in any
case, so if you pass in a key it is always buggy to assume it sticks
around.  Freeing the old key means that you can't even safely look up a
key from out of a dynhash and hold on to it, because some other matching
key might force it to be freed at any time.

In the new model, you can always get a key out of a dynhash with
ctf_dynhash_lookup_kv and hang on to it until the kv-pair is actually
deleted from the dynhash.  In the old model the pointer to the key might
be freed at any time if a matching key was inserted.

libctf/
	* ctf-hash.c (ctf_hashtab_insert): Free the key passed in if
	there is a key-freeing function and the key already exists.
This commit is contained in:
Nick Alcock 2020-06-02 21:48:12 +01:00
parent 809f6eb332
commit 5ceee3dba3
2 changed files with 7 additions and 2 deletions
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5
libctf/ChangeLog
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@ -1,3 +1,8 @@
2020-07-22 Nick Alcock <nick.alcock@oracle.com>
* ctf-hash.c (ctf_hashtab_insert): Free the key passed in if
there is a key-freeing function and the key already exists.
2020-07-22 Nick Alcock <nick.alcock@oracle.com>
* ctf-inlines.h: New file.

4
libctf/ctf-hash.c
View File

@ -171,15 +171,15 @@ ctf_hashtab_insert (struct htab *htab, void *key, void *value,
*slot = malloc (sizeof (ctf_helem_t));
if (!*slot)
return NULL;
(*slot)->key = key;
}
else
{
if (key_free)
key_free ((*slot)->key);
key_free (key);
if (value_free)
value_free ((*slot)->value);
}
(*slot)->key = key;
(*slot)->value = value;
return *slot;
}