Hi, Monty!
On Mar 31, Michael Widenius wrote:
> > > > --- a/sql/sql_string.h
> > > > +++ b/sql/sql_string.h
> > > > @@ -600,25 +600,34 @@ class Binary_string: public Static_binary_string
> > > >
> > > > inline char *c_ptr()
> > > > {
> > > > - DBUG_ASSERT(!alloced || !Ptr || !Alloced_length ||
> > > > - (Alloced_length >= (str_length + 1)));
> > > > -
> > > > - if (!Ptr || Ptr[str_length]) // Should be safe
> > > > - (void) realloc(str_length);
> > > > + if (unlikely(!Ptr))
> > > > + return (char*) "";
> > > > + /*
> > > > + Here we assume that any buffer used to initalize String has
> > > > + an end \0 or have at least an accessable character at end.
> > > > + This is to handle the case of String("Hello",5) efficently.
> > > > + */
> > > > + if (unlikely(!alloced && !Ptr[str_length]))
> > > > + return Ptr;
> > >
> > > No, this is not good. Note the difference between
> > >
> > > String a("Hello", 5)
> > >
> > > and
> > >
> > > char hello[5];
> > > String a(buf, 5);
> > >
> > > Your assumption should only apply to the first case, not to the second.
> > > In the first case alloced=Alloced_length=0, in the second case only
> > > alloced=0 and Alloced_length=5. So in the if() above you need to look
> > > at Alloced_length:
> > >
> > > if (!Alloced_length && !Ptr[str_length])
> > > return Ptr;
>
> Unfortunately this does not work good with our code.
>
> We have a lot of code that does things like this:
> String *new_str= new (thd->mem_root) String((const char*) name.str,
> name.length,
> system_charset_info)
> Where string is 0 terminated.
> With your proposed change, all of these will require a full realloc
> when using c_ptr().
Hmm, I don't understand. The difference between
String a("Hello", 5);
and
char hello[5];
String a(buf, 5);
is that in the first case the argument is const char*. And in that case
Alloced_length=0 and in that case you can expect the string to be \0
terminated.
In your example that we do "a lot", the first argument is const char*,
so String will have Alloced_length==0 and my suggestion will work
exactly as planned, it'll use a \0 terminated fast path.
Regards,
Sergei
VP of MariaDB Server Engineering
and secur...@mariadb.org
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