Re: Leaking file locks in Lua 5.3-beta and automatic cleanup of temporary resources
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- Subject: Re: Leaking file locks in Lua 5.3-beta and automatic cleanup of temporary resources
- From: Roberto Ierusalimschy <roberto@...>
- Date: 2014年11月21日 09:45:30 -0200
> To avoid problems with NUL-bytes when reading lines, Lua 5.3-beta
> reads single bytes in a loop instead of using `fgets` like previous
> Lua versions did. For better performance Lua uses unlocked I/O when
> available (i.e. on POSIX machines, though MS Windows has a similar
> API: `_lock_file`, `_unlock_file`, and `_getc_nolock`). I found the
> following piece of code in `liolib.c`:
>
> luaL_buffinit(L, &b);
> l_lockfile(f);
> while ((c = l_getc(f)) != EOF && c != '\n')
> luaL_addchar(&b, c);
> l_unlockfile(f);
>
> The problem I see here is that `luaL_addchar` could `longjmp` out of
> the loop when memory allocation fails without unlocking the file
> object. [...]
Thanks for the feedback. We will change that code to this:
luaL_buffinit(L, &b);
for (;;) {
char *buff = luaL_prepbuffer(&b); /* pre-allocate buffer */
int i = 0;
l_lockfile(f); /* no memory errors can happen inside the lock */
while (i < LUAL_BUFFERSIZE && (c = l_getc(f)) != EOF && c != '\n')
buff[i++] = c;
l_unlockfile(f);
luaL_addsize(&b, i);
if (i < LUAL_BUFFERSIZE)
break;
}
-- Roberto