Possible memory leak?

[Simon Marlow]

Chris Kuklewicz wrote:
> I was working on pulling library calling code from JRegex into 
> Text.Regex.Lazy
> and I am wondering if this code for compiling regex.h regular 
> expressions is a
> potential memory leak:
> 
>> regcomp pattern flags = do
>>   regex_fptr <- mallocForeignPtrBytes (#const sizeof(regex_t))
>>   r <- withCString pattern $ \cstr ->
>>          withForeignPtr regex_fptr $ \p ->
>>            c_regcomp p cstr (fromIntegral flags)
>>   if (r == 0)
>>      then do addForeignPtrFinalizer ptr_regfree regex_fptr
>>              return (Regex regex_fptr)
>>      else error "Text.Regex.Posix.regcomp: error in pattern" -- ToDo
> 
> 
> The (r/=0) path calls error, but never attaches the finalizer.  And the 
> man page
> for regex says:
> 
>>      The regfree() function frees any dynamically-allocated storage 
>> associated
>>      with the compiled RE pointed to by preg.  The remaining regex_t 
>> is no
>>      longer a valid compiled RE and the effect of supplying it to 
>> regexec() or
>>      regerror() is undefined.
> 
> 
> So it looks like the c_regcomp might allocate memory associated with 
> regex_fptr
> even in the event of an error, so this case needs the same finalizer.


We made the opposite change back in 2003:

Fri Jul 25 11:03:51 BST 2003  simonmar
   * [project @ 2003-07-25 10:03:51 by simonmar]
   regcomp: don't attach the regfree finalizer if c_regcomp failed.

     M ./Text/Regex/Posix.hsc -2 +2

diff -rN -u old-base/Text/Regex/Posix.hsc new-base/Text/Regex/Posix.hsc
--- old-base/Text/Regex/Posix.hsc       2006-07-19 12:50:43.000000000 +0100
+++ new-base/Text/Regex/Posix.hsc       2006-07-19 12:50:46.000000000 +0100
@@ -60,9 +60,9 @@
    r <- withCString pattern $ \cstr ->
          withForeignPtr regex_fptr $ \p ->
             c_regcomp p cstr (fromIntegral flags)
-  addForeignPtrFinalizer regex_fptr ptr_regfree
    if (r == 0)
-     then return (Regex regex_fptr)
+     then do addForeignPtrFinalizer regex_fptr ptr_regfree
+            return (Regex regex_fptr)
       else error "Text.Regex.Posix.regcomp: error in pattern" -- ToDo


So I'm guessing that calling regfree() should not be called if regcomp() failed. 
  I vaguely remember a bug report for this, but don't have it to hand.  If you 
have evidence to the contrary, then perhaps we should revert this.

Cheers,
	Simon