[Mono-list] String Marshalling for P/Invoke
Wed, 8 Jan 2003 21:42:50 -0600
Jaroslaw Kowalski recently brought up the point that
"When you write 'static string function(parameters)' the function is expected
to ALLOCATE the returned string on task heap (using CoTaskMemAlloc() under
Windows), so CLR will happily free the string when it's no longer used, but
unfortunately when you return the static pointer to the CLR, it will attempt
to free an unallocated memory block, which is a big BOOM."
I'm confused about how this works under Mono under Linux (and other POSIX-like
systems) because most libraries allocate heap storage using glibc's malloc(),
whereas Mono uses glib's -- not glibc's -- g_free() function to return freed
memory to the pool. I've gotten conflicting answers over whether returning
malloc()'ed memory with g_free() is legal or not. So far, I haven't observed
any specific problems, but as someone working on Qt#, which passes strings
back and forth a great deal, I'm concerned about the proper behavior.
Let me be more specific: Suppose under Mono for Linux that I have
static string stringFunction();
where stringFunction returns a pointer to a string whose storage was obtained
using malloc(). Will Mono's runtime properly dispose of the string's storage?
If so, how? Will mono call g_free() (is that okay, since the storage was
obtained with malloc)?