[Rd] Memory leak with tons of closed connections

[Gábor Csárdi]

Using dup() before fdopen() (and calling fclose() on the connection
when it is closed) indeed fixes the memory leak.

FYI,
Gabor

Index: src/main/connections.c
===================================================================
--- src/main/connections.c (revision 71653)
+++ src/main/connections.c (working copy)
@@ -576,7 +576,7 @@
     fp = R_fopen(name, con->mode);
     } else {  /* use file("stdin") to refer to the file and not the console */
 #ifdef HAVE_FDOPEN
- fp = fdopen(0, con->mode);
+        fp = fdopen(dup(0), con->mode);
 #else
  warning(_("cannot open file '%s': %s"), name,
  "fdopen is not supported on this platform");
@@ -633,8 +633,7 @@
 static void file_close(Rconnection con)
 {
     Rfileconn this = con->private;
-    if(con->isopen && strcmp(con->description, "stdin"))
- con->status = fclose(this->fp);
+    con->status = fclose(this->fp);
     con->isopen = FALSE;
 #ifdef Win32
     if(this->anon_file) unlink(this->name);

On Fri, Nov 11, 2016 at 1:12 PM, Gábor Csárdi <csardi.gabor at gmail.com> wrote:
> On Fri, Nov 11, 2016 at 12:46 PM, Gergely Daróczi
> <daroczig at rapporter.net> wrote:
> [...]
>>> I've changed the above to *print* the gc() result every 1000th
>>> iteration, and after 100'000 iterations, there is still no
>>> memory increase from the point of view of R itself.
>
> Yes, R does not know about it, it does not manage this memory (any
> more), but the R process requested this memory from the OS, and never
> gave it back, which is basically the definition of a memory leak. No?
>
> I think the leak is because 'stdin' is special and R opens it with fdopen():
> https://github.com/wch/r-source/blob/f8cdadb769561970cc42776f563043ea5e12fe05/src/main/connections.c#L561-L579
>
> and then it does not close it:
> https://github.com/wch/r-source/blob/f8cdadb769561970cc42776f563043ea5e12fe05/src/main/connections.c#L636
>
> I understand that R cannot fclose the FILE*, because that would also
> close the file descriptor, but anyway, this causes a memory leak. I
> think.
>
> It seems that you cannot close the FILE* without closing the
> descriptor, so maybe a workaround would be to keep one FILE* open,
> instead of calling fdopen() to create new ones every time. Another
> possible workaround is to use dup(), but I don't know enough about the
> details to be sure.
>
> Gabor
>
> [...]