Original bug ID: 3422
Reporter: administrator
Status: closed
Resolution: fixed
Priority: normal
Severity: minor
Category: ~DO NOT USE (was: OCaml general)

Bug description

The Mac OS X version of mldonkey has had a problem with orphaned file
descriptors. I was finally able to track down the source of the
problem and it has to do with the implementation of two of the unix
library routines "unix_accept" and "alloc_sockaddr". I've been working
the ocaml-3.08.0. Bascially the problem is that "unix_accept" calls
the unix routine "accept" which creates a file descriptor in "retcode"
(assuming no error). It then calls "alloc_sockaddr" and for some
reason, sometimes, the sa_family returned by unix "accept" does not
match any of the cases in "alloc_sockaddr". This causes "unix_error"
to be called in "alloc_sockaddr" which leave the file descriptor open
and there is no way in the user program to obtain and close it.

unix_accept is in otherlibs/unix/accept.c and is:

CAMLprim value unix_accept(value sock)
{
int retcode;
value res;
value a;
union sock_addr_union addr;
socklen_param_type addr_len;

addr_len = sizeof(addr);
enter_blocking_section();
retcode = accept(Int_val(sock), &addr.s_gen, &addr_len);
leave_blocking_section();
if (retcode == -1) uerror("accept", Nothing);
a = alloc_sockaddr(&addr, addr_len);
if (a == -1)
{
close(retcode);
unix_error(EAFNOSUPPORT, "", Nothing);
}
Begin_root (a);
res = alloc_small(2, 0);
Field(res, 0) = Val_int(retcode);
Field(res, 1) = a;
End_roots();
return res;
}

and "alloc_sockaddr" is in otherlibs/unix/socketaddr.c and is:

value alloc_sockaddr(union sock_addr_union * adr /in/,
socklen_param_type adr_len)
{
value res;
switch(adr->s_gen.sa_family) {
#ifndef _WIN32
case AF_UNIX:
{ value n = copy_string(adr->s_unix.sun_path);
Begin_root (n);
res = alloc_small(1, 0);
Field(res,0) = n;
End_roots();
break;
}
#endif
case AF_INET:
{ value a = alloc_inet_addr(&adr->s_inet.sin_addr);
Begin_root (a);
res = alloc_small(2, 1);
Field(res,0) = a;
Field(res,1) = Val_int(ntohs(adr->s_inet.sin_port));
End_roots();
break;
}
#ifdef HAS_IPV6
case AF_INET6:
{ value a = alloc_inet6_addr(&adr->s_inet6.sin6_addr);
Begin_root (a);
res = alloc_small(2, 1);
Field(res,0) = a;
Field(res,1) = Val_int(ntohs(adr->s_inet6.sin6_port));
End_roots();
break;
}
#endif
default:
res = (value) -1;
/*
unix_error(EAFNOSUPPORT, "", Nothing);
*/
}
return res;
}

The "unix_accept" routine should close the open file descriptor in
"retcode" if "alloc_sockaddr" gets an error. I tested this by moving
the "unix_error" routine out of "unix_accept" and instead returned a -1
to indicate an error. Then in each routine which called
"alloc_sockaddr" I tested the return value and called "unix_error" if
it was -1. Rebuilding mlnet (mldonkey) on Mac OS X with this change
eliminated the orphaned file descriptors. I do not know what value of
sa_family the unix "accept" command is returning to cause this error or
why it is returning a value that does not match your cases.

Since there appears to be no way for a user program that uses
"unix_accept" (ocaml Unix.accept) to obtain and close the file
descriptor opened by "unix_accept", I think that the library will have
to be changed to close "retcode" if alloc_sockaddr fails.

Thanks for your assistance.

Rand H. Childs