http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48587
Summary: Avoid exhausting unit number with NEWUNIT=
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: libfortran
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: j...@gcc.gnu.org
As was recently pointed out by Tobias Burnus in a thread on comp.lang.fortran,
the current implementation of NEWUNIT= doesn't reuse unit numbers. Hence it's
possible that a program might exhaust the available unit numbers (this requires
that the program repeatedly closes and reopens files, as OS's have limits on
the number of file descriptors a process may have concurrently opened,
typically 1024 or something like that)
Currently there is just a (mutex protected) static variable which is
decremented for each time an OPEN statement with NEWUNIT= is issued, with a
wraparound check that generates an error if wraparound is detected.
IMHO an elegant solution would be to just reuse the kernel provided file
descriptor. E.g.
int fd = open(...);
if (fd == -1)
{
/* Handle error... */
}
new_unit_number = -fd;
This should work because a successful open() will always return a positive fd
number (see
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html ), and
the kernel takes care of reusing file descriptor numbers of closed files.
