/*
 * call-seq:
 *
 *      Kgio::File.tryopen(filename, [, mode [, perm]])      -> Kgio::File or Symbol
 *
 * Returns a Kgio::File object on a successful open.  +filename+ is a
 * path to any file on the filesystem.  If specified, +mode+ is a bitmask
 * of flags (see IO.sysopen) and +perm+ should be an octal number.
 *
 * This does not raise errors for most failures, but installs returns a
 * Ruby symbol for the constant in the Errno::* namespace.
 *
 * Common error symbols are:
 *
 * - :ENOENT
 * - :EACCES
 *
 * See your open(2) manpage for more information on open(2) errors.
 */
static VALUE s_tryopen(int argc, VALUE *argv, VALUE klass)
{
        int fd;
        VALUE pathname, flags, mode;
        struct open_args o;
        int retried = 0;
        VALUE rv;

        rb_scan_args(argc, argv, "12", &pathname, &flags, &mode);
        if (rb_respond_to(pathname, id_to_path))
                pathname = rb_funcall(pathname, id_to_path, 0);
        o.pathname = StringValueCStr(pathname);

        switch (TYPE(flags)) {
        case T_NIL: o.flags = O_RDONLY; break;
        case T_FIXNUM: o.flags = FIX2INT(flags); break;
        case T_BIGNUM: o.flags = NUM2INT(flags); break;
        default: rb_raise(rb_eArgError, "flags must be an Integer");
        }
        switch (TYPE(mode)) {
        case T_NIL: o.mode = 0666; break;
        case T_FIXNUM: o.mode = FIX2INT(mode); break;
        case T_BIGNUM: o.mode = NUM2INT(mode); break;
        default: rb_raise(rb_eArgError, "mode must be an Integer");
        }

retry:
        fd = (int)rb_thread_blocking_region(nogvl_open, &o, RUBY_UBF_IO, 0);
        if (fd == -1) {
                if (errno == EMFILE || errno == ENFILE || errno == ENOMEM) {
                        rb_gc();
                        if (retried)
                                rb_sys_fail(o.pathname);
                        retried = 1;
                        goto retry;
                }
                if (fd == -1) {
                        int saved_errno = errno;

                        if (!st_lookup(errno2sym, (st_data_t)errno, &rv)) {
                                errno = saved_errno;
                                rb_sys_fail(o.pathname);
                        }
                        return rv;
                }
        }
        rv = rb_funcall(klass, id_for_fd, 1, INT2FIX(fd));
        set_file_path(rv, pathname);
        return rv;
}