G'day bernuli,

Welcome to the Monastery.

I haven't had a macOS system for some years, so I'm unable to test this for you; also, I don't recall ever using F_NOCACHE or seeing it documented.

The following is a possible workaround. This is on v5.36 but using Cygwin; I'm not expecting F_NOCACHE to be found. I ran some demo tests using this common alias of mine which reports many types of problems:

$ alias perle
alias perle='perl -Mstrict -Mwarnings -Mautodie=:all -MCarp::Always -E
+'
[download]

O_RDONLY is exported by default but F_NOCACHE is not:

$ perle 'use Fcntl; say O_RDONLY'
0

$ perle 'use Fcntl; say O_RDONLY; say F_NOCACHE'
Name "main::F_NOCACHE" used only once: possible typo at -e line 1.
0
say() on unopened filehandle F_NOCACHE at -e line 1.
[download]

F_NOCACHE cannot be explicitly imported:

$ perle 'use Fcntl qw{O_RDONLY F_NOCACHE}; say O_RDONLY; say F_NOCACHE
+'
"F_NOCACHE" is not exported by the Fcntl module
Can't continue after import errors at -e line 1.
        main::BEGIN() called at -e line 1
        eval {...} called at -e line 1
BEGIN failed--compilation aborted at -e line 1.
[download]

I can fake it like this (i.e. the "possible workaround"):

$ perle 'use Fcntl; use constant F_NOCACHE => 48; say O_RDONLY; say F_
+NOCACHE'
0
48

$ perle 'use Fcntl; use constant F_NOCACHE => 48; say O_RDONLY | F_NOC
+ACHE'
48

$ perle 'use Fcntl; use enum qw{F_NOCACHE=48}; say O_RDONLY; say F_NOC
+ACHE'
0
48

$ perle 'use Fcntl; use enum qw{F_NOCACHE=48}; say O_RDONLY | F_NOCACH
+E'
48
[download]

I've no idea idea if sysopen will accept that on your system. Curiously, it doesn't complain on mine:

$ perle 'use Fcntl; use enum qw{F_NOCACHE=48}; sysopen my $fh, "dummy_
+file", O_RDONLY | F_NOCACHE; close $fh'
[download]

I don't know if there's a way to build Perl such that F_NOCACHE is recognised but someone else might. To help with that, tell us how you built the current Perl you're using. It may also be helpful to show the output of `perl -V` (that's a capital V).

Thanks Ken and hv!

Using the raw numeric value worked! After opening the FILEHANDLE I added

fcntl($FI, 48, 1);

Which accomplished what I wanted. But I found the read performance to be much worse than expected. Also CPU usage went way up. Probably due to disk IO having to be managed more closely VS just buffering right into RAM.

So I will end up not using the F_NOCACHE for now. But good to know the option is available if I need it.

Thanks again!

Summary of my perl5 (revision 5 version 36 subversion 0) configuration
+:
   
  Platform:
    osname=darwin
    osvers=19.6.0
    archname=darwin-2level
    uname='darwin test-mac.local 19.6.0 darwin kernel version 19.6.0: 
+thu jan 13 01:26:33 pst 2022; root:xnu-6153.141.51~3release_x86_64 x8
+6_64 '
    config_args=''
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-fno-common -DPERL_DARWIN -mmacosx-version-min=10.15 -fn
+o-strict-aliasing -pipe -fstack-protector-strong -DPERL_USE_SAFE_PUTE
+NV'
    optimize='-O3'
    cppflags='-fno-common -DPERL_DARWIN -mmacosx-version-min=10.15 -fn
+o-strict-aliasing -pipe -fstack-protector-strong'
    ccversion=''
    gccversion='4.2.1 Compatible Apple LLVM 11.0.3 (clang-1103.0.32.62
+)'
    gccosandvers=''
    intsize=4
    longsize=8
    ptrsize=8
    doublesize=8
    byteorder=12345678
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=16
    longdblkind=3
    ivtype='long'
    ivsize=8
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=8
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags =' -mmacosx-version-min=10.15 -fstack-protector-strong'
    libpth=/Applications/Xcode.app/Contents/Developer/Toolchains/Xcode
+Default.xctoolchain/usr/lib/clang/11.0.3/lib /Applications/Xcode.app/
+Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sd
+k/usr/lib /Applications/Xcode.app/Contents/Developer/Toolchains/Xcode
+Default.xctoolchain/usr/lib /usr/lib
    libs=-lpthread -ldbm -ldl -lm -lutil -lc
    perllibs=-lpthread -ldl -lm -lutil -lc
    libc=
    so=dylib
    useshrplib=false
    libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=bundle
    d_dlsymun=undef
    ccdlflags=' '
    cccdlflags=' '
    lddlflags=' -mmacosx-version-min=10.15 -bundle -undefined dynamic_
+lookup -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_TIMES
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under darwin
  Compiled at Oct  7 2022 11:20:10
  @INC:
    /usr/local/lib/perl5/site_perl/5.36.0/darwin-2level
    /usr/local/lib/perl5/site_perl/5.36.0
    /usr/local/lib/perl5/5.36.0/darwin-2level
    /usr/local/lib/perl5/5.36.0
[download]

"Using the raw numeric value worked!"

That's basically good news and allows you to move forward.

Having said that, raw numbers appearing in your code is less good: their purpose would be unclear to a new maintainer, and possibly even to you when the code is revisited at some future time. I'd consider using F_NOCACHE, adding a comment to explain what it is, and maybe even a condition to only use it for macOS.

Although moot if you've decided not to currently use F_NOCACHE, that advice is valid generally, whenever numbers just appear in your code. I often use constant to provide names for array indices: for example, $data[PHONE] would be clearer than $data[7].

— Ken

The Fcntl module only provides access to the list of defines it knows about. The best I can suggest is either to use the raw numeric value with a comment, or put it in a constant sub:

# OSX-specific define: don't cache this file
sub F_NOCACHE () { 48 }
[download]

If you need greater portability, you could wrap it in some XS exactly as Fcntl does, or create something more generic using h2xs (ships with perl) or Alien::SWIG4 to export everything you find in fcntl.h.

That said, the Fcntl documentation has claimed since docs were originally added in 1995 that "this uses the h2xs program", which does not appear to have been true even then. So you could also consider filing a bug report that Fcntl should do what its docs claim, and make available all constants defined in that header - or just add F_NOCACHE.

Update: removed spurious '$' from prototype; thanks kcott.

G'day hv,

If you were going to do it like this, you'd want a prototype of (), not ($).

In perlsub, see "Prototypes" and "Constant Functions".

— Ken

Oops, thanks, corrected.

Or, equivalently,

use constant F_NOCACHE => 48;

My guess is that you would have to explicitly export F_NOCACHE as you do with other flags according to the documentation.

use Fcntl qw(F_GETFL F_SETFL O_NONBLOCK);
[download]

So yours would be:

use Fcntl qw(F_NOCACHE);
[download]

I don't have anything with iOS to be test it.

Thank you for the reply.

Unfortunately that does not work as my Fcntl.pm knows nothing of F_NOCACHE

Adding F_NOCACHE to the @EXPORT array of Fcntl.pm does not work either as the script dies with "F_NOCACHE is not a valid Fcntl macro".