Net::SSH2 issue in thread

roperl has asked for the wisdom of the Perl Monks concerning the following question:

I've have the following sub in my program

sub sftp_file {

    my ($file,$destfile,$host,$port,$user,$privpath,$pubpath,$pass) = 
+@_;

    my $ssh2 = Net::SSH2->new();
    $ssh2->connect( $host,$port ) or $logger->info("Connect failed: $!
+\n");

    if ( !$ssh2->error ) {
        $ssh2->auth( username => $user, publickey => $pubpath, private
+key => $privpath, password => $pass, passphrase => undef ) or $logger
+->info("Authent
ication failed: $!\n");
    }

    if ( $ssh2->auth_ok ) {

        my $sftp = Net::SFTP::Foreign->new( ssh2 => $ssh2, backend => 
+'Net_SSH2' );
        $sftp->error and $logger->info("Unable to establish SFTP conne
+ction: $sftp->error\n");
        $sftp->put( "$file", "$destfile", best_effort => 1 ) or ( $log
+ger->info("Put failed: $sftp->error\n") && return );
        return 1;
    } else {
        return 0;
    }
}
[download]

The sub works fine if I call it before I startup and threads. If I call it in a thread I get the following error:

Connect failed: Resource temporarily unavailable
[download]

When I turn on tracing of libssh2 and debug I see the following

[libssh2] 0.822042 Transport: session_startup for socket 5
[libssh2] 0.822225 Transport: Sending Banner: SSH-2.0-libssh2_1.8.0
[libssh2] 0.822280 Socket: Sent 23/23 bytes at fe7b1570+0
[libssh2] 0.822334 Socket: Recved 0 bytes banner
[libssh2] 0.822366 Failure Event: -13 - Failed getting banner
Net::SSH2::DESTROY object 0x3413458
[libssh2] 0.825767 Transport: Freeing session resource
[libssh2] 0.825807 Transport: Extra packets left 0
[libssh2] 0.825839 Transport: unable to reset socket's blocking state
[download]

Is there work around ?

Comment on Net::SSH2 issue in thread Select or Download Code

Replies are listed 'Best First'.
Re: Net::SSH2 issue in thread by Corion (Patriarch) on Jul 31, 2018 at 15:56 UTC
I would avoid mixing threads and C libraries (in this case, Net::SSH2). Most likely, the C library is not really thread-safe and will only ever work from within one thread. You don't show how you start up threads and how your threads use the object and the function `sftp_file`. Maybe only ever using `sftp_file` from one thread might work, but that's hard to say without seeing the code you're actually using.	[reply] [d/l] [select]
Re^2: Net::SSH2 issue in thread by roperl (Beadle) on Jul 31, 2018 at 16:39 UTC
According to the libssh2.org site, it is thread safe: "Thread-safe: just don't share handles simultaneously" I'm not sure if I am sharing handles simultaneously At the top of my code I call `use Net::SSH2;` [download] Then I create my threads `my $work_q = Thread::Queue->new(); my $thr = threads->new( 'file_worker', $work_q );` [download] In my file_work sub I call the sftp_file if the file is found and supply the required arguments `my $retval = sftp_file($file,$destfile,$host,$port,$user,$privpath,$pu +bpath,$pass);` [download]	[reply] [d/l] [select]
Re: Net::SSH2 issue in thread by salva (Canon) on Aug 01, 2018 at 06:59 UTC
Net::SSH2 is not thread safe. You might be able to use if from one thread, as far as objects are not shared between threads (and sharing could be just letting a `Net::SSH2` object be cloned by creating a new thread even if it is not used there at all, see issue 40). I (the de-facto current maintainer of `Net::SSH2`) have looked into that a couple of times, but fixing all the issues involved in order to make the module just usable in a threaded environment would be a mayor effort and the reality is that I lack the time to do it. So, unless somebody volunteers to do it (or offers to fund it!) I don't see it being fixed.	[reply] [d/l] [select]
Re^2: Net::SSH2 issue in thread by roperl (Beadle) on Aug 01, 2018 at 15:38 UTC
Salva, Thanks. I was hoping maybe there was a work around. Maybe I'll have my threaded program call another program that actually does the sftp.	[reply]