When computing needed number of processes take '-x' into account and

not only look at number of args

parallel

@@ -457,7 +457,7 @@ sub binary_find_max_length {
 }
 
 sub acceptable_command_line_length {
-    # Test if this length can run
+    # Test if a command line of this length can run
     # This is done using external perl script to avoid warning
     # (Can this be done prettier?)
     my $len = shift;
@@ -468,6 +468,148 @@ sub acceptable_command_line_length {
 }
 
 sub compute_number_of_processes {
+    # Number of processes wanted and limited by system ressources
+    my $opt_j = shift;
+    my $wanted_processes = user_requested_processes($opt_j);
+    my $system_limit = processes_available_by_system_limit($wanted_processes);
+    return $system_limit;
+}
+
+sub processes_available_by_system_limit {
+    # If the wanted number of processes is bigger than the system limits:
+    # Limit them to the system limits
+    # Limits are: File handles, number of input lines, processes, 
+    # and taking > 1 second to spawn 10 extra procs 
+    my $wanted_processes = shift;
+    my $system_limit=0;
+#GONE    my @args=();
+    my @command_lines=();
+#GONE    my $next_arg;
+    my $next_command_line;
+    my $more_filehandles;
+    my $max_system_proc_reached=0;
+    my $spawning_too_slow=0;
+    my $time = time;
+    my %fh;
+    DoNotReap();
+
+    # Reserve filehandles
+    # perl uses 7 filehandles for something?
+    # parallel uses 1 for memory_usage
+    for my $i (1..8) {
+	open($fh{"init-$i"},"</dev/null");
+    }
+    do {
+	$system_limit++;
+
+	# If there are no more command lines, then we have a process
+	# per command line, so no need to go further
+	$next_command_line = next_command_line();
+	if(defined $next_command_line) { 
+	    push(@command_lines, $next_command_line);
+	}
+
+#GONNE	# If there are no more arguments, then we have a process per argument
+#GONNE	# so no need to go further
+#GONNE	$next_arg = get_next_arg();
+#GONNE	if(defined $next_arg) { 
+#GONNE	    push(@args, $next_arg);
+#GONNE	}
+
+	# Every simultaneous process uses 2 filehandles when grouping
+	$more_filehandles = open($fh{$system_limit*2},"</dev/null") 
+	    && open($fh{$system_limit*2+1},"</dev/null");
+
+	# System process limit
+	$system_limit % 10 or $time=time;
+	if($child = fork()) {
+	    push (@children,$child);
+	} elsif(defined $child) {
+	    # The child takes one process slot
+	    # It will be killed later
+	    sleep 100000;
+	    exit;
+	} else {
+	    $max_system_proc_reached = 1;
+	}
+	debug("Time to fork ten procs ", time-$time, " process ", $system_limit);
+	if(time-$time > 1) {
+	    # It took more than 1 second to fork ten processes. We should stop forking.
+	    # Let us give the system a little slack
+	    debug("\nLimiting processes to: $system_limit-10%=".
+		  (int ($system_limit * 0.9)+1)."\n");
+	    $system_limit = int ($system_limit * 0.9)+1;
+	    $spawning_too_slow = 1;
+	}
+    } while($system_limit <= $wanted_processes 
+	    and defined $next_command_line
+	    and $more_filehandles
+	    and not $max_system_proc_reached
+	    and not $spawning_too_slow);
+    if($system_limit <= $wanted_processes
+	and not $more_filehandles) {
+	print STDERR ("Warning: Only enough filehandles to run ",
+		      $system_limit, " jobs in parallel. ",
+		      "Raising ulimit -n may help\n");
+    }
+    if($system_limit <= $wanted_processes
+	and $max_system_proc_reached) {
+	print STDERR ("Warning: Only enough available processes to run ",
+		      $system_limit, " jobs in parallel.\n");
+    }
+    if($system_limit <= $wanted_processes
+	and $spawning_too_slow) {
+	print STDERR ("Warning: Starting 10 extra processes takes > 1 sec.\n",
+		      "Limiting to ", $system_limit, " jobs in parallel.\n");
+    }
+    # Cleanup: Close the files
+    for (keys %fh) { close $fh{$_} }
+    # Cleanup: Kill the children
+    for $pid (@children) {
+	kill 15, $pid;
+	waitpid($pid,0);
+    }
+    wait();
+#    # Cleanup: Unget the args
+#    unget_arg(@args);
+    # Cleanup: Unget the command_lines
+    unget_command_line(@command_lines);
+    return $system_limit;
+}
+
+sub user_requested_processes {
+    # Parse the number of processes that the user asked for
+    my $opt_j = shift;
+    if(defined $opt_j) {
+	if($opt_j =~ /^\+(\d+)$/) {
+	    # E.g. -j +2
+	    my $j = $1;
+	    $processes = $j + no_of_cpus();
+	} elsif ($opt_j =~ /^-(\d+)$/) {
+	    # E.g. -j -2
+	    my $j = $1;
+	    $processes = no_of_cpus() - $j;
+	} elsif ($opt_j =~ /^(\d+)\%$/) {
+	    my $j = $1;
+	    $processes = no_of_cpus() * $j / 100;
+	} elsif ($opt_j =~ /^(\d+)$/) {
+	    $processes = $1;
+	    if($processes == 0) {
+		# -j 0 = infinity (or at least close)
+		$processes = 2**31;
+	    }
+	} else {
+	    die_usage();
+	}
+	if($processes < 1) {
+	    $processes = 1;
+	}
+    }
+    return $processes;
+}
+
+
+sub GONE_compute_number_of_processes {
     my $opt_j = shift;
     my $processes = 0; 
     if(defined $opt_j) {
@@ -514,7 +656,7 @@ sub compute_number_of_processes {
     return int $processes;
 }
 
-sub min_of_args_and_processes {
+sub GONE_min_of_args_and_processes {
     my $processes = shift;
     my $min_of_args_and_processes=0;
     my @args=();
@@ -564,7 +706,7 @@ sub NullReaper {
     while (waitpid(-1, &WNOHANG) > 0) { }
 }
 
-sub compute_no_of_free_filehandles {
+sub GONE_compute_no_of_free_filehandles {
     my $needed = shift;
     my $i=1;
     my %fh;
@@ -629,12 +771,21 @@ sub init_run_jobs {
 
 sub next_command_line {
     my $cmd_line;
-    do {
+    if(@Global::unget_next_command_line) {
-	$cmd_line = generate_command_line($Global::command);
+	$cmd_line = shift @Global::unget_next_command_line;
-    } while (defined $cmd_line and $cmd_line =~ /^\s*$/); # Skip empty lines
+    } else {
+	do {
+	    $cmd_line = generate_command_line($Global::command);
+	} while (defined $cmd_line and $cmd_line =~ /^\s*$/); # Skip empty lines
+    }
     return $cmd_line;
 }
 
+sub unget_command_line {
+    push @Global::unget_next_command_line, @_;
+}
+
+
 sub get_next_arg {
     my $arg;
     if(@Global::unget_arg) {